05000445/FIN-2007003-01
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Finding | |
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| Title | Residual Heat Removal Heat Exchangers Meet Design Safety Function |
| Description | An unresolved item was identified regarding inadequate design control measures for verifying the adequacy of the safety-related RHR system heat exchangers. The licensee stated that the RHR heat exchangers were not inspected and cleaned, due to ALARA dose consideration. The licensee also stated that the heat exchangers were not tested. Calculation RXE-LA-CPX/0-020, RHR Cooldown Calculations, and Calculation Number ME-CA-0229-2188, Component Cooling Water Heat Exchanger Fouling Factor Analysis, were used by CPSES to determine if the RHR heat exchanger would meet its design basis. The calculations only established an overall component cooling water (CCW) heat exchanger fouling factor and the allowable fouling for continued operations. This issue is unresolved for both significance and enforcement, since additional technical review by NRC was needed to assess this issue. Description: The inspectors reviewed Calculation RXE-LA-CPX/0-020, RHR Cooldown Calculations, Revision 9, which was prepared to demonstrate the RHR cooldown requirements could be met under various conditions. The licensee assumed an overall fouling factor for the CCW heat exchanger. In addition, the licensee used their computer code Cooldown program to determine the performance of the RHR heat exchanger under various operating conditions. The team reviewed the calculation and noted that many assumptions were used. The assumptions included CCW heat exchanger flow rate through the heat exchanger tubes, and an assumed CCW fouling -10- Enclosure factor. The CCW flow rate was 7604 gpm/train, which was about the same as the design basis flow rate of 7600 gpm/train. The inspectors noted that if the assumptions made were changed, the results of the calculation could vary. The inspectors reviewed Calculation ME-CA-0229-2188, Component Cooling Water Heat Exchanger Fouling Factor Analysis, Revision 6, which was used by CPSES personnel to determine if the RHR heat exchanger would meet its design basis by determining algorithms necessary to calculate an overall CCW heat exchanger fouling factor and the allowable fouling or margin for continued operation. The fouling factor for the CCW heat exchanger was determined by using recorded temperatures for the inlet and outlet of the CCW heat exchanger and the inlet and outlet temperatures of the safety-related station service water heat exchanger. In addition, the station service water system flow was measured. However, the inspectors noted the calculation stated that instrument uncertainties were not considered in the calculation. The inspectors noted that the instrument uncertainties could cause a large change in the calculation results which could make the results of the calculation using no instrument uncertainties meaningless. In order to complete the review of the RHR heat exchangers, the inspectors request the following information: The margin for the heat transfer rate is needed. The margin consists of the vendor determined heat transfer rate (BTU/hr) at the licensees design basis conditions for the supplied heat exchangers, and the required design basis heat transfer rate for the plant. Instrument uncertainties are required for Calculation ME-CA-0229-2188 in order to determine the worst case fouling factor for the CCW heat exchanger. Information should be supplied to the inspectors concerning the licensees computer code Cooldown and if it has been verified and validated. Analysis: At the time of writing, CPSES had not demonstrated that the RHR heat exchangers would meet their safety function. This issue is potentially more than minor because it could affect the Mitigating Systems Cornerstone objective by causing the safety-related RHR system to not transfer sufficient heat to the CCW system to support the safety-related systems. The licensee issued Smart Form SMF-2007-001669-00, dated May 17, 2007, to determine what monitoring or testing should be performed on the RHR heat exchangers. The licensee stated that the RHR heat exchangers were operable due to clean water in both the RHR and CCW closed system loops. Enforcement: Part 50 of Title 10 of the Code of Federal Regulations, Appendix B, Criterion III, Design Control, requires, in part, that design control measures shall provide for verifying or checking the adequacy of the design, such as by the performance of design reviews, by the use of alternative or simplified calculation methods, or by performance of a suitable testing program. Additional review by NRC is needed to determine if the RHR heat exchangers would meet their design safety -11- Enclosure function. Therefore, this item will be treated as an unresolved item pending additional review of material to determine if the RHR heat exchangers will meet their safety function: URI 05000445;446/2007003-01, Residual heat removal heat exchangers meet design safety function. |
| Site: | Comanche Peak  |
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| Report | IR 05000445/2007003 Section 1R07 |
| Date counted | Jun 30, 2007 (2007Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.07 |
| Inspectors (proximate) | J Braisted P Goldberg G Guerra C Smith G Pick W Walker B Tindell W Sifre M Young A Fairbanks J Kramerp Goldbergk Clayton G Guerra D Stearns A Sanchez D Allen S Alferink M Young A Fairbanks E Uribe |
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Finding - Comanche Peak - IR 05000445/2007003 | |||||||||
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Finding List (Comanche Peak) @ 2007Q2
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