George D. Kostrov
expert, JSC „ATOMPROEKT“
The article is devoted to issues related to the probabilistic justification of the safety of nuclear power plants (NPP) when a high-speed military aircraft falls. The random parameters are the recurrence of falls and the direction of the aircraft's trajectory. The conservative value of the recurrence of falls, given in the IAEA documents, was used, which ensures a high degree of NPP safety. The aircraft approach is assumed to be equally probable from either side. The trajectory slope is specified taking into account the IAEA documents and statistics of aviation accidents.
The aircraft impact load is applied to one of the structures, therefore the impact probability must be determined independently for each of them. It is proportional to the equivalent area of the building structure, depending on its size, shape, position in space and in relation to other structures. Expressions are given for the equivalent areas of structures of various shapes, typical for NPP. It is shown that if the aircraft crash is unintentional (accident), then with the usual dimensions of structures, the probability of an impact in them is less than the value, starting from which, according to Russian standards, it must be taken into account in the design basis of the NPP, i.e. it can be ignored. Dependencies are given for calculating the probability of an aircraft strike in the case of a deliberately organized accident (terrorist attack), in which the aircraft will surely fall on the territory of “Nuclear Island” of the NPP.
The procedure for setting the design loads on the building structures of a NPP in the case of a deliberate aircraft fall based on the allowed probability of their realization is described. It is shown that this method of setting the loads makes it possible to substantiate their significant reduction, which leads to a reduction in the cost of the NPP while guaranteeing its safety. A probabilistic assessment of structures safety of existing NPP in the event of an aircraft impact is discussed.
The article is devoted to taking into account random factors when an aircraft impact is included in the design basis of a nuclear power plant (NPP). The fall of transport and high-speed military aircrafts in cases of unintentional (emergency) and deliberately organized (terrorist act) crash is considered. It is shown that in case of an unintentional fall, the impact of an aircraft into structures of ordinary sizes can be ignored due to the too low probability. Two methods of probabilistic setting of design loads on building structures are proposed. A technique for probabilistic setting of floor response spectra (FRS) is proposed, by means of which dynamic loads on technological equipment are calculated. It is shown that the probabilistic approach can significantly reduce the design loads while maintaining the safety of NPP. The procedure for determining the coefficients of combinations for summing up of the same name internal forces, calculated by three components of the FRS, is described