05000302/LER-2003-002
| Crystal River Unit 3 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) |
| 3022003002R00 - NRC Website | |
At 19:58, on September 29, 2003, Progress Energy Florida, Inc., (PEF) Crystal River Unit 3 (CR-3) was in MODE 1 (POWER OPERATION) at approximately 80 percent RATED THERMAL POWER.
While performing surveillance procedure SP-650, "ASME Code Safety Valves Test," on the 'B' Once Through Steam Generator (OTSG) [SB, SG], the setpoint for main steam safety valve (MSSV) MSV-41 [SB, RV] was found below its required tolerance. The acceptance criteria specified in Improved Technical Specification (ITS) Table 3.7.1-1 is +1- 3 percent of the nominal setpoint.
MSV-41 lifted at -7.19 percent of the nominal setpoint. The MSSV was declared inoperable and actions associated with ITS 3.7.1, Condition A, became applicable.
There are two OTSGs at CR-3. Each OTSG has two main steam lines. Each main steam line has four MSSVs with staggered relief pressures of 1050 pounds per square inch gauge (psig), 1070 psig, 1090 psig and 1100 psig. The MSSVs are required to be tested for relief setpoint accuracy in accordance with the CR-3 Inservice Testing Pump and Valve Program. This program requires that each MSSV be tested once every five years. Six MSSVs were scheduled to be tested prior to the start of Refueling Outage 13 (R13) on October 4, 2003.
Three of the six MSSVs scheduled to be tested were found with setpoints below their required tolerance. Due to an extent of condition concern, the remaining six MSSVs, not planned for refurbishment, were tested. Of the twelve MSSVs tested, six had as-found setpoints below their nominal tolerance.
Tag Main Steam Line Design Pressure As-Found Pressure As-Found % MSV-35 B1 1050 997.5 -5.00 MSV-36 B2 1050 1015 -3.33 MSV-41 82 1070 993.07 -7.19 MSV-44 B1 1090 1055 -3.21 MSV-45 B2 1090 1053 -3.39 MSV-46 A2 1100 1062 -3.45 ITS 3.7.1 states that the MSSVs shall be operable as specified in Table 3.7.1-1 in MODES 1, 2 and 3. With one or more required MSSVs inoperable, THERMAL POWER shall be reduced to less than the reduced power limit of Table 3.7.1-1 within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> (Action A.1) and the nuclear overpower trip setpoint shall be reduced in accordance with Table 3.7.1-1 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> (Action A.2). Once declared inoperable, each MSSV was restored to an operable status within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
The existence of similar discrepancies in multiple relief valves is an indication that the discrepancies may well have developed over a period of time. Therefore, PEF concludes that multiple MSSVs were inoperable during plant operation for a period longer than allowed by ITS and the condition is reportable under 10CFR50.73(a)(2)(i)(B).
6/10, "Main Steam System," states the total MSSV capacity to be such that steam pressure will not exceed 110 percent of system design pressure (1155 psig) for the limiting overpressurization event.
The limiting event that challenges the MSSV capacity is the Turbine Generator trip that occurs at 112 percent rated thermal power. Since none of the tested MSSVs were found with setpoints above their nominal tolerance, the MSSVs were fully capable of providing OTSG overpressure protection.
The primary concern associated with MSSV setpoints being found below their nominal tolerance is the risk of over cooling the Reactor Coolant System (RCS). The SP-650 testing verified that the MSSVs were capable of closing at pressures that would not challenge the plant's ability to maintain acceptable post-accident RCS pressures and temperatures.
Based on the above discussion, REF concludes that the inoperability of MSV-35, MSV-36, MSV-41, MSV-44, MSV-45 and MSV-46 did not represent a reduction in the public health and safety. This event does not meet the definition of a Safety System Functional Failure.
CAUSE
The cause for the tested MSSV as-found setpoints being found below their nominal tolerance is test methodology used prior to R13. There were two deficiencies in test methodology. The first deficiency was use of higher than expected main steam operating pressures (925 psig to 940 psig versus 910 psig) to set the valves. The test gauge (Ashcroft/Dresser Type 1082, 0 to 1500 psig) used to measure main steam line pressure was not temperature compensated. Field measurements of the OTSG Al main steam line vent location measured 400 degrees Fahrenheit at the pipe cap where the gauge was connected. This condition resulted in inaccurate pressure readings. Prior to R13, the decision was made to install the pressure gauges between two Emergency Feedwater Initiation and Control pressure transmitters, where the ambient temperature would not significantly affect the accuracy of the test gauge.
The second deficiency was the practice of not requiring adjustment of the MSSVs if their as-found setpoint was within the +/- 3 percent tolerance (e.g., could be as-left at -2.99 percent), unless the valve was rebuilt.
A contributing factor was an improvement made to the actual test implementation. In previous SP-650 tests, the Dresser Industries 1566 Hydroset test equipment was used to establish MSSV setpoint pressure. An industry review concluded that the Trevitest method by Furmanite was more accurate and repeatable. The Trevitest equipment was used for SP-650 MSSV testing performed prior to the start of R13.
to an operable status within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of identifying the associated setpoints to be outside their required tolerance.
SP-650 was revised prior to R13 MSSV testing to require as-left setpoints for tested MSSVs to be set to within +1- 1 percent of their nominal tolerance. Engineering acceptance should be obtained and documented to leave a MSSV setpoint outside +1- 1 percent of the nominal tolerance, but within +1- 3 percent of the nominal tolerance.
Additional corrective actions are being considered and are being tracked in the CR-3 Corrective Action Program under Nuclear Condition Report 105988.
PREVIOUS SIMILAR EVENTS
No previous occurrences of MSSV setpoints being found below their required tolerance have been reported to the NRC. However, MSSV setpoints being found above their required tolerance were reported in Licensee Event Report 50-302/01-002-00, "Main Steam Safety Valve Setpoints Outside Required Tolerance Longer Than Allowed By Technical Specifications," dated November 19, 2001.
ATTACHMENTS
Attachment 1 - Abbreviations, Definitions, and Acronyms Attachment 2 - List of Commitments NOTES: � Improved Technical Specifications defined terms appear capitalized in LER text {e.g., MODE 1} Defined terms/acronyms/abbreviations appear in parenthesis when first used (e.g., Reactor Building (RB)).
The following table identifies those actions committed to by Progress Energy Florida, Inc., (PEF) in this document_ Any other actions discussed in the submittal represent intended or planned actions by PEF. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the Supervisor, Licensing & Regulatory Programs of any questions regarding this document or any associated regulatory commitments.
RESPONSE
SECTION
COMMITMENT DUE DATE
No regulatory commitments are being made in this submittal.