核设施地震危险性估计中的几个问题

总结了地震安全性估计方法的现状与发展趋势,指出我国在用确定性方法确定设计地震动时,有些不确定性并未考虑,不少主观决定并非总是足够安全的。文中推荐了概率方法。场地影响分析中,特别是座落于软基上的核设施,需要对输入面的选择及土层反应分析中的多种不确定因素进行考虑。最后指出场地地震相关反应谱对座落于软基上的核设施的重要意义,以及大远震与小近震对反应谱的不同影响

ON SEISMIC HAZARD ASSESSMENT OF SITES OF NUCLEAR FACILITIES

In the first part of the paper, the status and tendency of development of the methodology of seismic hazard assessment are reviewed with reference to recent documents such as Standard Specification ASCE 4-86 and IAEA 1991 Safety Guide, and in the remaining sections three main problems, i.e. the consideration of uncertainties, site effect and earthquake and site-dependent spectrum, are discussed. Under the topic of uncertainty, it is pointed out that the still popular deterministic method considers the uncertainty by empirical and subjuctive judgement, while the probabilistic method considers its explicity in terms of exceedance probability of occurrance of a given ground motion. There are two types of deterministic methods for seismic hazard assessment: one gives the most probable or average estimate and anothor the most conservative estimate, both being subjective. In China, many people believe that the later deterministic method gives always a safe estimate than the former with annual exceedance probability of 10-4. The paper explains that it may not be so because the deterministic method currently used in China did not consider the uncertainties and the subjective choices were not always safe enough. The probabilistic approach is recommanded. Under the topic of site effect analysis, the paper discusses firstly the importance of site effect analysis for nuclear facilities, especially those on soft sites, then the selection of input boundary and the uncertainties involved, and also the importance of considering earthquake-dependent and site-dependant design spectra, especially of those facilities on soft sites.