05000289/LER-2002-002

LER-2002-002,

Docket Number
Event date:
Report date:
2892002002R00 - NRC Website

III. Background

The Reactor Coolant System (RCS) serves as a barrier to prevent radionuclides in the reactor coolant from reaching the atmosphere. Establishing a system pressure limit helps to assure the integrity of the RCS. The design pressure of the RCS is 2500 psig. The maximum transient pressure of the RCS Pressure Vessel as specified by the American Society of Mechanical Engineers (ASME) Code,Section III, Article 9, Winter, 1968 is 110 percent of design pressure.

The maximum transient pressure of the RCS piping, valves, and fittings as specified by ANSI Section 831.7 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 steam cushion in conjunction with Pressurizer spray, the Pilot-Operated Relief Valve (PORV) and Pressurizer heaters. The RCS is protected from overpressure by the Reactor Protection System features such as the RCS high-pressure reactor trip, one PORV, and the two Pressurizer Code Safety Valves (PCSVs).

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 Pilot Operated Relief Valve lifts Reactor trips on high RCS pressure RCS High pressure alarm Pressurizer Spray valve opens 2500 psig 2450 psig 2355 psig 2255 psig 2205 psig The PCSVs IAB/RV] protect the RCS against over-pressurization 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 (RCDT).

Technical Specification (TS) 3.1.1.3 requires that both PCSVs be operable with a lift setting of 2500 psig plus or minus 1 percent whenever the reactor is critical. When a PCSV is installed on the pressurizer, it must have a lift setting of 2500 psig plus or minus 1 percent (referred to as the "as-left" setpoint). As discussed in the TS Bases, when a PCSV is removed from the pressurizer, it must demonstrate a lift setting of 2500 psig plus or minus 3 percent (referred to as the "as-found" setpoint).

TMI-1 has four Model 31739A PCSVs manufactured by Dresser Industries with two in service during operation. AmerGen uses the services of vendors to perform PCSV testing. Tests are performed at NWS Technologies (NWS) in accordance with AmerGen Specification and NWS procedures. During plant operation two of the four valves are installed on the Pressurizer as PCSVs (tagged RC-RV-1A and RC-RV-1B) 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. Although TMI-1 TS Table 4.1-2 requires that only one of the two installed valves be tested each refueling interval, due to Code requirements and current operating schedules, 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.

IV. � Event Description On May 29, 2002 AmerGen received the test report from NWS with the results of "as found" setpoint testing for PCSV bearing Serial Number (S/N) BR-06613. This valve had been installed on the Pressurizer as RC-RV-1B during Cycle 13 operation from October 18, 1999 through October 10, 2001 and was sent to NWS for testing following the Cycle 14 Refueling (1R14) Outage. The test report shows that the valve was lifted several times before making adjustments. The highest lift pressure recorded (2594 psig) was 3.8 percent above the TS setpoint, (.8 percent higher than the TS allowable "as found" lift pressure).

This PCSV Serial Number (S/N) BR-06613 had previously tested high, outside the 3 percent tolerance in 1993. This is the second occurrence for this particular valve to fail the 'as-found' test. In 1993, the cause was attributed to inadequate procedure based on the use of the "jack and lap" process by the test vendor. The use of this process has been eliminated and all of the PCSVs currently used have not had the "jack and lap" process applied to them since 1993.

Because valve BR-06613 tested greater than 2500 psig plus or minus 3 percent at the completion of Cycle 13 operation, this event is reportable under 50.73.a.2.i.B, as an operation or condition prohibited by the plant's TS.

The cause of valve BR-06613 exceeding its allowable "as found" lift set point is attributed to mechanical setpoint drift. Based on discussion with the valve manufacturer and the testing facility, the most probable root cause was determined to be the lack of contact area between the upper spring washer and spring, which allowed for relative movement from an external force (handling, vibration during operation on the pressurizer, etc.) These conditions provided a means for the setpoint of the valve to shift. (See Figure 1 for representations of these components.) Review of Pressurizer Code Safety Valve history from Cycle 5 operation to the present shows the following, in addition to the above:

• S/N BR-06612 is presently installed for Cycle 14 operation. This valve has never tested outside of the 3 percent as-found tolerance.

• SIN BL-08897 is presently installed for Cycle 14 operation. This valve tested outside of the 3 percent as-found tolerance in 1986. Review of 1986 testing data indicated that the high test lift was due to seat binding. Every "as-found" test since 1986 has been satisfactory (1990, 1993, and 2000.)

• S/N BR-06613 (the subject of this LER) was installed during Cycle 13 operation. This valve has been returned to TMI-1 from NWS, having been inspected and satisfactorily tested and certified.

• S/N BL-08898 was the other valve in operation during Cycle 13. This valve has never tested outside the 3 percent as-found tolerance. This valve has been returned to TMI-1 from NWS, having been inspected and satisfactorily tested and certified.

Therefore, upon review of past test and refurbishment reports, AmerGen concludes that the valves currently installed for Cycle 14 operation (BR-06612 and BL-08897) are fully operable and are in full compliance with Technical Specification requirements.

Component Failure Data:

The component, which failed TS test requirements, was a Model 31739A Code Safety Valve manufactured by Dresser Industries.

VI. Automatic or Manually Initiated Safety System Responses:

No safety system responses occurred or were required to occur.

VII. Assessment of the Safety Consequences and Implications of the Event:

There were no safety consequences associated with a Pressurizer Code Safety Valve Setpoint of 2594 psig. The safety limit of 2750 psig (110 percent of design pressure) represents the maximum transient pressure allowable in the RCS under the ASME Code Section III.

The PCSV would have lifted at 2594 psig. The most limiting overpressure transient analysis predicts that if a PCSV lifted at or below 2625 psig, the resultant RCS peak pressure will not exceed 2750 psig, the safety limit for the TMI-1 RCS.

VIII. Previous Events of a Similar Nature:

This event is the second occurrence of an "as found" test result greater than 3 percent above the 2500 psig setpoint. The previous occurrence was in 1993 and was also valve S/N BR- 06613 (reference TMI-1 LER 93-008-01).

IX. Corrective Actions :

Immediate Corrective Action; 1. � Valve BR06613 was completely disassembled and inspected by NWS Technologies personnel. The mating surfaces of the upper spring washer and spring were lapped to achieve optimum contact. The valve was reassembled and tested satisfactorily on May 31, 2002. The rebuilt valve will be retested after one round trip of normal shipping prior to use. (September 5, 2003) Corrective Action to Prevent Recurrence:

1. � Establish a specification for contact area between the upper spring washer and spring.

The specification will be established prior to the next refueling outage. (September 5, 2003) * Energy Industry Identification System (EIIS), System Identification (SI) and Component Function Identification (CFI) Codes are included in brackets, [SI/CFI] where applicable, as required by 10 CFR 50.73 (b)(2)(ii)(F).

WASHER

Figure 1