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9 Methods for VVER-1000 Fuel Testing Under Dry Storage Conditions Valentin B. Iano Institute of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences In order to guarantee safe long storage of spent nuclear fuel, it is necessary to develop a model of spent nuclear fuel behavior under different storage conditions in order to select safe conditions for its dry storage. Conditions include transient conditions (vacuum dehydration), standard storage conditions, abnormal events, and design-basis accidents. It is necessary to test the irradiated fuel at different temperatures, which simulate possible storage conditions in order to develop an appropriate model. Preservation of cladding integrity during the entire period of fuel rod storage is one of the main factors that ensures the dry storage safety of spent nuclear fuel. The following activities help ensure safe storage: • Certification of fuel rods using nondestructive examination techniques • Thermal testing of fuel rods • Intermediate nondestructive examinations of fuel rods between several successive tests (if they are performed) • Material science examinations of fuel rods after testing Figure 1 depicts the equipment for testing under dry storage conditions. Using this equipment, after visual examination fuel rods are subjected to eddy-current testing and measurements of diameter and length between tests. Refabricated fuel rods are subjected to additional measurements of volume. Gamma-scanning and cladding puncture followed by analysis of gas quantity and composition under the cladding are performed after the fuel rods are tested. 7

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7 METHODS FOR VVER-000 FUEL TESTING Gas control cabinet Air He EHM1 EHM2 EHM3 Hot cell Channel analyzer Control cabinet FIGURE 1 Structural schematic of dry storage testing equipment. 10-1.eps

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7 SPENT NUCLEAR FUEL STORAGE FACILITIES Three independent electric modules, which are located inside the hot cell, and systems of gaseous medium preparation and gas sampling from the modules and from the module operation and control system are used. Fuel rods under ex- amination are inserted into a leak-tight capsule that is placed in the module. The performance capabilities of the equipment are as follows: • Test temperature range of 300 to 600°С • Remote loading and unloading of fuel rods • Simultaneous testing of up to 18 irradiated full-size fuel rods from VVER-1000 reactors in three independent modules • Concurrent simulation of several storage conditions for spent nuclear fuel both in gaseous media and temperature • Recurrent gas sampling in any module • Profiling of the temperature field throughout the height of the fuel rod • Temperature cycling (simulation of daily or seasonal variations in ambi- ent temperature) • Nonuniformity of axial temperature distribution along the height of no more than ±3 percent, and nonuniformity of radial temperature distribution in the capsule of no more than ±2°C. Figure 2 depicts cycling of test and ambient temperatures. In Russia, equipment is available for testing VVER-1000 irradiated fuel rods to predict their behavior during long-term storage. Such investigations must be executed for all kinds of spent fuel before designing and commissioning a suit- able storage facility. Temperature Testing of fuel rods Examination of fuel rods Tt Ta Beginning End Time FIGURE 2 Schematic representation of test conditions for fuel rods: Tt and Ta—test temperature and ambient temperature, respectively. 10-2.eps