05000346/FIN-2007004-02
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Finding | |
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| Title | Reduced Flow Through Component Cooling Water 1 Heat Exchanger Because of Improper Valve Opening Limit Stop |
| Description | The inspectors determined that an unresolved item (URI) existed concerning the improper setting of the travel stops on Component Cooling Water Heat Exchanger 1 Service Water Outlet Valve SW-36. The setting, in the event of a safety feature system actuation, would limit service water flow to less than flows analyzed in the approved flow balance calculation. The improper setting apparently was made during a maintenance activity in August 2006 and was not discovered until flow balance testing on August 31, 2007. Description: On August 31, 2007, the licensee was conducting flow balance testing of service water train 1 components. Because of the design of the plant systems, which incorporates a service water pump, a component cooling water pump and heat exchanger, and a containment air cooler that can be aligned to either of the two TS required service water trains, multiple flow tests were required to verify all potential combinations of equipment. The procedure was a new procedure that had been developed to allow online flow balancing instead of the previous norm of conducting the flow balancing during outages. The licensee had successfully completed online flow balancing of service water train 2. The initial testing of the service water train 1 components had component cooling water (CCW) heat exchanger 1 aligned for train 1 testing. When the testing commenced, the personnel conducting the testing observed that the flow through the heat exchanger was approximately 1200 to 1500 gallons per minute (gpm) lower than they expected. The test was suspended and CCW train 1 was declared inoperable. The licensee entered the action statements for CCW and components cooled by CCW train 1. The licensee, after declaring CCW train 1 inoperable, removed CCW heat exchanger 1 from service and aligned CCW heat exchanger 3 as the heat exchanger for train 1. After observing expected service water flows through heat exchanger 3, the licensee declared CCW train 1 operable. The licensee determined that the cause of the low flow was an improper setting of the open stops for valve SW36 which is the throttle valve on the service water outlet from CCW heat exchanger 1. Valve SW36 is a 20 inch manual butterfly valve with a Limitorque manual operator. The operator contained mechanical stop limit devices consisting of nuts that ride on a stem. The nuts can be adjusted to provide both open and close stops. The position of the open stop was determined during required periodic flow balance testing that adjusted the service water system such that adequate cooling water flow was delivered to supplied components. The last flow balancing of the service water train 1 was in April 2006 during the units last refueling outage. The opening lock nut was positioned to set the required valve opening to approximately 40 to 45 percent open. Investigation into the August 2007 low flow condition identified that Valve SW36 was found to have an open limit setting less than that determined necessary by the previous flow balancing. The open limit should have been set to allow the valve to be opened an additional three turns; approximately 50 turns are required to move the valve from full close to full open. With the valve limit stop adjusted and valve SW36 opened the additional three turns, flow testing on September 4, 2007, demonstrated expected flows. 12 Enclosure Component cooling water heat exchanger 1 was declared operable on September 15, 2007. The licensees investigation determined that degraded actuator stop nuts for valve SW36 had been replaced in August 2006, after the flow balancing in April 2006. Licensee work orders used to perform work on the valve indicated that the replaced stop nuts were adjusted to positions consistent with those established in the April 2006 flow testing. Post maintenance testing to verify that the stop nuts were properly set was not conducted after the stop nuts had been replaced. The licensee concluded that the stop nuts had most likely been improperly set since August 2006. The improper setting of valve SW36 stop nuts would have resulted in less than desired flow through the CCW heat exchanger 1 in the event of accidents, such as a loss of cooling accident, during periods when CCW heat exchanger 1 was aligned for train 1 service. However, the reduced flow would have provided some cooling and the throttling effect of SW36 would have caused increased flow to components cooled by service water that were in service water branch lines parallel to the CCW heat exchanger. Those components include, among other things, safety train 1 containment air coolers. At the conclusion of the inspection period, the licensee had just completed an evaluation of the capability of CCW train 1 to perform its design function with CCW heat exchanger 1 inservice. The inspectors will review that evaluation during the next inspection period. Therefore, this issue is considered an unresolved item (URI 05000346/2007004-02) pending completion of inspector review of the past operability evaluation and determination of risk significance |
| Site: | Davis Besse  |
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| Report | IR 05000346/2007004 Section 1R17 |
| Date counted | Sep 30, 2007 (2007Q3) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.17 |
| Inspectors (proximate) | R Smith J Neurauter J Mcghee T Go C Acosta Acevedoj Jacobson J Rutkowskir Jicklingg Wright J Rutkowski M Bielby R Smith J Neurauter T Go K Barclay R Arrighi |
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Finding - Davis Besse - IR 05000346/2007004 | |||||||||||||
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Finding List (Davis Besse) @ 2007Q3
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