Blend systems of polystyrene-block-poly (ethylene-co-(ethylene-propylene))-block-polystyrene (SEEPS) triblock copolymer with three types of hydrocarbon oil of different molecular weight were prepared. The E 00 curves as a function of temperature exhibited two peaks; one peak at low temperature (% À50 C), arising from the glass transition of the poly[ethylene-co-(ethylene-propylene)] (PEEP) phase and a high temperature peak (% 100 C), arising from the glass transition of the polystyrene (PS) phase. The glass transition temperature (T g ) of the PEEP phase shifted to lower temperature with increasing oil content. The shifted T g depended on the types of oil and was lower for the low molecular weight oil. The T g of PS phase of the present blend system, were found to be constant and independent of the oil content, when molecular weight of the oil is high. However, for the lower molecular weight oil, the T g of the PS phase also shifted to lower temperatures. This fact indicates that the oil of high molecular weight is merely dissolved in the PS phase. The E 0 at (75 C, at which temperature both of PEEP and PS phases are in glassy state, was found to be independent of oil content. In contrast, at 25 C, at which temperature the PEEP phase is in rubbery state, the E 0 decreased sharply with increasing oil content. This result indicates that the hydrocarbon oil was a selective solvent in the PEEP phase. It mainly dissolved in the PEEP phase, although slightly dissolved into the PS phase as well, when molecular weight of oil is low.

The spent control rod assemblies are to be processed as a waste for an underground disposal (depth≥70 m). The spent control rod assemblies (4 m in length) need to be cut into 4 sections in order to be stored in the storage containers (1.6 m x 1.6 m x 1.6 m). When the control rod is cut, the B4C powder contained inside the rod is leaked into the water. Contaminating the surrounding water would increase the secondary treatment cost, and consequently the overall processing cost. In this study, we examined a cutting technology that combines press working and underwater plasma cutting, in order to seal the cut control rods and prevent the B4C from being scattered into the water. We cut the control rods underwater in a vertical upright position, and confirmed the effects of B4C scattering. After cutting, the water ingress of the neutron absorbers was 52.8 mg per control rod. The B4C leaked during cutting was 3.6 g. The ratio diffuse of B4C from per control rod was 0.05 %. In conclusion, the results showed that the cutting technology used in this study is effective, and the B4C can be reduced considerably during processing.