05000302/LER-2010-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 10-13-2010 |
|---|---|
| Report date: | 03-14-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| 3022010001R02 - NRC Website | |
pressure of the RCS pressure vessel, RCS piping, valves and fittings is 110 percent of design pressure. Thus a safety limit of 2750 psig has been established for the RCS. Before initial plant operation, the RCS was hydrostatically tested at 3125 psig.
Normal RCS pressure control is by the pressurizer [AB, PZR] steam cushion in conjunction with the pressurizer spray and pressurizer heaters. The RCS is protected from overpressure by the Reactor Protection System [JC] features, such as the RCS high-pressure reactor trip, one Power-Operated Relief Valve (PORV) [AB, PCV], and the two pressurizer code safety valves (PCSVs) [AB, RV]. Because of these other protective features, it is unlikely that the PCSVs will ever lift during operation. RCS pressure setpoints for these features are as follows:
Pressurizer Code Safety Valves 2500 psig Power-Operated Relief Valve 2450 psig Reactor trips on high RCS pressure 2355 psig RCS high pressure alarm 2255 psig Pressurizer Spray Valve opens 2205 psig The PCSVs protect the RCS against overpressurization during transients and accidents which involve a mismatch between the primary plant heat source and the secondary plant heat sink.
Effluent from the PORV and PCSVs discharges to the Reactor Coolant Drain Tank [AB, TK].
Improved Technical Specification (ITS) 3.4.9 requires that both PCSVs be operable with a lift setting of 2500 psig +1- 2 percent 2450 psig and 5 2550 psig) in Modes 1, 2 and 3. When a PCSV is removed from the pressurizer for testing, it shall be reset to +1- 1 percent of the nominal setpoint.
Crystal River Unit 3 (CR-3) has four Model 31739A PCSVs manufactured by Dresser Industries with two in service during operation. PCSV testing is performed by Wyle Laboratories. During plant operation, two of the four valves are installed on the pressurizer as PCSVs (Reactor Coolant Valves (RCV)-8 and RCV-9) and the other two valves are spares. Hence, the individual valves "rotate" through their assignment as PCSVs on a once-per-fuel-cycle basis between tests. Both valves are removed at the end of each operating cycle, sent out for testing, and the two valves which had been tested and stored at the site since the previous cycle are installed on the pressurizer.
EVENT DESCRIPTION
On September 1, 2010, Progress Energy Florida, Inc., (PEF) CR-3 was in NO MODE (core off loaded) at 0 percent RATED THERMAL POWER when Wyle Laboratories provided a Notice of Anomaly for a PCSV (Serial Number BU-03149). This valve had been installed on the pressurizer as RCV-9 during Cycle 16 operation and was sent to Wyle Laboratories during the � specifications surveillance tests should be assumed to occur at the time of the test unless there is firm evidence, based on a review of relevant information (e.g., the equipment history and the cause of the failure) to indicate that the discrepancy occurred earlier." Relevant information at this time did not support a reportable condition.
On October 5, 2010, CR-3 was in NO MODE (core off loaded) at 0 percent RATED THERMAL POWER when Wyle Laboratories provided a Notice of Anomaly for a second PCSV (Serial Number BL-08899). This valve had been installed on the pressurizer as RCV-8 during Cycle 16 operation and was sent to Wyle Laboratories during R16. The highest lift pressure recorded (2552 psig) was 2.08 percent above the ITS setpoint and 0.08 percent higher than the ITS maximum allowed "as-found" lift pressure. This condition was documented in the CR-3 Corrective Action Program as NCR 426852 on October 13, 2010.
The above condition is considered to be reportable based on the further guidance of NUREG- 1022, Section 3.2.2, Example 3, "However, the existence of similar discrepancies in multiple valves is an indication that the discrepancies may well have arisen over a period of time and the failure mode should be evaluated to make this determination. If so, the condition existed during plant operation and the event is reportable under 10 CFR 50.73(a)(2)(i)(B).
Valve Serial Number Set Pressure Acceptable Range As-Found Result %Set Pressure RCV-9 BU-03149 2500 psig 2450 - 2550 2633 + 5.32 RCV-8 BL-08899 2500 psig 2450 - 2550 2552 + 2.08 ITS 3.4.9 states that the two PCSVs shall be OPERABLE in MODES 1, 2 and 3. With one PCSV inoperable, restore the valve to an OPERABLE status within 15 minutes or be 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 be in MODE 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. With two PCSVs inoperable, be 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 be in MODE 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Since CR-3 was in NO MODE when the PCSVs as-found lift setpoints were identified as being outside of the maximum allowable tolerance range, ITS 3.4.9 Required Actions A.1, B.1 and B.2, were not applicable.
Both PCSVs being inoperable during plant operation is a condition prohibited by the CR-3 ITS.
This condition is reportable under 10CFR50.73(a)(2)(i)(B).
CAUSE
A conclusive "root" or "common" technical cause could not be identified following the evaluation by CR-3 and review of the PCSVs (BU-03149 and BL-08899) refurbishment and calibration reports. A "selected" cause (a causal factor that most likely describes the root cause of the event) was therefore identified.
0 testing has not met expectations due to failure to provide a proper relief valve specification to the vendor, including a detailed testing procedure, repair plan and acceptance criteria.
Currently, the specification consists of Progress Energy acceptance criteria for the relief valve that are followed by the vendor. The vendor uses their testing procedure and repair plan to achieve the acceptance criteria of the Progress Energy specification. Progress Energy has not provided sufficient guidance in the current mini-specification to ensure critical aspects of testing are specified.
A contributing factor is the current ITS 3.4.9 requirement that states that PCSVs removed from the pressurizer for testing shall be reset to +/- 1 percent of the nominal setpoint. Long-term storage conditions after rebuild and certification testing prior to installation creates the potential for setpoint drift. Additionally, the internal moving parts of the valve are not lubricated from the process fluid due to the lack of actuation during the operating cycle, causing the parts to adhere to each other. These factors result in a greater potential for initial as-found test failures to be high over the maximum setpoint pressure with the present as-left pressure acceptance criteria of +/- 1 percent of the nominal setpoint.
SAFETY CONSEQUENCES
The design pressure for the RCS is 2500 psig. Enhanced Design Basis Document Tab 6/1, "Reactor Coolant System," states the total PCSV capacity to be such that RCS pressure will not exceed 110 percent of system design pressure (2750 psig) to protect the RCS from exceeding the American Society of Mechanical Engineer (ASME) code safety limit. The set pressure of the PCSVs is +/- 2 percent (a 2450 psig and 5 2550 psig) of the lift setpoint (2500 psig) with a design capacity for each valve of 317,973 pounds mass per hour.
AREVA NP Inc. Technical Data Record 12-9154488-000, "CR-3 Pressurizer Code Safety Valve Analysis for Licensee Event Report," was approved on February 24, 2011. The safety analyses contained in the CR-3 Final Safety Analysis Report (FSAR), Chapter 14, were reviewed to determine which analyses were potentially affected by the high as-found PCSV setpoints.
Three accidents were identified during this review. A thermal-hydraulic analysis of these accidents was performed with the RELAP5/MOD2-B&W computer program.
The Startup Accident is the limiting event for RCS overpressure. The limiting case was rerun with the as-found PCSV setpoints. The resulting RCS pressure was 2719.9 psia (2705.2 psig).
This is less than the acceptance criteria of 2750 psig.
The Loss of Feedwater Accident challenges the RCS overpressure criteria. The limiting case was rerun with the as-found PCSV setpoints. The resulting peak RCS pressure was 2752.1 psia (2737.4 psig). This is less than the acceptance criteria of 2750 psig.
The Main Feedwater Line Break Accident challenges the RCS overpressure criteria. The limiting case was rerun with the as-found PCSV setpoints. The resulting peak RCS pressure was 2731.3 psia (2716.6 psig). This is less than the acceptance criteria of 1.25 percent of 2500 psig (3125 psig) for a limiting fault and is less than the more restrictive acceptance criteria in the CR-3 FSAR of 2750 psig.
Functional Failure as defined in Nuclear Energy Institute (NEI) 99-02, "Regulatory Assessment Performance Indicator Guideline.
A probabilistic safety assessment evaluation was performed for the identified condition. With either PCSV failing to open, the change in Core Damage Frequency (CDF) was less than 1e-06 (low safety significance). With both PCSVs failing to open, the change in CDF was approximately 5e-05 (high to moderate safety significance). However, failing both PCSVs is not representative of the identified condition. Using the change in CDF associated with one PCSV failing to open is more accurate, although still a very conservative bounding analysis, since the as-found condition is that the PCSVs opened late instead of failing to open. The overall conclusion is that the identified condition is of low safety significance.
PEF concludes that the inoperable condition of RCV-8 and RCV-9 did not represent a reduction in the public health and safety.
CORRECTIVE ACTIONS
Purchase Order 00494187 has been revised to require the as-left pressure acceptance criteria for valves BU-03149 and BL-08899 to be + 0/- 1 percent of the nominal setpoint.
Progress Energy engineering source surveillance has been completed for re-testing valves BU 03149 and BL-08899 to verify the as-left pressure acceptance criteria of + 0/- 1 percent of the nominal setpoint.
Additional corrective actions developed as part of the root cause evaluation that are being tracked in the CR-3 Corrective Action Program under NCR 426852 include, but are not limited to:
Replace the currently installed PCSVs with recently refurbished valves BU-03149 and BL 08899 that have an as-left pressure acceptance criteria of + 0/- 1 percent of the nominal setpoint. This will occur prior to entering MODE 3 from the current extended refueling outage.
Revise Catalog IDs 66081638 (valves BU-03149 and BL-08900) and 66081640 (valves BU-03148 and BL-08899) to include the revised as-left pressure acceptance criteria, and other administrative repair/test detail to serve as an interim process until an Engineering Change (EC) is issued.
Obtain the services of Dresser Industries to create a test procedure for steam testing the PCSVs to meet Progress Energy standards.
Issue a PCSV specification under the EC process to include specific repair requirements, surveillance requirements, valve settings, documentation requirements and the test procedure obtained from Dresser Industries.
� NRC FORM 366A (10-2010) PRINTED ON RECYCLED PAPER