Accumulation of gadolinium isotopes in used nuclear fuel - 14374

Conference · Tue Sep 15 00:00:00 EDT 2015

OSTI ID:23100847

Suyama, Kenya; Kashima, Takao ^[1]

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1. Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Naka-gun, 319-1195 (Japan)

For the criticality safety control of damaged nuclear fuel, i.e., fuel debris, accounting for burnup credit (BUC) may become important if higher initial-uranium-enrichment fuel almost 5 wt% loaded into the reactor. In this case, if the presence of fission products (FP) could be confirmed, the negative reactivity effect of FP allows us to treat a substantially greater quantity of fuel debris in one removal and storage operation. In the technical development of the criticality safety control for fuel debris from the Fukushima accident in Japan, adopting BUC assuming the presence of the FP is being considered because the fuel used in the Fukushima Daiichi Nuclear Power Plant had a higher initial {sup 235}U enrichment, i.e., almost 5 wt%, than the fuel used at TMI-2. The Expert Group on Burnup Credit Criticality Safety (EGBUC) under the Working Party on Nuclear Criticality Safety (WPNCS) in the OECD/NEA Nuclear Science Committee carried out international burnup calculation benchmarks 'Phase-IIIB' and 'Phase-IIIC' for BWR fuel assemblies. In these benchmarks, the differences in the {sup 155}Gd calculation results of the participants generated keen interest because these differences were rather large. As the coordinators of the Phase-IIIC benchmark, the authors have conducted additional analyses on the accumulation of the gadolinium isotopes in used nuclear fuel during burnup. Without cooling time, the assembly-averaged amount of {sup 155}Gd against the burnup value depends on the burnout property of gadolinium in burnable poison rods. This is because the amount of gadolinium isotopes accumulated owing to the fission reaction is less than the residual gadolinium in the burnable poison rods. After the burnout of gadolinium isotopes in the burnable poison rods, the amount of {sup 155}Gd isotopes remains almost constant, which is defined by the balance between depletion due to the neutron capture reaction and generation due to beta-decay of {sup 155}Eu generated by the fission reaction. However, after a few years of cooling, the amount of {sup 155}Gd drastically increases owing to {sup 155}Eu decay. This effect is important for higher burnup fuel. In this case, the amount of gadolinium isotopes in the burnable poison rods is of less importance. This means that for better prediction of {sup 155}Gd, the adopted parameters and data pertaining to {sup 155}Eu generation have significantly greater importance than the burnup treatment of the burnable poison rods. The release behavior of europium as well as gadolinium during the severe accident should be examined. This paper provides basic information for considering {sup 155}Gd in the criticality safety evaluation of fuel debris. (authors)

• Research Organization: American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 23100847
• Resource Relation: Conference: ICNC 2015: 2015 International Conference on Nuclear Criticality Safety, Charlotte, NC (United States), 13-17 Sep 2015; Other Information: Country of input: France; 6 refs.; available on CD Rom from American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (US)
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
42 ENGINEERING
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BETA DECAY
BURNABLE POISONS
BURNUP
BWR TYPE REACTORS
EUROPIUM 155
FISSION PRODUCTS
FUKUSHIMA DAIICHI NUCLEAR POWER STATION
GADOLINIUM 155
ISOTOPE SEPARATION
NEUTRON REACTIONS
NUCLEAR FUELS
PERFORMANCE
REACTOR ACCIDENTS
SAFETY ANALYSIS
SEVERE ACCIDENTS
URANIUM 235