Part 21 Report - 1995-016
ACCESSION #: 9411280210 NTD-NRC-94-4344 Westinghouse Energy Systems Box 355 Electric Corporation Pittsburgh, Pennsylvania 15230-0355 November 15, 1994 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Subject: Closeout of an Interim Report of an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2) Reference: (1) ET-NRC-94-4303, Interim Report of an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2), dated September 19, 1994 The attached information is provided as a closeout to Interim Report 94-012. Preliminary information was previously provided per Reference 1 pursuant to the requirements of 10CFR Part 21 to submit an Interim Report on issues that will not be completed within 60 days from the discovery of the deviation or failure to comply. A closeout to Interim Report 94-012 is enclosed for the following Potential Issue under Westinghouse evaluation: 1. Reactor Coolant Pump (RCP) Support Column Tilt If you have any questions regarding this matter, please contact Mr. H. A. Sepp of my staff at 412/374-5282, or myself. Sincerely, N. J. Liparulo, Manager Nuclear Safety Regulatory and Licensing Activities Attachment Westinghouse Electric Corporation Energy Systems P.O. Box 355 Pittsburgh, PA 15230-0355 Interim Report No. 94-012 Date: 11/16/94 SUBJECT: Closeout to an Interim Report of an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2). TITLE: Reactor Coolant Pump (RCP) Support Column Tilt BASIC COMPONENT SUPPLIED BY: Westinghouse Electric Corporation NATURE OF DEVIATION: As provided in the original issue of Interim Report 94-012, Westinghouse identified a potential issue related to certain reactor coolant pump (RCP) support columns that may be tilted beyond design parameters. Specifically, certain three and four loop plants have a loop piping layout in which the crossover leg piping interferes with the front inside support column of the RCP. The other columns on the RCP are oriented to be vertical in the normal full power condition. This condition was recognized by the support designer and changes were made to the column layout to accommodate the interference between the column and the crossover leg. The change consists of moving the base of the one RCP column toward the reactor pressure vessel approximately 6-12 inches so that the tilted column no longer interferes with the crossover leg piping. The required tilt is from approximately 2 to 5 degrees depending on the column length and amount of movement. This condition was apparently reconciled during the design phase and was not considered a significant issue. The actual change in the value of the vertical stiffness is small, but there is an impact on the thermal expansion of the system. There are tolerances in the RCP columns that would potentially absorb some of the vertical movement associated with the column rotation. SAFETY ASSESSMENT Analyses have been performed to evaluate the impact of the RCP column tilt on the plant with the most severe tilt. A plant with a column tilt associated with a 12 inch movement of the column base from the front inside pump column was chosen for this evaluation. The additional loadings associated with column tilt originate from the use of a support stiffness that has been rotated from vertical by a few degrees. This rotated stiffness at one of the three column locations acts to restrain and rotate the RCP. For a loop piping system thermal expansion of approximately 1.8 inches, the vertical displacement associated with the rotation of an RCP column will vary from about 10 mils for a nearly vertical column to about 1.30 mils for an upper bound tilted column. This difference in displacements at the three RCP columns is what causes a rotation in the pump not previously accounted for. This source of additional loading varies from plant to plant based on the primary equipment support design. There are plants with pin-ended columns that will not have this type of additional loading. There are a number of plants that have support details not of Westinghouse design. Many of the Westinghouse designed supports have a tilt that is approximately half of that analyzed as a part of this evaluation. When this enhancement was made to the thermal analysis, different system loadings resulted. The bending moment at the RCP outlet nozzle for the example plant increased by more than 100%. The RCP column loads also changed. The tilted column went from a compression load to a tension load. The change in column loading met applicable Code allowable limits. The loop Leak-Before-Break (LBB) evaluation was of particular concern for system load changes. The LBB evaluation is performed with the goal of achieving certain margins. The new loadings were reviewed for all 12 weld locations in the primary loop for the example plant, and acceptable margins were maintained. The loop evaluation performed for the example plant, for column tilt loads, met acceptable stress levels. The column tilt for the example plant is approximately twice (12 inches versus 6 or 6.5 inches) that of most other plants. It has been determined that due to the overwhelming plant specific nature of both RCS loops and the RCP column design, the example plant configuration is not generic nor necessarily enveloping, but is representative of a typical Westinghouse configuration. Every plant affected by the RCP column tilt issue has a plant-specific loop analysis that has a unique set of margins. Because loadings local to the RCP can be quite different due to the inclusion of column tilt, those plants that have small margins in this area may require additional analysis. As mentioned, there are conservative margins that are part of the licensing basis associated with LBB. Even in the event that LBB licensing margins are not satisfied, previous experience in the use of the margins associated with LBB lead to the conclusion that the LBB design basis continues to apply. A review of the increased loadings on our example plant yielded acceptable results in all areas reviewed. For the example plant evaluation, there were significant margins available in the areas where loadings increased. If specific modeling techniques are the cause of lower margins, additional analysis may reduce some of the potential conservatism that led to the low margins. Westinghouse has determined that there is no RCS pressure boundary integrity concern due to the RCP column tilt issue, and as such, this issue is not reportable pursuant to 10 CFR part 21. DATE OF DISCOVERY OF DEVIATION: July 20, 1994 CORRECTIVE ACTIONS TO DATE: Westinghouse has completed an extensive evaluation of this issue. It has been determined that the RCP Column Tilt issue does not pose a challenge to the reactor coolant system pressure boundary and therefore, a substantial safety hazard does not exist. Westinghouse has published a Nuclear Safety Advisory letter to communicate this information to affected utilities. EVALUATION COMPLETION SCHEDULE DATE Complete N. J. Liparulo, Manager Nuclear Safety Regulatory and Licensing Activities *** END OF DOCUMENT ***
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