Safety Approach and Ageing Management in Czech Rules and Standards

Abstract

There are basic technical (protection) objectives determined for assurance of nuclear power plant safety and the following generally belong among them: - Reactor pressure vessel shut down, - Long term maintenance of sub-critical state, - Long term cooling, - Prevention of radioactivity leakage. To ensure these objectives multi-step concept of deep protection is used for the design of a nuclear power plant and it includes: - Prevention of failures during normal and abnormal operation, - Control of failures and their consequences, - Minimizing of risks during accidents. Failure of operating systems is conservatively postulated for determination of systems requirements using for failure ensure as piping breaks. Ensure of these postulated failures come under multilevel safety approach. Failure consequences should be mainly ensured by design measures as separation of high energy piping, whip piping restrains etc. Efficiency of design measures have to be demonstrated. This passive safety procedure during design of new NPP can be applied. Application of this passive procedure for operating NPP can lead to technical and economical problems. It can be done by non precise and non sufficient requirements, current standards and documents. Leak before break concept (LBB) is very often out due to break operation conditions for successful concept usage. Beak preclusion concept was defined in Germany thirty years ago. The concept is developed from this time. Required quality of SSC is basic of this concept. The quality has to be received during manufacturing and assembly of new components to system or the quality passport has to be documented for SSC in operation before enlistment to the concept. During next operation they are sufficient and redundant measures necessary to control and to manage ageing phenomena (conceptual, technological, and physical) for exclusion of premature ageing. This proactive approach is also basic of documents from the last year’s required ageing and lifetime management. In Czech NPPs postulated failures and their consequences in accord with producer knowledge state at that time were insured. Postulated failures and their consequences were insured partly design measures and partly design supposed quality too. It is very difficult to realize new requirements on needed design provision on NPP in operation. It is impracticable in any cases. Needed national law for approach application exists in Czech from 1997. Regulation on lifetime management and national nuclear standards with specific requirements exist in Czech too. There are backgrounds for application proactive approach as it is used in Germany NPPs. New safety approach was provided in Czech NPPs. SSC are separated into three groups on the base safety approach: - SSC must not fail (guarantee of quality), - SSC may fail in rare case (preventative maintenance), - SSC may fail (failure orientated maintenance). The contribution deals about new Czech safety concept aspects, boundary conditions, needed document and proactive measures.