05000272/LER-2005-004
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | 10-25-2005 |
|---|---|
| Report date: | 12-27-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2722005004R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse - Pressurized Water Reactor Charging/Safety Injection (SI) System {CB} * Residual Heat Removal (RHR) System {BP} * * Energy Industry Identification System (EIIS) codes and component function identifier codes appear in the text as {SS/CCC}.
IDENTIFICATION OF OCCURRENCE
Event Date: October 26, 2005 Discovery Date: October 26, 2005
CONDITIONS PRIOR TO OCCURRENCE
Salem Unit 1 was in its seventeenth refueling outage (1R17). No structures, systems or components were inoperable at the time of the discovery that contributed to the event.
DESCRIPTION OF OCCURRENCE
The design of the containment sump, located on elevation 78' consists of two compartments: the containment sump and the Emergency Core Cooling System (ECCS) sump. The two Residual Heat Removal (RHR) {BP} pumps take suction from the ECCS sump at the 70' elevation. A sump curb, at elevation 78' 9", prevents floor debris a direct access to the sump. A basket type strainer with 0.125 inch mesh size protects the intrusion of debris into the ECCS portion of the sump. A trash rack surrounds the screened basket to prevent large debris.
During the seventeenth Salem Unit 1 refueling outage (1R17), PSEG (licensed and non-licensed personnel) performed an inspection of the Salem Unit 1 containment sump. The inspection revealed gaps of approximately 0.75 inches between the top of the containment sump cage mesh and the removable sump cover, and at the top of the containment sump steal plate where pipes and conduits penetrate into the containment sump. Gaps internal to the sump were also noted in the containment sump upper screen mesh that provides clearance for the vortex plate support rods.
These gaps could allow low density debris and debris that is neutrally buoyant in water to pass through these gaps during the recirculation phase of a Loss of Coolant Accident (LOCA), when sump operation is required. Debris having a density higher than water would sink to the bottom and remain on the bottom.
DESCRIPTION OF OCCURRENCE (cont'd) Although, the configuration and location of the gaps would have made it difficult to transport material through these gaps, about three feet above floor level; it is difficult to definitively establish that downstream throttle valves or line orifices would not have been blocked. Therefore, without a positive determination that components would not have been blocked, this event is being reported per the requirements of 10CFR50.73(a)(2)(v) as a condition that could have prevented the fulfillment of a safety function of structures or system designed to remove heat or mitigate the consequences of an accident.
PREVIOUS OCCURRENCES
A review of reportable events for Salem Generating Station in the last two years did not identify any prior similar occurrences relative to the containment sump.
CAUSE OF OCCURRENCE
The apparent cause for the gaps noted in the sump upper screen mesh that provides clearance for the vortex plate support rods has been attributed to poor implementation and maintenance practice during the installation of vortex breakers within the sump and original sump construction.
There are two significant factors that contributed to the failure to identify this condition earlier. First, the location of the openings was on the top screen below the top solid plate. This space, approximately 1.5 feet between the screen and the floor inside the sump, is a high contamination area and crawling or sliding between the screen and the floor is very difficult due to its physical size, and constitutes a personnel contamination hazard. Poor lighting conditions inside the sump made it difficult to find these openings. Secondly, the sump inspection procedure was too general and did not provide specific inspection guidance or acceptance criteria for all aspects of the containment sump strainer.
Currently, an ongoing containment sump design review per Generic Letter 2004-02 is in progress. The new sump design is expected to be significantly different than the current design. Therefore, the current environmental conditions and inspection procedure deficiencies will be eliminated with the new strainer design. Installation of the strainers is currently scheduled for the next refueling outages for Salem 2 and Salem 1 respectively.
SAFETY CONSEQUENCES AND IMPLICATIONS
There was no actual safety consequences associated with this event.
The safety implications are minimal due to the configuration and location of the openings. The configuration and location of the openings would have made it difficult to transport material through the gaps. Because the gaps were located approximately three feet above floor level, it would not have been possible that heavy metallic objects (e.g., those that might have been dislodged as a result of impingement forces during a LOCA), to have been transported to the sump. Any heavier material would have settled on the containment floor or stopped at lower strainer locations. Material that is neutrally buoyant or less dense than water could have been transported through the gaps. Neutrally buoyant material is generally not considered a threat to the mechanical operability of the pumps, but could potentially present a clogging hazard for downstream orifices, nozzles or valves. However, this neutrally buoyant material is generally light, non-rigid, mostly fibrous material, and would have been more likely to pass through the system due to the differential pressure across the valve, orifice or nozzle. The surface area of the sump screen is large when compared to the surface area of the identified gaps, making it highly probable that any neutrally buoyant material would have been stopped from entering the sump by the screen mesh rather than passing through the gap location.
A review of this event determined that a Safety System Functional Failure (SSFF) as defined in NEI 99 02, Regulatory Assessment Performance Indicator Guidelines, occurred.
CORRECTIVE ACTIONS
1. The deficiencies that could have allowed debris to enter the containment sump were corrected during the seventeenth refueling outage.
2. The Salem Unit 2 sump was examined for similar conditions; the Salem Unit 2 sump does not have a similar condition.
COMMITMENTS
This LER contains no commitments.