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Report No.

Literature review on experiments and models associated with degradation and oxidation of boron carbide control material during severe accidents

Zheng, X.; Ishikawa, Jun; Ito, Hiroto; Tamaki, Hitoshi; Maruyama, Yu

Boron carbide (B$$_{4}$$C) is one kind of neutron absorbing control rod/blade materials used in light water reactors (LWRs). In Fukushima Daiichi Nuclear Power Station (NPS), all units used B$$_{4}$$C as absorber material. The degradation of control rod/blade will affect the early phase of in-vessel core melt progression. Furthermore, the release of carbon compound gases including carbon dioxide (CO$$_{2}$$) as well as boron compounds due to the oxidation of B$$_{4}$$C with steam is possible to affect source terms of radioactive materials. Past experiments related to B$$_{4}$$C degradation and oxidation and numerical modeling in severe accidents codes are investigated in the current report with a main view to apply the acquired knowledge into the modification of THALES-2 developed at JAEA as an integral severe accident analysis code. The eutectic interactions of B$$_{4}$$C with other materials such as stainless steel and Zircaloy will lower the melting point of control rod/blade. The Nagase's correlations for eutectic interaction are selected as one of candidates to be applied into THALES-2. The oxidation reaction of B$$_{4}$$C with steam will release considerable amount of thermal energy, and form CO$$_{2}$$, boric acids and boron oxide, which could make an impact onto source terms by changing the pH value of a water pool where those dissolve. The IRSN correlation is chosen to be used in the modeling of oxidation reaction in THLAES-2.



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