Effect of B4C Absorber Material on Melt Progression and Chemical Forms of Iodine or Cesium under Severe Accident Conditions

• Published in: Nihon Genshiryoku Gakkai wabun ronbunshi = Transactions of the Atomic Energy Society of Japan Vol. 14; no. 1; pp. 51 - 61
• Main Author: HIDAKA, Akihide
• Format: Journal Article
• Language: Japanese; English
• Published: Atomic Energy Society of Japan 2015
• Subjects: B4C pellet absorber; B4C powder absorber; cesium borate; cesium source term; eutectic reaction; iodine source term; melt progression; organic iodide
• ISSN: 1347-2879; 2186-2931
• DOI: 10.3327/taesj.J14.021

Boron carbide (B4C) used for BWR or EPR absorbers could cause phenomena that never occur in PWR with silver-indium-cadmium absorbers during a severe accident. B4C would undergo a eutectic interaction with stainless steel and enhance core melt relocation. Boron oxidation could increase H2 generation, and the change of liberated carbon to CH4 could enhance the generation of organic iodide (CH3I). HBO2 generated during B4C oxidation could be changed to cesium borate (CsBO2) by combining it with cesium. This may increase cesium deposition into the reactor coolant system. There could be differences in the configuration, surface area, and stainless-steel to B4C weight ratio between the B4C powder absorber and pellet absorber. The present task is to clarify the effect of these differences on melt progression, B4C oxidation, and the iodine or cesium source term. Advancement of this research field could contribute to further sophistication of prediction tools for melt progression and source terms of the Fukushima accident, and the treatment of organic iodide formation in safety evaluation.