05000237/FIN-2008003-03
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Finding | |
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| Title | Corrective Actions to Prevent the Blocking of the 3B LOW Pressure Coolant Injection (LPCI) Heat Exchanger Tubes by Relic Clamshells |
| Description | The inspectors identified an unresolved item regarding the corrective actions implemented to prevent the blocking of the 3B LPCI heat exchanger tubes by relic clamshells laying on the inlet tubesheet of the 3B LPCI heat exchanger which caused the degraded thermal performance of the heat exchanger. Description: During the most recent Unit 3 refueling outage, D3R19 (November 2006), a large amount of relic clamshells were discovered laying on the inlet tubesheet of the 3B LPCI heat exchanger. The cause appeared to be clam shells breaking loose from the walls in Bay 13 due to running containment cooling service water pumps while performing the quarterly HPCI system surveillance test on September 16, 2006. At that time it was unknown whether the condition of the 3B LPCI heat exchanger was degraded to a point that it could not perform its intended function. Approximately 25 percent of the inlet tubes (300 tubes) had some degree of tube blockage. Design conditions for the LPCI heat exchanger assume a 95 degree F inlet water temperature and a heat removal capability of 71 MBtu/hr. Further review determined that the inlet water temperature required to remove 71 MBtu/hr, under this degraded condition, was about 85.5 degrees F. The licensee determined that the inlet water temperature had been less than 85.5 degrees F for the time period between September 2006 and D3R19; therefore 3B LPCI heat exchanger was determined to have been operable during that time. One of the corrective actions implemented to prevent the blocking of the 3B LPCI heat exchanger tubes by relic clamshells was to return to quarterly cleanings of crib house Bay 13. This event was documented in IR 556633. On March 20-21, 2008, thermal performance data was collected for the 3B LPCI heat exchanger. Data reduction was performed and the initial analysis indicated that the 3B LPCI heat exchanger thermal performance, when extrapolated to design conditions (95 degrees F inlet water temperature), was approximately 0.6 percent below the UFSAR value (70.586 vice 71 MBtu/hr). The cause of the degradation was unknown, but the most probable fouling mechanism was either macro (debris that block tubes) or micro (microbial/slime that inhibit heat transfer within the tubes). Further evaluation determined that with a heat removal capability of 70.586 MBtu/hr the maximum allowable inlet water temperature for three months and six months from the original test was 93.5 degrees F and 92.5 degrees F, respectively. On April 21, 2008, the inlet tubesheet of the 3B LPCI heat exchanger was examined using a boroscope. The boroscope inspection found that approximately 10 percent of the inlet tube openings were covered with clams. As a result, the heat exchanger was opened on May 12, 2008. The as-found inspection confirmed that approximately 10 percent of the inlet tubes openings were covered with clams and, in addition, that approximately 80 percent of the inlet tubes had some degree of tube blockage. One tube could not be cleared of debris and had to be plugged. The level of macrofouling increases when the system is operated. The source of macrofoulants (relic clamshells) was Bay 13. Per Parameter Requirement (PMRQ) 243-04, D2/3 Qtr PM Insp/Cln Fire Pump Bay/Dwnstrm Screen with Diver, Bay 13 is cleaned every quarter to ensure the introduction of macrofoulants into the system is minimized. In April 2007, the licensee decided not to perform the cleaning of Bay 13 due to personnel safety issues that affected the divers performing the cleaning despite the increase in clamshells and did not clean the bay until July 2007. At the end of the inspection period, the licensee was still working on an equipment apparent cause evaluation report to evaluate all causal factors related to this issue. The due date of this evaluation is July 25, 2008 (IR 776598). The inspectors considered the determination of the reason the 3B LPCI heat exchanger became plugged after corrective actions were previously identified to be an unresolved item pending inspector review of licensee evaluation efforts. (URI 05000249/2008003-03 |
| Site: | Dresden  |
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| Report | IR 05000237/2008003 Section 1R15 |
| Date counted | Jun 30, 2008 (2008Q2) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | T Bilik D Melendez-Colon W Slawinski C Phillips C Brown M Ring C Acosta Acevedoj Bozga J Draper R Murray E Sanchez-Santiago R Winter F Ramirezd Mcneild Melendez-Colon W Slawinski C Phillips M Ring A Barker R Walton B Cushman |
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Finding - Dresden - IR 05000237/2008003 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Dresden) @ 2008Q2
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