Nuclear Energy & Infrastructure Systems Division

Engineering Mechanics and Infrastructure Group

Plant Aging and License Renewal

BNL has worked for 20 years on plant aging and recently on license renewal evaluations. NEISD staff is supported NRC’s program to develop regulatory guidance on the capability of age-degraded structures and passive components. This project included development of analytical methods to evaluate age-related degradation of reinforced concrete, buried piping, tanks, anchorages, and masonry walls; probability-based evaluations of degraded structures and components; and determination of the impact of aging degradation on plant risk. Probabilistic risk assessments were performed to develop degradation acceptance criteria for the NRC.

NEISD conducts detailed evaluations of selected sections of license renewal applications covering the containment, other structures and structural components, reactor coolant systems, electrical components, and associated aging management programs. As of 2007, NEISD has supported the NRC review of 15 applications. In prior work, NEISD developed technical criteria for aging management of existing nuclear power plants for an additional twenty-years of operation.

Wire Aging

While aging of wire systems has been a concern in the nuclear industry for a number of years, increasingly this problem is recognized as an important public health and safety issue that transcends specific industries. To address this concern, NEISD is identifying issues related to aging of wire systems and facilitating collaborative research programs with industry to address these issues. Toward that end, NEISD organized an international conference, held in April of 2002, on wire system aging for the NRC.

NEISD has conducted original research on an ultrasonic stimulation/IR imaging cable condition monitoring technique and has worked with two U.S. companies to perform demonstration testing of promising condition monitoring techniques they developed by
applying them to NPP cables. Thermal aging ovens and a new environmental test chamber at the Electric Component Test Facility (ECTF) were used to prepare aged cable test specimens for this research. NEISD also worked as a subcontractor to Raytheon on a Federal Aviation Administration project addressing wire aging as it relates to aircraft. The work involved accelerated aging and life testing of various types of aircraft wiring to determine if a limit should be placed on their service life when used in commercial aircraft. The test program included accelerated aging and electrical testing of the aircraft wiring at the ECTF.
 

E. Grove and R. Lofaro testing cable in the Electric Component Test Facility.

Effects of Switchgear Aging on Energetic Faults

Recent events have raised a concern that some U.S. nuclear power plants may be susceptible to energetic faults, in which electrical faults that are not immediately cleared by the protection system can lead to explosions, fire, and severe damage to plant equipment and systems. Aging of the electrical components that are supposed to pre-vent such faults may further exacerbate this situation. In this program, NEISD reviewed past operating experience from national databases to characterize the aging of electrical switchgear and associated components and to identify aging trends that could potentially lead to an increase in the frequency and/or severity of energetic faults. As part of this work NEISD developed computer models of typical NPP electrical distribution systems to identify and analyze the electrical system characteristics that could contribute to the occurrence and severity of energetic faults and to evaluate the impact of equipment aging on the susceptibility of the plant to energetic faults. The program also included a review of typical protective relaying schemes and an evaluation of potential improvements that could provide increased protection to the plants.

NUPEC shaking table test of concrete wall.

Large Scale Seismic Tests of Nuclear Power Plant Structures

NEISD is active in looking at seismic issues in an NRC sponsored program carried out in collaboration with the Japan Nuclear Energy Safety Organization (JNES), which was established October 2003, and prior to that the Nuclear Power Engineering Corporation (NUPEC) of Japan. NEISD has worked on the planning, conduct and evaluation of large-scale seismic tests of nuclear power plant structures, systems and components conducted in Japan over the past 20 years. The program includes information exchange and simulation analyses on a number of full-scale seismic fragility tests of nuclear plant components being performed in Japan. The current activities include collaboration on soil-structure interaction tests, multi-axis loading tests of reinforced concrete shear walls, ultimate strength piping tests, degraded piping and component tests, and equipment fragility tests. The figure below shows one face of a reinforced concrete box-shaped wall damaged during a shaking table test. NEISD performed finite element analyses of the test models and evaluated the results with the JNES/NUPEC test data.

C. Hofmayer, G. DeGrassi, J. Xu, J. Braverman and R. Morante study dry cask drop analysis.

Dry Cask Storage

NEISD contributed to the development of a Probabilistic Risk Assessment (PRA) for the handling and storage of spent nuclear fuel in dry casks at a specific plant. In this project, NEISD has performed drop and impact studies using both simplified calculation methods and also detailed finite element analyses (LS-DYNA computer code). The detailed finite element analyses included drop accidents of the cask system at various heights, orientations, and targets. Nonlinear material properties, rupture strain, contact impact elements, buckling, and concrete crushing were considered. The PRA is intended to provide a framework for a general methodology applicable to other dry cask systems at other locations. The generic PRA model and the plant-specific PRA will be used to assess the potential risk to the public from the storage of spent nuclear fuel, and to assist in the development of safety goals for dry cask storage.

Vulnerability of Structures to Aircraft Impact

The NRC performed integrated vulnerability assessments for U.S. nuclear power plants to determine the effect of terrorist attacks and effective means to reduce the vulnerability. NEISD performed finite element analyses using the LS-DYNA computer code to evaluate the response of typical structures to impact loads. NEISD upgraded its computing capability by purchasing a workstation for performing classified calculations. This computer has dual processors to take full advantage of LS-DYNA’s (for structural analysis) parallel processing capability and two large-capacity removable hard drives to meet DOE security requirements.

Seismic Analysis Methodologies for Deeply Embedded and/or Buried (DEB) Structures

Motivated by many NPP design considerations, several conceptual designs for advanced reactors propose that the entire re-actor building and a significant portion of the steam generator building be partially or completely embedded below grade. For the analysis of seismic events, the soil-structure interaction (SSI) and passive earth pressure for these types of DEB structures will have a significant influence. NEISD is conducting an NRC-sponsored research program to assess the significance of these proposed design features for advanced reactors, and to evaluate the existing analytical methods to determine their applicability and adequacy in capturing the seismic behavior of the pro-posed designs. Computer programs such as SASSI2000, CARES and LS-DYNA are being used by NEISD to test methodologies. It is expected that the findings and recommendations from this program will be used to confirm the applicability of exiting criteria or to develop new acceptance criteria, if necessary.

P-CARES Software Development

P-CARES, the Probabilistic Computer Analysis for Rapid Evaluations of Structures, is an efficient tool for the NRC staff to perform probabilistic site response and SSI analyses using relatively simple soil and structural models. Its predecessor CARES was first developed by NEISD about two decades ago. A recent major upgrade by NEISD has incorporated probabilistic simulation schemes to allow explicit treatment of the uncertainties inherent in the site soil pro-file and the NPP structure. A graphical user interface has also been implemented to greatly improve its usability and productivity. P-CARES development involved mixed programming in Python and FORTRAN for rapid application development and greater maintainability. This software development approach has been proven to be an efficient way to modernize valuable historical FORTRAN codes.

New Reactor Design Certification

NEISD has been providing technical assistance to the NRC for evaluation of new reactor standard plant designs for over 15 years, including GE’s ABWR and ESBWR, Westinghouse’s AP600 and AP1000, CE’s Sys-tem 80+, and AREVA’s EPR. The scope of effort includes the seismic design criteria, containment design, design of other structures and structural components, and piping system design. As part of the confirmation of design adequacy, NEISD conducts detailed confirmatory analyses using state-of-the-art computational methods.

Technical Assistance for Regulatory Guidance Updates

NEISD is providing technical assistance to the NRC for updating the regulatory guidance contained in the Standard Review Plan and associated Regulatory Guides, in the seismic and structural areas. This is a high-priority effort to modernize the guidance prior to the expected submittal of a significant number of new plant applications.

Licensing Issues Related to Seismic Siting

NEISD performed an evaluation of recently developed performance-based and risk-consistent methods used to define seismic design criteria for safety-related structures, systems, and components. These new methods ensure plant safety by requiring that nuclear facilities be designed to achieve quantitative probabilistic target performance goals. The evaluation effort led to the development of guidance for the NRC staff to use when reviewing licensing applications utilizing the performance-based method for seismic qualification. This research effort included the review of spatial incoherency models for soil-structure interaction to re-duce the response of building foundations to the high frequency components of earth-quake motions. In addition, NEISD is assisting the NRC in reviewing early site permit applications for new plants in areas related to the stability of subsurface materials and foundations.

Last Modified: February 1, 2008
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One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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