Abstract
To understand the risk induced by tornado missiles, we need to evaluate both the degree of potential damage incurred and the frequency of the occurrence. In the paper, we show two methodologies effective to evaluate the degree of potential damage and the probability of the occurrence of tornado-borne missile strikes on structures, systems, and components in a nuclear power plant. One methodology is based on a tornado wind hazard model TOWLA, and a deterministic tornado-missile analysis code TONBOS, both of which were developed by the CRIEPI researchers including the present authors. The other is based on a probabilistic tornado-missile analysis code TONBOS-pro, and an annual missile-strike probability evaluation code TOMAXI-pro, both of which were developed by the first and third authors. To concretely show the effectiveness of the proposed methods, the annual probability that trucks on a straight road collide with a structure was evaluated by the two methods. The numerical results were compared with each other to indirectly confirm the validity of both evaluation methods. As a result, it turned out that the annual strike frequency computed by the deterministic evaluation method was much higher than that of the probabilistic evaluation method. Since the former method includes conservative assumptions, the results are consistent with the evaluation presumptions, reasonably indicating the validity of both methods.
