ML18057A781
| ML18057A781 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 03/06/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18057A780 | List: |
| References | |
| NUDOCS 9103140054 | |
| Download: ML18057A781 (4) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION.
WASHINGTON. D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF FOR THE CONTAINMENT AIR COOLER LEAKAGE CONSUMERS POWER COMPANY
.PALISADES NUCLEAR POWER PLANT DOCKET NO. 50-255
1.0 INTRODUCTION
By letter dated January 16, 1991, and as amended February 11, and February 27, 1991, Consumers Power Company (CPCo) requested relief from the post-repair zero leakage requirements of the ASME Boil~r and Pressure Vessel (B&PV) Code,Section XI, Table IWD-2500-1, Examination Category D-B, Item No. 02.10, and IWA-5250, for containment_air coolers VHX-1, 2, 3, and 4.
The Palisades ~uclear Plant containment air coolers (VHX-1-4) are air handling and cooling units located entirely in the containment building. Plant service water from the critical service water header is circulated through the units' cooling coils. The units are designed to control containment temperature during normal operation arid condense steam during certain accident scenarios to help
. limit peak containment pressure. The coolers are classified as safety Class 3 per Regulatory Guide 1.26. Section 50.55a(g)(4)'of Title 10 of the Code of*
Federal Regulations states that components which are classified as ASME Code Class 1, 2 and 3 shall meet the requirements of Section XI of the B&PV Code, to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The applicable sections of the B&PV Code, referenced above, require a Class 3 system to be examined and to exhibit zero leakage during post-repair hydrostatic testing.
Each cooler *consists of eight sets of coils composed of 5/8-inch tubes pip~d to manifolds.for supply and return connections to the critical service water system.
Some of the coils' header~to-tube connections have exhibited leakage. Attempts have been made to repair those leaks~ While some of these leak repairs have been successful, CPCo has stated that limitations of the cooler design, age-related degradation of the materials, and configuration make achievement of the post-repair zero leakage requirement impractical.
In addition to the design limitations, the licensee states that adequate lead time did not exist to redesign, fabricate, and.procure new cooler coils and install them during the present refueling outage.
2.0 EVALUATION Consumers Power Company's Evaluat.ion *.
CPCo has completed an analysis and safety review which show how much leakage can be tolerated from each coil and cooler, and has established a program to
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9103140054 910306 PDR ADOCK 05000255 P
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.L periodically inspect the coolers in order to assure compliance with these leakage limits. As an alternative to maintaining zero leakage, Palisades will, or has, performed the following actions:
- a.
All cooler leaks on piping greater than one inch shall be repaired and tested during shutdowns in accordance with B&PV Code,Section XI requirements.
- b.
All leaks on cooler piping one inch or less shall be reduced to the lowest possible level within the requirements of the safety evaluation.
For coolers discovered to be leaking, an air pressure drop test shall be performed (during shutdowns of sufficient duration) to quantify leakage.
Total containment air cooler leakage will be maintained at less than 4 gpm.
- c.
An actuation of the air coolers sump float switch requires Operations to check the cooler for coil leakage. Should any cooler become inoperable due to leakage, the limiting conditions for operation (LCO) and action statement of Technical Specification Section 3.4, "Containment Cooling,"
would apply. This LCO allows one cooler to be out of service for up to 7 days before placing the reactor in hot shutdown.
- d.
The replacement of existing cooler coils, utilizing a modified tube-to-header joint configuration, appears to be the best long-term solution.
Failure studies were performed on containment air cooler coils in 1986 and 1987.
Recommendations from these studies led to design engineering and modification of available spare cooling coils. These modified coils were installed in containment air cooler VHX-4 during the present 1990 refueling outage. Palisades will monitor the operation of these coils, and given satisfactory experience with the.modified coils, CPCo intends to continue modifying and replacing coils in future outages for the remaining containment air coolers (VHX-1, 2, and 3). Until replacement coils are available, the current repair and testing methods (brazing,' hydrotest, air pressure test), provide appropriate leakage control.
- e.
Small amounts of cooler leakage will be monitored and identified as follows; two containment sump high level alarm switches (LS-0358 and LS-0360) are located approximately 4 inches from the bottom of the sump.
The sump contains about 950 gallons at this level. Operations Alarm Response Procedure (ARP) No. 8 presently requires the operators to evaluate the cause for the alarm and determine if the.alarm is due to normal leakage or unexpected or abnormal leakage.
The alarm response procedure will be modified to readily alert the operators that abnormal leakage may be due to the containment air coolers and that they should be sensitive to the coolers as a contributor to the sump's level. The revised procedure will require the operators to contact the Duty and Call Superintendent if containment air cooler leaks greater than 4 gpm are identified. Cooler leakage as high as 4 gpm and the subsequent increase in containment flood level has been shown to have no adverse affect on plant response to any analyzed accident.
Normally, the containment sump is drained before the high level alarm comes in. The control room operators are sensitized to containment sump level as a potential indicator of other in-containment system. leaks.
An i ncreas,e in the number of times the sump is drained wou 1 d a 1 so be an indication to the operators that some additional leakage is contributing
- to the sump level.
When the sump is drained, it enters the dirty waste drain tank which holds approximately 3800 gallons.
- From there, the water is pumped to one of three 20,000 gallon miscellaneous waste hold tanks.
When a miscellaneous waste tank is full it is sampled and processed through the radwaste system.
As part of the plant's program to minimize radioactive ~aste during the course of a normal work week, the Operations Plant Support Supervisor for Radwaste routinely inventories the radwaste system's total volume.
Part of this inve*ntory is to trend the dirty waste drain tank level to assure that the plant's normal daily waste water generation is kept to a minimum.
Any noticeable trend towards an increase in normal daily waste water generator would be reported to the shift operations staff to determine the source of the leakage.
Recent experience exists to show that leaks in the containment on the.
order of one gallon per minute can be readily identified.
As an example, when the plant's shield cooling system began leaking at about this rate~
it was through the above process that the leak was detected, which then
- resulted in an on-line containment inspection which determined the leakage source. All four containment air coolers are located on the 590' elevation of the containment building and are accessible for inspection during power operation.
- f.
The coolers have been verified as being capable of performing their safety function with a minimal amount of leakage (up to 4 gpm per cooler) without adversely affecting the outcome of any analyzed event or accident. This verification has been documented in the safety evaluations for Palisades deviation report D-PAL-86-218 and permanent maintenance procedure SWS-M-6.
These evaluation are maintained at the plant and are available for review.
NRC Staff Evaluation
The NRC staff reviewed CPCo reasoning and bas~s for requesting relief from the ASME Code,Section XI requirements for the containment air cooler leakage *. The NRC staff agrees that because of fabrication problems, age-related degradation design, geometry, and materials of construction, the containment cooler cooling coils can not be maintained leak tight as required by ASME Code,Section XI, Table IWD-2500-1.
The staff agrees that the coolers would be expected to maintain their. structural integrity under design conditions. Although leakage may.be expected during operation, the administrative limit of 4 gpm imposed by the licensee on service water leakage in the containment from the containment air cooler system and the commitment to enter the limiting conditions for operation in Technical Specification (TS} 3.4.2 is considered adequate to provide an
- e. acceptable level of safety. For the purposes of assessing air cooler leakage, the licensee has stated that the total leakage of 4 gpm from all containment air coolers will be treated as one inoperable cooler to be consistent with the TS. The staff agrees this is prudent. Further, if the leakage cannot be reduced to less than 4 gpm total within 7 days, the licensee stated that TS 3.4.2 requirements to place the reactor in hot shutdown will be followed. The staff finds that sufficient time would be available to take necessary actions to mitigate any excessive leakage that might occur during the postulated accident conditions.
The staff expects that any repairs of the coolers will be in accordance with ASME Code,Section XI.
If temporary repairs other than those meeting the Code
- are to be accomplished to limit leakage, relief from ASME Code,Section XI is required..
- 3. 0 CONCLUSION The NRC staff has reviewed and evaluated the information submitted by CPCo in support of the relief requests for the containment air cooler leakage at the
. Palisades Nuclear Power Plant. The staff concluded that the ASME Code,Section XI, zero leakage requirement is impractical to meet at this time. Further, the safety review of this item established that the containment air.cooler leakage is within the limits imposed by.the governing technical specifications. The.
staff has determined that granting relief, pursuant to 10 CFR 50.55a(g)(6)(i),
. for one operating cycle, is authorized by law and will not endanger life or*
property, or the conunon defense and security and is otherwise in the public interest. The relief is granted effective i11111ediately and shall expire upon the completion of refueling outage No. ~or April 30, 1992, whichever occurs first. In making this determination, the staff has considered compliance resulting in a hardship without a compensating increase in safety and the impracticality of performing the required testing considering the burden if the requirements were imposed.