International Workshop INFLUENCE OF ATOMIC DISPLACEMENT RATE ON

RADIATION-INDUCED AGEING OF POWER REACTOR COMPONENTS: EXPERIMENTAL AND MODELING

Ulyanovsk State University, Russia, 3 – 7 October 2005

MAIN PROGRAMS AND TECHNIQUES FOR

EXAMINATION OF BEHAVIOUR OF THE WWER

HIGH-BURNUP FUEL IN THE MIR REACTOR

А.V. Burukin, S.А. Ilyenko, V.А. Ovchinikov, V.N. Shulimov

FSUE «SSC RIAR», Russia

FSUE SSC RF RIAR

Programs and techniques for in-pile examination of the WWER

fuel are aimed at obtaining of experimental data to validate

serviceability of the WWER fuel taking account of the

following up-to-date trends:

Increase of burn-up and extension of the reactor cycle;

Introduction of maneuvering conditions;

Observance of the up-to-date requirements established

for fuel behaviour under design-basis accidental conditions

(«Small LOCA», maximum design-basis accident, RIA)

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Performance of the WWER standard fuel under normal,

transient and accidental operating conditions is simulated by

conducting different tests including repeated irradiation and

transient tests of full-size (FSFR) and refabricated (RFR) fuel

rods as well as tests of the refabricated fuel rods under design-

basis accidental (LOCA and RIA type) conditions and also

tests of defective fuel rods.

A high neutron flux density and heat removal conditions allow

the performance of experiments with fuel having a burnup

of ~ 50...80 MWd/kgU at a linear power (LP) of

~ 50…100 kW/m.

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Parameter WWER-1000 MIR Maximum LP, kW/m 44.7 Higher values are possiblePressure, MPa Up to 17.7 ProvidedCoolant temperature inlet/outlet, оС 290…340 Provided

Water-chemical conditions Boric acid concentration, g/kg Gas content in the coolant at STP, cm3/kg О2

Н2

Ammonia-boric-potassiumUp to 10

0.005…0.0525…50

ProvidedUp to 10*

ProvidedProvided

Coolant velocity, m/s 5.7 ProvidedFuel burnup, MWd/kgU ~ 55 Up to 85…100Determination of the moment of failure Impossible PossibleAcceleration of burnup processes,increase of LP and cycle number

Impossible Possible

Intermediate control of fuel rod states No Possible in the pool and shielded hot cell

Change of parametersof water-chemical conditions

No Possible

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Comparison of the main fuel testing conditions of the MIR loop facilitieswith operating conditions of the WWER-1000 fuel rods

The MIR reactor is a channel-type, pool-type and beryllium-moderated reactor. It has several high-temperature loop facilities, which provide necessary coolant parameters for WWER fuel testing.

*- 4…5 g/kg - average level of index for WWER water-chemical conditions for long-term testing

Lay-out of the WWER experimental fuel rods in irradiation rigs FSUE SSC RF RIAR 5

62.2

12.75

12.75

60

~300

mm

50

0 m

m

500

mm

640

mm

64

0 m

m

460

mm

49

0 m

m

200

mm

200

mm

Cor

e h

eigh

t

500

mm

50

0 m

m

Core average

plane

WWER fuel rod dummy

(fuel column)

FSFR (fuel column)

RFR (fuel column)

Square 42

Types and characteristics of gauges for irradiation rigs and fuel rods Parameter Design type Measurement

rangeError Dimensions, mm

Diameter Length

Temperature of coolant and fuel rod cladding

Chromel-alumel thermocouple,cable-type

Up to 1100 оС 0.75% 0.5

Fuel temperature

Chromel-alumel thermoprobe, cable-type

Up to 1100 оС 0.75% 1…1.5

Fuel temperature

Thermoprobe WRe-5/20,casing Мо + ВеО

Up to 2300 оС(up to 1750 оС*)

~ 1.5% 1.2…2

Cladding elongation

LDDT (0…5) mm ± 30μm 16 80

Diameter change

LDDT (0…200) μm ± 2μm 16 80

Change of gas pressure in fuel rod

Bellows + LDDT (0…20) MPa ~ 1.5 % 16 80

Neutron flux density (relative units)

Neutron detector (ND)(Rh, V, Hf)

1015…1019

1/m2s ~ 1% 2…4 50…100

Volume steam content in coolant

Cable-type 20…100% 10% 1.5

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* - experimental data for high-burnup fuel rods

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Repeated irradiation of refabricated and full-size fuel rods

Tests of theWWER high-burnup fuel rods in the

MIR reactor

Power ramping (RAMP) and stepwise

increase of power (FGR)

Testing under design-basis RIA conditions

Testing under fuel rod drying, overheating

and flooding conditions (LOCA)

Testing under power cycling conditions

Testing of defective fuel rods

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The test objective is to determine the change of fuel rod state under burnup increase conditions at a specified power level and to prepare fuel rods with increased burnup for special tests (RAMP, LОСА and RIА).

Repeated irradiation of refabricated and full-size fuel rodsfrom spent WWER fuel assemblies up to high-burnup values

Type of fuel rod

Number of fuel rods

Length of fuel column of fuel

rod, m

Initial burnup, MWd/kgU

Final burnup, MWd/kgU

Maximum LP, kW/m

Repeated irradiation test No. 1

WWER-1000 2 3.53 49…50 62…63 18…30

WWER-1000 1 0.95 49 63 19…31

WWER-440 2 2.42 61 72 17…28

WWER-440 1 0.94 60 72 19…31

Repeated irradiation test No. 2

WWER-1000 5 3.53 53…55 74…75 18…24

WWER-1000 3 0.4 53…58 74…78 18…24

General data on repeated irradiation testsof the WWER fuel rods in the MIR reactor

Designation Number

of fuel

rods

Burnup,

MWd/kgU

Initial LP,

kW/m

LP increment

on ramping,

kW/m

Max. LP

increase rate,

kW/m/min

FGR-1 6 ~ 49…61 9…12 15 + 6 + 11 0.3

FGR-2 6 ~ 49…59 12…15 8 + 5 + 7 + 9 0.3

FGR-3 6 ~ 56…61 12…17 9 + 9 0.1

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Testing under power ramping conditions

The tests aimed at determination of the effect of power ramping parameters (RAMP) (including FGR) on serviceability of fuel rods with different burnup.

General information about FGR tests with the WWER fuel rodsin the MIR reactor

Range of burnup and LP amplitudes in the course of RAMP testsof the WWER fuel rods in the MIR reactor

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0

10

20

30

40

50

60

70

80

90

100

110

120

0 10 20 30 40 50 60 70

LP

, kW

/m

Burnup, MWd/kgU

○ Tight WWER-1000 fuel rods (E110 (Zr-1%Nb))

Tight WWER-1000 fuel rods (E110 (Zr-1%Nb)) with cracks on the cladding ◊ Tight WWER-1000 fuel rods (E635) ♦ Failed WWER-1000 fuel rods (E635) ∆ Tight WWER-440 fuel rods Tight WWER-440 fuel rod with cracks on the cladding▲ Failed WWER-440 fuel rod □ Combined fuel rod (cladding - E110 (Zr-1%Nb), fuel - France) ■ French fuel rods (cladding - Zr-4F) Damage threshold of the KWU fuel rods (Germany) Damage threshold of the KEP fuel rods (Japan)

Testing under power cycling conditions (CMP-1, CYCLE 1, CYCLE 2)

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The objective of testing was to obtain experimental data that characterize a change in the cladding strain, gas pressure in the free volume of a fuel rod, fuel temperature in course of power changing and fuel rod state after testing.

Type of

fuel rod

Number

of fuel

rods

Instrumenta

tion

Burnup,

MWd/kgU

Initial

LP,

kW/m

LP increment

during

cycling, kW/m

LP increase

rate,

kW/m/min

WWER-440 1 РF + L+ D 51 19 10 0.3

WWER-440 2 Т 51 19 10 0.3

WWER-440 3 --- 51…60 15…19 8…10 ~ 0.3

The main data of the CMP-1 test

Type of fuel

rod

Number

of fuel

rods

Instrumen

tation

Burnup,

MWd/kgU

Max.

initial

LP,

kW/m

LP increment

during

cycling,

kW/m

Max. LP

increase

rate,

kW/m/min

CYCLE-1 test

WWER-440 4 T, T 52…61 18 11 ~ 0.9

CYCLE-2 test

WWER-1000 2 Т, L 49…50 21; 21* 9; 21* 0.6; 0.9*

WWER-1000 2 РF, L 49…50 21 9 0.6

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General information about the CYCLE-1 and CYCLE-2 tests

*- maximum values of initial LP, increment and power increase rate under ramping conditions after maneuvering

The main examination tasks are as follows: Formation of parametric dependences of fission product release (different physical-

chemical groups and separate nuclides) on fuel burnup, power level, type and size of the cladding and location of the cladding defect;

Definition of kinetics and features of the cladding defect evolution including generation of the secondary defect

Testing of defective fuel rods with high-burnup FSUE SSC RF RIAR 13

Equipment Measurement results Final data

Standard leak-control system of fuel rod cladding of a loop facility

Logging intensity of n–radiation of loop facility coolant

Change in the release of delayed neutron carriers into coolant

Special sampling system.On-line gamma spectrometer

Nuclide activity in the coolant measured directly in the pipeline of a loop facility and in the coolant samples with separation of liquid and gas phases

Fission product release rate into the coolant through the cladding defectFuel wash-out rate by coolant coming in contact with fuel in the defect area

Standard sensors of a loop facility

Coolant parameters:flow rate, pressure and temperature.Power of an EFA

Coolant parameters: rate, pressure, and temperature. Local power, cladding temperature, heat removal mode

Types of experimental data obtained during examinationof fission product release into coolant

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Registration of the coolant n-radiation in the loop facility

Registration of the coolant γ- radiation

On-line gamma spectrometer on the control

Special coolant sampling system

New equipment

Cross-section of irradiation rig for testing defective fuel rod

Lay-out of the special equipment for determination of fission product release into the coolant of the loop facility primary circuit in the MIR reactor

Reference fuel rods

Defective fuel rod

381

Testing under fuel rod drying, overheatingand flooding conditions (LOCA)

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The objective of the tests is to verify or refine serviceability criteria of fuel

rods and fuel assemblies, determine ultimate parameters, which allow

the core disassembling after operation under deteriorated heat transfer

conditions, and to obtain data for code verification and improvement.

Testing of the WWER fuel assembly fragments under «Small

LOCA» conditions was performed in accordance with a special program

that provided a wide range of environmental conditions.

Experiment

Composition, number and

burnup of fuel rods in EFA

Pressure in the

primary circuit of

a loop facility,

MPa

Implemented temperature

range, оС

Drying duration,

min

Exposure at max.

temperature, min

Fuel rod state

Unirradiated

fuel rod

Fuel rod with

burnup, MWd/kgU

Tight Failed

Experiments at increased pressure in the primary circuit of a loop facility (cladding compression)

SL-1 18 - 12 530…950* 72 72 +

SL-2 19 - 12 Up to 1200 100 3 +

SL-5 6 1/52 4.9 750…1250 40 2 +

SL-5P 6 1/49 6 700…930 40 40 +

Experiment at decreased pressure in the primary circuit of a loop facility (cladding swelling)

SL-3 19 - 4 650…730 25 25 +

The WWER-1000 fuel assembly fragments were tested in the SL-1, SL-2 and SL-3 experiments; the WWER-440 fuel assembly fragments were tested in the SL-5 and SL-5P experiments.

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The main parameters of «Small LOCA» experiments

*- short-term duration, non-instrumented corner fuel rod

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Testing of the WWER-1000 fuel assembly fragmentunder maximum design-basis accidental conditions

These tests were aimed at obtaining information about the behaviour of the fuel rod bundle and also data for codes of fuel rod thermomechanical state and for the estimation of radiation consequences of cladding failure.

1, 3, 4, 6, 8, 12, 18 – unirradiated and non-instrumented fuel rods;5, 11 - unirradiated fuel rods instrumented with one thermoprobe in the fuel;2, 10, 17, 15 – unirradiated fuel rods instrumented with three thermoprobes on the cladding;7, 9, 13 – unirradiated fuel rods instrumented with PF and one thermoprobe on the cladding;14, 16 – non-instrumented refabricated fuel rods;19 – refabricated fuel rod instrumented with one thermoprobe in the fuel (Numerals in figure correspond to cell numbers)

Location of fuel rods and gauges in the EFA for «Large LOCA» test

9

16

17

10

19

15

5

6

8

7

18

11

4

14

13

12

3

2

1

I - evaporation conditions (up to 5 hours); II – exposure of fuel rod cladding at drying temperature (150…250 s); III - (180…240 s); IV - (120…150 s); V - (60…120 s) –

maximum design-basis accidental conditions (II stage) (Ts - saturation temperature)

Temperature scenario of «Large LOCA» test

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200300400500600700800900

-300

-200

-100

0 100 200 300 400 500 600Time, s

Tem

pera

ture

of

fuel

rod

cla

ddin

g, о

С

I

II

IVV

III

Тs

up to 5 hours

Temperature range of test

A program and technique for testing in the MIR loop facilities were developed to obtain experimental data on behaviour of high-burnup fuel rods under design-basis RIA conditions. In the MIR loop channel it is possible to provide rated LP and parameters of the WWER-1000 primary circuit coolant as initial ones, the fuel rod operating conditions being simulated in full-scale.

FSUE SSC RF RIAR 19Testing of the WWER-1000 high-burnup fuel rods

under design-basis RIA conditions

Technological parameters of the WWER-1000 primary circuitPressure, MPa 15.7Coolant temperature, оС up to 290Coolant velocity, ms up to 6Initial LP, kWm up to 25

Parameters of the neutron power impulseImpulse rise time, s 0.5…1.0Impulse amplitude, relative units 3.5…4Impulse half-width, s 1.5…2Shape of neutron power impulse triangular or trapezoidInitial fuel enthalpy, cal/g (kJ/kg) 60…70 (251…293)Fuel enthalpy increment, cal/g (kJ/kg) up to 100 (up to 419)

Simulated parameters

FSUE SSC RF RIAR 20Impulse shape in the MIR reactor

( - exposure time at maximal LP)

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10Time, s

En

ergy

rel

ease

, rel

ativ

e u

nit

s

12

34

1.0E+5

1.5E+5

2.0E+5

2.5E+5

3.0E+5

3.5E+5

4.0E+5

4.5E+5

0 5 10 15 20Time, s

En

thal

py,

J/k

g

Mean radial fuel enthalpy1 - = 0.5s; 2 - = 0.75s; 3 - = 1s; 4 - = 1.25s

1

2

34

200

600

1000

1400

1800

2200

0 5 10 15 20Time, s

Tem

per

atu

re, о С

Temperature in the center of the fuel column1 - = 0.5s; 2 - = 0.75s; 3 - = 1s; 4 - = 1.25s

ConclusionsThe in-pile examination programs and techniques of the WWER

fuel presented in the paper allow obtaining of experimental data

on the high-burnup fuel behaviour under different operating

conditions. These data can be used for:

Checking the conformity of the WWER fuel with the licensing

requirements involving the majority of criteria;

Estimation of the radiation consequences as a result of cladding

failure;

Checking and updating of calculation codes;

Estimation of the fuel rod state

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