05000318/LER-2013-002

LER-2013-002, Pressurizer Safety Valve Setpoint High Due to Insufficient Margin

Calvert Cliffs Nuclear Power Plant, Unit 2
Event date:	03-12-2013
Report date:	05-02-2013
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3182013002R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS

Unit 2 was in Mode 6, Refueling, on March 12, 2013.

B. EVENT

On March 12, 2013, during scheduled testing at the offsite testing facility, the as-found lift setting for pressurizer safety valve (PSV) Serial Number BN04375 was measured at a higher lift value than the Technical Specification allowable value. The valve had been installed in Unit 2 at the 2RV200 location (Unit 2 PSV) and was removed during the 2013 Unit 2 refueling outage for scheduled testing and maintenance. The valve was subsequently disassembled and inspected by the vendor and system manager. The valve was refurbished, reassembled, and as-left testing was performed on the valve with no issues noted. The apparent cause of BN04375 lifting high is insufficient margin to address time-related drift.

This event is applicable to Calvert Cliffs Nuclear Power Plant Unit 2 only.

TO THE EVENT

Unit 2 PSV BN04375 was determined to be inoperable while it had been installed in the plant.

That inoperable condition is the basis for this report. The extent of condition review determined that the condition applied to BN04375 (2RV200) only.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

December 2010 As-left testing performed on BN04375. The as-left setting was 2520 psia.

March 2011 BN04375 installed during the 2011 Unit 2 refueling outage.

March 12, 2013 BN04375 as-found lift tested at offsite vendor facility. As-found lift setting measured higher than Technical Specification allowable value.

March 2013 BN04375 disassembled, inspected, and refurbished at offsite vendor facility.

As-left testing was performed with no issues noted.

April 2013 The apparent cause of BN04375 lifting high was determined to be insufficient margin to address time-related drift.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED

No other systems or secondary functions were affected.

Operator action was not required for the subject valve, as the valve was removed from the unit when the condition was identified.

H. SAFETY SYSTEM RESPONSES

There were no demands for safety system actuations during this event. The condition was discovered after the component was removed from the system.

II. CAUSE OF EVENT:

The apparent cause of BN04375 lifting high was insufficient margin to address time-related drift.

There were no deficiencies or mechanical binding identified during refurbishment of BN04375 which would indicate that the valve was assembled incorrectly or was degraded.

The pre-installation as-left testing was performed in December 2010 and the as-left pressure value of the PSV was within the range identified in Procurement Engineering Specification PES-5103 revision 27, "Repair/Overhaul for 2 1/2" Dresser Pressurizer Safety Valve." However, the time-related drift experienced by BN04375 exceeded the allowed as-found pressure range when tested in March, 2013.

III. ANALYSIS OF THE EVENT:

Each Unit at Calvert Cliffs Nuclear Power Plant has two PSVs (1/2RV200 and 1/2RV201) designed to limit Reactor Coolant System (RCS) pressure to a maximum of 110 percent of design pressure (2500 psia). The Technical Specification defined setpoints for these valves are as follows:

As-Found As-Left Valve Lift Setting (psia) Lift Setting (psia) 1/2RV200 4= 2475 and 1/2RV201 4= 2514 and The Technical Specification Bases state that the as-found setpoints are the limits for operability, i.e., if a valve lifts outside of those setpoints it is inoperable. Calvert Cliffs owns eight PSVs, four sets of two that are rotated between a specific location.

BN04375 was installed at 2RV200 location in March 2011 and removed from the plant in March 2013. The as-found lift setting for BN04375 on March 12, 2013 was 2558 psia. This is higher material condition was identified during refurbishment of BN04375 which would indicate that the valve was assembled incorrectly or was degraded. The valve subsequently passed the as-left testing on March 20, 2013.

With these test results, it is reasonable to conclude that for some period of time while BN04375 was installed in the plant, the lift setting was not within the Technical Specification Surveillance Requirement defined setpoint limit. With one PSV inoperable, the Technical Specification Limiting Condition for Operation (LCO) 3.4.10.A required action is to restore the valve to operable status within a 15 minute completion time. If this required action cannot be met, Technical Specification LCO 3.4.10.B requires the plant to be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to reduce all RCS cold leg temperatures to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The subject condition may have existed longer than the Technical Specification completion times for the associated required actions. The failure to meet the requirements of Technical Specification LCO 3.4.10 also would have required entry into Technical Specification LCO 3.0.3. Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B).

There were no actual nuclear safety consequences incurred from this event. Two PSVs (2RV200 and 2RV201) are located on the Unit 2 pressurizer to provide overpressure protection of the RCS. Only one of the PSVs was affected by the subject condition. BN04375 should have been considered inoperable for some period of time while installed during the applicable modes. While installed (2011-2013), BN04375 was susceptible to lifting later than assumed in the safety analyses. Realizing that the valve could have lifted late if challenged, a probabilistic risk assessment analysis was performed. The risk assessment determined that the estimated increase in core damage frequency and the estimated increase in large early release frequency are negligible for the subject condition.

This event has no impact on the NRC Reactor Oversight Process Performance Indicators.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL

STATUS:

1. BN04375 internal components were inspected and refurbished.

2. As-left testing of the refurbished valve was performed.

B. PREVIOUS LERs ON SIMILAR EVENTS

A review of Calvert Cliffs' events over the past several years was performed. A previous LER documented a similar event that occurred on Unit 2 in 2011 and was reported in lift outside of specifications. The affected valve was refurbished and retested. A root cause investigation was conducted and the site is in the process of completing the corrective action identified to revise Technical Specification 3.4.10 to increase PSV as-found setpoint tolerance.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT

REFERRED TO IN THIS LER:

IEEE 803 IEEE 805 Component EMS Function System ID Pressurizer Safety Valves RV AB Pressurizer PZR AB

D. SPECIAL COMMENTS

None