Optimization of safety and seismic classification during the design stage of non-reactor nuclear facilities

Safety and seismic classifications are part of the seismic design concept of a nuclear facility. Due to the framework of international agreements, seismic design concepts are mandatory for licensing of nuclear facilities. Nevertheless, most countries do not have methods and guidance for safety and seismic classifications of non-reactor nuclear facilities that are prescribed by the regulatory body. In Germany and Russia the seismic design of a nuclear facility is derived from possible seismic hazards and a seismic classification of its structures, systems and components (SSC). During the seismic classification SSC are categorized in terms of their importance to safety in the event of a design basis earthquake. Therefore, the seismic classification is highly dependent on the safety classification of the facility. Currently the safety and seismic classifications of the components are typically based on a time-consuming case by case assessment. An approach for systematic safety and seismic classifications of non-reactor nuclear facilities derived from the Russian safety and seismic classifications of nuclear power plants is presented. The systematic approach provides a user-friendly tool to optimize safety and seismic classifications of components in non-reactor nuclear facilities. Using a single transparent tool for safety and seismic classifications leads to more reasonable classifications as it allows comparisons between classifications of components in different facilities. A higher level in safety or seismic classification leads to higher efforts when manufacturing a component. The presented tool provides information concerning the safety and seismic classification in an early design stage of the facility. This enables the user to make changes in the seismic design of the facility that allow a possibly lower level of safety and seismic classification at this stage. The systematic approach is tested at a waste treatment/conditioning facility. It is intended to provide footing for future planned user-friendly software. The software is to design in a way that users not familiar with the national norms concerning safety and seismic classification are able to use it successfully. Hence, experience and expert knowledge in safety and seismic classification is easily accessible. Furthermore, the systematic approach is being used to discuss the application of seismic probabilistic risk analysis for non-reactor nuclear facilities. Compared to the existing procedure, the innovative concept of the seismic safety evaluation applies available data (Safety margin factors) from the design of the facility, which is already available during planning stage of the facility. This concept prevents expensive remediation of the facility after the construction and displays possibilities of safety margin reductions at the right time. The seismic safety evaluation is particularly suitable for nuclear facilities with a low level of safety relevant facility components (non-reactor nuclear facilities and facilities without nuclear fuel). Those facilities are often classified very conservatively by nuclear related legislation. By applying the seismic safety evaluation the too conservative safety margin factors can be displayed and fortified with concrete values, so that design changes can be applied to reach reasonable safety margin factors. (authors)