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Relationship towards Engineering, Quality Assurance and 10CFR50.59 in the Design Change Process at the Krško NPP

The paper discusses the relationship between the Krško NPP design change engineering practice, quality assurance and the USA Nuclear Regulatory Commission 10 Code Federal Rule 50.59 (10CFR50.59). Together these controls ensure that plant design bases are maintained and yield a safe design. The 10CFR50.59 has been applied in Krško NPP plant specific procedure entitled ESP-2.303 "Authorization of Changes, Tests and Experiments" (Safety Evaluation Screening) since 1994. All the proposed changes requiring Safety Evaluations are being submitted to the SNSA (Slovenian Nuclear Safety Administration). If the proposed change is constituting an "Unreviewed Safety Question" the formal licensing procedure shall be completed before design change can be implemented otherwise the proposed design change is rejected. The procedure (ESP-2.303) provides the methodology to be followed in determining if a proposed activity involves an unreviewed safety question. An "Unreviewed Safety Question" is essentially the same as defined in 10CFR50.59(a)(2): "A proposed change, test or experiment shall be deemed to involve an unreviewed safety question (1) if the probability of occurrence or consequences of an accident or malfunction of equipment important to safety previously evaluated in the [updated] safety analysis report may be increased; or (2) if a possibility for an accident or malfunction of a different type than any evaluated previously in the [updated] safety analysis report may be created; or (3) if the margin of safety as defined in the basis for any technical specification is reduced." The paper discusses the following Krško NPP Safety Evaluations aspects: 1. Defense in Depth Design Philosophy 2. Methodology 3. Definitions and Applicability of Terms 4. Evaluation Process Guidanceand Documentation Process 5. Krško NPP Lessons Learned

NPP Krško; design change; USA Nuclear Regulatory Commission; 10 Code Federal Rule 50.59; plant design bases; SNSA; safety evaluation

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