ML20059C405
| ML20059C405 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/25/1993 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20059C403 | List: |
| References | |
| NUDOCS 9311010145 | |
| Download: ML20059C405 (5) | |
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! NUCLEAR REGULATORY COMMISSION g ..... ,/ WASHINGTON. D.C. 20555 0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED 10 THE INSERVICE TESTING PROGRAM RELIEF REQUESTS NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NUMBER 50-263 1.0 DNTRODUCTION j The Code of Federal Regulations,10 CFR 50.55a, requires that inservice testing (IST) of certain American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 pumps and valves be performed in accordance with Section XI i of the ASME Boiler and Pressure Vessel Code and applicable addenda, except l where relief has been requested and granted or proposed alternatives have been authorized by the Commission pursuant to 10 CFR 50.55a(a)(3)(i), (a)(3)(ii),
or (f)(6)(i). In order to obtain authorization or relief, the licensee must demonstrate that: (1) conformance is impractical for its facility; (2) the proposed alternative provides an acceptable level of quality and safety, or (3) compliance would result in a hardship or unusual difficulty without a compensa.ing increase in the level of quality and safety. Section 50.55a (f)(4)(iv) provides that inservice tests of pumps and valves may meet the requirements set forth in subsequent editions and addenda that are incorporated by reference in 10 CFR 50.55a(b), subject to the limitations and modifications listed, and subject to Commission approval. NRC guidance contained in Generic Letter (GL) 89-04, " Guidance on Developing Acceptable Inservice Testing Programs," provided alternatives to the Code requirements determined to be acceptable to the staff and authorized the use of the alternatives in Positions 1, 2, 6, 7, 9, and 10, provided the licensee follow l the guidance delineated in the applicable position. When an alternative is ,
proposed which is in accordance with GL 89-04 guidance and is documented in the IST program, no further evaluation is required; however, implementation of the alternative is subject to NRC inspection.
Section 50.55a authorizes the Commission to grant relief from ASME Code requirements or to approve proposed alternatives upon making the necessary findings. The NRC staff's findings with respect to granting or not granting the relief requested or authorizing the proposed alternative as part of the licensee's IST program are contained in this safety evaluation (SE).
In rulemaking to 10 CFR 50.55a effective September 8, 1992, (see 57 federal Register 34666), the 1989 edition of ASME Section XI was incorporated in 10 CFR 50.55a(b). The 1989 edition provides that the rules for IST of pumps and valves shall meet the requirements set forth in ASME Operations and Maintenance Standards Part 6 (OM-6), " Inservice Testing of Pumps in Light-Water Reactor Power Plants," and Part 10 (OM-10), " Inservice Testing of Valves in Light-Water Reactor Power Plants." Pursuant to 10 CFR 50.55a(f)(4)(iv),
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portions of editions or addenda may be used provided that all related requirements of the respective editions or addenda are met, and subject to Commission approval. Because the alternatives meet later editions of the Code, relief is not required for those inservice tests that are conducted in accordance with OM-6 and OM-10, or portions thereof, provided all related requirements are met. Whether all related requirements are met is subject to NRC inspection. ]
Northern States Power Company submitted Relief Requests GR-7 and RCIC-6 to its i Pump and Valve Inservice Testing Program in a letter dated June 30, 1993. An SE of both relief requests is included below. The Monticello IST Program was developed to the 1986 Edition of ASME Section XI, for the third 10-year i interval which began on May 31, 1992. l 1
2.0 RELIEF RE0 VESTS 2.1 RELIEF RE0 VEST GR-7 The licensee has requested relief from the test procedure requirements of ASME Section XI, paragraph IWV-3512, for all relief valves with set point pressures of 70 psi or less. The licensee has proposed to specify the set point pressure tolerance for the applicable relief valves to be 1 2 psi as required for design functioning by the ASME Boiler and Pressure Vessel Code,Section III, paragraphs NB-7525(b), NC-7525.3, and ND-7525.3. i l
2.1.1 Licensee's Basis for Reauestina Relief i The licensee states: ,
i OM-1-1981 requires that if a relief valve exceeds its stamped set pressure by 3% or greater then the valve requires corrective i action. This requirement is unnecessarily restrictive for valves with a set pressure of 70 psi or less as it is smaller than the design and construction tolerances. The ASME Boiler and Pressure ;
Vessel Code,Section III, specifies a tolerance of plus or minus 2 '
psi for the design and operation of overpressure protection safety l valves with a set point of up to 70 psi. Applying a 2 psi tolerance for periodic testing of relief valves with a set point up to and including 70 psi is within the requirements of Section ,
III of the Code and is of no threat to the pressure boundary of !
power piping designed to nuclear quality standards. '
2.1.2 Alternate Testina l
The licensee proposes:
For relief valves with a set point less than or equal to 70 psi, I the set point acceptance criteria will be i 2 psi. For relief ;
valves with set points greater than 70 psi, the set point l acceptance criteria will not exceed 3% of the stamped set pressure. If a more restrictive acceptance band is required by l the system design or license basis, then that criteria shall j govern. l l
e 2.1.3 Lyaluation The licensee's IST program is based on the requirements of the 1986 Edition of the ASME Code,Section XI. Paragraphs IWV-3511, IWV-3512, and IWV-3513 of Section XI reference ANSI /ASME OM-1-1981 (OM-1) for test frequency, test procedure, and corrective action requirements respectively of safety and j relief valves. The licensee has requested relief from the requirements of OH-1 for Class 1, 2, and 3 pressure relief valves not meeting the acceptance criteria listed in paragraphs 1.3.3.1.5(b) and 1.3.4.1.5(b) of that code. The licensee has proposed that Class 1, 2, and 3 pressure relief valves with set point pressures of 70 psi or less have an acceptance criteria of i 2 psi.
Commercial operation of Monticello started on June 30, 1971. The 1971 Edition of ASME Section III established rules for construction of nuclear power plant components during the construction phase of Monticello. Sections NB-7614.1 and NC-7614.1 state that the acceptable tolerance for Class 1 and 2 pressure relief valves respectively was 3% above set pressure. This is consistent with the requirements of OM-1, Sections 1.3.3.1.5(b) and 1.3.4.1.5(b). However, the 1989 Edition of ASME Section III, paragraphs NB-7525(b), NC-7525.3, and ND-7525.3, specify a tolerance of i 2 psi for Class 1, 2, and 3 pressure relief valves with set pressures of 70 psi or less.
OM-1 would require corrective action for a pressure relief valve set at 70 psi if the valve lifted at 72.1 psi or higher. The differences in pressure set )
point tolerances between the licensee's proposal and the OM-1 requirement of 2 3% would be less than 2 psi in all cases. In addition, the licensee stated that if a more restrictive set point tolerance is required by system design or i license basis for pressure relief valves with pressure set points at or below I 70 psi, then that criteria shall govern. These criteria would ensure that a system with a ht,Ser pressure relief valve set point tolerance than specified by OM-1 would not result in the occurrence of an unanalyzed design basis l event. Therefore, the proposed alternative testing provides an acceptable l level of safety. '
The licensee did not provide a list of safety and relief valves which are applicable to this relief request. Although it is a general relief request, ,
the licensee should include a list of the applicable safety and relief valves !
in the IST program document.
2.1.4 Conclusion The proposed alternative to the 0M-1 safety and relief valve requirements is authorized pursuant to 10 CFR 50.55a(a)(3)(i) based on the alternative providing an acceptable level of quality and safety.
2.2 RELIEF RE0 VEST RCIC-5 The licensee is requesting relief from the power-operated valve stroke time test and corrective action requirements of ASME Section XI, paragraphs IWV-3413 and IWV-3417(a), for the reactor core isolation cooling (RCIC) turbine exhaust line pressure boundary valve SV-4283. The licensee proposes to verify the valve is closed quarterly by observing that there is no excessive steam i leakage past the valve seat during RCIC turbine operation.
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2.2.1 Licensee's Basis for Reouestino Relief The licensee states: I SV-4283 is a normally closed 1 inch solenoid valve. It has a closed safety position to maintain the system pressure boundary.
The open position is to mitigate the possibility of a vacuum in ,
the exhaust line and is not considered a safety position. The- 1 only control logic is an interlock to open SV-4283 for 180 seconds after the turbine steam admission valve closes. The valve does not have manual control capability or position indication.
Therefore, stroke timing methods are not feasible.
i 2.2.2 Alternate Testino !
l The licensee proposes:
Verify the closed position of the valve quarterly by visually )
determining that there is no significant steam leak past the valve '
seat while the RCIC turbine is operating.
2.2.3 Evaluation The RCIC system is used to maintain sufficient reactor coolant inventory in the event that the reactor vessel is isolated from the main condenser following a reactor scram without the condensate and feedwater system operating. The RCIC turbine is driven by steam produced from decay heat which ,
is extracted from the main steam line upstream of the main steam isolation l valves. Steam is directed through the single stage turbine and exhausted into -I the suppression pool. There are two separate vacuum relief systems installed !
on the RCIC turbine exhaust line at Monticello in order to prevent damage to '
the exhaust line check valves and improve the operation of the RCIC turbine at reduced loads.
UFSAR Figure 10.2-7b shows that valve SV-4283 is a 1-inch solenoid operated' valve located on a tap off the exhaust line upstream of check valve RCIC-9.
The licensee stated in the relief request that this valve has no function during RCIC turbine operation except to remain closed to preserve the pressure boundary. The valve control logic opens the valve for 180 seconds after the steam admission valve on the RCIC steam inlet line closes. Valve position cannot be determined because the solenoid valve is enclosed with no external position indication.
In a phone conversation on September 16, 1993, the licensee stated that this valve opens a line which exhausts into the RCIC pump room. During the quarterly RCIC pump test, the valve is known to be closed because no steam is observed exiting the vacuum line. When SV-4283 opens, a " puff" of steam can sometimes be seen coming from the vacuum line. The licensee also stated that this valve is energized to open and they had not experienced a failure during the life of the plant.
The safety function of solenoid valve SV-4283 is to prevent the discharge of ,
steam from the RCIC exhaust line into the RCIC pump room. Such an event could l cause contamination of the RCIC pump room following a design-basis accident. l l
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4 Because this valve is normally closed and is not required to mov to fulfill its safety function, it would ordinarily be categorized as a Category "B" passive valve. As a Category B passive valve, the Code requirements for stroke-time testing would not apply. However, the licensee has no practical method of verifying closure following the opening of 180 seconds after the RCIC steam admission valve closes when pump testing is completed. This precludes categorizing the valve as " passive."
The licensee's method to determine valve closure of valve SV-4283 consists of conducting the RCIC pump test and observing whether any steam flows from the vacuum line into the RCIC pump room. This method of verification does not ensure the valve is closed following the RCIC pump test. If steam is observed coming from the vacuum line during RCIC pump testing, the valve failure most likely occurred during the previous RCIC system operation. The licensee should develop a method to verify closure of SV-4283 after completion of the quarterly RCIC pump test and recategorize the valve as Category B passive. If no practical method can be established to accomplish the verification, the licensee should determine the consequences if the valve fails to close and prevent contamination of the RCIC pump room. If the release into .he room from this line could be released outside, the impact on the 10 CFR Part 100 limits should be discussed. If the licensee determines that there are no consequences, reassessment of including this valve in the IST program should be considered.
Because both verification of closure and stroke timing are impractical, an interim period of relief for further evaluation is necessary. To immediately meet the Code requirements, design modifications or new testing techniques would be required, resulting in a burden to the licensee. The proposed method of verifying the capability of the valve to close, though not following the pump test, provides adequate assurance of operational readiness for the interim period, considering the impracticalities of design and the burden of immediate imposition of the Code requirements.
2.2.4 Conclusion Relief for a period of 1 year or until the next refueling outage, whichever is later, is granted pursuant to 10 CFR 50.55a(f)(6)(i) based on the impracticality of meeting the ASME Code requirements immediately, the burden if the requirements were imposed without a period for further evaluation, and in consideration of the assurance of operational readiness afforded by the proposed testing during the interim period.
3.0 CONCLUSION
The staff has determined that the proposed alternative to the ASME Code requirements in Relief Request GR-7 provides an acceptable level of quality and safety and therefore authorizes its use pursuant to 10 CFR 50.55a(a)(3)(i). In addition, the staff has also determined that the granting of Relief Request RCIC-6 is authorized pursuant to 10 CFR 50.55a(f)(6)(i) and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the Code requirements were immediately imposed on the facility.
Trincip l Contributor: Joseph Colaccino Date: (htober 25,1993