November-December 2018 NPJ

78 www.NuclearPlantJournal.com Product & Service Directory–2019 STPNOC’s risk-informed GSI- 191 approach represents a significant assessment of the safety implications associated with emergency containment strainers and the recirculation mode of emergencycorecoolingsystemoperation. The analyses performed have illustrated thecomplexitiesandthecompetingeffects ofthephysicalphenomenaassociatedwith postulatedLOCAs. Pipe break size, break location, insulation amount, insulation type and location, containment geometry, strainer tested capacity, and fuel tested capacity aremajor factors associatedwith long-term core cooling and associated phenomena. Cost Savings Impact The Rove rD r i s k - i n f o rmed methodology produces considerable cost benefits. The cost of having to replace/ modify fibrous insulation in the reactor containment building and dispose of it is estimated tobe on the order of $55million for a two-unit site. The associated cost avoided by STPNOC with the approval of the license amendment is estimated to be $43 million. STP expects that the 90-day action statement in the debris-specificTechnical Specifications associatedwith theRoverD license amendment may avoid unplanned shutdowns. An unscheduled outage of a unit typically results in loss of at least three days production. The RoverD risk- informedmethodologyanddebris-specific Technical Specifications will likely also avoid the possible, future need for debris- related request for Notice of Enforcement Discretion (NOED), call-out of off-duty station personnel, and other associated regulatory actions. The approval allowed STPNOC to avoid the additional radiation dose, avoided expense of removing/modifying fibrous insulation and to use a debris- specificTechnical Specification toprovide a reasonable limit on the time to resolve a degraded/non-conforming debris issue. Productivity/Efficiency The resulting framework provides STPNOC the flexibility to address potential issues on a risk-informed basis. Use of the risk-informed methodology provides an efficient vehicle to close GSI- 191 and GL 2004-02. Implementation of the revised Technical Specifications associated with thelicenseamendmentwasstraightforward and resulted in minimal impact on plant operations. The 90-day duration to address possible future debris-related issues allowed by the revised Technical Specifications is a productivity/efficiency Risk Informed... ( Continued from page 77) improvement since more time is given to address the issue. Resources would be more efficiently applied to the possible issue than otherwise with a much shorter allowed duration. Transferability Th e r i s k - i n f o rme d Rove rD methodology andTechnical Specification changeproducessignificantandcontinuing cost savings and improvements in plant maintenance, operations, and production. The concept and application are relatively simpleandcanbeusedbyanynuclearplant in the country to realize similar benefits. Most, if not all, plants have already performed plant-specific testing that can be used to quantify the deterministic amount of fiber debris that is acceptable. CASA Grande (or a program that has similar capability) can be used to identify the smallest break size and location that can generate more debris than the amount tested. The risk from that break size can be determined through the use of NUREG-1829 and compared to the risk acceptance criteria in RG 1.174. The risk-informed process to resolve GSI-191 is easily transferable across the industry. There are plant-specific inputs, but the process is generic such that it can be applied to all plants. Detailed PRA modeling is not required to implement the RoverD process; the principle inputs are the Level 1 (CDF) and Level 2 (LERF) PRA values that are used as inputs to RG 1.174 for determining the applicable risk region. The STP approach is consistent with RG1.174, draft RG1.229, Risk-Informed Approach for Addressing the Effects of Debris on Post-Accident Long-Term Core Cooling, and draft rule change 10CFR50.46c. Contact: Amanda Sitka, STP Nuclear Operating Company, telephone: (979) 253-8777, email: asitka@stpegs. com.