Experimental study for subcriticality measurement of fuel debris in the Fukushima Daiichi reactor - 14582

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

OSTI ID:23100942

Gunji, Satoshi; Yoshioka, Kenichi; Matsumiya, Hiroshi; Kumanomido, Hironori; Hayashi, Yamato ^[1]

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1. Toshiba Corporation, Power Systems Company, 8 Shin-Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa-ken, 235-8523 (Japan)

Fuel debris defueling in the Fukushima Daiichi reactors is planned. Furthermore, retrieved fuel debris will be packed and stored in casks for a long time. In these processes, from the viewpoint of criticality safety, the subcriticality of the fuel debris should be confirmed. Although there are some subcriticality measurement methods, the applicability of these methods to the fuel debris must be investigated because the elemental composition and shape of the fuel debris are unknown. In this study, we focus on the exponential experiment method which is able to measure a wide range of subcriticality. Basic experiments to validate the methods were carried out using Toshiba Nuclear Critical Assembly (NCA) and {sup 3}He Position Sensitive Detector (PSD). The decay curves of neutron flux distributions were measured by the PSD detector and fitted to a theoretical formula. The elemental compositions and neutron spectrum of the fuel debris have been estimated with a severe accident code and a Monte Carlo code. In the experiment, the neutron spectrum of the fuel debris was simulated in the NCA core. The porosity of the fuel debris was assumed to be 60%, which corresponds to be H/U=7.5 and Volume Ratio=1.5. In order to evaluate the effect of the uncertainty of the compositions on the measured subcriticality, a homogeneous region and a heterogeneous region were configured in an experimental core. These regions consisted of fuel rods with different UO{sub 2} enrichment zone or different gadolinia concentration zone in the axial direction. The effective multiplication factors deduced by the exponential experiment method were a range of 0.94 to 0.98. (authors)

• Research Organization: American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 23100942
• 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; 7 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

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
42 ENGINEERING
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
CONCENTRATION RATIO
CRITICALITY
ENRICHMENT
FUEL RODS
FUKUSHIMA DAIICHI NUCLEAR POWER STATION
GADOLINIUM OXIDES
MONTE CARLO METHOD
MULTIPLICATION FACTORS
NEUTRON FLUX
NEUTRON SPECTRA
POROSITY
POSITION SENSITIVE DETECTORS
SAFETY
SEVERE ACCIDENTS
SIMULATION
URANIUM DIOXIDE
ZERO POWER REACTORS