05000272/LER-2015-006
| Salem Generating Station - Unit 1 | |
| Event date: | 08-26-2015 |
|---|---|
| Report date: | 10-23-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| Initial Reporting | |
| ENS 51349 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition |
| 2722015006R00 - NRC Website | |
0001, or by Internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Salem Generating Station — Unit 1 05000272
PLANT AND SYSTEM IDENTIFICATION
Westinghouse - Pressurized Water Reactor {PWR/4} Pressurizer Power Operated Relief Valves (PORVs) {AB/PCV} Energy Industry Identification System (El IS) codes and component function identifier codes appear as {SS/CCC}.
IDENTIFICATION OF OCCURRENCE
Event Date: August 26, 2015 Discovery Date: August 26, 2015
CONDITIONS PRIOR TO OCCURRENCE
Salem Units 1 and 2 were in Operational Mode 1, operating at approximately 100 percent power at the time this issue was identified. Since this was an analytical issue, the current status of structures, systems, and components did not impact the evaluation of the issue.
DESCRIPTION OF OCCURRENCE
On August 26, 2015, a fire scenario was identified that could cause spurious operation of the Pressurizer Power Operated Relief Valves (PORVs) coincident with loss of power assumptions for Appendix R scenarios, thus preventing the ability to manually close the associated PORV Block Valves. This fire scenario would invalidate the assumptions in the Safe Shutdown Analysis with respect to Reactor Coolant System (RCS) inventory and pressure control.
As documented in the Salem Fire Protection Safe Shutdown Analysis, the current Appendix R strategy for isolation of the High/Low Pressure Interface for a postulated fire in the Control/Relay Rooms is to close the Pressurizer PORVs (PR1/PR2) and Pressurizer PORV Block Valves (PR6/PR7) from the control room prior to evacuation. However, the current Safe Shutdown Analysis does not include the required evaluations to credit these actions.
Following evacuation of the Control Room, plant procedures provide steps to de-energize the DC distribution cabinets, and local closure of the PORV Block Valves by manual operation of the bypass switches located at the associated Motor Control Center (MCC). Since offsite power is assumed to be unavailable and the Emergency Diesel Generators (EDGs) are not available at the beginning of this scenario due to fire induced failures, manual closure of the block valves from the local MCCs will be delayed until the EDGs are restored.
This strategy was implemented to resolve spurious operation of the PORVs concurrent with failure of the PORV Block Valves for a fire in the control room and relay rooms that was identified in control was not accounted for during the delay to close the PORV block valves.
An eight-hour NRC Event Notification (EN) was required by 10 CFR 50.72(b)(3)(ii)(B), "Any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant Safety." EN 51349 was completed on August 26, 2015, at 1630. This LER is being submitted pursuant to the requirements of 10 CFR 50.73 (a)(2)(ii)(B).
CAUSE OF EVENT
The cause of this issue was a failure to validate that actions taken in 1999 to correct the issue ensured compliance with Appendix R. A review of the procedure changes did not take into account the regulatory requirements and assumptions of Appendix R, including timelines to implement the procedure actions.
SAFETY CONSEQUENCES AND IMPLICATIONS
As a nuclear power plant in operation prior to January 1, 1979, Salem Unit 1 is committed to the Fire Protection Program as described in 10 CFR 50, Appendix R. Even though Salem Unit 2 was licensed after January 1, 1979, it also follows Appendix R through a license condition which endorses the approved fire protection program.
When considering the effects of fire, those systems associated with achieving and maintaining safe shutdown conditions assume major importance to safety because damage to them can lead to core damage resulting from loss of coolant through boil-off. Because fire may affect safe shutdown systems and because the loss of function of systems used to mitigate the consequences of design basis accidents under post-fire conditions does not per se impact public safety, the need to limit fire damage to systems required to achieve and maintain safe shutdown conditions is greater than the need to limit fire damage to those systems required to mitigate the consequences of design basis accidents.
Although this issue was identified as a non-conformance with Appendix R, the likelihood of a fire scenario that could cause spurious operation of the PORVs that results in loss of inventory and pressure control is low due to the following:
- After completion of the current procedure steps for initial fire response, multiple circuit failures would be required for fire induced spurious operation of the PORVs.
- Control cables at Salem are equipped with metal shields which would eliminate the potential circuit failure when cables are located in cable trays. The circuit failure type is still credible inside the control cabinets where the metal shielding is removed.
- In accordance with IEEE Standard 384, the Relay Room is considered a Limited Hazard Area.
The standard defines a Limited Hazard Area as a plant area "from which potential hazards such as missiles, non-electrically induced fires, and pipe failure are excluded." It also states, that in a Limited Hazard Area, the only energy available to damage electrical circuits is that energy associated with failure or faults internal to electrical equipment or cables within the area. Transient combustible loading is strictly controlled in the relay rooms. In addition, the Relay Rooms are inspected by plant operators and fire protection personnel.
- In the 100 foot elevation Relay Room, smoke and thermal detectors are provided. Smoke detectors are provided in the exhaust ventilation duct. Detector alarms are annunciated in the Control Room. Fire suppression is provided by an automatic, total flooding Halon-1301 system automatically actuated by cross-zoned smoke detection. Actuation of the Halon-1301 system is indicated on the fire protection panel in the Control Room.
Even though the consequences of loss of reactor coolant inventory and pressure control are serious, the fire induced spurious operation of the PORVs is a very low probability event. Therefore, this issue has minimal safety significance.
SAFETY SYSTEM FUNCTIONAL FAILURE
A review of this event determined that this event was not a Safety System Functional Failure (SSFF) as defined in Nuclear Energy Institute (NEI) 99-02, Regulatory Assessment Performance Indicator Guideline.
PREVIOUS OCCURRENCES
A review of Salem Unit 1 and 2 Licensee Event Reports for the previous three years identified one similar occurrence. LER 272/2013-004000 reported in January 2014, identified the existence of unfused ammeter circuits which also resulted in an unanalyzed condition due to not fully meeting the requirements of 10 CFR 50, Appendix R, Section III.G.
Additionally, this issue was previously identified and reported in October 1999, in LER 272/99-009-000, when a review of the Salem Post-fire Safe Shutdown analysis identified a similar concern with the PORV and associated block valves.
CORRECTIVE ACTIONS
- Compensatory actions have been implemented in the affected areas of the plants.
- Develop and install plant modifications to restore compliance with 10 CFR Appendix R.
COMMITMENTS
This LER contains no regulatory commitments.