Results of First Stage of VVER Rod Simulator Quench Tests 11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, 2005 Presented by I. Kuzmin RIAR, Dimitrovgrad, Russia

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Stage A : “Study of the irradiated fuel rod segments behavior under reflood conditions” Project ISTC “Examination of the VVER fuel behavior under the severe accidents. Reflooding stage”  Simulator cladding and fuel characteristics, preoxidized cladding failure character on the quench stage  Hydrogen generation  Fission products release The purpose of the tests: Expansion of an experimental database for the irradiated fuel rod characteristics after reflooding

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Study of the spent fuel rod segments behavior under reflood conditions. Stages of work Designing and manufacturing the test rig Experiments with unirradiated fuel rod simulators  Working out the experimental technique  Comparison with results of the similar tests carried out in FZK  Expansion of an experimental database for the unirradiated VVER fuel rod characteristics after reflooding Executing the tests with the irradiated fuel rod simulators.

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Unirradiated fuel rod simulator cladding material E110 alloy cladding length 150 mm fuel pellets UO 2 VVER-1000 type Pre-oxidation parameters temperature 1200 °C environment Ar-O 2 mixture oxidation time100 s oxide thickness  m Instrumentation 3 Pt/Rh thermocouples were fixed at the elevation of 27, 77 and 127mm on the cladding outer surface by a Pt/Rh wire 1 W/Re thermocouple was located in the fuel pellets hole at the elevation 75mm

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Heating module 1 – sample 2 – operating channel 3 – vapor-argon-hydrogen mixture outlet 4 – sample movement drive 5 – sample suspension 6 – thermocouples 7 – argon inlet of sample suspension 8 – current supply of heater 9 – thermal protection 10 – molybdenum screens 11 – split tubular molybdenum heater 12 – water sampling 13 – argon (vapor-argon mixture) inlet 14 – water inlet 15 – heated quench tank Based on the resistive heating Specimen is flooded by means of its movement into the quench tank filled with water at the set speed 7

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27,  steam flow rate 10 mg/(s·sm 2 )  the steam generator is switched off before heating up to quenching temperature, but some steam still supplies from the quench tank  specimen is dropped at water level in the quench tank with a speed of 245 m/s  specimen is immersed into water heated up to 90  C with a speed of 15 mm/s Design test regime

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results # of sample 123 Oxidation time at 1400°С, s Flooding temperature, °С Hydrogen release per whole experiment, mg Hydrogen release at flooding, mg ECR, %3230- Thickness of ZrO 2 outer layer along the sample height*,  m top center bottom Cladding metal thickness along the sample height *,  m top center bottom * - the section coordinate is calculated from the sample lower end Sample No1: upper cross-section 114mm, central cross-section – 57, lower cross-section – 27mm. Sample No2: upper cross-section –127mm, central cross-section –77mm, lower cross-section 27mm

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Temperature and hydrogen concentration. Simulator #2

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Temperature and hydrogen release rate at the flooding of simulator #2

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Total hydrogen production

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Sample claddings appearance after tests crack visualization crack visualization Sample #1 oxidation 800 s, quenching 1400°C Sample #2 Sample #3 oxidation 240 s, quenching 1600°C

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Fuel pellet state Sample #1 crossection appearance (57 mm) after test (oxidation 800 s, quenching 1400°C)  Pellets after the tests are in the stable state  There are narrow crakes in the pellets  The interaction between cladding and fuel was observed (samples #1 and #3)  The cracks in the cladding are observed in the areas of its tight contact with fuel

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Sample #1 cladding state (oxidation time 800 s, flooding temperature 1400°С) upper cross-sections (114 mm) center cross-sections (57 mm) bottom cross-sections (27 mm)

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Sample #2 cladding state (oxidation time 240 s, flooding temperature 1600°С) upper cross-sections (127 mm) center cross-sections (77 mm) bottom cross-sections (27 mm)

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Experimental results Cladding state  The monolithic oxide film without any tangential cracks is observed on the samples.  In the cladding of both samples there are radial cracks spreading from the inner surface to the outer oxide film.  The majority of cracks ends in the oxide layer.  There are no any oxide films on the crack surfaces.  The distribution of the thickness of oxide films and metal part of the cladding confirms that the center of samples was placed lower maximum temperature.

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, Conclusion  The facility to study the release of hydrogen and fission products from single fuel rods under the conditions typical for the VVER core flooding during the LOCA accident was developed. The facility operation is based on the indirect resistive heating of the specimen.  The experiments with unirradiated VVER fuel rod simulators were performed under the reflooding conditions in the frame of the first testing stage.  The hydrogen release into the gas phase is measured both at the stage of preliminary oxidation of the simulator claddings and at the flooding stage.  The experiments with unirradiated simulators will be continued to expanse the database for the irradiated fuel rod characteristics after reflooding. At present, the facility is being prepared for the experiments with simulators fabricated from spent VVER fuel rods at a burn up of 45-50MW*day/kgU.