ABSTRACT

Dissolution behavior of Sr and Ba is crucial for evaluating secondary source terms via coolant water from ex-vessel debris accumulated at Fukushima Daiichi Nuclear Power Station. To understand the mechanism, knowing the distribution of Sr and Ba in the ex-vessel debris is necessary. As a result of reaction tests between simulated corium and concrete materials, two-layered structures were observed in the solidified sample: (A) a silicate glass-based phase-rich layer in the upper region and (B) a (U,Zr)O₂ particle-rich layer at the inner region. Measurable concentrations of Sr and Ba were observed in layer (A) (approximately 1.7 times that in the layer (B)). According to thermodynamic analysis, (U,Zr)O₂ is predicted to solidify, in advance, in the concrete-based melt around 2177°C. Then, the residual melt is solidified as a silicate glass, and Sr and Ba are preferentially dissolved into the silicate glass. During the tests, (U,Zr)O₂ particles sank in the melt because of its higher density, and the silicate glass relocated to the upper layer. In the actual situation, the crust layer might form on the top surface with cracks and cavities, and therefore the water is possible to contact with upper silicate glass containing Sr and Ba.

摘要

Sr和Ba的溶解行为对于评估来自福岛第一核电站蓄积的前容器碎片中的冷却剂水产生的二次能源而言至关重要。要了解其机理，必须了解前舱碎片中Sr和Ba的分布。作为模拟的皮质和混凝土材料之间反应测试的结果，在固化的样品中观察到两层结构：（A）上部区域中的硅酸盐玻璃基富相层；（B）（U，Zr）内部区域富含O ₂颗粒层。在层（A）中观察到可测量的Sr和Ba浓度（约为层（B）的1.7倍）。根据热力学分析，（U，Zr）O ₂预计在2177°C左右的混凝土基熔体中会预先凝固。然后，将残留的熔体固化为硅酸盐玻璃，并且将Sr和Ba优先溶解在硅酸盐玻璃中。在测试过程中，（U，Zr）O ₂颗粒由于其较高的密度而沉入熔体中，并且硅酸盐玻璃移至上层。在实际情况中，可能在具有裂纹和空腔的顶表面上形成结壳层，因此水可能会与含有Sr和Ba的上层硅酸盐玻璃接触。