IMPACTS OF OPERATIONAL CHANGES ON LLW SCALING FACTORS

摘要

Since the implementation of 10CFR61 in 1984,US nuclear power plants have adopted,as a routine,sampling and radiochemical analysis for the determination of difficult to measure radionuclides limited by 10CFR61 for shallow land disposal.Samples are collected on, approximately,an annual basis and the results are used in the determination of scaling factors. NRC guidance on the characterization and classification identifies the need to update the sample basis for the scaling factors more frequently if there are significant changes in plant conditions that might potentially change the scaling factors by more than a factor of 10. rnA number of examinations of industry experience with sampling and scaling factor development have been completed.In these studies data is assembled as a single database and ratios are analyzed to determine overall averages broken down by streams.All of the conditions that might give rise to changes in the scaling factors for an individual plant are averaged over in the composite grouping.This gives little guidance on how to handle local changes in plant conditions. rnSince 1984,several significant changes in plant water chemistry management have been introduced.These include for BWRs,zinc injection to limit the incorporating of Co-60 in the corrosion layer,hydrogen water chemistry to displace oxygen to limit stress corrosion.There have also been changes in PWR water chemistry such as varying lithium concentrations to control formation of corrosion layers.In addition,there have been both BWR and PWRs that have experienced fuel failure episodes,extended outages,and have undergone major decontaminations.It is generally believed that such changes and transient conditions cause temporary or permanent changes in scaling factors but to date no attempt has been made to show which scaling factors were affected or the extent of the effect. rnThis work was undertaken for the Electric Power Research Institute.The paper will focus on an explanation of the project,analytical methods,and provide an overview of some of the findings.