Test Rig and Techniques for Quench Tests with Irradiated VVER Rod Simulators

1. Test Rig and Techniques for Quench Tests with Irradiated VVER Rod Simulators Presented by A. Leshchenko, RIAR, Russia

2. ICTS Project 1648.2 :“Examination of the VVER fuel behavior under the severe accidents. Reflooding stage” Stage A :“Study of the irradiated fuel rod segments behavior under reflood conditions” The purpose of the tests: Extension of an experimental database for irradiated fuel rod characteristics after reflooding Reqiured examinations: • Change in simulator cladding and fuel structure,pre-oxidized cladding failure character on the quench stage • Hydrogen production • Fission product release

3. In-cell rig to test the VVER spent fuel rod simulators under conditions typical for severe LOCA at the reflood stage The test rig comprises: • Heating module • Gas lines • System to control and register the experimental parameters. Simulation of oxidation in steam-argon medium and cooling of a fragment of a single irradiated fuel rod with water at the fragment temperature upto 1700 C

4. 5 6 Heating module 4 • Based on the resistive heating • Specimen is flooded by means of its movement into the receiver filled with water at the givenspeed 7 3 1 – sample2 – working channel 3 – vapor-argon-hydrogen mixture outlet 4 – sample movement drive 5 – protection tube of the sample suspension6 – thermocouples 7 – argon inlet of sample suspension8 – current supply of heater 9 – thermal protection 10 – molybdenum screens11 – split tubular molybdenumheater12 – water sampling 13 – argon (vapor-argon mixture) inlet 14 – water inlet15 – flooding tank 2 8 1 9 10 11 15 12 13 14

5. ps ps Gas lines system layout V 5 TF – thermo-filterMFC 1, MFC 2 – gas mass flow controllerGPS – gas pressure stabilizerG1 – G7 – gas flow metersV1 – V5 – electromagnetic valves P1, P3 – pressure-gaugesP2, P4 – pressure sensors G 7 V6 Ar + Н2 + H2O + FP G 5 C MFC 2 P 4 γ G 4 GPS MS P 1 P 2 G 1 V4 MFM MFC 1 TF P 3 V 2 GA V3 G 2 V1 Ar Ar C – condenser γ– Ge(Li) detectorMS – mass-spectrometer MFМ – gas mass flow meterGA – gas analyzer Ar + H2O Flooding Tank steam generator

6. System of experiment control and test parametersregistration Computer-based system of data acquisition and control over the experiment Electric power supply system Software logic Step drive controller Auxiliary equipment Heating module Suspension Measurement of experimental parameters Gas line system

7. Characteristics of samples The simulators are fabricated from the VVER-1000 fuel rod fragments with an average burnup of 45-50 MW*day/kgU. Fragment length is 150 mm. Preliminary examinationsof fuel rods: • profilometry • gamma-scanning • eddy current defectoscopy • initial oxide layer thickness (fisherscopy) • determination of the gaseous fission products(GFP) content and composition under the fuel rod cladding

8. Stages of simulator investigation • Testing of simulators under reflood conditions • Gamma-spectrometric analysis of fuel samples before and after testing to determine the relative cesium release • Determination of GFP content in the fuel samples • Determination of equivalent cladding reaction (ECR) • Metallographic examinations of samples • Determination of hydrogen content in the claddings of tested samples

9. Testing of simulators under reflood conditions Basic parameters to be measured: Temperature regimeof test • Temperature in the central hole of the fuel column at a distance of 75 mm from the simulator lower edge • Activity of 85Kr in argon • Mass fraction of 134Xe in argon • Concentration of H2 in argon • Gas flow rate through the working channel

10. Gamma-spectrometric analysis of fuel samples before and after tests to determine the relative cesium release (1) Relative FP release: A0 – initial specific activity of selected FP, Bq/g Af– specific activity of FP after quench test, Bq/g Specific activity: (2) S– area of photo peak - effectiveness of registration - gamma-yield for decay  - spectrum acquisition time, s m–fuel samplemass, g If spectrum acquisition time is the same before and after the test then relative FP release is (3) SK, S0 – area of photo peak of the tested fuel sample and reference sample, pulse

11. Gamma-spectrometric analysis of fuel samples before and after testing to determine the relative cesium release Assuming that 154Eu does not release from fuel during the test, the areas of 154Eu photo peaks (1274 keV) are in proportion to the mass of samples Relative release of the selected nuclide (e.g. 137Cs) is calculated by gamma-line i: (4) Si, S1274 – photo peak area of gamma-line i and that of 1274 keV 154Eu. (5) Relative error Fi :

12. Determination of GFP content in the fuel samples The content of gaseous fission products in fuel of the reference samples and tested simulators is determined by dissolving of fuel sample and registration of released radioactive 85Kr by gamma-spectrometer and non-radioactive 134Xe by mass-spectrometer during the whole period of dissolving. The kinetic dependences of the 85Kr and 134Xe releases are integrated to determine the total gas amount.

13. Determination of GFP content in the fuel samples 85Kr specific activity isregisteredduring whole dissolving time: (6) • i–acquisition time of spectrum i, s • Ii – average intensity during the spectrum acquisition, pulse/s • G – carrier-gas flow rate, cm3/s • V – volume of tube wired on the gamma-detector, cm3 • – effectiveness of registration •  – decay constant of 85Kr, s–1 • – gamma-yield for decay m – fuel mass in spacemen

14. Determination of GFP content in the fuel samples Specific activity of 85Kr in the reference sample is taken as the initial one. 85Kr relative release: (7) Indices "R" and "T" are the values for reference specimen and specimen dissolved after quench test Relative error of the 85Kr relative release: (8) where, Ii– absolute error of average intensity of gamma-line 85Kr (514 keV) in spectrum i

15. Determination of equivalentcladding reaction • Determination of the sub-sample length of the oxidized cladding • Determination of the sub-sample mass • Extra oxidation of the sub-sample in a crucible at 1200 within about 5 hours (till the mass increment stops) • Determination of the sub-samplemass gain EquivalentCladding Reaction: (9) Δmex ‑ sub-sample mass increment at extra oxidation Zr, O – molar mass of zirconium and oxygenlsub - sub-sample lengths- cladding linear density (10) ECRrelative error:

16. Metallographic examinations of samples • Making of photos of macro- and microstructure of fuel and cladding • Measurement of the interaction layers thickness of cladding material with steam • Measurement of micro-hardness Determination of hydrogen content in the claddings of tested samples • Thermo-extraction method: • Melting of sample in the graphite crucible in the flow of inert carrier-gas • Purification from carbon oxides • Determination amount of the extracted hydrogen by means of thermal conductivity detector

17. Program of experiments Matrix of experiments in the frame of stage A Spent ROD-QUENCH Project “Examination of the VVER fuel behavior under the severe accidents. Reflooding stage " 18 tests are planned in total

18. Conclusions Within the frame of Stage A “Spent ROD-QUENCH: Investigation of irradiated fuel rod fragments under reflooding conditions” a test rig was developed. Test rig allowssimulation of oxidation in vapor-argon medium and cooling of a fragment of a single irradiated fuel rod with water at the fragment temperature upto 1700 C A set of techniques to examine simulators of spent fuel rods tested under reflood conditions was proposed as follows: • Gamma-spectrometric analysis of fuel samples before and after testing to determine the relative cesium release; • Determination of GFP content in the fuel samples; • Determination of equivalent cladding reaction; • Metallographic examinations of samples; • Determination of hydrogen content in the claddings of tested samples.