Fall 2018 CAMP Meetinghe Fall 2018 CAMP Meeting was hosted by the U.S. Nuclear Regulatory Commission on December 11 – 13, 2018 at the agency’s Three

White Flint North facility in North Bethesda, Maryland (USA). It was another successful CAMP meeting with a notable attendance.

TThe meeting was opened by Dr. Chris Hoxie. Dr. Hoxie welcomed CAMP members to the Fall Meeting, and thanked everyone for taking the time to attend. He introduced Michael Case, who works behind the scenes to help enable CAMP. Mr. Case joined NRC in 1989, and has nearly three decades of experience at NRC,

(Continued on page 2)

TRACE/SNAP Advanced WorkshopTRACE/SNAP Advanced Workshop was held December 3-6, 2018 at the System Source Training Facility in Columbia, Maryland (USA).

This workshop was directed toward advanced users who are well-experienced with TRACE/PARCS and SNAP and have moderate T/H system code experience. The workshop focused on the following topics:

A An overview of new features in TRACE. An introduction to the TRACE Exterior

Communications Interface (ECI) for coupling to other codes. Use of ECI to break up TRACE

models into subdomains for parallel execution on multiple cores was also covered.

An introduction to setting up uncertainty quantification job streams in SNAP.

Using TRACE for thermal-hydraulic analysis, including identifying modeling errors, improving agreement with experimental results, and interpreting/evaluating the cause of trends seen in results. Specific analysis techniques that help formalize and sharpen analysis skills will be presented and used in exercises.

An introduction to PARCS and coupled TRACE/PARCS modeling.

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Thermal-Hydraulic Thermal-Hydraulic Codes NewsCodes News

S p o n s o r e d b y t h e U . S . N u c l e a r R e g u l a t o r y C o m m i s s i o nVolume 19 / Number 1 / April 2019

EMAIL FOR TRACE BUGS:Any TRACE bugs can be reported to the following email address: TRACE.Bugs@nrc.gov

Thermal-HydraulicCode News

Committed to the support of the T/H Codes User Community

Contents: Fall 2018 CAMP Meeting TRACE/SNAP Advanced Workshop TRACE User Problems Recent RELAP5 User Problems Status of NUREG/IAs Upcoming Spring CAMP Meeting Other Items of Interest

(Continued on page 3)

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Fall 2018 CAMP Meeting(continued from page 1)

and has served in many responsible positions over that time. He is well-versed in regulatory and budgetary matters, and has spent time at the Office of International Programs (OIP). This diverse background fits well for a successful CAMP program.

Mr. Case is the Director of the Division of Safety Analysis in the NRC Office of Research, and he oversees the CAMP, CSARP, and RAMP programs. Mr. Case thanked CAMP members for their time and energy; the CAMP program is successful primarily through CAMP members’ efforts. He welcomed CAMP members and said he hopes for a fruitful and productive meeting.

Mr. Case talked about agency issues from a higher level. Internally at NRC, there is a lot of change that has occurred. At the highest level, there are five commissioners that lead the agency. As of June, they now have a full complement of commissioners. There has also been change at the senior management level. Of the roughly 16 managers, about three-fourths are in different positions. And the Office of Research has a new boss as well. So, there has been a lot of leadership change. Mr. Case assured CAMP members however that this change should have no implications for CAMP. Many managers speak of the benefits of CAMP to senior management, so they are well-acquainted. Mr. Case stated that NRC relies on international partners to help develop the CAMP codes, so this brings benefits to the agency, and not just cost.

Mr. Case also discussed some process issues. NRC right now has considerable interest in issues like intellectual property rights. Code sharing practices across the U.S. federal government have been under review. Programs like CAMP are doing very well, but

have some areas in which to improve, e.g., Non-Disclosure Agreements (NDAs). The NRC needs to understand the users that are using the codes, and why they’re using them. Presently, all NDAs are different, so they are looking to standardize the NDAs. CAMP members can expect to start seeing new NDAs in the future. NRC is being more watchful on the terms and conditions in the NDAs, e.g., regarding third party use of the codes. Also, from a security perspective, there will be some changes to code distributions.

Next, Mr. Tarek Zaki, CAMP program manager at NRC, added his thanks to everyone for attending. Mr. Zaki sent out the minutes from the Spring 2018 CAMP Meeting about 10 days prior to the Fall 2018 CAMP Meeting, and as of this printing, had received no comments, so it looks like they can be finalized.

The meeting then focused on the NRC code status, with detailed reports for TRACE, PARCS, RELAP5, and SNAP. This was followed by an update on CAMP activities by the following countries: Slovenia and Sweden. Then, on the second day of the meeting, CAMP members from Croatia and Korea provided updates on activities in those countries.

The remainder of the second day of the meeting focused on member technical reports. These presentations included the following:

Tomasz Kozlowski (University of Illinois, USA), “Nuclear Engineering and Thermal-Hydraulics Research at the University of Illinois”

Kanglong Zhang (KIT, Germany), “Coupling of TRACE and CFD Code with ICOCO”

Fulvio Mascari (ENEA, Italy), “ENEA TRACE Application in Fission and Fusion Field”

Hao Chun Chang (National Tsing Hua University, Taiwan R.O.C.), “LBLOCA Uncertainty Analysis of Maanshan Nuclear Power Plant with RELAP5/SNAP and DAKOTA”

Jeremy Bousquet (GRS, Germany), “PARCS/ATHLET for SFR Safety Assessment: Recent Developments and Applications”

Oleg Orlov (Kinectrics, Canada), “Modelling of Well-mixed Flow Two-phase Pressure Drop in TRACE”

Byung-Gil Huh (Korea Institute of Nuclear Safety (KINS), Korea), “Best-Estimate Calculation for LBLOCA Analysis of APR1400 Using TRACE Code”

Andong Shin (Korea Institute of Nuclear Safety (KINS), Korea), “Multi-Layer Fuel Model Effect on the LBLOCA Case”

Kyung Won Lee (Korea Institute of Nuclear Safety (KINS), Korea), “Assessment of Condensation

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Heat Transfer Models of TRACE in a Nearly Horizontal Tube”

Davide Papini (Nuclear Power Plant Gösgen-Däniken AG, Switzerland), “Status of TRACE Model Development and Validation at NPP Gösgen in Switzerland”

All presentations from the Fall CAMP meeting are available on the https://www.nrccodes.com/CAMP/ web site.

The Technical Program Committee (TPC) meeting was held on December 13, 2018, following the conclusion of the general meeting. The TPC meeting focused on NUREG/IA status (see article on Page 16 of this newsletter), along with a discussion of In-Kind contributions. The CAMP action items, both “In Progress” and “Not Started,” were then reviewed and status updates were provided for each. Dr. Chris Hoxie then closed the meeting with some concluding remarks and Mr. Antony Calvo gave some details on the NRC Op Center tour that followed the close of the TPC meeting.

TRACE/SNAP Advanced Workshop(continued from page 1)

The Workshop was held in a computer laboratory equipped with PCs suitable for running TRACE/SNAP. Attendance was limited to one participant per computer. For this training, space was limited to 36 trainees. Priority was given to CAMP member organizations, the T/H Codes User Support Group, and attendees from the NRC staff and contractors.

TRACE User Problemshe following is a report on TRACE user problems and resolutions. Open trouble reports identified in the previous newsletters with no new progress

are not discussed, but can be found in the TRACE trouble report system (BugZilla) on the NRC Codes website (https://www.nrccodes.com).

TFor the time period January 1, 2018 through December 31, 2018, 41 new trouble reports were submitted to Bugzilla and 46 trouble reports were either resolved or closed. As of August 31, 2018, there were 883 trouble reports in the bug reporting system. Of those, 8 are for the PARCS code, 2 are bugs for the AVScript, 14 are bugs entered to test the system, 1 bug number (452) was skipped, 1 is associated with the python testing scripts used to test different versions of

TRACE, and 1 is associated with SNAP and was passed on to the SNAP development team. There were 856 TRACE-specific bugs in the system at the end of the reporting period; 39 of those were open, with the remainder resolved or closed. This implies that ~95% of the TRACE trouble reports have been resolved or closed.

A resolved trouble report indicates that it has been addressed with an update or documentation change that is pending. A closed trouble report indicates that it has either been addressed by successfully re-running the test problem(s) of interest with a current version of TRACE, it has been closed by incorporating a pending update into the NRC developmental version of TRACE, is a duplicate of another trouble report, or has been declared “won’t fix.” A closed “won’t fix” trouble report is typically a trouble report where the resources required to fix far outweigh the potential benefit of fixing the trouble report. A pending update implies that it has been tested, documented, reviewed, and submitted to the NRC, but has not been included in the developmental version of TRACE. Inclusion of a pending update into TRACE typically requires additional review and testing by the NRC staff.

The developmental version of TRACE is Version 5.1220 as of December 31, 2018. Updates up to Version 5.1220 are listed on the TRACE build page of the NRC Codes website:

https://www.nrccodes.com/TRACE/Build/default.aspx

New Trouble Reports Still Open

Trouble Report 846 – Explicit axial conduction limit not calculated for 2nd order finite element conduction solver.

While developing the FxDTMINLogic update it was determined the coding to calculate the explicit axial conduction limit for the 2nd order finite element conduction solver was missing. The FxFEDifMin update is under development to address this issue. This trouble report is still open.

Trouble Report 851 – Unexpected large pressure drop at the exit of the recirculation pump that discharges into the lower plenum.

This relatively large pressure drop at the exit of a recirculation pump was observed for a steady-state calculation. Renoding the lower plenum so that the recirculation exit does not discharge into a dead-end cell at the bottom of the lower plenum appears to resolve this issue. Potential user guidance is under investigation to address this issue. This trouble report is still open.

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Trouble Report 854 – When fuel temperature/Doppler is an important phenomenon, then the fine mesh algorithm for adding/deleting fine mesh nodes should include axial temperature gradients in the fuel rod.

Users determined that for BWR stability analysis for ATWS transients that accurate simulation of the Doppler reactivity feedback required a relatively large number of permanent fine mesh axial nodes in the fuel rod heat structures. Currently the fine mesh logic for adding and deleting fine mesh axial levels into a heat structure is based on temperature gradients in the cladding. However, if there are significant axial temperature gradients in the fuel, then fine mesh logic should be modified to include axial temperature gradients for the fuel center line. This trouble report is under investigation. This trouble report is still open.

Trouble Report 857 – Documentation needs to make it clear concerning table evaluation for steady-state calculations.

In general tables associated with trip will not be evaluated unless the trip ID has been input as a negative number. However, there are two logic paths in TRACE for evaluation of tables. One of the logic paths follows this general rule, while another does not. For example, the POWER component assumes that during a steady-state calculation the reactor power is constant and will not evaluate the reactivity table or reactor power table, even if the trip ID is negative. Therefore, during a steady-state calculation the reactivity table cannot be used to obtain a user desired reactor power as a function of the reactivity. Documentation for tables and trips needs to be updated to make it clear which tables can be accessed during a steady-state. This trouble report is still open.

Trouble Report 860 – For IRPWTY = 4 programmed reactivity was not available for graphics and general table reactivity did not trip as expected.

Developer had a test problem with IRPWTY = 4, which implies a programmed reactivity table that comes on with a trip. The programmed reactivity was to simulate a reactor scram and the POWER component also included a general reactivity table that resulted in a positive reactivity addition. The trip for the POWER component reactivity table was based on a reactor high power trip. However, the POWER component general reactivity table is not evaluated until the POWER component trip is tripped on. This implies that the positive reactivity from the general table was never evaluated. This can be simulated with the general reactivity table changed to simulate the reactor scam and include with the general table the over power trip. The POWER component reactivity table would be changed to be the positive

reactivity addition and tripped on at time zero. Update FxGenReacTble is under development to add programmed reactivity as a graphics variable, even though reactivity feedback is not included in this input model. Current coding in TRACE only includes programmed reactivity as a graphics variable if reactivity feedback is included in the point kinetics model. During testing the steady-state power component was for one case read in from the restart file and in another case was included in the TRACE ASCII input file. There were some differences in the results. These differences in results based on whether the POWER component was included in the ASCII input file or read from the restart file is under investigation. This trouble report is still open.

Trouble Report 862 – Non-Null Restart Issues.

Five non-null restarts issues were discovered in TRACE Version 5.1167. These restart issues are:

1) Inconsistencies for the horizontal stratified flow model across the restart.

2) Inconsistencies in the initialization of the macroscopic solute or boron density for the VESSEL component.

3) Inconsistencies in the initialization of the heat structure material properties.

4) Inconsistencies in the initialization of the solute concentration array for the VESSEL component.

5) Inconsistencies in the core average boron plot for the POWER component across a restart.

Issue 1 was fixed with the HelicalBugFx that went into version 5.1175. Updates to fix issues 2, 4, and 5 are under development. Issue 3 is still under investigation. This trouble report is still open.

Trouble Report 863 – No code failures for out-of-bounds pressure.

When an SJC PUMP or FILL sets a flow rate BC such that flow goes into a dead-end fluid component, but has no outlet, then the pressure will increase without bound. When the pressure goes above the maximum pressure of the steam tables, then the pressure is limited to the maximum pressure allowed and if the change in pressure is larger than the convergence criteria the time step will be repeated with a smaller time step size. If the time step size is small enough then the maximum change in relative pressure will be small enough that the TRACE outer iteration will converge, even though the pressure is not allowed to go above the maximum pressure of the steam tables. Under these conditions, the TRACE calculation can continue and the user may not be aware that the results are not valid. A proposed solution is to count the number times the calculated

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pressure goes above the maximum allowed pressure and stop the calculation after a fixed number of maximum pressure failures. Another proposal is to stop the calculation as soon as the pressure goes above the maximum allowed pressure. Solution to this trouble report is under investigation and is currently still open.

Trouble Report 870 – Heat Structure (HTSTR) conduction equations based on fixed dimensions, with time dependent density.

HTSTR component conduction equations are based on fixed dimensions. However, HTSTR material density can change with time, which implies that heat structure material mass associated with each HTSTR node is not constant. Update FxHSDen is under development to address this issue. This trouble report is still open.

Trouble Report 874 – Regression test problem PbBi_H2O_withSJC is incorrect.

Comments in this test problem input indicates that this test problem should be the same as test problem PbBi_H2O_test, except the PbBi_H2O_withSJC should include a Single Junction Component (SJC). There is currently no SJC component in the PbBi_H2O_withSJC input. This trouble report is still open.

Trouble Report 884 – Unexplained fuel melt in coupled TRACE/PARCS steady-state calculation.

Fuel melt was calculated during a coupled TRACE/PARCS steady-state calculation. This was determined to be due to logic errors in the communication of fuel rod power between the TRACE and PARCS computer codes. Update to address this problem is under development. This trouble report is still open.

Trouble Report 885 – Choking relaxation constants no longer used.

The TRACE choking model has been improved so that it is no longer necessary to use a relaxation model for robustness and stability. The name list input for these relaxation constants have not been removed to support older input models. The User Guide needs to be updated to indicate that these inputs are no longer used. Since there appear to be very few existing input models that include this input, removal of this input should be considered. This trouble report is still open.

Trouble Report 887 – Large Non-Condensable Gas (NCG) fractional change during a TRACE steady-state calculation.

During a TRACE steady-state calculation large NCG fractional change was observed. During a BWR steady-state there no source of NCG in the primary system. The NCG in the input model is in the CONTAN component and should not appear in the BWR primary system during a steady-state calculation. This behavior was traced to logic that allowed NCG to transport across a closed VALVE. Update NCGFx is under development. This trouble report is still open.

Trouble Reports Closed

During the time period January 1, 2018 through December 31, 2018, the following trouble reports were closed. A trouble report is closed by: (1) rerunning the test problem of interest successfully with the latest version of TRACE, (2) updating documentation to address the trouble report, (3) incorporating an update into the NRC development version of TRACE, or (4) it was decided that the resources required to fix the trouble report far outweigh the benefits. In some cases, a combination of these three fixes may be used.

Trouble Report 382 – Modeling of BWR Drywell and connection between Drywell and BREAK component.

The BWR drywell for this input model was simulated with a PIPE component with pipetype = 8. This effectively turns off the droplet condensation model in the PIPE component. It was found that entrainment of droplets in the drywell was affected by the side junction orientation that simulated the break from the BWR primary system to the drywell pipe. Reasonable results were obtained with the side junction angle input as 90 degrees (See trouble report 391). The best results were obtained when the drywell, suppression pool, etc. were simulated using the CONTAN component. This trouble report is closed.

Trouble Report 573 – Python build scripts on LINUX2 operating system with INTEL and NAG compilers were failing.

This trouble report was closed by updating to the most current SConscript files. With these SConscripts, the python build scripts for LINUX2 worked as expected.

Trouble Report 686 – TRACE HS to CONTAN fluid compartment failed.

The test problem provided with this trouble report resulted in a negative heat transfer coefficient (HTC) between the TRACE HTSTR component and a CONTAN fluid compartment. Update FxSphericalHSContan resolved this negative HTC and went into version 5.873. Additional testing indicated a relatively large number of failures to converge for the

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calculation of the interface temperature between the liquid film on the HTSTR surface and steam/air mixture in the CONTAN compartment. Additional testing with the most recent versions of TRACE no longer exhibit this behavior. This trouble report is closed.

Trouble Report 742 – Problems running TRACE/PARCS coupled Regression test problems.

A number of TRACE/PARCS coupled Regression test problems were failing with run time errors. A fix in the PARCS logic to initialize a logical to .FALSE. went into version 5.1090 and resolved this trouble report. This trouble report is closed.

Trouble Report 751 – TRACE version 5.1003 with test problem mslb_trace_htrd_ss dies with run time error.

TRACE/PARCS coupled test problem mslb_trace_htrd_ss dies with end-of-file internal read error. This is a duplicate of trouble report 742 and when trouble report 742 was closed, this trouble report was also closed.

Trouble Report 762 – PARCS input file mslb_trace_htrd_ss.parcs_inp appears to be a TRACE input file.

This trouble report is a duplicate of trouble report 742 and when trouble report 742 was closed this trouble report was also closed.

Trouble Report 769 – The HeatArray module is not used and should be removed from TRACE.

The FxHeatArray update removes this module from TRACE and went into version 5.1152 and closed this trouble report.

Trouble Report 789 – D2O tests in the Regression test problem set do not function properly.

These tests were rerun with the TRACE version 5.1155 with scalars and arrays initialized to undefined (NaN) and saw no code failure and results were as expected. This trouble report was closed with the successful rerun of these test problems.

Trouble Report 792 – LOFT Regression test problem failing with run time error.

A division by zero run time error occurred for a LOFT test problem when spacer grid model predicted a gas phase emissivity of 1.0. Coding was added to the grid spacer radiation heat transfer model to avoid division by zero as emissivity approaches 1.0. This fix was added

to the ImpCB update that went into version 5.1166 and closed this trouble report.

Trouble Report 803 – Mass balance checker mass flow rates in error for choked SJC.

A number of Regression test problems were identified as having estimated mass balance errors that were orders of magnitude larger than expected. These test problems involved the offtake model with an SJC PIPE connected to the side of a PIPE component and the flow in the SJC PIPE was choked. This is a typical small break modeling approach. It was determined the mass balance checker mass flow rate calculation was using the wrong upstream void fraction. This logic was fixed with update FxEMass that went into version 5.1162 and closed this trouble report.

Trouble Report 804 – Derivatives of the control block output given a change in the input signal for control block type 14 is in error when CBCON1 is not equal zero.

A review of the TRACE control system evaluation logic identified an error in logic for the derivative control block (CB) type 14, when CBCON1 is not equal to zero. For this CB when CBCON1 is input as zero, then the CB output is CBGAIN * input(1) / input(2), where input(1) is the first input signal, input(2) is the second input signal, and CBGAIN is the user input gain for this control block. When CBCON1 is not zero, then the CB output is CBGAIN * CGCON1 / input(1). When CBCON1 is not zero, the derivative of the CB output given a change in the first input signal is –CBGAIN * CBCON1 / input(1)2

and the derivative of the CB output given a change in the second input signal is zero. The original coding in TRACE had these derivatives reversed. While debugging this fix it was determined that implicit control block loop logic in TRACE was using a mixture of two iterative methods for solving the (i.e., Newton-Raphson and iterative successive relaxation method). Testing indicated that improved convergence could be obtained by using only the Newton-Raphson method. The FxDrvCB update includes the fix for the derivative of the CB type 14 and implementation of a consistent Newton-Raphson iterative method. Update FxDrvCB went into version 5.1165 and closed this trouble report.

Trouble Report 806 – Non-zero FILL mass flow rate when expecting zero mass flow rate.

FILLs connected to a VESSEL component to simulate LPCS pumps where expected to have a zero-mass flow rate until the reactor pressure vessel pressure dropped below 1.96 MPa. These FILLs started out with a non-zero initial mass flow rate. The logic error that caused this behavior was fixed with two separate updates

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(FxTPOW that went into version 5.1146 and FillZeroVel that went into version 5.1179). This trouble report has been closed.

Trouble Report 811 – NaN values in TPR persistent data blocks.

Scans of the TPR restart data dumps during investigation of the TRACE backup logic uncovered undefines for the solute solubility limit model. For this specific test problem, ISOLUT was input as zero, so the solute solubility limit model was not used and constants within this model were not defined, but were included in the TPR restart data dump. Logic was added to the FxFixedHTC update to default these parameters to -1.0, to ensure that they were defined when written to the TPR restart data file. Update FxFixedHTC went into version 5.1176 and closed this trouble report.

Trouble Report 812 – Derivatives of the control block function incorrect when part of an implicit control block loop.

When debugging the non-convergence for the implicit control block loops in test problems CnSysM, CnSysDelt1, and CnSysDelt2, it was determined that the derivative function was in error when it was part of an implicit control block loop. Implicit control block loops are solved each time step using the Newton-Raphson iterative method. The derivative for a given control block is formed as (presVal – prevVal)/dtcon, where presVal is the new value for this control block and prevVal is the old-time value for this control block. However, the iterative logic for the Newton-Raphson method was resetting prevVal to the solution from the previous iteration. Logic was modified so that prevVal was not changed during the Newton-Raphson iterations. This fix was included in the FxDrvCB update that went into version 5.1165 and closed this trouble report.

Trouble Report 813 – Incorrect values in Core Inlet and Outlet Integrated Mass Flow Rates in TPR dump file.

The core inlet and outlet integrated mass flow rates are output variables calculated for user convenience and do not directly or indirectly feed into the TRACE thermal-hydraulics solution. These parameters correctly appear in the TPR dump/restart file. However, these parameters were not in the TRACE auto backup state parameter data sets. So, if TRACE backs up, these parameters would be in error. The fix is to add these parameters to the TRACE auto backup state parameter data set for the VESSEL component. This fix was included into the FxFixedHTC update that went into version 5.1176 and closed this trouble report.

Trouble Report 818 – Too much cpu time required to initialize control system.

A provided input model had 4607 signal variables, 4901 control blocks, and 393 trips. The user reported that the initialization of this input model took ~26 cpu minutes. TRACE makes a number of passes through the TRACE control system input in an attempt to order the signal variables, control blocks, and trips into a stack that allows for a once through evaluation of the control system. The user can define implicit control blocks, which are solved separately using an iterative solution. The process of ordering this stack involves 5 nested do loops where the four outer do loops loop over the number of control blocks in the system and the final inner do loop is over the signal variables, control blocks, and trips. For this test problem, the total number of passes through the inner do loop would be 49014 x (4901 + 4607 + 393) = 5.71239x1018. The logic was modified so that the outer 4 do loops are only over the control blocks that have not been stacked and the inner do loop was replaced with some indirect addressing logic to determine which set of inputs were associated with control blocks that had been stacked. These fixes were incorporated into ImpCBSort update, which went into version 5.1167 and closed this trouble report. With the ImpCBSort update the initialization of this test problem was reduced to 7 cpus.

Trouble Report 820 – Inconsistency in the HTC BC for Heat Structures.

A developer noticed that the results of a Brown’s Ferry BWR model for a Residual Heat Removal (RHR) heat exchanger showed more energy transfer than was expected when user-input heat transfer coefficients were used. In this case, the outside surface of the RHR was effectively fixed to a constant temperature of 305 K. The inside surface HTC was determined via a control block, which set the inside surface HTC to the fluid at ~15000 W/m2-K. The problem is that this HTC was used for wall to liquid heat transfer, for wall to gas phase heat transfer, and for wall to saturation temperature heat transfer (boiling heat transfer), even though the fluid flow was only single-phase liquid. Update FxFixedHTC fixed this logic so that the user specified boundary condition HTCs can only be used for the phase that is present (i.e., liquid or gas) and not double account for the heat transfer. This update went into version 5.1176 and closed this trouble report.

Trouble Report 822 – The NAG compiler identified runtime errors in the BreakShared and FillShared modules related to GRAV/IELV parameters.

The NAG compiler memory was initialized to undefined. Parameters used to calculate GRAV and elevation

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changes for a FILL/BREAK connected to an SJC cell edge that were not initialized resulted in an arithmetic exception with the NAG compiler when IELV = 2. The Intel compiler initialized the memory to zero and test problems Sepd_Test0 and COTINO_0deg ran without the runtime error when IELV = 2. Calculation of the parameters needed to calculate GRAV for FILL/BREAK components connected to a SJC cell edge were moved up to occur before they were needed when IELV = 2. This fix was included in update FxSJIELV2, which went into version 5.1163 and closed this trouble report.

Trouble Report 834 – Initialization of CONTAN initial air mass is in error if the compartment liquid mass is zero.

If a CONTAN compartment input has the initial liquid water mass (RML) input as zero, then the EOS input checking logic for the TRACE steam tables would set the initial non-condensable gas (NCG) partial pressure to zero. A NCG partial pressure of zero for this CONTAN compartment makes all of the gas in the compartment steam. A simple workaround for this logic error is to input a small non-zero value for RML. The FxInitContan update corrects the default void fraction in the CONTAN component so that the steam tables can compute a non-zero partial pressure of NCG. The update went into version 5.1170 and closed this trouble report.

Trouble Report 835 – Input error for EOS = Helium gas for SJC.

TRACE does not allow two phase flow when the EOS model is for Helium, Nitrogen, or air. Therefore, when the Equation of State (EOS) for a fluid component is Helium, Nitrogen, or air, then the user-input void fraction is expected to be one. If not one, then an input error occurs. For a Single Junction Component (SJC), the user input is for a cell edge and the fluid properties associated with the SJC may be required as input but will not be used. In TRACE the default void fraction for the SJC was zero. When an SJC was input with Helium as the EOS, then the input checking logic for Helium would indicate that the initial void fraction of zero was in error. The HEFix update changes the default void fraction for SJC from zero to one if EOS is Helium, Nitrogen, or air. This solved this logic error. Update HEFix went into version 5.1164 and closed this trouble report.

Trouble Report 838 – Routine WriteTimeStepEdit has a typo and uses vmaxt for the calculation of the 1D Courant Limit and should use vmaxt1.

The edits for the 1D Courant Limit for a given TRACE calculation were in error. The system wide Courant Limit was used for the 1D Courant Limit edit. Update HEFix

resolved this trouble report and went into version 5.1164. This closed this trouble report.

Trouble Report 839 – Error message not meaningful when VALVE component has JUN2 = 0.

There are two fluid components that can have a dead-ended junction (i.e., PIPE and PRIZER). A dead-ended junction for a fluid component is when JUN1 or JUN2 or JUN3 is input as zero. A VALVE component cannot have JUN1 or JUN2 input as zero. The error message when a VALVE component had JUN2 = 0, was confusing and did not indicate this specific problem with the input. Update FxJunZero resolved this trouble report. This update went into version 5.1172 and closed this trouble report.

Trouble Report 841 – Array bounds failure for restart to continue CSS BWR calculation.

User was attempting to restart a long running Constrained Steady-State (CSS) calculation and continue the CSS calculation. The restart continuing the CSS calculation resulted in an array bounds run time error. An error in the CSS restart logic resulted in the array bounds error. The logic error was in a logic block that was attempting to determine the MIN/MAX for a CSS control block on the restart file. This block of coding had been added to TRACE to offset an index error in the CSS initialization logic. When the CSS initialization logic was fixed, then logic block to determine MIN/MAX for CSS restart was no longer needed. The fix for these logic errors was included in the FxCSSRst update, which went into version 5.1171. This closes this trouble report.

Trouble Report 842 – Surface wave limit controls time step size when no liquid in neighboring fluid cells.

The static pressure difference between two horizontal fluid cells with different stratified liquid level heights is computed explicitly and included in the TRACE momentum equation solutions. This results in a time step stability limit that is based on the height of the liquid level at the cell edge where the momentum equations are solved. However, current coding does not take into account that if there is no liquid present, a stratified liquid level cannot form and therefore there should be no surface wave time step size control. A relatively large BWR steady-state model time step size was controlled by surface wave time step size even though there was no liquid in the fluid cells controlling the time step size. This logic was fixed with update FxSurfWave that went into version 5.1177 of TRACE. This trouble report is closed.

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Thermal-Hydraulics Codes News April 2019

Trouble Report 843 – Input error when STDYST = 5 and IPMPTR /= 0.

When STDYST = 5, then TRACE runs a static head check with no flow for the PUMP components and no power to the heat structures. If the total static head around each flow loop is zero, then flows in the loops will approach zero. If the flow in a loop does not approach zero, then elevation change around that flow loop is not zero. When STDYST = 5, then the PUMP component trip ids are automatically set to zero. Input checking added to the PUMP component did not allow for IPMPTR = 0 for certain PUMP types, so this automatic behavior for STDYST = 5 resulted in an input error. Update FxCSSRst fixed this logic error and went into version 5.1171. This closed this trouble report.

Trouble Report 847 – User requested that RANS – decay heat multiplier be applied for all decay heat models.

User requested that the decay heat multiplier (RANS) be applied for all decay heat models. The POWER component documentation indicated that RANS was only used for the ANS 79 decay heat model and not used for the ANS 94 decay heat model. The TRACE coding used the RANS parameter for both the ANS 79 and ANS 94 decay heat models. The user was expecting that the total reactor power would change when RANS was changed from 1.0 to 1.2. The point kinetics model in TRACE needs the power that is from fissions in order to start the time dependent solution of the point kinetics equations. When the point kinetics model is turned on, the reactor power from fissions is determined by the difference between the total power and the initial decay heat power. If the decay heat power is increased by a factor of 1.2 when RANS is input as 1.2, then the initial fission power is reduced consistent with user input for the total power. The total reactor power will not change when RANS is changed from 1.0 to 1.2, if the user-input total reactor power is the same. If the initial decay heat fraction of the total reactor power is 6% and the user wants the total reactor power to increase when RANS is changed from 1.0 to 1.2, then the total reactor power should change by 6 * 0.2 = 1.2 %. The POWER component documentation was modified to make it clear which decay heat models use the RANS parameter and these documentation changes were included in the FxSmallConc update. This update went into version 5.1169 and closed this trouble report.

Trouble Report 848 – User reported a mass error for all nitrogen system with 1 cell PIPE connected to a BREAK.

The input provided with this trouble report was a single cell PIPE connected to a BREAK with nitrogen as the working fluid. The flow from the PIPE to the BREAK is

choked and pressure in PIPE decreases. Based on the initial and final conditions and the ideal gas law the final gas pressure and temperature can be determined. Results of hand calculations consistent with nitrogen gas were not consistent with the results of the TRACE calculations. This input model had one non-condensable gas (NCG) and no water in the system. The input had IGAS = 1, which implies that the NCG is air and not nitrogen. When there is only one NCG present, user input for IGAS is used to determine the NCG present. TRACE calculations were consistent with air. When IGAS was changed to 5, then the TRACE calculations were consistent with nitrogen. If the user needs to simulate a mixture of NCGs, then IGAS must be input as greater than 10. The initial mass fractions for this mixture of NCG will be input with the XGNB array, which is input for the H2O fluid components. If there is no steam present, then the total pressure would be input the same as the initial NCG gas partial pressure. The fluids array input should be used when there is more than one working fluid present. For example, a heat exchanger that has water on one side and Helium on the other side. This trouble report is closed.

Trouble Report 849 – User reported that change in core average void fraction between versions 5.0P4 and 5.0P5 was too large.

User was using Regression test problem pbtt_trace_sa to simulate Peach Bottom steady-state and between versions 5.0P4 and 5.0P5 the core average void fraction changed by 6%. This Regression test problem is used to test data communication between TRACE and PARCS and has not been verified and assessed as an accurate model for the simulation of the Peach Bottom reactor. Improvements in the TRACE linearization of the interfacial drag was included between versions 5.861 and 5.870. These improvements in the TRACE interfacial shear model had some impact on the core average void fraction prediction. However, the most significant change in the core average void fraction was due to fixes in the CHAN component leakage path model. The sensitive of the core average void fraction on the core bypass flow was because for this input model the core bypass flow was an order of magnitude larger than expected. This large core bypass flow was not important for this test problem, because it was used to test data communication logic between TRACE and PARCS. When the core bypass input for this test problem was update to give the correct order of magnitude for the core bypass there was no significant change in the core average void fraction between versions 5.0P4 and 5.0P5. Changes to the input for Regression test problem was included into the FxAdL update, which went into version 5.1171. This trouble report is closed.

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Thermal-Hydraulics Codes News April 2019

Trouble Report 856 – Zero time POWER table checking failed when the initial reactivity was negative.

User reported an unexpected input error failure for an input model that contained a POWER component with an initial negative reactivity in the power component reactivity table. Input checking for the POWER component checks to verify that the first time zero point in reactivity table is consistent with the initial reactivity input for the POWER component. This input logic did not take into account that the time zero reactivity could be negative. The code fix for this logic error was included in the FxSmallConc update that went into Version 5.1169. This closed this trouble report.

Trouble Report 864 – Potential logic errors for moderator density cross-section corrections for core bypass and water rods for coupled TRACE/PARCS BWR applications.

While testing the FxNotAuto update for TRACE a potential problem with how the TRACE calculated moderator densities for water rods and core bypass were used by PARCS to calculate cross-sections. Typically, BWR cross-sections are calculated using infinite lattice code calculations based on a reference moderator density in the water rods and core bypass and then corrections to these cross-sections are developed based on perturbations or changes in the water rod/core bypass moderator densities. TRACE was passing back to PARCS the moderator density in the water rods and core bypass and not the change in moderator density. This potential problem was passed onto the PARCS development team and they indicated that this logic has been fixed. This trouble report was closed.

Trouble Report 869 – Surface roughness for SJC PIPE.

User reported that different results were obtained for two input models that were the same, except in one input model an SJC PIPE was added to the simple BREAK->PIPE->PIPE->BREAK input model. An SJC PIPE is a TRACE input capability to allow the user to define a cell edge that connects two fluid cells. When the original simple input model was changed to BREAK->PIPE->SJC PIPE ->PIPE->BREAK, then the results in terms of mass flow rate for the given constant pressure boundary conditions would be expected to be the same. However, the SJC PIPE had a different input value for surface roughness (EPSW), than for the same cell edge in the original input model. When EPSW was input for the SJC PIPE consistent with the original input model, then the results were the same. This closed this trouble report.

Trouble Report 871 – User wanted to specify fuel rod gram-moles array for detailed fuel rod model for the CHAN components.

The CHAN component input processing did not support input for the gram-moles of gap gas when the detailed fuel rod model was activated. Update FxCHANGmles1 resolved this issue and went into version 5.1181. This trouble report was closed.

Trouble Report 873 – XML header error in FillVelocity-10-rst Regression test problem.

Regression test problem FillVelocity-10-rst had a error in the XML header that resulted in an unexpected input error. The XML header for this test problem was fixed and the modified input was included into update FxPreInput, which went into version 5.1191. This trouble report was closed.

Trouble Report 875 – Regression test problem CSS-Test-Rev1-Rst has one assertion test failing.

Test problem CSS-Test-Rev1-Rst is a null-transient restart (transient restart with constant boundary conditions), which restarts from test problem CSS-Test-Rev1. Test problem CSS-Test-Rev1 is a Constrained Steady-State (CSS) test problem. The CSS-Test-Rev1 test problem does not reach a stable steady-state, so the null-transient steam generator heat transfer will drift from the restart conditions. The assertion testing success criteria for the steam generate heat transfer rate was changed from 0.1% to 0.3%. This resulted in changing the failed assertion testing for the steady-generator heat transfer rate to change to a success. This input model change was included into the CHF_Groen_2006 update that went into version 5.1220.

Trouble Reports Resolved with Updates Pending

During the time period January 1, 2018, to December 31, 2018, the following Trouble Reports were resolved with updates or documentation modifications pending. These Trouble Reports are awaiting NRC review and a decision to implement or not to implement the associated code updates or document modifications into TRACE. Please note that at the time of publication, these trouble reports may have already been closed.

Trouble Report 677 – Regression test problem CONTANDirectControllers-RST1 dies with programming error.

This test problem restarts test problem CONTANDirectControllers and ends up backing up because the pool temperature has increased to 5K above the tSat. The backups eventually result in the

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calculation stopping and the error message incorrectly indicates a programming error. The cause of the backups was traced to the restart test problem changing DTMAX from 0.1 to 1.0. In addition, these test problems used the TRAC-P EOS fits, rather than the TRACE steam tables. With DTMAX changed back to 0.1 and using the TRACE steam tables, these test problems run without failure. These input changes were included in the HTAbovePCrit update, which is pending NRC review and resolved this trouble report.

Trouble Report 681 – Solute mass balance is not consistent with SETS or fully implicit numerical methods options.

The solute concentration may be adjusted at the end of a time step if the solute concentration is calculated to be above the solubility limit. This implies that the new time macroscopic density for the solute used by the SETS and fully implicit numerical methods may not be consistent with the adjusted upstream solute concentration. There was also a concern that the solute concentrations used when a two-phase level is present may not be consistent with the level tracking model. The FxBoronDensity and FxSoluteBackup updates were developed to make the solute mass balances consistent with the SETS and fully implicit numerical methods. These updates went into versions 5.850 and 5.861, respectively. However, the concern about whether or not the correct solute density was used when a level was present required that this trouble report stay open. Included in update HTAbovePCrit is test problem CoreAvBoronConcen.Mod22 that is a boil off test problem with the level tracking and solute tracking models turned on. This test problem demonstrates that the solute mass balance equations are consistent with the level tracking model. This resolves this trouble report.

Trouble Report 784 – B10 mass conservation equation solved by TRACE not documented.

When ISOLUT > 0, the TRACE solute tracking model is turned on. The solute is typically boric acid or sodium pentaborate. The neutron absorber in these solutions is B10. If the boron in the solute is enriched to a constant B10 concentration, then there is no need to solve the B10

mass conservation equation. The fraction of the solute that is B10 will be a constant. However, in some cases the B10 enrichment for load following may be different than the B10 enrichment for emergency shutdown. If the B10 enrichment is not a constant for a given plant, then the B10 mass conservation equation must be solved to determine the B10 concentration in each fluid cell. The documentation changes required to document the B10

mass conservation equation are in file B10Doc.tar.gz (gzipped tar file), that was submitted as documentation

changes to the TRACE Development Cloud. This resolves this trouble report.

Trouble Report 801 – Enthalpy flows at cell edges.

Several Regression test problems were failing because these test problems included control system models to estimate enthalpy flows (offset_up_rev04, offset_up_rev05, and offset_up_rev06). These test problems were based on an earlier version that had a PIPE component replaced with an SJC PIPE. The control system logic was failing because signal variable references to obtain upstream fluid properties were now referencing SJC PIPE components. A SJC PIPE has no fluid cells associated with it, since it only represents a cell edge. Therefore fluid cell properties cannot be obtained from a SJC PIPE. Update EditsMB includes a code fix that allows TRACE to calculate and store the flow enthalpies. These three test problems were modified to use that capability, so that upstream fluid properties were not required by the control system to calculate the flow enthalpy. The EditsMB update is pending NRC review and resolves this trouble report.

Trouble Report 816 – Browns Ferry RHR heat exchanger initial pressure is too large during steady-state.

For a Browns Ferry steady-state model the initial pressure for a Residual Heat Removal heat exchanger was ~3 atms and was expected to be ~1 atm. At steady-state the initial pressure in this fluid component was determined by the static head from the cell center of the wetwell to the cell center in the RHR pipe. The flow path length from the edge of the wetwell to the RHR was 4.55 m. However, the flow path length from the cell center of the wetwell to the edge of the wetwell was 19 m. The angle of the side junction was 90 degrees, which implies that the flow path length is the hydraulic diameter divided by 2 or 19 m. GRAV for this side junction was 1.0, which implies that it is pointing down and the RHR was ~22 m below the cell center of the wetwell. This is not the correct elevation change for this RHR. The flow path length of 19 m for the wetwell is in a horizontal direction and therefore should contribute no change in elevation. The change in elevation should only be associated with the flow path length from the wetwell edge to the center-center of the RHR PIPE. The FxSideTubeGrav update makes the change in TRACE so that elevation change for a side junction from the cell center to the side junction cell edge is determined by the orientation of the primary pipe and the angle of the side junction. The GRAV input for the side junction cell edge is the flow path length from the side junction cell edge to the fluid cell center that is connected to the side junction. For the Browns Ferry RHR, the wetwell is a vertical pointing PIPE component with a side junction at 90 degrees,

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which indicates that from the cell center of the wetwell to the side junction cell edge there is no change in elevation. The GRAV = 1.0 for the side junction cell edge points that flow path down 4.55 m. The total change in elevation for the RHR is 4.55 m. Update FxSideTubeGrav is pending NRC review and resolves this trouble report.

Trouble Report 830 – Wall heat transfer above the critical point.

Above the critical pressure, the TRACE steam tables set the water and steam properties to the same values consistent with the supercritical water properties obtained from the steam tables. The decision on whether the void fraction should be zero or one is based on the initial void fraction. If it is close to zero, then it is forced to be zero and if it is close to one, then it is forced to be one. The expectation was that this would force the TRACE heat transfer models into single phase heat transfer. However, if the void fraction is zero, then subcooled boiling could be calculated and if the heat flux is larger than the critical heat flux, then the TRACE heat transfer could be forced into post-CHF heat transfer regimes. Update HTAbovePCrit forces the heat transfer to be single phase heat transfer if the local pressure is above the critical pressure. This update is pending and resolves this trouble report.

Trouble Report 831 – Missing documentation in Chapter 2 of the Users Guide for significant difference testing output file.

The output file for significant difference testing (.sno file) was not included in the TRACE documentation. The significant difference testing capability in TRACE is used by code developers to determine and investigate differences between two different versions of TRACE. Command-line help documentation for this .sno file was added to the MergeGraphOut update. This update was submitted to the NRC for review and resolved this trouble report.

Trouble Report 833 – Duplication of coding to calculate mass flow rates and flow enthalpies.

As TRAC-B and RELAP5 capabilities were added into TRACE, blocks of coding to calculate mass flow rates and flow enthalpies were duplicated in a number of routines to support different sets of new output variables used by TRAC-B and/or RELAP5. These calculations were for output or graphics variables that were not used directly or indirectly in the TRACE thermal-hydraulics solution. The MergeGraphOut update addresses this trouble report by merging more routines for graphic output variables together. This reduces the number of

places where mass flow rates and flow enthalpies are calculated.

Trouble Report 837 – Logic in RestoreEdges for PLENUM component is in error.

The logic in routine RestoreEdges was in error for PLENUM components and did not correctly loop over all of the junctions associated with a given PLENUM component. Fixes for this logic were included in the EditsMB update. The EditsMB update was resubmitted to the NRC for review and resolves this trouble report.

Trouble Report 844 – Divide by zero in V5.1154 in subcooled choking model.

While debugging a SJC to VESSEL connection, a developer came across a case where the subcooled choking model would fail. For this specific problem, the upstream pressure was approaching a small number and the iterative solution solving for the subcooled choking model found a case where the perturbation in the solution was so small that change in the function was zero, but the function had not reached a converged solution. The change in the function was used in the denominator of a given expression and resulted in division by zero. The fix was to exit this iterative loop if the perturbed function was the same as the unperturbed function, with converge set to false. This forced the choking model to use a homogeneous equilibrium choked flow mass flux. This fix was included into the FxDTMINLogic update. The FxDTMINLogic update was submitted to the NRC for review and resolves this trouble report.

Trouble Report 845 – Code runs with time step sizes below DTMIN in version 5.1154.

It was observed that TRACE versions 5.1154 and earlier could run with time step sizes less than DTMIN. TRACE is expected to stop if the time step size goes below DTMIN, which indicates either a code problem or that DTMIN is too large. Investigation of this indicated that there were a number of time step controls applied after the adjustment to DTMIN that could force the time step size to be less than DTMIN. The FxDTMINLogic update modified this logic so that time step sizes below DTMIN were not allowed. This update was sent to the NRC for review and resolved this trouble report.

Trouble Report 849 – User reported change in core average void fraction between versions 5.0P4 and 5.0P5 was too large.

User reported that change in core average void fraction for test problem pbtt_trace_sa between versions 5.0P4 and 5.0P5 was larger than expected. Investigation of

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Thermal-Hydraulics Codes News April 2019

this problem indicated that the change in core average void fraction could be traced to improvements in the linearization of the interfacial drag terms and a fix to the CHAN component leakage path momentum equation solution. The pbtt_trace_sa test problem is a Regression test problem that is used to test communication logic between TRACE and PARCS and is not a reviewed Peach Bottom model. The bypass flow fraction for this input model was significantly larger than expected. With the bypass leakage flow significantly larger than expected, the fix to the momentum equation for the leakage path resulted in a significant change in the core average void fraction. When the leakage flow path input model was modified to provide a reasonable steady-state leakage flow, then the differences in core average void fraction between the code versions were not significant. Fixes for the Regression test problems pbtt_trace_sa and pbtt_trace_ss were included into update FxCSSRst and resolved this trouble report.

Trouble Report 850 – For pressures above the critical pressure if NCG is present, then the current EOS logic in ThermIAPWS and ThermD2oST is in error

When the pressure is above the critical pressure, the TRACE steam table logic forces the void fraction to be zero or one. However, if non-condensable gas (NCG) is present, then the void fraction cannot be zero. Update HEMAbovePCrit and TsatAbovePCrit were developed to address this trouble report and were submitted to the NRC for review.

Trouble Report 852 – HEM for supercritical flow.

When NCG is present with the total pressure larger than the critical pressure there are two possible flow regimes: 1) void fraction of one with a mixture of steam and NCG, 2) non-zero void fraction with compressed supercritical liquid and the gas phase a mixture of steam and NCG. The steam can be supercritical or subcritical depending upon the partial pressure of the steam. The evaporation of liquid phase to steam or the condensation of steam requires an effective saturation temperature. In addition, heat transfer correlations for supercritical flow require a pseudo-critical temperature, which is defined to be the temperature when the specific heat reaches a maximum at a constant pressure. The TsatAbovePCrit update was developed to include a pseudo-critical temperature for supercritical flows. The CleanHTAbovePC update adds logic to the steam table initial and boundary condition checking that ensures that appropriate initial conditions and boundary conditions for supercritical flows are set. These two updates were submitted to the NRC for review. This trouble report is resolved.

Trouble Report 853 – Version 5.1156 fails null backup with test problem grid_chan.Rev1R.

The non-null backup failure for this test problem was traced to the grid spacer modeling using arrays vlx and vvx. These two arrays are used as temporary storage by other models in TRACE. When the grid spacer model was changed to use vln and vvn, then this backup problem was resolved. This fix was included in the TsatAbovePCrit update, which is a pending update. This resolves this trouble report.

Trouble Report 855 – When NDIA1 = 2, incorrect hydraulic diameter is supplied to the TMin correlations.

When NDIA1 = 2, the hydraulic diameter that is normally passed to the heat transfer coefficient models in TRACE is replaced with a user input thermal diameter. However, the Shumway minimum temperature for film boiling model uses a Reynolds number based on the hydraulic diameter. The TminHydDFix update fixes this logic error so that the Shumway correlation uses the correct diameter. Update TminHydDFix was submitted to the NRC for review and resolves this trouble report.

Trouble Report 859 – Input checking for consistency for tube bank dimensions needs to be added to TRACE.

Current versions of TRACE do not include input checking on tube bank pitch-to-diameter in the longitudinal direction (P/D), tube diameter (D), number of tube rows in the longitudinal direction (tubeRows(j)), and axial height of the fluid cell (dz(j)). At a minimum dz(j) must be larger than or equal to (P/D) x D x tubeRows(j). The total height of the tube bank must also be smaller than or equal to the total height of the fluid cells that contain the tube bank. These input checks for tube bank dimensions were added to the MergeGraphOut update. The MergeGraphOut update was submitted to the NRC for review and this resolves this trouble report.

Trouble Report 861 – Logic errors in PUMP model and PUMP documentation needs to be updated.

Logic errors were discovered in the PUMP model for pump type 2. These logic errors were associated with the expected PUMP behavior when the PUMP trip was initially off, then turned on, and then at a later time turned back off. For example, when the pump trip is initially off, then the pump speed is constant at the input pump rotational speed. The pump trip changing to on is then used to cause the PUMP component to simulate a pump coast down. When the pump is tripped back off then the pump speed could be forced to be zero to simulate a locked rotor condition. Update FxOMGOFF fixes the logic errors for the PUMP component and updates the PUMP documentation. Update FxOMGOFF was submitted to NRC for review and resolved this trouble report.

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Trouble Report 865 – Inconsistencies in the Decay Heat Model gFactor.

Developer noted inconsistencies in the TRACE decay heat model neutron capture effect. Specifically, the ANS standard indicated that the neutron capture effect fit was only valid for shutdown times less than 10000 seconds. In addition, the ANS standard include a table for the neutron capture effect that covered times out to 109

seconds. The ANS neutron capture effect fit includes dependency upon operating time, time after shutdown, and number of fission per fissile atoms, while the table assumes infinite operating time. Updates FxGFactor and FxGFactor2 were developed to resolve this trouble report. Update FxGFactor went into version 5.1168 and update FxGFactor2 has been submitted to the NRC for review. Update FxGFactor included the ANS standard table for neutron capture effect and smoothed the transition from the neutron capture fit to the table to take into account that the fit was not for infinite operation. The FxGFactor2 corrects the default time for infinite operations to be consistent with the ANS decay heat standard and adds consistent documentation changes to the Theory Manual and Users Guide. This update resolved this trouble report.

Trouble Report 868 – Roundoff error in the Churchill wall friction factor correlation.

It was observed during a TRACE debug session that the Churchill correlation was sensitive to round-off. This is to be expected, since the correlation involves terms raised to the power 16 and then raised to the power of 1/12. As Reynolds number approaches zero, the Churchill correlation approaches laminar fanning friction factor of 16/Re. As Reynolds number increases, through the transition between laminar and turbulent flow the Churchill correlation approaches full turbulent wall friction. Was not able to find the appropriate logic to smooth the transition between laminar friction factor, Churchill, and full turbulent wall friction that significantly reduced the sensitively of the wall friction factor to round-off error and did not significantly impact a number of Regression test problems. It was decided to not fix this problem. This resolves this trouble report.

Trouble Report 872 – Inconsistency in CANDU horizontal pressure tube input processing between TRACE V5.0P5 and TRACE user manual (and therefore SNAP.

HTSTR BC option 14 implies that HTSTR surface is connected to a CANDU horizontal pressure tube. When HTSTR BC option 14 was used, then input processing for the input variables HCOMIN, HCELLII, HCELLJI, HCELLKI, ZOVERD, HCOMON, HCELLIO, HCELLJO, and HCELLKO did not use load format. For other

HTSTR BC options, these inputs would use the load format. Load format input capability gives the user vector input capability. Such as repeat input data values and fill vector with value, and interpolation of input between boundary points in the input. Update FxHGen includes user manual corrections to make documentation consistent with the TRACE input processing. This update has been submitted to the NRC for review. This resolves this trouble report.

Trouble Report 876 – Mass of hydrogen produced from Zr-H2O reaction was in error.

It was determined that the formula for the calculation of the mass of hydrogen produced for the TRACE metal-water reaction model was in error. For cylindrical geometry the TRACE formula for the mass of hydrogen produced included a factor of 0.5, that was removed. For spherical geometry the TRACE formula for the mass of hydrogen produced was missing a factor of 1/3. These formulas were corrected with the FxGen update, which has been submitted to the NRC for review. In addition, documentation was update to make it clear the basis of these formulas. This resolves this trouble report.

Trouble Report 877 – User wanted to simulate grid spacers for electrical heated rods.

User requested to be able to simulate grid spacers for electrical rods. Current coding in TRACE assumes grid spacer model is associated with fuel rod heat structures, which implies nofuelrod = 0. However, for electrical heated rods nofuelrod would equal 1. In addition, user requested plot variables for heat structure cell number where grid is located, grid spacer heat flux, and rewet status. Update FxGridSpacer resolves this trouble report and was submitted to the NRC for review. This resolves this trouble report.

Recent RELAP5 User ProblemsELAP5 user problems reported or resolved are summarized in each issue of the newsletter. If you encounter a problem with RELAP5, please

report it to Joseph Staudenmeier (Joseph.Staudenmeier@nrc.gov) and Doug Barber (dbarber@islinc.com). The complete list of RELAP5 user problems, including a description of the problem, status (resolved, in work, on hold, or unresolvable) and, if resolved, the manner of resolution is available on the https://www.nrccodes.com web site.

R

Since the last TH newsletter was published, seven new RELAP5 user problems were submitted. A description of these user problems is provided below.

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No. 2018-01 (02-14-18), Resolved

Code Versions Affected: RELAP5/Mod3.3Patch5

The user reported a rather large error (up to 15%) in mass conservation. The provided input model consisted of one single volume (0.1 m3) which is filled from a time-dependent volume with noncondensable nitrogen. The single volume is initialized as only noncondensable at 3.5e5 Pa and 323 K. The time-dependent volume has constant pressure of 5.5e5 Pa and temperature of 433 K all nitrogen. In between the volumes is a leakage junction with area 2.1e-8.

A comparison of the change of mass by the integrated mass flow was performed:(1) Δmrelap = mflowj-10000 * dt= 4.41e-3 kg(2) Ideal gas law: mgas = (P2V)/(RT2) - (P1V)/(RT1) = 5.13e-3 kg(3) Change due to density: Δmρ = V(ρ2 – ρ1) = 4.87e-3 kg

It was noted that It was noted that Δmrelap is consistent with what is reported by RELAP5 as emass. The total mass of the system is about 0.3kg so the relative error with respect to the total mass is about 0.1%. It's a bit surprising that this small relative error would lead to an error in mass flow of 15%.

The user tried different choking models, moody and ransom-trap, but it made little difference. It is noted that somehow steam enters the system. The volume NC quality (quala) is 0.9988.

The user wanted to know if this a bug, expected error or user error.

Resolved 02-14-18: In order to model pure NC, as the user was attempting to do, the g-flag must be set to 2 on Word 5 of Card 120. Without this flag, the code will attempt to seed the volume with a little bit of liquid. That's why quala was 0.9988 instead of 1.0.

The input was therefore modified by adding the following card:

120 3010000 0.0 h2o system 2

With this change, the integrated mass flow of volume 3010000 and the change in mass due to change in density are both equal to 4.41e-3 kg.

No. 2018-02 (02-15-18), In Work

Code Versions Affected: RELAP5/Mod3.3Patch5

The user reported an error in the RELAP5 manuals related to the calculation of the length scale for a crossflow junction in the junction geometry input. The basis stated for calculating the y-length scale is inappropriate in some cases. For instance, when there is a small cross section flow area, the length scale will be very large and can substantially exceed the dimensions of the node to which the crossflow junction is connected. If this length is used in a momentum equation it will result in too low of an acceleration for the crossflow. It seems that a better length scale would be ½ of the distance from the crossflow exit to the node boundary in the direction of the crossflow.

No. 2018-03 (06-11-18), Resolved

Code Versions Affected: RELAP5/Mod3.3Patch5

The developer discovered an error in the Groeneveld 2006 tables that went into version 3.3ka.qTab(3,18,5) was set to 115674.0, but it should have been 11567.

Resolved 06-22-18: The correction identified by the developer was implemented into the code.

No. 2018-04 (06-12-18), In Work

Code Versions Affected: RELAP5/Mod3.3Patch5

The user reported differences between 3.3Patch02 and 3.3Patch05 in the prediction of void fraction at the break which significantly influences evolution of the transient in general. This was for code validation against PKL H1.2 test (1% downward oriented SBLOCA). The difference is troubling since 3.3Patch05 appears to give worse results than 3.3Patch02.

No. 2018-05 (08-15-18), In Work

The user ran a test of the thermal radiation system with R5M33P05 standard, e.g., without my modifications. Running new was ok, but when running restart with additional radiation sets added, the user got a segmentation fault and iradht reported destroyed values of view factors. The problem is caused when calling ftbsft at the end of rradht. Before this call the view factors are correct, but after the call the view factors are destroyed.

No. 2018-06 (08-29-18), In Work

Code Versions Affected: RELAP5/Mod3.3Patch5

The user reported an error in subroutine rpipe.ff at line 1186 when reading cards CCC2101 or CCC2201.

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Argument l3c(2) should be replaced with l3ex(2), i.e., call inp5(l3ex(1), l3ex(2), 1, 3, 0, nv, 3, 1, 1, jj, ...

No. 2018-07 (11-16-18), In Work

Code Versions Affected: RELAP5/Mod3.3jz

The user reported that RELAP5/ MOD3.3 (build jz) generates an error message when negative weighting factors are entered on cards 300017nn or 300018nn. Surprisingly, this happens only if the last card of the block of weighting data contains a negative number. Negative numbers on previous cards are read without problem.

For example, this input:* volume weighting factors30001701 121010000 0 1.530001702 122010000 0 -0.5

generates an error message: 0Volume weighting factors 0 vol.no. weight factor vol.no. weight factor121010000 1.50000122010000 -0.5000000******** Volume density weighting factor less than or equal to zero. etc...

Whereas the following input does not:* volume weighting factors30001701 121010000 0 -0.530001702 122010000 0 1.5

It looks like the negative weighting factors are read and used correctly by the code. Physically the meaning is that the local reactivity feedback has a different sign than the global. The user has places where there is a local positive temperature feedback, and therefore would like to use negative weighting factors. A request was made to consider removing the error message or converting it into a warning message to let the user decide if such values are intended.

Status of NUREG/IAsince the Spring 2018 CAMP meeting, there have been several NUREG/IAs completed or published. The following is a list of recently

completed NUREG/IAs:S

NUREG/IA-0481, Evaluation of TRACE Spacer Grid Model with FLECHT-SEASET Reflood Test (Rep. of Korea)

NUREG/IA-0482, Using TRACE, MELCOR, CFD, and FRAPTRAN to Establish the Analysis

Methodology for Chinshan Nuclear Power Plant Spent Fuel Pool (Taiwan, ROC)

NUREG/IA-0483, Loss of Flow Analysis of Maanshan Nuclear Power Plant with RELAP5/SNAP (Taiwan, ROC)

NUREG/IA-0484, PACTEL Small Break LOCA Experiment SBL-30 Calculation with TRACE Code (Finland)

NUREG/IA-0486, Simulation of the G3.1 Experiment at PKL facility using RELAP5/Mod3.3 (Spain)

The following is a list of pending NUREG/IAs:

NUREG/IA-0497, IBLOCA analysis for Vandellòs-NPP using RELAP5/MOD3.3. Sensitivity calculations to EOP actions. (Spain)

NUREG/IA-0489, RELAP5 Model of a CANDU-6 (Embalse) Nuclear Power Plant: Application to a Turbine Trip Event (Argentina)

NUREG/IA-0508, Validation of RELAP5/MOD3.3 Friction Loss and Heat Transfer Model for Narrow Rectangular Channels (Korea)

NUREG/IA-0491, Assessment of the Wall Condensation Model with non-condensable Gas in RELAP5 and TRACE for Vertical Tube and Plate Geometry (Korea)

NUREG/IA-0492, Assessment of TRACE V5.0 Patch 4 Code Against PWR PACTEL Loop Seal Clearing Experiments (Finland)

NUREG/IA-0494, RELAP and TRACE Simulation of Hot Leg Break LOCA Experiment on LSTF (Slovenia)

NUREG/IA-0502, Post-Test Analysis of Cold Leg Small Break 4.1% at PSB-VVER Facility using TRACE V5.0 (Czech Rep.)

NUREG/IA-0511, Simulation of ROSA-2 Test 2 Experiment. Application to Nuclear Power Plant (Spain)

NUREG/IA-0504, Assessment of TRACE 5.0 against ROSA-2 Test 3 Counterpart test to PKL (Spain)

NUREG/IA-0487, Simulation of the PKL-G7.1 experiment in a Westinghouse Nuclear Power Plant using RELAP5/Mod3.3 (Spain)

NUREG/IA-0488, Simulation of the LSTF-PKL Compartment G7.1 Test at PKL facility using TRACE 5 (Spain)

NUREG/IA-0485, TRACE VVER-440/V213 Model Validation (Ukraine)

NUREG/IA-0490, TRACE VVER-1000/V320 Model Validation(Ukraine)

NUREG/IA-0493, The Ultimate Response Guideline Simulation and Study for Lungmen (ABWR) Nuclear Power Plant Using RELAP5/SNAP (Taiwan ROC)

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Thermal-Hydraulics Codes News April 2019

NUREG/IA-0512, Simulation of ROSA-2 Test 3 Counterpart with TRACE 5, Application to Nuclear Power Plants (Spain)

NUREG/IA-0513, Semiscale S-NC-02 and S-NC-03 natural circulation tests performed by RELAP5/MOD3.3 Patch5 (Slovenia)

NUREG/IA-0503, Post Test Analysis of ROSA-2 Test 2 (IBLOCA) with TRACE (Spain)

NUREG/IA-0505, Assessment of TRACE 5.0 against ROSA-2 T5 (MSLB) with SGTR (Spain)

NUREG/IA-0495, Assessment of NEPTUN Reflooding Experiment 5050 and 5052 with TRACE V5.0 Patch (Finland)

NUREG/IA-0501, Investigation of the Loop Seal Clearing Phenomena for the ATLAS DVI Line and Cold Leg SBLOCA Tests using MARS-KS and RELAP5/MOD3.3 (Korea)

NUREG/IA-0496, The Analysis and Study of the ELAP Event and Mitigation Strategies using TRACE code for Maanshan PWR (Taiwan ROC)

NUREG/IA-0498, Core Exit Temperature Response during an SBLOCA Event in the Asco NPP (Spain)

NUREG/IA-0499, Post Test Calculation of the PKL2 G7.1 using Relap5/Mod3.3 (Spain)

NUREG/IA-0500, Post Test Calculation of the ROSA2 Test 3 using Relap5/Mod3.3 (Spain)

NUREG/IA-0509, LBLOCA Uncertainty Analysis of Maanshan Nuclear Power Plant with RELAP5/SNAP and DAKOTA (Taiwan)

CAMP members are reminded that there is a simplified NUREG/IA process and that members should submit an NRC form 426 with a signature in Item 4.8. Members should use Microsoft Word styles to configure the document, and that recently posted reports can be examined in order to follow the style. Specifically, the Arial font should be used as much as possible, since it is the NRC preferred font; this makes conversion to the final PDF format less troublesome. A new Word template is available for CAMP members on NRCCodes.com.

The CAMP members’ responsibility is to follow the guidelines so that all NUREG/IA have a uniform format. Members can refer to a previously published, NUREG-0650, Revision 2, as the reference for formatting their report. Members should also have a technical editor review the report before submitting it.

CAMP members can e-mail Dr. Kirk Tien at Kirk.Tien@nrc.gov or Mr. Tarek Zaki at Tarek.Zaki@nrc.gov, or call Dr. Tien at 301-415-1606. Members should inform NRC of proposed NUREG/IA titles for next year as soon as possible. The NRC publishing branch would like to plan their resources and support based on this estimate. The preferred

procedure is to bring up the country proposed In-kind contribution during the TPC meeting at CAMP meetings, and have CAMP members concur on the topic report. It is also preferred that reports be uploaded in Word format to the country folder on NRCCodes.com.

Upcoming Spring CAMP Meetinghe Spring 2019 CAMP Meeting is scheduled for May 29-31, 2019, and will be hosted in Valencia, Spain. The TPC meeting is scheduled to be held

on the afternoon of May 31st. The meeting is being hosted by Prof. Sebastian Martorell of the Polytechnic University of Valencia (UPV) and Miguel Sánchez of Nuclear Safety Council (CSN) and will take place at the Universitat Politècnica de València (Polytechnic University of Valencia), Nexus Building (Building 6G), Avenida de Los Naranjos, Valencia, Spain.

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Details and registration information are posted on the NRCCodes Sharepoint site (https://www.nrccodes.com). Please contact Tarek Zaki (Tarek.Zaki@nrc.gov) or Doug Barber (dbarber@islinc.com), if you have any questions regarding the meeting.

Other Items of Interestode users are encouraged to visit the SharePoint site, https://www.nrccodes.com. You can join in discussions, download relevant

documents, access TRACE (Bugzilla) and RELAP5 User Problem descriptions, and for CAMP members, access information on the CAMP program including status of proposed and active in-kind contributions, announcements and a calendar of upcoming events. The discussion area supports asking questions and sharing experiences. As a reminder, TRACE bugs may now be reported to the following email: TRACE.Bugs@nrc.gov.

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Christopher Murray is the contact point for the SharePoint site. If you have any problems accessing the site, or if you have any questions or would like additional information on the NRC TH codes, please contact Christopher Murray at Christopher.Murray@nrc.gov.

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