[en] This paper describes a portion of the analysis and results of the NRC/INEL participation in the SHAG (high-level shaker tests) Seismic Research Program conducted by Kernforschungszentrum Karlsruhe (KFK) at the Heissdampfreaktor (HDR), a decommissioned nuclear reactor. The objective of this activity was to analyze the responses of a piping system and associated line-mounted equipment when subjected to various seismic and hydraulic loadings. The studies compare the influence that piping support system flexibility has on piping system responses. The results of the studies will contribute to the technical basis for assessing the responses of light water reactor (LWR) piping and line-mounted equipment to earthquakes

[en] As part of the US Nuclear Regulatory Commission's Nuclear Plant Aging Research (NPAR) Program, methods are being developed to evaluate the risk effects of aging. These methods are being developed under the Risk Evaluations of Aging Phenomena (REAP) Project. As part of the effort under REAP, more comprehensive approaches for prioritizing the risk effects of component aging have been developed. These risk prioritization approaches do not have the limitations of previously developed approaches which have been published. Straightforward formulas are obtained which incorporate both the risk importance of the component and the aging effects on the component failure rate. Available Probabilistic Risk Analyses (PRA's) can be utilized to efficiently prioritize systems, components, and aging mechanisms. The linear aging failure rate model is specifically utilized in the general formulas to demonstrate the usefulness and applicability of the approaches. The Calvert Cliffs PRA model is used for illustration

[en] The US Nuclear Regulatory Commission (NRC) is developing a policy for renewing the operating licenses of commercial nuclear power plants. Several license renewal issues have been identified as a result of NRC's public comment process and its own consideration of the regulatory requirements for relicensing. This paper provides a discussion of the safety issues associated with license renewal and of the options identified to address those issues. The key safety issues are related to the age-related degradation, licensing design basis, and operations and management aspects of plants to be relicensed. The regulatory options are described in terms of the technical information needed for safety review of license renewal applications. The options are intended to be further evaluated and integrated to provide a basis for license renewal policy development

[en] Sequential testing methodologies were discussed by examining amount of oxygen consumed in organic materials in simultaneous and sequential environments of heat and irradiation, effects of pre-conditioning methods on degradation of material and test conditions on water sorption of materials in steam/spray environments of simulated LOCA in order to assure the validity of the short term sequential method for qualification of electric wires and cables for nuclear uses. The degradation behavior of various jacketing and insulation materials such as chloro-sulfonated polyethylene, ethylene-propylene rubber, cross-linked polyethylene, chloroprene, and silicone rubber were investigated. From these experimental results, it is concluded that the irradiation conditions such as sequential ordering of irradiation and thermal aging, dose rate and irradiation temperature, and presence of air in the LOCA stream/spray environments are important factors in the qualification testing methodology. 22 figures

[en] Despite the fact that motors are proven to be relatively reliable components and maintenance practices are extensive, motors still experience failures. The operating experience of motors in nuclear power plants clearly indicates that the insulating system and bearing assembly are the dominant failure modes, accounting for almost 70% of the reported failures. Maintaining and monitoring the state of these two subcomponents, using cost effective techniques, could eliminate many untimely failures and thus could improve the overall motor reliability and, hence, the plant safety. This paper discusses the results of the motor study performed under the auspices of the NRC Nuclear Plant Aging Research (NPAR) program. The study included determination of appropriate functional indicators suitable for monitoring the condition of the above-mentioned two subcomponents. This was achieved by performing various bearing and insulation tests on aged motors and evaluating various test procedures

[en] In Phase I of the Component Fragility Program, Brookhaven National Laboratory (BNL) has developed a procedure to establish the seismic fragility of nuclear power plant equipment by use of existing test data and demonstrated its application by considering two equipment pieces. In Phase II of the program, BNL has collected additional test data, and has further advanced and is applying the methodology to determine the fragility levels of selected essential equipment categories. The data evaluation of motor control center, switchboard, panelboard and power supply has been completed. Fragility levels have been determined for various failure modes of each equipment class and the deterministic results are presented in terms of test response spectra. In addition, the test data have been analyzed for determination of the respective probabilistic fragility levels. The zero period acceleration and the average spectral acceleration over a frequency range of interest are used as inputs in the statistical analysis. The resulting fragility parameters are presented in terms of a median value, an uncertainty coefficient and a randomness coefficient. Ultimately, each fragility level is expressed in terms of a single descriptor called an HCLPF value corresponding to a high (95%) confidence of a low (5%) probability of failure. The important observations and recommendations for future research work in the fragility area are included in this paper. One of the important needs is to study the applicability of the fragility results to the earlier vintage equipment for which little or no test data exist

[en] At the request of the NRC Office of Nuclear Reactor Regulation, the Lawrence Livermore National Laboratory is performing a study of the structural response of a motor control center (MCC) subjected to high-level seismic fragility testing, including how input motions are amplified by the MCC structure. This study is based on fragility test data developed by LLNL as part of the NRC-sponsored Component Fragility Research Program (CFRP), the purpose of which is to investigate the ability of nuclear power plant components to withstand the effects of large earthquakes. This work is being conducted in two parts. The first, discussed in this report, is a study of kinematic amplification, in other words, amplification defined as the ratio of measured in-cabinet response to measured input motion. This definition of amplification factor (usually based on zero period acceleration or on response at some other specified frequency) is typical of the approach used in design and layout of cabinets housing electrical devices. The second part of the study, in which amplification is being based on alternate parameters (e.g., power spectral densities of input and response motions) is currently in progress and will not be discussed here in detail

[en] Two major research areas were investigated in the Phase I snubber aging studies. The first area involved a preliminary evaluation of the effects of various aging mechanisms on snubber operation; failure modes of mechanisms were identified and their contributions to aging degradation were assessed relative to other failure modes. The second area involved estimating the efficacy of existing tests and examinations that are intended to determine the effects of aging and degradation. Available data on snubber behavior and operating experience were reviewed, using licensee event reports and other historical data for the 10-year period from 1973 through 1983. Value-impact was considered in terms of (1) exposure of workers to radioactive environments for examination/testing and (2) the cost for expansion of the snubber testing program due to failed snubbers. Results from the Phase I studies identified the need to modify or improve examination and testing procedures to enhance snubber reliability. Based on the results of the Phase I snubber studies, the seals and fluids were identified as the two principal elements affected by aging degradation in hydraulic snubbers. Phase II work, which was initiated in FY 1987, will develop cooperative activities between PNL and operating utilities through the Snubber Utility Group (SNUG), who will work to establish a strong data and experience base for both hydraulic and mechanical snubbers based on actual operating and maintenance history at nuclear power plants. Application guidelines for snubbers will be recommended based on the study results

[en] During the fiscal years up to FY 85, tests on microconcrete scale model shear deformation-dominated structures were performed. The results indicated that these structures responded to seismic excitations with frequencies that were reduced by factors of 2 or more over those calculated based upon an uncracked cross section strength-of-materials approach. During FY 86, a large TRG type structure, referred to as TRG-3, (4-in walls of real concrete, No. 3 rebar, and with about 15 tons of added mass) was tested seismically at the Construction Engineering Research Laboratory (CERL) in Champaign, Illinois. Prior to this test, a 1/4-scale microconcrete model of TRG-3 had been seismically tested at LANL. This scale model, referred to as TRG-1, and its prototype provided information both on reduced stiffness and on the scalability of microconcrete response to the response of structures made from typical concrete and rebar. Also included in the current phase of this program was the quasi-static load cycle testing of TRG type structures. These tests were intended to measure stiffness of the shear walls during well instrumented, controlled tests and to separate the stiffness into shear and bending components. Separation of the stiffness components was aimed at providing more data for identifying a mechanism for the previously observed reductions in stiffness. In addition to the static tests, low-level modal tests were performed on these structures as a further method of identifying their dynamic properties. The results from the testing on the first, third, and fourth TRG structures are summarized and a discussion of these results, in light of what they have learned about the seismic response of the actual low aspect ratio shear wall structure seismic response, is presented

[en] Most seismic design experts agree that nuclear power plants are capable of withstanding earthquakes much larger than their original design basis without compromising their ability to safety shutdown and remain in a safe shutdown condition. However, only recently through the efforts of the Seismic Design Margins Program, have they had the tools to effectively and efficiently quantify the inherent overall seismic capability of nuclear power plants, and to do so in a way that can be used directly for licensing decisions. The successful completion of the Maine Yankee seismic margins review in March 1987, and the issuance of a NNR Safety Evaluation Report based on this review are major milestones in the seismic evaluation of nuclear power plants. The Seismic Design Margins Program (SDMP) developed a new seismic evaluation methodology to better evaluate the ability of nuclear plants to withstand earthquakes above their design basis level. The approach involves the screening of components based on their importance to safety and their seismic capacity. The products of a margins review are High Confidence of Low Probability of Failure (HCLPF) capacities for components, accident sequences and the plant. The HCLPF value is a lower bound estimate of seismic strength that explicitly considers the confidence in this estimate. Systems analysis is used to determine those plant systems and components that are important contributors to seismic core melt. The paper discusses how the methodology was used in the Maine Yankee review. Ongoing and future SDMP tasks are also mentioned