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口頭

The Characterization of the CLADS-MADE-01 and -02 BWR control blade degradation test debris by Raman spectroscopy

Pshenichnikov, A.; 永江 勇二; 倉田 正輝

no journal, , 

One of the promising methods of debris characterization - a Raman spectroscopy was utilized for investigation of simulated debris obtained after two control blade degradation tests CLADS-MADE-01 and CLADS-MADE-02. New results allowed to refine a mechanism of the B$$_{4}$$C degradation during the beginning phase of a severe accident. A partial transformation of B$$_{4}$$C granules into pure graphite promotes formation of particular phases in the debris based on the oxidative or reducing environment. This knowledge would provide new insights for understanding of the absorber blade degradation mechanism under specific accident conditions close to 1F Unit 2 and Unit 3 reactors.

口頭

Status and first results of the CLADS-MADE-02 BWR control blade degradation test under steam-rich conditions related to 1F Unit 3 accident

Pshenichnikov, A.; 山崎 宰春; 永江 勇二; 倉田 正輝

no journal, , 

Preliminary results on the CLADS-MADE-02 control blade degradation test related to the problem of 1F Unit 3 accident under sufficient steam conditions will be discussed. Control blade debris distribution obtained in oxidative environment, possibility of B$$_{4}$$C interaction with hot steam, consequences of its reaction with surrounding stainless steel and Zircaloy are very important for 1F decommissioning. Experimental information with in situ video of an melt progression will be presented at the 25th international QUENCH workshop famous for attracting experts dealing with nuclear safety.

口頭

Difference in oxidation behavior of heterogeneous BWR fuel assembly under steam-starved condition

永江 勇二; 山下 晋; 倉田 正輝

no journal, , 

BWR has heterogeneous configuration of fuel assembly, especially control blade. Growth and reduction behavior of oxidation depend on steam fraction. The oxidation behavior affects the reaction between SUS and Zry in an early stage of accident progression. According to ANSYS-fluent using oxidation growth and reduction models depending on steam fraction, oxidation behavior drastically change above 1200$$^{circ}$$C. Steam fraction on the surface of channel box covered by control blade decreases up to steam-starved condition around 1200$$^{circ}$$C, which means oxidation growth rate decreases depending on steam fraction. Oxidized layer grows continuously even steam-starved condition using a model of oxidation behavior independent of steam fraction. According to experimental integral tests without pre-oxidation, a reaction between SUS-B$$_{4}$$C and Zry occurs under low steam flow rate because the reaction rate is higher in the case of thin oxidized layer. Almost full oxidization occurs on the surface of Zry under a sufficient steam flow condition, except for thin oxidation at a top part of the test body. The reaction between control rod and Zry occurs at the top part. In addition, an observation of oxidation behavior in an integral test with pre-oxidation show us that a thickness of oxidized layer in a part of Zry covered by control blade is thinner and the interaction between SUS-B$$_{4}$$C and Zry begins even pre-oxidation. The model will be implemented into JUPITER code developed by Nuclear Science and Engineering Center.

口頭

Post-test analysis of the CMMR-4 test bundle

間所 寛; 山下 拓哉; 佐藤 一憲

no journal, , 

The test bundle of the latest test CMMR-4, Core-Material Melting and Relocation experiment, consists of 48 fuel rods filled with ZrO$$_{2}$$ simulant pellets with Zircaloy claddings, a control blade with B$$_{4}$$C particles in SS tube and sheath, two Zircaloy channel box walls, and lower support structures. The height of the test bundle was 80 cm and the heating system of the test was the plasma heating, which enabled melting of the oxide simulant fuel pellets. The test confirmed that macroscopic gas permeability existed until the ceramic-fuel melted and that the hot fuel rods tended to remain as columns in the core region, which suggests the heating of the support structure in earlier phase is unlikely. This information is useful not only for 1F decommissioning but also for further understanding of a BWR severe accident progression. The test bundle was cut by using the abrasive waterjet (AWJ) technique that uses abrasive garnet of 150-300 micro m with feed rate of approximately 1.5 kg/min. In order to cut off about 30 mm of ZrB$$_{2}$$ spot contained in the relocated melts, 750 liters of water, 84 kg of garnet and one nozzle replacement were necessary. The EPMA and XRD analyses of the cross-section showed that the place where repelled the garnet-contained waterjet contained ZrB$$_{2}$$. Since the cutting by AWJ technique has the property of selectively abrading the soft spots of the material, it must be noted that, in case of utilizing the technique in 1F decommissioning, garnet might be repelled by a hard boride and abrades places which were not expected.

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