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As Japan faces a super-aging society, the increasing number of elderly people who are bedridden due to fall fractures has become a major social issue. Hip protectors have, thus, been proposed to prevent femoral fractures in cases of tumbling or falling; however, they are not widely used because the tightness of the equipment and the hassle of wearing it. In recent years, flooring materials with high buffer performance have been attracting special attention in the prevention of bone fractures in cases of tumbling or falling. So far, however, the “floor hardness test,” which is an evaluation method for cephalopathy (concussion of the brain), is the only risk assessment method for injury risks caused by flooring materials, and no such evaluation method is available for femoral fracture risks. Therefore, we fabricated a test instrument (pendulum tester) that reproduces the load that the femur received at the point of falling on the floor and developed a mechanism to assess fracture risks with high accuracy on the basis of the measured load. The pendulum tester is characterized by the following features: (1) has an impactor simulating the shape of the femoral region (made using the femoral computed tomography image of the elderly as a reference) and (2) has a dummy skin reproducing the buffering performance of human soft tissue. On conducting fracture risk assessment of four types of commercially marketed flooring materials using the pendulum tester, we found that the merits and demerits of the safety vary greatly by comparing with the evaluation results of the floor hardness test. The above-mentioned results show that an appropriate flooring material evaluation method should be chosen depending on the lesion site and type of injury.

The loss-of-reactor-level (LORL) where the coolant circulation path is lost is one of the important accident types of loss-of-heat-removal-system (LOHRS) in loop-type sodium-cooled fast reactors (SFRs). Due to the non-negligible possibility obtained by probabilistic risk assessment (PRA), pipe failures and succeeding sodium leakage in two points both occurred in primary heat transport system (PHTS) was assumed in this study, unlike the conventional studies assuming single pipe failures. The sodium level in reactor vessel (RV) is affected by many elements such as leakage position, guard vessel volume, operational state of pumps, and countermeasures to maintain sodium level which are sodium pump-up into RV and siphon-breaking of the pipe between RV and pump. Thus, a calculation program was developed in this study to evaluate and discuss the effectiveness of the countermeasures and safety margins for the loss of coolant circulation path. In addition, the crack size was discussed and evaluated realistically, and t 2 (t : pipe thickness) was obtained for a sufficiently conservative value, instead of Dt/4 (D : pipe diameter) that was assumed in the conventional studies. Time interval between two leakages was also given by PRA, considering failure rates of the pipes and components. Representative sequences and leakage positions where the sodium level can decline below emergency sodium level (EsL) were chosen, and the sodium level transient in RV was calculated where the crack size of the second leakage was set t 2. The calculations were also conducted where the larger crack size, Dt/4, was set for both the first and second leakage, in order to investigate additional requirements to maintain the RV sodium level. The evaluation results clarified that the coolant circulation loop can be maintained even after the second leakage in PHTS, taking into account the effects by the countermeasures.