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

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) 2

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 ~ MWd/kgU at a linear power (LP) of ~ 50…100 kW/m. 3

ParameterWWER-1000MIR Maximum LP, kW/m44.7Higher values are possible Pressure, MPaUp to 17.7Provided Coolant temperature inlet/outlet, о С290…340Provided Water-chemical conditions Boric acid concentration, g/kg Gas content in the coolant at STP, cm 3 /kg О 2 Н 2 Ammonia-boric-potassium Up to … …50 Provided Up to 10* Provided Coolant velocity, m/s5.7Provided Fuel burnup, MWd/kgU~ 55Up to 85…100 Determination of the moment of failureImpossiblePossible Acceleration of burnup processes, increase of LP and cycle number ImpossiblePossible Intermediate control of fuel rod statesNo Possible in the pool and shielded hot cell Change of parameters of water-chemical conditions NoPossible 4 Comparison of the main fuel testing conditions of the MIR loop facilities with 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 5

Types and characteristics of gauges for irradiation rigs and fuel rods ParameterDesign typeMeasurement range ErrorDimensions, mm DiameterLength Temperature of coolant and fuel rod cladding Chromel-alumel thermocouple, cable-type Up to 1100 о С0.75%0.5 Fuel temperature Chromel-alumel thermoprobe, cable-type Up to 1100 о С0.75%1…1.5 Fuel temperature Thermoprobe WRe-5/20, casing Мо + ВеО Up to 2300 о С (up to 1750 о С*) ~ 1.5%1.2…2 Cladding elongation LDDT(0…5) mm± 30μm1680 Diameter change LDDT(0…200) μm± 2μm1680 Change of gas pressure in fuel rod Bellows + LDDT(0…20) MPa~ 1.5 %1680 Neutron flux density (relative units) Neutron detector (ND) (Rh, V, Hf) … /m 2  s ~ 1%2…450…100 Volume steam content in coolant Cable-type20…100%10%1.5 6 * - experimental data for high-burnup fuel rods

7 Repeated irradiation of refabricated and full-size fuel rods Tests of the WWER 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

8 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 rods from 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 …5062…6318…30 WWER …31 WWER …28 WWER …31 Repeated irradiation test No. 2 WWER …5574…7518…24 WWER …5874…7818…24 General data on repeated irradiation tests of 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-16~ 49…619… FGR-26~ 49…5912… FGR-36~ 56…6112… 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 rods in the MIR reactor

Range of burnup and LP amplitudes in the course of RAMP tests of the WWER fuel rods in the MIR reactor 10

Testing under power cycling conditions (CMP-1, CYCLE 1, CYCLE 2) 1 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-4401РF + L+ D WWER-4402Т WWER …6015…198…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-4404T, T52…611811~ 0.9 CYCLE-2 test WWER-10002Т, L49…5021; 21*9; 21*0.6; 0.9* WWER-10002РF, L49… 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 13 EquipmentMeasurement resultsFinal 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 defect Fuel 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 examination of fission product release into coolant

14 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

Testing under fuel rod drying, overheating and flooding conditions (LOCA) 15 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.

Experi ment Composition, number and burnup of fuel rods in EFA Pressure in the primary circuit of a loop facility, MPa Implemented temperature range, о С Drying duration, min Exposure at max. temperature, min Fuel rod state Unirra diated fuel rod Fuel rod with burnup, MWd/kgU TightFailed Experiments at increased pressure in the primary circuit of a loop facility (cladding compression) SL …950*72 + SL Up to SL-561/ … SL-5P61/496700… Experiment at decreased pressure in the primary circuit of a loop facility (cladding swelling) SL … 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. 16 The main parameters of «Small LOCA» experiments *- short-term duration, non-instrumented corner fuel rod

17 Testing of the WWER-1000 fuel assembly fragment under 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

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 18

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 Testing of the WWER-1000 high-burnup fuel rods under design-basis RIA conditions Technological parameters of the WWER-1000 primary circuit Pressure, MPa15.7 Coolant temperature, о Сup to 290 Coolant velocity, m  s up to 6 Initial LP, kW  m up to 25 Parameters of the neutron power impulse Impulse rise time, s0.5…1.0 Impulse amplitude, relative units 3.5…4 Impulse half-width, s1.5…2 Shape of neutron power impulsetriangular or trapezoid Initial 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

2020 Impulse shape in the MIR reactor (  - exposure time at maximal LP) Mean radial fuel enthalpy 1 -  = 0.5s; 2 -  = 0.75s; 3 -  = 1s; 4 -  = 1.25s Temperature in the center of the fuel column 1 -  = 0.5s; 2 -  = 0.75s; 3 -  = 1s; 4 -  = 1.25s

Conclusions The 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 2121