ML18101B086
| ML18101B086 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 11/06/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18101B085 | List: |
| References | |
| NUDOCS 9511080397 | |
| Download: ML18101B086 (7) | |
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I UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO REQUEST FOR RELIEF FROM STOP VALVE CONTROL AND INTERLOCK REQUIREMENTS OF SECTION III. ARTICLE 9. OF THE 1968 EDITION OF THE ASME BOILER AND PRESSURE VESSEL CODE PUBLIC SERVICE ELECTRIC AND GAS COMPANY SALEM NUCLEAR GENERATING STATION. UNITS I and 2 DOCKET NOS. 50-272 AND 50-311
1.0 INTRODUCTION
In an August 28, 1995, letter, Public Service Electric and Gas Company (the licensee) requested permanent relief from Article 9 of Section III of the 1965 Edition, Winter 1966 Addenda and the 1968 Editfon of the American Society oft Mechanical Engineers Boiler and Pressure Vessel Code (the ASME Code).
The
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relief would allow the licensee to use specific administrative controls on the manual isolation valves in the volume control tank (VCT) and the regenerativ*
heat exchanger {RHE) relief valve discharge lines at Salem Units I and 2.
- specifically, the licensee requested relief for the following chemical and volume control system (CVCS) manual isolation valves:
Unit.I VCT line 11BR151, 12BR151, 13BR151 RHE line ICV272 Descriptions of these valve installations follow.
Volume Control Tank Relief Valve Line Unit 2 21BR151, 22BR151, 23BR151 2CV272 Figure I shows a schematic of the VCT manual isolation valve/relief valve configuration, which is typical for both units. The manual isolation valves are locked open in the relief valve 1CV241 and 2CV241 discharge paths. The relief valves provide overpressure protection for the VCT.
The relief valves discharge t~ one of three available holdup tanks that contain the radioactive gas or liquid released.
(Holdup Tank #12 has been administratively removed from service.
The assoctated manual isolation valve 12BR151 is maintained in the locked closed position at all times.)
The purpose of the manual isolation valve~ is to allow processing of individual holdup tank contents and to allow individual holdup tank testing without incapacitating the entire system or VCT overpressure protection.
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- Regenerative Heat Exchanger Relief Valve Line Figure 2 shows an RHE manual isolation valve/relief valve configuration schematic that is typical for both units. The manual isolation valves are in the inlet path of spring loaded thermal relief check valves 1CV273 and 2CV273.
The relief valves provide overpressure protection for the RHE if the CVCS malfunctions.
Each relief valve discharges to the reactor coolant system (RCS).
The purpose of the manual isolation valves is to facilitate RHE maintenance.
The 1968 Edition of the ASME Code,Section III, Article 9, paragraph N-910.8 specifies in part:
Any stop valve or similar device on the inlet or discharge side of a protective... shall be so constructed, positively controlled and interlocked... under all conditions of operation of the system.
The ASME issued Code Interpretation No. III-l-80-67R in March 1989 to clarify what it meant by controls and interlocks. The interpretation specified that' controls and interlocks were pressure-sensing devices that would activate the stop valve to provide fluid access to the relief valve.
The interpretation also made it clear that administrative control of block valve positions was not acceptable.
The ASME incorporated these provisions into the 1989 Code Edition.
2.0 EVALUATION Pursuant to 10 CFR 50.55a(a)(2), reactor systems and components must meet-the ASME Code requirements specified in 10 CFR 55.55a(b) through (g). Section 10 CFR 50.55a gives the NRC two methods for granting relief from ASME Code requirements.
The NRC may authorize alternatives to the requirements of the Code pursuant to 10 CFR 50.55a(a)(3)(i) or 10 CFR 50.55a(a)(3)(ii). Paragraph 10 CFR 50.55a(a)(3){i) requires the licensee to demonstrate that its proposed Code alternative would provide an acceptable level of quality and safety.
Paragraph 10 CFR 50.55a{a){3)(ii) requires the licensee to demonstrate that complying with Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The licens~e requested relief on the basis that complying with Code requirements would result in hardship or unusual difficulty without a compensating increase in_ the level of quality and safety.
The licensee stated that the mariual isolation valve and relief valve configurations were part of the vendor's original standard design.
The licensee also stated that having to comply with Code requirements would require backfit design modifications to install controls and interlocks for the subject manual isolation valves.
Instead, the licensee proposed maintaining the following manual isolation valve administrative controls:
- (1)
Volume Control Tank Relief Valve Line Manual isolation valves 11BR151 and 13BR151 (Unit 1) and 21BR151, 22BR151 and 23BR151 (Unit 2), respectively are locked open and controlled in accordance with the Tagging Request Inquiry System {TRIS).
(As previously noted, 12BR151 is maintained in the locked closed position because Holdup Tank #12 has been removed from service.)
Administrative controls assure that at least one manual isolation valve will be locked open when the VCT is aligned for service thereby ensuring that the VCT flowpath to the Holdup Tanks is maintained.
(2)
Regenerative Heat Exchanger Relief Valve Line Manual isolation valves 1CV272 and 2CV272 for Units 1 and 2, respectively are locked in the open position, and controlled in accordance *with TRIS when the RHE is in service.
The licensee stated the current configuration provides an acceptable level of quality and safety. It concludes that mispositioning these manual isolation valves, although not desirable, would not impair plant shutdown capability or emergency core cooling system (ECCS) operation.
The licensee addressed the consequences of losing VCT and RHE relief valve line overpressure protection as shown below.
Volume Control Tank Manual Isolation Valve Failure Consequences The VCT provides surge capacity to accommodate programmed pressurizer level changes during the normal charging mode of operation. The VCT functions are not safety related. The manual isolation valves 11BR151, 12BR151 and 13BR151 (Unit. 1) and 21BR151, 22BR151 and 23BR151 (Unit 2), are located in the discharge path of relief.valves 1CV241 and 2CV241 for Units 1 and 2, respectively. These relief valves discharge to three parallel paths to the Holdup Tanks (Two paths for Salem Unit 1). The relief valves are not required to operate during or following a design basis accident to safely shut down the plant.
Due to the administrative controls previously discussed the possibility of concurrent inadvertent closure of the manual isolation valves during power operation is extremely low.
Nonetheless, if all manual isolation valves were postulated to be closed concurrently during operation, the pressure relief function of the relief valves would be def~ated. Without overpressure protection, VCT overpressurization could potentially result in failure and release of RCS liquid and gases to the Auxiliary Building.
- Chapter 15 of the Salem Updated Final Safety Analysis Report {UFSAR) provides an analysis of the consequences of a passive failure of the VCT.
This analysis demonstrates that a complete failure of the VCT due to the inadvertent closure of manual isolation valves is bounded by the VCT rupture analysis contained in UFSAR Chapter 15.
Regenerative Heat Exchanger Manual Isolation Valve Failure Consequences The RHE is designed to recover heat from the CVCS letdown flow by reheating charging flow, which reduces thermal effects on the RCS piping. The letdown stream flows through the shell of the RHE and the charging stream flows through the tubes.
The RHE functions are not safety related.
To preserve the integrity of the RHE in the event of a malfunction, reactor coolant on the charging side of the RHE may be relieved to the RCS through the thermal (spring loaded) relief check valves 1CV273 and 2CV273 for Units I and 2, respectively. Manual isolation valves 1CV272 and 2CV272 are located upstream of the relief valves.
The thermal relief check valves are not required to operate during or following a design basis accident to safely shutdown the plant.
Due to the administrative controls previously discussed the possibility of inadvertent closure of the manual isolation valve during power operation is extremely low.
Nonetheless, if the manual isolation valve is postulated to be inadvertently closed during power operation, the pressure relief function of the thermal relief check valves would be defeated. Without adequate overpressure protection, RHE overpressurization could potentially result in a failure and a release of reactor coolant gases and liquid to the containment.
The Small Break Loss of Coolant Accident (SBLOCA) is analjzed in Chapter 15 of the UFSAR.
The limiting case is a 4" diameter break in the RCS cold leg.
Since the charging and letdown lines to and from the RHE are 3 inches in diameter and the RHE is isolable from the RCS, a postulated rupture of the RHE would result in consequences which are already bounded by the existing SBLOCA accident analysis contained in UFSAR Chapter 15.
We have determined that the licensee's locking open manual isolation valves, together with operating procedures, makes overpressurizing parts of the eves unlikely.
We also found the plant configuration still does not meet all of the ASME Code requirements.
However, the licensee has shown that compliance with the ASME Code requirements would result in hardship or unusual difficulty without a compensating i-0crease in the level of quality and safety of the plant.
In order to meet the Code, the licensee would have to modify the design of the subject manual isolation valves to install controls and interlocks. The proposed alternative is sufficient for safe operation.
The licensee has shown that the consequences of losing eves thermal pressure relief capability and the resulting eves loss are acceptable and do not result in the licensee's inability to safely shut down the plant.
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3.0 CONCLUSION
We have determined that the previously identified CVCS manual isolation valve installed configurations do not meet all of the 1965 Edition, Winter 1966 Addenda and the 1968 Edition of Section III of the ASME Code, Article 9 requirements. These Code editions are the applicable ASME construction codes for Salem, Units 1 and 2.
However, the licensee has demonstrated that compliance with the ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety of the plant.
We also find that mispositioning the manual isolation valves and subsequent overpressurizing and eves loss would not impair the licensee's ability to safely shut down the plant. Therefore, pursuant with 10 CFR 50.55a(a)(3)(ii), we authorize the proposed alternative to the ASME requirements regarding control and interlock requirements for relief valve*
discharge line stop valves as required by 10 CFR 50.55a(a)(2).
Principal Contributor:
L. Olshan Date: November 6, 1995 Attachments:
Figures 1 and 2
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H2lCV241 VOLUME CONTROL TANK 11 (21)
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LO 13<23lBR151 13<23lBR152 Note 1= Solem Unit 1 Hold-up tonk No. 12 hos been removed from service. Manual isolation valve 12BR151 is maintained in the Locked Closed Position.
Figure 1 Volume Control Tank
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LO 1121CV273 1121CV272 NO FO CHARGING 1121CV78 1121CV274 1121CV77 1121CV74 NC FO LETDOWN 1121CV7'1 NC FC 1121CV75 Figure 2 Regenerative Heat Exchanger