05000318/LER-2017-001
| Calvert Cliffs Nuclear Power Plant, Unit 2 | |
| Event date: | 02-20-2017 |
|---|---|
| Report date: | 04-19-2017 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3182017001R00 - NRC Website | |
| ML17111A972 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 04/19/2017 |
| From: | Tierney T A Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 17-001-00 | |
| Download: ML17111A972 (7) | |
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
I. DESCRIPTION OF EVENT:
A. PRE-EVENT PLANT CONDITIONS:
Unit 2 was in Mode 6 (Refueling) when the condition was discovered. The valve was not installed in the system when the condition was discovered.
B. EVENT:
In February 2017 during scheduled testing at the offsite testing facility, Calvert Cliffs discovered that the as-found lift setting for the pressurizer [PZR] safety valve (PSV) [RV] previously installed in Unit 2 measured outside the limits specified in Technical Specification Surveillance Requirement (SR) 3.4.10.1. The valve had been installed at the 2RV200 location and was removed during the 2017 Unit 2 refueling outage for scheduled testing and maintenance. On February 20, 2017, during as-found testing for PSV Serial Number BN04375 (previously installed at 2RV200 location) the valve opened at 2427 psia. The low end Technical Specification SR limit is 2475 psia.
C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED
TO THE EVENT:
Unit 2 PSV 2RV200 (BN04375) was determined to be inoperable. The inoperable condition for the valve provides the bases for this report.
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:
March 2015 BN04375 (2RV200) installed during the 2015 Unit 2 refueling outage.
February 2017 BN04375 (2RV200) removed during the 2017 Unit 2 refueling outage.
February 2017 BN04375 (2RV200) as-found lift tested at offsite vendor facility.. As-found lift setting measured lower than Technical Specification allowable value. The valve was disassembled, inspected, and setpoint drift was determined to be the cause of the as-found lift setting. Valve assembly and necessary adjustments were made. The valve was as-left certified. The post-test leak check was performed satisfactorily on the valve.
LICENSEE EVENT REPORT (LER) Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- CONTINUATION SHEET 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 (See NUREG-1022, R.3 for instruction and guidance for completing this form impose an information collection does not display a currently valid OMB http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Calvert Cliffs Nuclear Power Plant, Unit 2 05000-318 2017 -- 001 -- 00
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:
There were no other systems or secondary functions affected. This event is applicable to Calvert Cliffs, Unit 2 only.
F. METHOD OF DISCOVERY:
The condition was self-identified during scheduled testing at the offsite testing facility.
G. MAJOR OPERATOR ACTION:
No operator action was required for the subject valve. The valve was not installed in the plant when the condition was identified.
H. SAFETY SYSTEM RESPONSES:
No safety system responses were expected. None occurred.
II. CAUSE OF EVENT:
The event is documented in station condition report number IR 03976328.
The apparent cause of the PSV failure is due to setpoint drift. After a detailed inspection, the valve was assembled and had any needed adjustments made. The valve was as-left certified at its setpoint. The post-test leak check was performed satisfactorily for the valve.
Based on previous operating experience with these valves, the valve was set in the lower range of the as-left criteria to account for positive setpoint drift in 2015. The valve setpoint drifted low instead of the previously trended high setpoint drift. Since it was initially set at the low end of the as-left range, setpoint drift in the low direction caused it to drift beyond the Technical Specification SR as-found limits. It was determined from more recent operating experience that these style valves were not consistently drifting high any longer. Therefore, the vendor test procedure was modified to address the more recent operating experience (drifting low) and the valve is set in a higher portion of the Technical Specification as-left range than previous practice. In addition, a checklist is created for engineer review prior to setpoint testing and setting to ensure that the latest operating experience is considered during valve as-left setting.
The extent of condition review noted that there are three other locations where a similar style valve is used. Those valves currently installed, or which are certified for installation, were reviewed for setpoint drift issues and post-test seat leakage. None were identified.
LICENSEE EVENT REPORT (LER) Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- CONTINUATION SHEET 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 (See NUREG-1022, R.3 for instruction and guidance for completing this form impose an information collection does not display a currently valid OMB http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Calvert Cliffs Nuclear Power Plant, Unit 2 05000-318 2017 -- 001 -- 00
III. ANALYSIS OF EVENT:
Each unit at Calvert Cliffs has two PSVs (1/2RV200 and 1/2RV201) designed to limit Reactor Coolant System (RCS) [AB] pressure to a maximum of 110 percent of design pressure (design pressure = 2500 psia). The Unit 2 Technical Specification (prior to the refueling outage) defined setpoints for these valves are as follows:
As-Found As-Left Valve Lift Setting (psia) Lift Setting (psia) 1/2RV200 >1= 2475 and 1/2RV201 >1= 2514 and 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. The as-found lift setting for 2RV200 (BN04375) measured in March 2017 was 2427 psia, which is lower than the Technical Specification SR allowed value of 2475 psia.
The valve was refurbished at the offsite facility in 2013 and subsequently passed as-left acceptance testing prior to being installed during the 2015 refueling outage. Based on previous operating experience with these valves, the valve was set in the lower range of the as-left criteria to account for positive setpoint drift. While installed in the plant (March 2015-February 2017), there were no setpoint events associated with this valve. The valve was removed from its location for scheduled testing and refurbishment in February 2017 during the Unit 2 refueling outage. Although an exact duration cannot be determined, it is reasonable to conclude that for some period of time while the valve was installed in the plant, most likely its lift setting was not within the Technical Specification SR defined setpoint limit. With one PSV inoperable, the Technical Specification Condition 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, or if two PSVs are inoperable, Technical Specification Condition 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 301 degree F (Unit 2) within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The failure to recognize and meet the requirements of Technical Specification Condition 3.4.10.6 also should have required entry into Technical Specification LCO 3.0.3. We believe that the subject condition (for the PSV) existed longer than the Technical Specification Completion Times for the associated Required Actions. 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. For some time, while installed, 2RV200 was susceptible to an early lift. Realizing that if challenged, the valve could have lifted at a time different than assumed in the applicable safety analyses, the Calvert Cliffs Updated Final Safety Analysis Report (UFSAR) was reviewed and a probabilistic risk assessment analysis was performed.
LICENSEE EVENT REPORT (LER) Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- CONTINUATION SHEET 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 (See NUREG-1022, R.3 for instruction and guidance for completing this form impose an information collection does not display a currently valid OMB http://www.nrc.govireading-rm/doc-collections/nuregs/staff/sr1022/r3/) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Calvert Cliffs Nuclear Power Plant, Unit 2 05000-318 2017 -- 001 -- 00 The probabilistic risk assessment analysis determined that the estimated increase in core damage frequency was less than 1E-07 and the estimated increase in large early release frequency was less than 1E-08 per year for the subject condition. The deviations in the relief valve setpoint would have no significant impact as it would still perform the function modeled in the probabilistic risk assessment. This issue would be "GREEN" using the NRC's Significance Determination Process.
The Calvert Cliffs UFSAR was reviewed to evaluate the design basis events impacted by a decreased lift setting for 2RV200. The evaluation determined that the results presented in the UFSAR were bounding for all impacted design basis events. In all cases, overpressure protection of the RCS was maintained. Therefore, the condition of 2RV200 would not have prevented the system from fulfilling its safety function.
This event has no impact on the Nuclear Regulatory Commission Reactor Oversight Process Performance Indicators.
IV. CORRECTIVE ACTIONS:
A. ACTION TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:
The degraded valve has been refurbished and certified for use in the plant. As scheduled, a spare valve was installed during the 2017 Unit 2 refueling outage.
B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:
To account for the limited as-found setpoint range for the PSVs, the vendor test procedure was revised to state the preferred as-left range of the PSVs to be the upper TS range. This provides additional margin to the lower as-found setpoint. An additional checklist is created to address critical parameters to be reviewed prior to vendor testing.
V. ADDITIONAL INFORMATION:
A. FAILED COMPONENTS:
The subject valve is an American Society of Mechanical Engineers Boiler and Pressure Code approved PSV designed to limit RCS pressure to a maximum of 110 percent of design pressure.
The safety valve is a totally enclosed, back pressure compensatory, spring-loaded valve. The valves are manufactured by Dresser Consolidated, Inc. (EPIX Identification number D243). The valve affected by the subject condition is 2RV200 (BN04375).
LICENSEE EVENT REPORT (LER) Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- CONTINUATION SHEET 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 (See NUREG-1022, R.3 for instruction and guidance for completing this form impose an information collection does not display a currently valid OMB http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Calvert Cliffs Nuclear Power Plant, Unit 2 05000-318 2017 -- 001 -- 00
B. PREVIOUS LERS ON SIMILAR EVENTS:
A review of Calvert Cliffs' events over the past several years was performed. The site has had several instances of PSV set point testing (low and high) abnormalities. The following LER's are identified from this review:
degradation of internal components that move when spring is actuated.
variations.
variation, License Amendment Request submitted to expand the allowable set point range.
approval of License Amendment Request.