IN-PROCESS ELECTROCHEMICAL CORROSION POTENTIAL...

17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors August 9-13, 2015, Ottawa, Ontario, Canada

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IN-PROCESS ELECTROCHEMICAL CORROSION POTENTIAL MONITORING EXPERIENCE AT BOILING WATER REACTORS UTILIZING ON-LINE

NOBLECHEM™ FOR MITIGATION OF INTERGRANULAR STRESS CORROSION CRACKING

Susan Garcia1, Steve Williams2, Collin Custer3, Brian Colson4, Joe Giannelli5, Dave Morgan5, and Jeremie Varnam5

1Electric Power Research Institute, 3420 Hillview Ave., Palo Alto, CA 94304 2Duke Energy – Brunswick Nuclear Plant, 8520 River Rd SE, Southport, NC 28461

3Exelon – Nine Mile Point Nuclear Station, P.O. Box 63, Lycoming, NY 13093 4Southern Nuclear – Edwin I. Hatch Nuclear Plant, 11028 Hatch Parkway N., Baxley, GA 31515

5Finetech, Inc., 959 U.S. Highway 46 East Suite 403, Parsippany, NJ 07054

ABSTRACT

Reduction of electrochemical corrosion potential (ECP) of Boiling Water Reactor (BWR) vessel and internals is essential for mitigating intergranular stress corrosion cracking (IGSCC). Hydrogen water chemistry in moderate concentrations (HWC-M) or at reduced injection rates with noble metals are IGSCC mitigation strategies employed by BWRs. In-vessel lower plenum ECP measurements have been obtained during operating conditions for BWRs utilizing normal water chemistry, HWC-M and NMCA. ECP monitoring for BWRs with OLNC has mainly been performed using probes mounted in external piping in contact with reactor coolant sample streams. The chemistry conditions and radiolysis effects at these locations are typically not as aggressive as in the lower vessel head region, where no direct in-vessel ECP measurements have previously been made during an OLNC injection.

Brunswick 1 has utilized HWC-M as a mitigation strategy for protection of IGSCC since 1989. Two platinum ECP electrodes and a pre-oxidized stainless steel billet were installed in a modified local power range monitor (LPRM) during the 2014 refueling outage, and a HWC benchmark test was performed while operating under HWC-M. In August 2014, the station transitioned to On-Line NobleChem™ (OLNC). This paper will present the industry-first lower plenum in-vessel ECP measurements prior to and during the transition from HWC-M to OLNC. It will also summarize BWR experiences at plants utilizing OLNC with in-process ECP monitoring at reactor recirculation piping and bottom head drain line locations.

Keywords: intergranular stress corrosion cracking, Electrochemical Corrosion Potential, noble metals, On-Line NobleChem™

1. INTRODUCTION

Reduction of electrochemical corrosion potential (ECP) of Boiling Water Reactor (BWR) vessel and internal stainless steel surfaces is essential for mitigating intergranular stress corrosion cracking (IGSCC). Hydrogen water chemistry in moderate concentrations (HWC-M) or at reduced injection rates with Noble Metal Chemical Application (NMCA), the original NobleChem™ process, are IGSCC mitigation strategies employed by BWRs and implemented worldwide. In-vessel lower plenum ECP measurements have been obtained during operating conditions for BWRs utilizing normal water chemistry, HWC-M and NMCA, demonstrating the effectiveness of HWC-M and NMCA chemistry regimes for IGSCC mitigation [1]

A third IGSCC mitigation strategy employed by BWRs is On-Line NobleChem™ (OLNC) with reduced HWC, a second generation noble metals process where the catalyst (platinum) is injected into the feedwater stream over a ten day period during power operation. Applications are performed


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approximately once a year (typically every 11 to 16 months), beginning about 90 days after start-up from a refuel outage. The now obsolete NMCA was performed during a unit shutdown (either mid-cycle or for the refuel outage) approximately every six years. The quantity of noble metal injected during an OLNC application is a factor of 3 lower than the quantity that had been injected during NMCA [1].

As shown in Figure 1, most BWRs are now implementing or plan to implement OLNC as the IGSCC mitigation strategy. Demonstration of the effectiveness of OLNC for IGSCC mitigation has been limited to ECP monitoring with probes mounted in external piping (recirculation, reactor water cleanup and bottom head drain lines) and external monitoring skids. The chemistry conditions at these locations are typically not as aggressive as in the lower vessel head region, for different reasons:

The coolant in the recirculation loops has a low oxidant concentration because of radiolysis-driven recombination from radiation fields in the lower downcomer.

The coolant in the reactor water cleanup system is drawn primarily from the recirculation loops.

The bottom head drain line coolant will have about the same total oxidant concentration as in the lower plenum, but a lower ratio of peroxide to molecular oxygen as a result of peroxide decomposition in the piping.

External monitoring skids draw coolant from either the recirculation loops or reactor water cleanup.

There had previously been no direct in-vessel ECP measurements during an OLNC injection at full power, with ECP probes in the lower plenum at a conservative location well below the core plate. At this location, coolant chemistry is unaffected by radiation from the core, which would drive recombination reactions that would reduce the oxidant concentration and ECP. ECP probes were installed in a modified LPRM at Brunswick 1 to measure ECP during the transition from HWC-M to OLNC. The expectation was that this first OLNC application at a plant without prior NMCA would reduce the ECP below -230 mV(SHE), the threshold for IGSCC mitigation. If successful, the data would demonstrate the effectiveness of OLNC to:

1. Deposit sufficient catalytic material on surfaces in regions where IGSCC mitigation is targeted, and,

2. Mitigate IGSCC in regions of high oxidant concentration.

Mitigation of IGSCC in the more aggressive environment will add to the laboratory and plant experience demonstrating that OLNC is a viable IGSCC mitigation strategy. These measurements further support the industry position on the effectiveness of OLNC that is presented in BWRVIP-62 Revision 1 [1].

This paper presents industry-first lower plenum in-vessel ECP measurements during the transition from HWC-M to OLNC with HWC at Brunswick Unit 1. The station’s technical basis for reactor vessel internals IGSCC mitigation strategy and monitoring is discussed along with ECP measurements of the two chemistry regimes and associated hydrogen ramp tests. BWR experiences at other plants utilizing OLNC with in-process ECP monitoring at reactor recirculation piping and bottom head drain line locations are also summarized.

2. BRUNSWICK 1 EXPERIENCE

2.1 Background

Brunswick Nuclear Plant (BNP) Units 1 and 2 have utilized moderate HWC-M as a mitigation strategy for protection of IGSCC of reactor vessel internals and reactor recirculation piping since 1989. To reduce operational radiation exposure associated with HWC-M, Unit 1 implemented OLNC in August 2014. In the March 2014 refueling outage prior to the chemistry regime transition, Brunswick Unit 1 installed ECP probes. While all of the OLNC industry experience associated with ECP monitoring has been associated


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with probes mounted in external piping and monitoring skids, Duke Energy Progress made the decision to install probes in an accessible, but more aggressive chemistry location.

The station decided to install two platinum ECP electrodes and a pre-oxidized stainless steel billet in a modified local power range monitor (LPRM). The coolant flow holes in the LPRM were shifted downward to coincide with a flow hole made by electrical discharge machining (EDM) in the in-core housing, allowing reactor coolant from well below the core plate to flow past the probes. The location is considered conservative because the oxidant concentration is higher than in external monitoring locations, and chemistry is unaffected by radiation from the core, which would drive recombination reactions that would reduce the oxidant concentration and ECP [2]. Brunswick Unit 2 has implemented similar modifications for ECP monitoring and scheduled implementation of OLNC as an IGSCC strategy in August 2015.

A schematic of an ECP electrode placement inside an LPRM cover tube is shown in Figure 2. Instead of using an iron/iron oxide electrode as shown in the figure, Brunswick Unit 1 installed a pre-oxidized stainless steel billet so that ECP measurements could be taken with confidence early on in the cycle as the new LPRM surface oxidized.

After start-up from the Brunswick Unit 1 outage, the unit continued with HWC-M chemistry for approximately 90 days before the initial OLNC application was performed at full power in August 2014. ECP data were collected during HWC-M, and pre- and post-OLNC.

2.2 Brunswick 1 HWC-M Hydrogen Injection Ramp Test

For the HWC-M IGSCC mitigation regime, a hydrogen injection ramp test was conducted in May 2014 to determine the minimum hydrogen injection rate to achieve IGSCC mitigation of reactor recirculation piping and targeted reactor internal components and welds. Brunswick Unit 1 installed a pre-oxidized stainless steel billet in-lieu of an iron/iron oxide probe so that ECP measurements could be taken with confidence early in the operating cycle as the new LPRM surfaces oxidized. By trending the stainless steel working electrode to LPRM surface potential difference, station personnel would know when the LPRM oxidation approached that of the pre-oxidized stainless steel working electrode. As the LPRM surface oxidizes, the potential difference between the LPRM surface and stainless steel billet (GND-SS) should approach 0 mV (±30 mV). Prior to the HWC ramp test, the potential difference between the LPRM surface and stainless steel billet was near -212 mV, indicating the LPRM surface had not yet fully oxidized. For purposes of the ramp test, the potential differences between the platinum probes and the pre-oxidized stainless steel working electrode were used for assessing IGSCC mitigation.

On May 22, 2014, the hydrogen ramp test for the HWC-M chemistry regime was commenced for Brunswick Unit 1. After an initial data collection period with feedwater hydrogen injection at the maximum set point of 39.8 scfm, hydrogen was lowered to 35 scfm. A three to four hour holding period commenced followed by another round of frequent data collection and evaluation. Based on the results, the hydrogen injection rate was either held to allow additional time for chemistry to stabilize or a recommendation was provided to plant operator to lower the hydrogen injection rate another 4 scfm. This pattern was repeated until the calculated ECP for the platinum to stainless billet was well above -230 mV(SHE). A similar process was utilized to raise the feedwater hydrogen injection rate by 4 scfm to recover IGSCC mitigation. Table 1 provides the timeline of the hydrogen injection rate changes.

ECP data collected during the hydrogen ramp test are shown below chronologically in Figure 3 and versus feedwater hydrogen concentration in Figure 4. In Figures 3 and 4, the difference between the two platinum reference probes and the LPRM surface is shown as “Pt1(2) – GND” while the difference between the platinum reference probes and the stainless steel working electrode is shown as “Pt1(2) – SS”. Initially, ECP was near -550 mV(SHE) at the maximum hydrogen injection rate of 39.8 scfm at the beginning of the cycle. As hydrogen was lowered, ECP values increased, as expected. Using the most conservative probe indication, the hydrogen ramp test indicated that approximately 0.52 ppm (21.2 scfm)


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feedwater hydrogen was required to reduce the ECP in the lower vessel head to <-230 mV(SHE). ECP data collection was repeated as feedwater hydrogen injections rates were raised, with ECP responding with lower values as expected. The data collected during the ramp test allowed station personnel to benchmark the primary parameter ECP results to secondary parameters, such as feedwater dissolved hydrogen and main steam line radiation monitor (MSLRM) readings. They were also able to benchmark results to radiolysis modelling software and demonstrate an effective IGSCC mitigation program with HWC-M.

At the conclusion of the ramp test, the station initially held the feedwater hydrogen injection rate at 27 scfm, with ECP in the lower plenum <-300 mV(SHE). The station later raised the injection rate to 33.6 scfm, above the rate required to reach the IGSCC mitigation threshold for the lower plenum of 21.2 scfm, to provide conservative margin for IGSCC mitigation of reactor recirculation piping and welds of interest (particularly core shroud horizontal weld, H4). The benchmarked BWR radiolysis model [4] was applied to predict the feedwater hydrogen concentration required to reduce ECP at the H4 weld below -230 mV(SHE).

2.3 Brunswick 1 OLNC Application

Following the HWC-M ramp test, Brunswick Unit 1 continued with a feedwater hydrogen injection rate of 33.6 scfm until OLNC injection commenced on August 4, 2014. Prior to lowering the hydrogen injection rate from 33.6 scfm to the new target injection rate for noble metals conditions, the hydrogen injection system was intentionally tripped to swap from the high hydrogen flow train to the low flow train. This allowed the station to restart hydrogen injection at a rate of 9.5 scfm for OLNC operation. The new hydrogen injection rate target was based on radiolysis modelling software [4] to achieve a hydrogen to oxidant molar ratio of 4:1 in the upper downcomer. After a short conditioning period, the OLNC application commenced on August 5, 2014, as indicated by the dotted vertical line in Figure 5.

ECP values plotted in Figure 5 were calculated from the platinum to stainless steel working electrode data. Prior to the application, the station was using these data to assess IGSCC mitigation as there was still a large potential difference between the stainless steel working electrode and LPRM ground surface, indicating that the LPRM oxidation was not equal to that of the pre-oxidized billet. After the OLNC application, this was a not an issue as the potential difference between the stainless steel billet and LPRM ground approached 0 mV, due to platinum deposition.

Following the start of the OLNC application, ECP readings quickly reduced to -400 mV(SHE) within the first day and were near -490 mV(SHE) after two days of application. The ECP data collected is similar to experience at other plants that measured ECP at external locations during OLNC applications. The ECP data from the more aggressive chemistry location at Brunswick 1 during the application provides additional confirmation that catalytic material (platinum), in combination with excess hydrogen in the coolant, suppresses ECP in regions where IGSCC mitigation is targeted. The use of OLNC, with reduced hydrogen injection rates, also provided the station with reduced operational dose rates at the main steam line radiation monitor, as shown in Figure 6. With OLNC, the dose impacts associated with N-16 are near those associated with normal water chemistry.

Additional monitoring during the remainder of the cycle has shown that OLNC with reduced HWC has maintained IGSCC mitigation goals with some upward drift of ECP, as expected. An OLNC reapplication will be performed in August 2015, along with the initial application on Brunswick 2. The Brunswick 1 experience demonstrates that OLNC can be effective even if the station does not have a prior history with NMCA.

3. NINE MILE POINT 1 EXPERIENCE

Most noble metal plants monitor ECP of reactor coolant in the mitigation monitoring system (MMS). During plant operations, the “as read” ECP values from the MMS skid may not be representative of the


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ECP of reactor internals and piping due to low dissolved oxidant concentration in the source water, noble metal deposition in the MMS ECP manifold from prior NMCA or OLNC application, or oxidant depletion by catalytic recombination on noble metal deposited in the supply line upstream of the MMS.

Nine Mile Point 1, a BWR-2 design, has two platinum ECP electrodes installed in a chemical decontamination flange on the suction side of one of the five reactor recirculation system (RRS) pumps and one working platinum ECP electrode in a Mitigation Monitoring System (MMS) skid manifold using RWCU inlet as the source water. It is believed that the sample line to the MMS ECP manifold has platinum deposits from prior NMCA and OLNC applications. Nine Mile Point 1 performed an NMCA application in May 2000 with approximately annual OLNC applications starting in 2006. ECP measurements and chemistry results from Nine Mile Point 1 allowed for a comparison between the MMS and RRS ECP responses during a hydrogen benchmark test.

An HWC benchmark test was performed starting on June 4, 2013. As shown in Figure 7, as the feedwater hydrogen injection rate was lowered from 6 scfm to 2.7 scfm, the MMS raw ECP (CUGnd(Pt) in Figure 7) remained stable while the recirculation system raw ECP values (RGnd(Pt1) and RGnd(Pt2) in Figure 7) became more negative, indicating an increase in ECP(SHE) as expected.

It is clear from the ECP and reactor coolant inlet (RCI) dissolved hydrogen (DH) and oxygen (DO) responses that there is a change in chemistry when the hydrogen (H2) injection rate is lowered to 2.7 scfm. There is a difference of several minutes between the response of the reactor recirculation ECP, MMS ECP and reactor coolant dissolved oxygen and hydrogen measurements. This difference is most likely due to the transit time of the coolant to the MMS and reactor coolant sample panel. The recirculation flange ECP probes, in direct contact with reactor coolant, respond first, followed by the MMS ECP and then by the reactor water dissolved oxygen concentration.

The reactor water hydrogen concentrations and raw ECP responses should follow changes in the hydrogen injection rate, with both decreasing as feedwater hydrogen is lowered. The RRS ECP probe response followed this trend while the MMS ECP probe response was stable, indicating the high likelihood of catalytic deposition on the sample supply line or ECP manifold, forcing low dissolved oxygen conditions. The reactor water dissolved oxygen response may be sluggish due to film oxidation reactions in the sample line as the oxidant concentration increases. The increase in oxygen may have reflected changes at a higher injection rate. However, the shift in dissolved gas concentrations is significant at this level, driving excess hydrogen near zero (excess hydrogen ~ DH – DO/8) . The maximum reactor coolant dissolved oxygen concentration was near 35 ppb, resulting in excess dissolved hydrogen near 7 ppb, indicating a molar ratio >2.The actual values for reactor water dissolved hydrogen and excess hydrogen are likely much lower than represented in Figure 7, apparently due to the short hold time to allow parameters to stabilize before hydrogen injection rates were increased.

During the feedwater hydrogen injection rate reduction period, the raw reactor recirculation ECP values were gradually decreasing, and no increase above zero was observed. This is most likely caused by the platinum probe de-activating on low excess hydrogen (excess hydrogen values are required to convert raw ECP signals to standard hydrogen electrode scale). The response from the reactor recirculation probes is not inverted so lower raw ECP values result in higher ECP(SHE) values (SHE - standard hydrogen electrode scale). However, the reactor recirculation probes show a small but sharp spike at 2.7 scfm, indicating that the molar ratio is less than 2 and that the platinum probes are no longer active.

The MMS ECP raw values remained near 0 mV as the feedwater hydrogen injection rate was lowered. When the feedwater hydrogen injection rate was near 2.7 scfm, the raw MMS ECP values began to rapidly increase at about the same time as spiking of the reactor recirculation raw ECP values. The sharp upward shift in raw ECP values for all 3 platinum probes indicate a hydrogen concentration at which the probes are approaching deactivation (molar ratio approaching 2). The reactor water DO response was somewhat delayed, indicating the need for relatively long hold times for the sample line to equilibrate with the change in chemistry.


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After the station determined that the inflection point had been reached during the ramp test, the feedwater hydrogen injection rate was raised back to the normal set point of 6 scfm in small steps over the course of 4 hours. While this did not allow sufficient time to accurately monitor changes in reactor chemistry to confirm the exact inflection point, a small spike in ECP was observed when feedwater hydrogen was raised from 2.4 scfm to 3.2 scfm, which was the same range where the inflection point was observed during the hydrogen benchmark test as the hydrogen injection rate was lowered.

The Nine Mile Point 1 ramp test validated requirements per BWRVIP-62 Revision 1 Section 5.4.3 [1] for effectively implementing hydrogen injection. Even though the MMS ECP did not respond earlier to a reduction of feedwater hydrogen injection rates, there was a clear response, validated by response of the reactor recirculation ECP probes and by the noticeable shift in dissolved gas concentrations, when the molar ratio dropped below two. The “as-read” ECP, data from the MMS during normal plant operations provide confirmation that sufficient hydrogen is being injected to maintain a molar ratio >2 in reactor coolant. However, the reactor recirculation ECP measurements show variations in response due to changes in plant radiolysis conditions, feedwater hydrogen concentration or local losses of catalytic activity.

4. HATCH 1 EXPERIENCE

Hatch 1 is a BWR-4 design with an extensive history of in-process ECP monitoring at LPRM and Bottom Head Drain Line (BHDL) locations, both pre- and post-NMCA. Hatch was a host site as part of an ECP measurement and mitigation program sponsored by the Japanese BWR Owner’s Group in the late 1990’s through early 2000’s [5]. The experience collected at Hatch, shown in Figure 8, demonstrated that low ECP values can be obtained in the lower vessel head region with HWC-M and NMCA.

While the LPRM ECP electrodes, shown in the upper right hand corner of Figure 8, are no longer in place following the study, Hatch 1 still performs ECP monitoring at the BHDL location along with the MMS skid. The BHDL ECP monitoring flange at Hatch 1 is located in the drain line and not a sample line from the drain, resulting in a short transit time (7 to 12 seconds) of reactor water from the lower plenum [3]. The source water for the MMS skid at Hatch 1 is the Reactor Recirculation System.

In the late 2000’s, Hatch began observing a difference between the “as read” ECP measurements at the BHDL and MMS locations, as shown in Figure 9. Beginning in 2009, there is a gradual increase in ECP at the BHDL location, which is expected nearly four years after an NMCA application due to some loss of catalytic material. A similar trend between ECP measurements at the two locations is also seen following the initial OLNC application. During these two time periods, the ECP at the MMS location remained stable, indicating one of the following three scenarios:

Low ECP values due to catalytic material deposition in the MMS ECP manifold, resulting in recombination of hydrogen and oxygen to produce a low oxygen environment

Low ECP values due to catalytic material deposition in the MMS supply, resulting in recombination of hydrogen and oxygen to produce a low oxygen environment

Low dissolved oxygen in the Reactor Recirculation System source water to the MMS

Following installation of a new MMS ECP manifold, a low oxygen environment was confirmed, likely as a result of prior noble metal deposition in the supply lines to the MMS skid. ECP measurements did not shift, as would be expected if oxygen was not depleted, following the ECP manifold replacement. A shift in ECP values of approximately 40 mV was observed in 2013 as the calculation to convert raw ECP signals to the standard hydrogen electrode scale was revised.

For the purposes of IGSCC monitoring during power operations, both the BHDL and the MMS probes demonstrate that the molar ratio is >2 and can be used towards justification of inspection relief. The BHDL measurements may also allow trending of the loss of catalytic activity under the hydrodynamic


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conditions at that location. Noble metal deposition in the Reactor Recirculation System supply piping to the MMS skid from two prior NMCA applications and multiple OLNC applications is likely driving recombination of hydrogen and oxidants to produce an oxygen depleted environment and low ECP values, which continue to be applicable for demonstrating that IGSCC mitigating chemistry is being maintained.


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CONCLUSIONS

Installation of ECP electrodes in a modified LPRM allowed Brunswick Unit 1 to demonstrate effective mitigation of IGSCC at a conservative location (aggressive environment). The station was able to demonstrate that HWC-M and OLNC are effective strategies towards achieving IGSCC mitigation in the BWR environment. The station also demonstrated the effectiveness of an OLNC application at a nuclear plant that had no prior NMCA history. Future OLNC applications are targeted at Brunswick Unit 1 every 11 to 16 months. Brunswick Unit 2 has installed LPRM ECP monitoring and plans to implement OLNC August 2015.

The Nine Mile Point 1 MMS ECP probes did not respond to a reduction of feedwater hydrogen injection rates while the molar ratio remained greater than two, but there was a clear response, validated by response of the in-process reactor recirculation ECP probes, when the molar ratio dropped below two. The “as read” ECP data from both the MMS and the RRS ECP probes during normal plant operations provide confirmation that sufficient hydrogen is being injected to maintain a molar ratio >2 in reactor coolant. In addition, with molar ratio >2 the RRS ECP measurements may respond to changes in plant conditions such as feedwater hydrogen concentration, radiolysis shifts with cycle age, or local losses of catalytic activity.

The Hatch 1 experience with MMS ECP probes demonstrate that ECP measurements may have stabilized after two prior NMCA applications and multiple OLNC applications. As discussed above for Nine Mile Point 1, the MMS ECP measurements provide confirmation that sufficient hydrogen is being injected to maintain a molar ratio >2 in reactor coolant. The BHDL probes respond to changes in feedwater hydrogen concentration and local losses of catalytic activity, as observed at the end of NMCA chemistry operation. Such trends, although they reflect local conditions, may be useful for predicting when reapplication would be recommended. Either the MMS or the BHDL probes may be used to demonstrate that sufficient hydrogen is being injected for IGSCC mitigation and inspection relief. The BHDL probes, in addition, will demonstrate IGSCC mitigation in the more aggressive environment and may provide data trends showing the effects of changes in plant conditions or local losses of catalytic activity.

Although there is an extensive history of ECP monitoring at the MMS skid, in-process ECP monitoring will provide a more representative indication of conditions affecting ECP at a location of interest while the molar ratio is >2. At some in-process ECP measurement locations, particularly those at or near the bottom vessel head (i.e., modified LPRM or BHDL), reactor coolant chemistry is unaffected by radiation from the core, which would drive recombination reactions to reduce the oxidant concentration and ECP. ECP measurements in the more aggressive environment will be more sensitive to changes in plant conditions and losses of catalytic activity than measurements in the MMS.

REFERENCES

[1] BWRVIP-62 Revision 1: BWR Vessel and Internals Project. Technical Basis for Inspection Relief for BWR Internal Components with Hydrogen Injection. EPRI, Palo Alto, CA: 2011. 1022844.

[2] BWRVIP-62-A: BWR Vessel and Internals Project, Technical Basis for Inspection Relief for BWR Internal Components with Hydrogen Injection. EPRI, Palo Alto, CA: 2010. 1021006.

[3] BWRVIP-268 BWR Vessel and Internals Project: Electrochemical Corrosion Potential Sourcebook. EPRI. Palo Alto, CA: 2012. 1025138.

[4] BWR Vessel and Internals Application (BWRVIA) Version 3.1 Radiolysis and ECP Analysis (BWRVIP-258). EPRI, Palo Alto, CA: 2011. 1023222.

[5] Koyabu, K., Takamori, K., Suzuki, S., and Hettiarachchi, S. “In-reactor ECP Measurements in BWR Plants,” Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia Proceedings, 2009.


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NOMENCLATURE

N/A

ACKNOWLEDGEMENTS

The authors would like to thank Brunswick Nuclear Plant personnel and Duke Energy Progress staff involved in plant modifications and engineering change packages for ECP probe installation and the implementation of the second generation noble metals technology. Special thanks to General Electric – Hitachi and the Electric Power Research Institute (EPRI) for support during ECP probe installation, hydrogen ramp tests, and noble metals application at the Brunswick Nuclear Plant. The data provided by Hatch and Nine Mile Point chemistry personnel was greatly appreciated for this paper.


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TABLES

Table 1: Brunswick 1 Hydrogen Injection Steps for HWC-M Ramp Test

Step Date/Time Injection Rate (scfm)

1 --- 39.8

2 5/22/2014 01:00 35.0

3 522/2014 09:11 31.0

4 5/22/2014 22:25 27.0

5 5/23/2014 04:30 23.0

6 5/23/2014 10:25 19.0

7 5/23/2014 16:10 15.0

8 5/23/2014 19:00 19.0

9 5/23/2014 22:00 23.0

10 5/24/2014 02:00 27.0

FIGURES

Figure 1: Number of U.S. BWRs Implementing OLNC


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Figure 2: Typical Schematic of ECP Electrode Placement Inside an LPRM Cover Tube [3]

Figure 3: Brunswick 1 ECP Chronological Data during HWC-M Ramp Test

Platinum to LPRM surface potential difference shown as "Pt1(2)-GND". Platinum to stainless steel electrode potential difference shown as "Pt1(2)-SS".


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Figure 4: Brunswick 1 ECP Data versus Feedwater Hydrogen Concentration during HWC-M Ramp Test

Figure 5: Brunswick 1 LPRM ECP Data during OLNC Application

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Figure 6: Brunswick 1 MSLRM Data during OLNC Application

Figure 7: Nine Mile Point 1 Cycle 21 HWC Ramp Test Chemistry Data

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Figure 8: ECP Response of Hatch of Pre- and Post-NMCA at LPRM and BHDL Locations [5]

Figure 9: Hatch 1 ECP Data

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