05000321/FIN-2008002-01
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Finding | |
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| Title | Residual Heat Removal Service Water Hanger Failures |
| Description | During a walkdown of the Unit 1 torus room, the licensee found two broken RHRSW supports (1E11-RHR-H98 and 1E11-RHR-H291). These discoveries were documented in CR2008101477 and CR2008101507, respectively. Additionally, Unit 1 Torus Room Penetration No. 25, RHRSW, was identified with linear indications in the weld area where each lug (four total) was welded to the wall sleeve facing, and documented in CR2008101702. CR2008101568 was created to provide an overall evaluation and apparent cause determination for all three previously mentioned condition reports. Both RHRSW flow control valves (one for each loop of RHRSW) were designed to control flow through the RHRSW system while minimizing downstream cavitation via a series of orifices. Design Change 93-019 modified the RHRSW flow control valves and was intended to insert a number of larger diameter orifices in the upper 1.0 of the orifices corresponding to 87% of valve stroke. The intent of the modification was to minimize the possibility of control valve clogging in the event that significant debris accumulated in the system (e.g. failed strainer). The actual modification drilled holes in the upper 1.5 of the orifices which corresponded to 81% of valve stroke. One consequence of the modification appears to have been a significant increase in cavitation downstream of the flow control valves when operated past the first 81% of their stroke with two RHRSW pumps operating. No changes in the RHRSW operating procedures were incorporated to minimize time spent in that portion of the operating envelope (two pump operation with valve stroke beyond 81%) that produced increased cavitation. This increased cavitation appears to have been a direct contributor to the failure of the RHRSW piping hangers (H98 and H291). Following discovery of the Unit 1 hanger failures, the licensee performed a VT-3 examination of all A and B loop RHRSW piping supports downstream of the RHR heat exchanger (which included the flow control valve). These exams revealed there were no additional failed supports. The licensee performed an operability determination and determined there were no past operability concerns. The licensee has instrumented the piping of concern and was operating within the bounds of ANSI/ASME OM3-1982, Requirements for Preoperational and Initial Start-up Vibration Testing of Nuclear Power Plant Piping Systems. Due to similar concerns for the Unit 2 RHRSW piping supports, the licensee issued CR2008102081 to perform a root cause evaluation. This issue is unresolved pending completion of the NRC review of the licensees Root Cause Evaluation, and the Hanger H98 and H291 Failure Analysis Report and is identified as URI 05000321/2008002-01, RHRSW Hanger Failures |
| Site: | Hatch  |
|---|---|
| Report | IR 05000321/2008002 Section 1R08 |
| Date counted | Mar 31, 2008 (2008Q1) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.08 |
| Inspectors (proximate) | S Shaeffer E Michel L Miller J Hickey B Caballero P Capehart P Niebaum A Raos Shaeffere Michel J Hickey P Niebaum R Williams |
| INPO aspect | |
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Finding - Hatch - IR 05000321/2008002 | |||||||||||||||||||||||||
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Finding List (Hatch) @ 2008Q1
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