05000272/LER-2007-002

LER-2007-002, MManual Reactor Trips Due to Degraded Condenser Heat Removal

Docket Number
Event date:	04-24-2007
Report date:	06-25-2007
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2722007002R00 - NRC Website

PLANT AND SYSTEM IDENTIFICATION

Westinghouse — Pressurized Water Reactor (PWR/4) Reactor Protection System (JC/-) Circulating Water System (KE/ SCN) * Energy Industry Identification System {El IS} codes and component function identifier codes appear as {SS/CCC}

IDENTIFICATION OF OCCURRENCE

Event Date: April 24 and 30, 2007 Discovery Date: April 24 and 30, 2007

CONDITIONS PRIOR TO OCCURRENCE

Salem Unit 1 was in Operational Mode 1 at 40% reactor power prior to the April 24 trip and in Operational Mode 1 at 80% reactor power prior to the April 30 trip.

No structures, systems or components were inoperable at the time of the discovery that contributed to the event.

DESCRIPTION OF OCCURRENCE

On April 24 and 30, 2007, Salem Unit 1 was removed from service due to the loss of Circulating Water Pumps. During both events the Salem Station was experiencing extremely heavy river debris loadings that affected the ability of plant equipment to function. The heavy loadings overwhelmed the Circulating Water Traveling Screens (CWTS) {SCN}, causing high differential levels. Screen differential levels of 10' across the CWTS causes a trip of the Circulating Water Pumps.

On April 24, 2007 at approximately 2248, a manual reactor trip was initiated with reactor power level at approximately 40%. The manual reactor trip was initiated in response to a degraded Circulating Water {KE/}(CW) system and in accordance with operating procedures. At the time of this trip, Abnormal Operating Procedure S1.0P-AB.CW-0001 Circulating Water System Malfunction was in effect because two (2) of the six (6) CW pumps were out of service. One CW pump had been taken out of service to allow plant personnel to clean the associated condenser water box, and another CW pump had tripped due to high differential levels across its associated traveling screen. When the licensed Plant Operator (PO) noted a rapid increase in differential levels on the remaining four CW traveling screens, a manual reactor trip was initiated per procedure.

�NRC FORM 366 (6-2004) PRINTED ON RECYCLED PAPER DESCRIPTION OF OCCURRENCE (Cont'd) Unit 1 was returned to service (synchronized to the grid) on April 26, 2007 at 1236, following the cleaning of water boxes and the lowering of river debris levels.

On April 30, 2007, at approximately 1502, with the unit at approximately 80% power a sudden localized high amount of river water debris affected the CWTS in a very short time resulting in the loss of four (4) CW pumps due to high screen differentials. A manual reactor trip was initiated in accordance with the abnormal operating procedure due to the loss of the CW pumps.

Both reactor trips were uncomplicated; the unit was stabilized in Mode 3 with the reactor at normal operating temperature and pressure with core cooling provided by the Auxiliary Feedwater System.

This report is being made in accordance with 10CFR50.73(a)(2)(iv)(A), "any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B)....

PREVIOUS OCCURRENCES

A review of LERs at Salem Station dating back to 2003 identified one other occasion of a reactor trip due to excessive grassing. LER 311/2003-001 "Manual Reactor Trip Due to Degradation of Condenser Heat Removal, " was initiated March 29, 2003. As part of the corrective actions of this LER, a Circulating Water/Service Water project was established to improve the response and reliability of the CW system. The corrective actions associated with this LER would not have prevented the occurrence of these events. Various upgrades and improvements were made which proved beneficial to the station as demonstrated by successfully operating through the high detritus levels of 2005. The magnitude and severity of the grassing experienced in 2007 were the result of a combination of unusual and severe external environmental conditions.

CAUSE OF OCCURRENCE

The cause of manual reactor trips is attributed to unusual and severe external environmental conditions resulting in record high amounts of river debris loadings. The heavy amount of debris loading caused the high differential levels across the CWTS. A screen differential level of 10' across the CWTS causes a trip of the CW Pumps.

During the period from April 14 through 16, 2007, the Delaware River drainage area received excessive rainfalls. These rainfall amounts led to significantly increased Delaware River flows and several dams on tributaries leading to the Delaware River were required to release significant quantities of water.

Additionally, there were high winds during and after the storm, as well as exceptionally high tides due to lunar influence on a 10-year cycle. All these conditions combined to flush the various marshes, riverbanks, and low-lying areas, producing a record amount of detritus that was sustained over a period of greater than one (1) week. The weekly rolling average of detritus was approximately 30% higher than the previous record high in 2005.

SAFETY CONSEQUENCES AND IMPLICATIONS

There were no actual safety consequences associated with this event. Operators appropriately responded to the degraded CWS (loss of circulating water pumps) and the potential loss of normal heat sink (condenser) by manually tripping the reactor. Plant response to the manual reactor trips was normal. All safety systems operated as required.

A review of this event determined that a Safety System Functional Failure (SSFF) as defined in NEI 99­ 02, Regulatory Assessment Performance Indicator Guidelines, did not occur. There was no condition that alone could have prevented the fulfillment of a safety function of a system needed to remove residual heat.

CORRECTIVE ACTIONS

1. Circulating Water traveling screens and condenser waterboxes were cleaned, inspected and returned to service.

2. A root cause evaluation was initiated to identify causes and initiate corrective actions that can be made to:

a) Improve predictive tools and actions on high river debris conditions, and b) Further improve the availability and reliability of the Circulating Water System.

COMMITMENTS

No commitments are made in this LER.