July-August 2019 NPJ

Nuclear Plant Journal, July-August 2019 NuclearPlantJournal.com 15 New Documents & Videos EPRI 1. Chloride-Induced Stress Corrosion Cracking (CISCC) Canister-to-Environment Flow Rate Technical Basis . Product ID: 3002015062. Published June, 2019. One potential mode of aging degradation for dry cask storage systems that use welded stainless steel canisters is chloride-induced stress corrosion cracking (CISCC) of the canisters. Investigation into the potential consequences of a through-wall crack in a canister resulting from CISCC can help utilities better assess aging management actions to address potential CISCC of welded stainless steel canisters. A key input to the consequence evaluation is the flow rate through the postulated through-wall flaw. Estimates that reflect the characteristics of stress corrosion cracking (SCC) and the conditions inside a sealed canister at the time of breach are desirable for input to future consequence assessments. The objective of this report is to provide calculated flow rates (and resulting changes in canister backfill inventory) for postulated CISCC through-wall flaws in different welded stainless steel canister designs. The results based on best- estimate input parameters are presented along with sensitivity study results where input parameters are varied to evaluate the impact of key inputs and assumptions. Two primary modeling considerations are addressed in this report: 1) assessing intact canister internal temperature and pressure conditions as a function of time, and 2) performing flow rate calculations that consider crack morphology and atmospheric conditions impacting flow and air-helium exchange through the postulated CISCC breach in a canister wall. 2. Evaluation of Commercial Filters for Improved Reactor Coolant Purification: PWR Chemistry Technical Strategy Group Report . Product ID: 3002015882. Published June, 2019. Levels of various radionuclides in the reactor coolant circuit are controlled using mechanical filters and ion exchange resins located in a side-stream purification system, the Chemical and Volume Control System (CVCS). In order to reduce worker radiation dose, there is an incentive for improvement of purification media performance. However, commercial filters for this purpose must be independently tested because suppliers test their filters under differing conditions, making it difficult to compare and understand filter performance under reactor coolant conditions. The key technical objective of this projectwastoassessthecharacteristicsand relative performance of three commercial ultrafiltration filters that may offer improved reactor coolant purification—a 0.05 µm filter and 0.01 µm filter from Pall Corporation and a Nano 0.07 µm filter from DCS Controls. Techniques used in the assessment included scanning electron microscopy (SEM), tensile strength, thickness, leachables testing, capillary flow porometry, pycnometry, mercury porosimetry, and filter performance testing. Areas assessed included pure water flux, initial retention efficiency employing standard test media, and preparation of surrogate magnetite suspension solutions based on pressurized water reactor (PWR) coolant chemistry. This report provides details of the characterization of the three filter media and the results of filter performance testing. 3. 2018 Feasibility Study and Evaluation for Informing Fuel Enrichment and Burnup Limits . Product ID: 3002014625. Published June, 2019. Commercial light water reactors generate electricity using low-enriched uranium (LEU) fuel. On average, fuel costs comprise approximately 20% of a nuclear power plants’ total generating costs [1]. Few other individual cost components have such a large impact on the economics of the nuclear fleet. A site’s fuel costs depend on two factors, the price of the fuel components (uranium feed, conversion, enrichment, and fabrication) and the efficiency of the core design. Fuel component costs are driven by supply and demand and are largely outside the control of an individual utility. The efficiency of a core design determines the quantity of nuclear material needed to meet a plant’s energy objectives. While a utility can improve the efficiency of the core design, this efficiency is ultimately limited by the specific constraints of the core design. A review of the current fuel management practices, based on equilibrium cycle designs, has shown that 99% of the variation in fuel cycle efficiency is attributable to variations in initial uranium enrichment and discharge burnup. Many sites are currently constrained by the existing regulatory limits on one or both of these parameters. As part of the Accident Tolerant Fuel/Advanced Technology Fuel (ATF) initiative, this report describes an analysis of the potential benefits and challenges associated with increasing the current fuel enrichment and burnup limits. Revising these limits impacts a large portion of the nuclear fuel cycle as well as the licensing bases for both plant operators and fuel suppliers, including both front-end and back-end. While there are economic advantages to making these changes, they also require long-term capital investment and regulatory changes. Revising these limits will also provide potential savings through additional cycle length flexibility, reduced high level waste storage and disposal requirements, and a positive benefit on the environmental impact of the fuel cycle. Relaxed fuel enrichment limits are expected to provide economic benefits for both conventional and ATF fuel designs, as well as providing a foundation for Generation IV reactors. However, additional benefits may be available for ATF design concepts that support higher fuel burnup levels. This initial analysis is U.S. centric but can be adopted to include the international nuclear community. This analysis complements a regulatory review conducted by the Nuclear Energy Institute (NEI). The two evaluations are incorporated into a NEI white paper [2] which informs stakeholders of the issues associated with making these regulatory limit changes. The final decision to pursue new limits must consider not only the expected benefits but the business risks associated with such an undertaking. The above EPRI documents may be ordered by contacting the Order and Conference Center at (800) 313-3774, Option 2, or email at orders@epri.com . (Continued on page 33)

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