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Oral presentation

JAEA studies on spent fuel pool severe accident, 2; Thermal-hydraulic research plan for evaluating capability of spray cooling

Nagatake, Taku; Liu, W.; Koizumi, Yasuo; Takase, Kazuyuki; Yoshida, Hiroyuki; Nemoto, Yoshiyuki; Kaji, Yoshiyuki

no journal, , 

In the Fukushima Daiichi NPP accident, loss of cooling capabilities for spent fuel pool (SFP) occurred. As a result, a water level of the SFP decreased and it was concerned that the spent fuels were damaged. Therefore, safety measures for the SFP cooling are required in order to prevent the failure of the fuel rods. In one of the safety measures for the SFP, a portable spray system is considered as a device to cool the spent fuels. Then a capability of spray cooling have to be evaluated to validate the applicability of portable spray cooling systems as the safety measure for severe accident in the SFP. In this research project, the numerical simulation method for evaluating the capability of spray cooling has been developed. To develop this method, we mainly focus on the thermal-hydraulic behavior of two-phase flow generated by the spray cooling systems at a top and inside of the fuel assembly. In addition, we are planning to the spray cooling experiment in order to obtain a knowledge and validation data for numerical simulation method. In this presentation, current status of development of numerical simulation method and experimental plan of this research project will be shown and discussed.

Oral presentation

JAEA studies on spent fuel pool severe accident, 1; Results of cladding air oxidation experiments

Nemoto, Yoshiyuki; Ogawa, Chihiro; Kaji, Yoshiyuki; Nakashima, Kazuo*; Tojo, Masayuki*; Goto, Daisuke*

no journal, , 

To improve the severe accident codes for the analysis of spent fuel pool (SFP) accident with water level decrease, it is necessary to model the air oxidation behavior of the cladding based on experimental data. For the air oxidation modeling, it is necessary to understand the influence of temperature distribution along axial direction of the cladding in SFP accident condition. In addition, it is important to evaluate the influence of oxide film formed on surface of cladding during operation in nuclear power plant. In this study, bare specimens and pre-oxidized specimens of Japanese zircalloy-4 were investigated. Longer specimens of cladding were tested in air with temperature distribution along the axial direction of the cladding simulating the SFP accident condition. Shorter specimens were adopted for tests in thermogravimetry to obtain basic data. Experimental data were compared and the authors discussed on influence of the temperature distribution and oxide film for the air oxidation behavior.

Oral presentation

Investigation of cesium chemisorption behavior on the stainless steel surface

Nakajima, Kunihisa; Di Lemma, F. G.; Yamashita, Shinichiro; Osaka, Masahiko; Nagase, Fumihisa

no journal, , 

Knowledge of accurate Cs-deposition properties is essential to evaluate radiation dose of workers at the Fukushima Daiichi Nuclear Power Plants (1F-NPPs), encountered during retrieval of fuel debris from the radioactive Cs deposits onto structural materials and equipments in the RPV and PCV. The Cs chemisorption tests were performed to investigate its behavior on stainless steels. As the results, we observed that Cs congruently distributes with silicon (Si), which agrees with previous studies. But the results of the XRD and EDS analyses suggest that the reaction product is not Cs$$_{2}$$Si$$_{4}$$O$$_{9}$$ but a new proposed compound CsFeSiO$$_{4}$$. Further, it was suggested from our XRD analysis and leaching test that the amounts of the Cs deposit at 800$$^{circ}$$C were higher than those of the Cs deposit at 1000$$^{circ}$$C, though the previous studies indicated the reaction rate increased monotonously up to 1000$$^{circ}$$C.

Oral presentation

Reaction experiment on core melt concrete interface under temperature gradient

Sudo, Ayako; Onozawa, Atsushi; Takano, Masahide

no journal, , 

To characterize the layer structure and respective temperatures of MCCI products, MCCI experiments using a light-concentrating furnace were performed. As the core-melt constituents, a powder mixture of (U$$_{0.5}$$Zr$$_{0.5}$$)O$$_{2}$$ (No.1) and (U$$_{0.5}$$Zr$$_{0.5}$$)O$$_{2}$$/Zr/SUS316L/B$$_{4}$$C (No.2) were compacted into tablets (10 mm in diameter) respectively. The tablet was placed on a cylindrical piece of basaltic concrete (25 mm in diameter). The light was concentrated on the tablet under argon gas flow and samples were heated. After heating, the vertical cross-section of the solidified sample piece was subjected to phase identification and elemental analysis by XRD and SEM/EDX. No.1 sample seemed to maintain original shape, but EDX analysis showed the inner region melted. This melt was identified as-melted (U,Zr)O$$_{2}$$ particle and silicate glass containing U and Zr. Ca, Fe and Mg oxide were dissolved in the particle. UO$$_{2}$$ and ZrO$$_{2}$$ were dissolved in the silicate glass. No.2 sample had same phases, but Fe-Cr oxide deposits from SS was identified.

Oral presentation

Degradation test using control blade applied for BWRs in Japan

Shibata, Hiroki; Tokushima, Kazuyuki; Sakamoto, Kan*; Kurata, Masaki

no journal, , 

In this study, control blade degradation test under the conditions of axial temperature gradient and high temperature increase rate in Ar-atmosphere was performed as preliminary test in steam atmosphere to investigate the relocation of control blade melt and interaction with channel box under the conditions. It was found that the molten products redistribute to axial direction and interaction between S.S./B$$_4$$C-melt and Zry-4 progresses significantly in the condition that a few micron oxide layer exists on Zry-4. Moreover, as preliminary test in steam atmosphere, reaction test between the materials of control blade and channel box was carried out to investigate the effect of oxide layer formed on the surface of Zry-4 in steam atmosphere. It was found that in the condition of supplying oxygen continuously, the liquefaction interaction between Zry and S.S./B$$_4$$C-melt is considered to be prevented.

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