ML20235N730
| ML20235N730 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 02/20/1989 |
| From: | Fay C WISCONSIN ELECTRIC POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CON-NRC-89-021, CON-NRC-89-21 GL-88-14, VPNPD-89-090, VPNPD-89-90, NUDOCS 8903010376 | |
| Download: ML20235N730 (5) | |
Text
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,, - y Wisconsin 1
' fEk)CfDC POWER COMPANY i
1 231 W M chigan. RO. Box 2046. Mitwoukee, WI 53201 (414)221 2345 l
l VPNPD-8 9 -090 NRC-8 9 -021 February 20, 1989 j
U.S. NUCLEAR REGULATORY COMMISSION Document Control Desk Mail Station Pl-137 Washington, D.C.
20555 Gentlemen:
I l
DOCKET NOS. 50-266 AND 50-301 RESPONSE TO GENERIC LETTER NO. 88-14 INSTRUMENT AIR SYSTEM PROBLEMS AFFECTING SAFETY-RELATED EQUIPMENT POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 Generic Letter 88-14 concerns the failure of safety-related i
equipment to perform its safety function due to air system failures.
These problems are discussed in NUREG-1275, Volume 2,
" Operating Experience Feedback Report - Air System Problems."
Generic Letter 88-14 requested that each licensee review NUREG-1275, Volume 2 and perform a design and operations verification of the instrument air system.
Generic Letter 88-14 also included four specific actions which define the scope of the requested design and operations verification.
These four action items are listed below, each followed by the results of our verification.
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Action Item 1 - Testing:
j Verification by test that actual instrument air quality is consistent with the manufacturer's recommendations for individual components served.
PBNP Verification:
Air quality requirements were evaluated by reviewing technical manuals for typical Point Beach Nuclear Plant (PBNP) pneumatic equipment.
Quantitative air quality requirements were not included in the original specifications; rather, general guidance such as " free of dirt or oil" or " clean, dry, and non-corrosive" were specified.
To quantify our system air quality, we referred to the requirements of American National Standard ISA-S7.3, 1975,
" Quality Standard for Instrument Air."
It is our judgment that ISA-S7.3 constitutes a standard of air quality equal to or superior to the intent of the original guidance.
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Document Control Desk February 20, 1989 Page 2 Two air samples were drawn and tested at PBNP, one from each unit.
Sample locations were chosen at low points in the instrument air system.
The Unit 1 sample was evaluated as being fully in compliance with ISA-S7.3.
The Unit 2 sample was substantially in compliance with ISA-S7.3; however, a small concentration of particles greater than the allowable three micron size was identified (0.86 particles per liter).
Microscopic examination of the particles indicated that these larger particles were agglomerations of smaller (less than three micron) particles.
Additionally, the larger particles were not metallic in appearance.
It is our judgment that these larger particles were agglomerations of desiccant duct originating from the air system dryer.
Considering the extremely low concentration of agglomerated particles, we consider the air quality to be in compliance with ISA-S7.3.
Action Item 2 - Maintenance, Procedures, and Training:
Verification that maintenance practices, emergency procedures, and training are adequate to ensure that safety-related equipment will function as intended on loss of instrument air.
PBNP Verification Pneumatic safety-related equipment at PBNP is limited to valves.
In general, pneumatic safety-related valves fail to a safe position such that instrument air is not necessary for any component or system to perform its safety-related function.
This design feature was specifically reviewed and is discussed in Item 3 below.
The primary means of ensuring that safety-related pneumatic valves will perform their safety function is through testing in accordance with the Point Beach Nuclear Plant Inservice Testing (IST) Program.
Reliability of safety-related pneumatic valves is further enhanced by Maintenance Instruction (MI) 5.2,
" Air Diaphragm-Operated Control Valve Maintenance."
MI 5.2 provides guidance on dismantling, assembly, and overhaul of air-operated control valves.
Abnormal Operating Procedure AOP-5B, " Loss of Instrument Air,"
addresses emergency operation on the loss of instrument air.
AOP-5B describes the actions that may be required to identify and isolate an instrument air leak, provides the operators with a guide for recovery from a loss of instrument air, and provides operators with a listing of component failure positions due to loss of instrument air and the actions that might be necessary for various systems and/or components.
Additionally, periodic training is conducted both on the instrument air system and AOP-5B.
o Document' Control Desk February 20, 1989 Page 3 We note that the PBNP instrument air system is currently being modified under Modification Request (MR)85-243, " Increased Instrument Air System Capacity and Reliability."
Maintenance practices, emergency procedures, and training will all be reviewed in conjunction with MR 85-243 to ensure that they are compatible with the modified instrument air system.
It is our conclusion that maintenance practices, emergency procedures, and training are adequate to ensure that safety-related equipment will function as intended on loss of instrument air.
Action Item 3 - Design:
Verification that the design of the entire instrument air system including air or other pneumatic accumulators is in accordance with its intended function, including verification by test that air-operated safety-related components will perform as expected in accordance with all design-basis events, including a loss of the normal instrument air system.
This design verification should include an analysis of current air operated component failure positions to verify that they are correct for assuring required safety functions.
1 PBNP Verification As previously stated, the design intent of the PBNP instrument air system is such that no component should require air to perform its safety function, nor should loss of air prevent a safety function from being accomplished.
All safety-related pneumatic equipment at PBNP is designed to fail to a safe condition with the safety function being tested in the PBNP IST Program.
This design intent was reviewei and found, in general, to be met.
Discrepancies identified in our review are discussed below.
The discharge control valves for the two PBNP electric-driven auxiliary feedwater pumps are air-operated valves designed to fail open upon loss of instrument air.
For most design basis events, this is an acceptable fail-safe position.
However, in the case of a steam line rupture inside containment, the fail open position could potentially lead to over-feeding the steam generators, resulting in exceeding the maximum design pressure inside containment.
We are currently studying this issue to determine if, in fact, such a condition exists, and to determine the most practicable course of action.
We expect to complete our study and determine our intended course of action, if any, prior to July 31, 1989.
Document Control Desk February 20, 1989 Page 4 The containment purge supply and exhaust valves are air-operated butterfly valves.
These valves are locked shut to provide for containment integrity unless the reactor is in the cold or refueling shutdown condition.
Since the valves are administratively locked shut, operation of the valves is not tested in the IST. program.
During our review of these valves, it was noted that the valve seats use air pressure to provide the seal between the valve disk and valve body.
Our investigation noted that each purge supply and exhaust valve was supplied with i
I an air accumulator and check valve such that the accumulator would provide seal pressure to the valve in the event of a loss of instrument air.
This function, however, is not tested in the IST program.
The Unit 2 purge supply and exhaust valves were tested with a loss of instrument air during the Fall 1988 outage.
Three of the four accumulator check valves were found to leak, resulting in the purge supply and exhaust valves being inoperable.
The check valves were replaced and the purge supply and exhaust valves were retested satisfactory.
The Unit 1 purge supply and exhaust valves will be tested during the upcoming Spring 1989 outage.
l Results of the Unit 1 test will be provided to the NRC upon completion of the test.
Also, the IST program will be revised by January 1, 1990 to include testing of the valve seal under loss of l
instrument air conditions.
t The final discrepancy identified in our design verification concerns the crossover steam dump (OS) system dump valves.
The OS system operates in conjunction with the independent overspeed protection system to limit the ultimate overspeed of the main turbines.
The dump valves use air-operated pilot valves.
The OS system is required to be operable at power levels at or above 480 MWe and is tested quarterly to verify operability, Quarterly testing, however, does not include verifying operability under loss of instrument air conditions.
A review of the system to determine failure mode under loss of instrument air conditions was indeterminate; the system could fail-safe (dump valves open) or fail as is (dump valves closed).
Accordingly, the Unit 1 and Unit 2 OS systems were tested.
Six of eight dump valves failed as is (closed) on loss of air, two of the eight dump valves failed open.
Thus, we concluded that the OS system is not operable upon loss of instrument air.
We have originated two modifications to upgrade the air supply to the OS system.
These modifications are MR 88-171 for Unit 1 and MR 88-172 for Unit 2, both titled,
" Instrument Air Accumulator For Crossover Steam Dump Valves."
The modifications are expected to be installed by the Spring 1991 outage for Unit 1 and by the Fall 1990 outage for Unit 2.
In the interim, appropriate operations personnel have been iniormed that upon loss of instrument air, the OS system should be considered inoperable and power should be reduced to less than 480 MWe.
Document Control Desk February 20, 1989 Page 5 Action Item 4 - Proper Air Quality:
Each licensee / applicant should provide a discussion of their program for maintaining proper instrument air quality.
PBNP Verification:
Proper instrument air quality is maintained at PBNP through a program of effective maintenance and monitoring of air supply equipment.
We have reviewed the periodic maintenance recommended by the compressor and air dryer manufacturers and found that the recommended maintenance is performed.
In some cases, it was noted that maintenance. intervals were longer than those recommended by the vendor.
The extended intervals were justified, however, based on equipment operating experience.
We also reviewed the log readings taken to monitor system performance and concluded that they are effective toward ensuring proper system operation.
Our review of the instrument air system supply equipment maintenance and monitoring practices, coupled with the favorable sample results described in Action Item 1 above, lead us to conclude that the present maintenance practices are adequate.
We would be pleased to answer any questions you may have regarding our response.
Very truly yours,
.k.
OJ al C.
W.
Fay Vice President Nuclear Power Copies to NRC Regional Administrator, Region III NRC Resident Inspector Subscribed and sworn to before me thisAod' day of February 1989.
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