海洋投棄用放射性廃棄物容器に関する研究 (第2報)

Abstract

The investigation on the hydraulic strength of the mortar container and the corrosion resistance of the metal covering, with reference to the disposal of radioactive wastes into the sea have been described in the previous report.As the sea water easily permeates into the concrete container in the conditions of high hydraulic pressure on the deep sea floor, it is feared that the water soluble radioactive wastes may leak out from the container by the action of the molecular diffusion and then may contaminate the surrounding sea water. In order to investigate the abovementioned problem, studies were carried out on the diffusion in the container wall made of mortar.“The results on diffusion in mortar” which are obtained from experiments using NaCl solution as a tracer at the first step, will be reported in this paper. The concentration of chloride ion was determined by the method of titration by silver nitrate according to F. MOHR. In the investigation, the authors define that “the diffusion coefficient in mortar” is the physical constant which is mainly attributed to two factors, namely, the diffusing energy of solution and the porosity of the mortar.As for chloride ion, the diffusion coefficient in the mortar of standard proportion is about 1.4×10-9 to 5.4×10-9 (cm2/sec). Moreover, we obtained the following relationship between the diffusion coefficient (D) and the coefficient of permeability (P), i. e. D is equal to a×P0.5, where a is 3.16×10-5, when D and P are larger than 10-9 (cm2/sec, cm/sec respectively), and we estimated that D is equal to P when both D and P are smaller than 10-9 (cm2/sec, cm/sec respectively).Considering only about the present results with respect to chloride ion, we could not neglect the contamination of sea water resulting from the diffusion in mortar. We, however, are continuously carrying out the similar studies on the diffusion making use of water-soluble radio-isotope as a tracer, for the purpose of getting more details about the diffusion in mortar.