05000327/FIN-2017008-03
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Finding | |
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| Title | Potential Inadequate Use of Thermal Aging and the Arrhenius Methodology |
| Description | Introduction: The inspectors identified a URI for the licensees use of the Arrhenius methodology without consideration for the limits of extrapolation and confidence bounds for statistical uncertainties. Description: The licensee did not consider the limits of extrapolation specified for Category 1 qualification in NUREG 0588 Section 4 and IEEE 323-1974 Section 6.5, Determination of Qualification. NUREG-0588, Section 4(5) required, in part, that known material phase changes and reactions should be defined to insure that no known changes occur within the extrapolation limits, (staff position: claims that conservative extrapolation limits have been implemented must be supported). Standard IEEE 323-1974, Section 6.5, specified, in part, that the qualified life shall be based upon the known limits of extrapolation of the time dependent environmental effects if an accelerated aging test was used to determine the mathematical model. Ancillary quality standards to IEEE 323-1974 and nuclear industry EPRI reports specified that
9 extrapolating beyond the extrapolation limits could invalidate the results of the Arrhenius methodology. The ancillary standards used for qualification of the various examples specified the limits of extrapolation to be no greater than 30 oC from the test data used to determine activation energies. In addition, the licensee did not consider adequate confidence bounds to account for the statistical uncertainties present when using the Arrhenius methodology. The inspectors noted that the uncertainties grow exponentially when exceeding the extrapolation limits. The Limitorque MOV motor life line appeared to have been extrapolated from test data at 240 C to 50 C, which is 190 C from the test data. The silicone rubber cable, life line appeared to have been extrapolated from test data at 210 C to 51.67 C, which is 188.3 C from the test data. The ASCO Valves, life line appeared to have been extrapolated from test data at 266 C to 40 C, which is 226 C from the test data. The Target Rock Valves, life line appeared to have been extrapolated upward from the test data. The Westinghouse RHR Motor rewind, life line appeared to have been extrapolated from test data at 180 C to 58.6 C, which is 121 C from the test data. 275 C is 216 C from test data The ancillary quality standards used in the qualification of these examples included IEEE 98-1972, IEEE Standard for the Preparation of Test Procedures for the Thermal Evaluation of Solid Electrical Insulating Materials; IEEE 101-1972, IEEE Guide for the Statistical Analysis of Thermal Life Test Data; IEEE 117-1974, IEEE Standard Test Procedure for Evaluation of Systems of Insulating Materials for Random-Wound AC Electric Machinery, and other quality standards. IEEE 98-1972, Section 10, Temperature Exposures, specified, in part, that the lowest test temperature shall be chosen so that the extrapolation necessary to establish the temperature index will not be more than 25 C. IEEE 101-1972, Section 1.3, Extrapolation, specified, in part, that extrapolation of the [qualified life] line below the range of test temperatures may cause erroneous predictions if the chemical reactions controlling the insulation aging are different at lower temperatures or if other conditions affecting the aging or the mode of failure are different. Therefore, the methods outlined in this guide are applicable only if all of the assumptions behind the use of the Arrhenius equation are met [identified in references]. IEEE 117-1974, Section 3.3.1, Thermal Aging, specified, in part, for any system being evaluated, tests are made for at least three different temperatures. The lowest test temperature should be no more than 25 C above the system temperature rating. The highest temperature test should be at least 40 C above lowest temperature test, and temperature points should be selected to give approximately equal temperature intervals. The average life at the highest temperature shall be no less than 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />. The inspectors are concerned that the licensee did not meet the aforementioned Category 1 requirements in their licensing basis. The licensee has captured these concerns in their corrective action program as CR 1366022. The inspectors need further information from the licensee and NRC technical staff to evaluate the concerns. This URI is opened to determine if a performance deficiency exists. (URI 05000327/2017008-03, 05000328/2017008-03, Potential Inadequate use of thermal aging and the Arrhenius methodology) |
| Site: | Sequoyah  |
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| Report | IR 05000327/2017008 Section 1R21 |
| Date counted | Dec 31, 2017 (2017Q4) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21N |
| Inspectors (proximate) | T Fanelli M Greenleaf C Franklin S Walker |
| Violation of: | Pending |
| INPO aspect | |
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Finding - Sequoyah - IR 05000327/2017008 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Sequoyah) @ 2017Q4
Self-Identified List (Sequoyah)
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