ML20005F944

LER 89-060-00:on 891212,standby Gas Treatment Sys Charcoal Filter a Discovered to Be Degraded W/Possible Bypass Leakage Paths.On 891218,filter B Found W/Similar Condition.Caused by Failure of Spot Welds.Filters repaired.W/900110 Ltr

ML20005F944
Person / Time
Site:	Limerick
Issue date:	01/10/1990
From:	Endriss C, Mccormick M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-060, LER-89-60, NUDOCS 9001170419
Download: ML20005F944 (7)

Text

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[ N L.: PHILADELPHIA ELECTRIC' COMPANY l LIMERICK GENER ATING STATION P. O BOX A SAN ATOG A, PENNSYLV ANI A 19464 (218) 3271200 Exv. 2000 m, s. u.c c.nu ec a e.c. ' January 10, 1990 4.,,

u. . . ./.' C' .".'.",'U ".. .. .. Docket Nos. 50-352. 'i 50-353  ;

License Nos. NPF-39 NPF-85  ;

U.S. Nuclear Regulatory Commission ,

Attn: Document Control Desk ,

N Washington, DCL 20555 +

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SUBJECT:

Licensee Event Report-  !

Limerick Generating Station - Units 1 and 2 '

This LER reports a condition that could have prevented the '

Standby Gas Treatment System (SGTS) from fulfilling its safety function and resulted in Operations prohibited by Technical Specifications. .This event'was caused by failure of charcoal  ;

filter assembly welds that resulted in possible bypass leakage  ;

paths through the filter acsembly.

Reference:

Docket Nos. 50-352 50-353 Report Number: 1-89-060 Revision" Number: 00 Discovery Date: December 13, 1989 Report Date: January 10, 1990 Facility: Limerick Generating Station l P.O. Box A, Sanatoga, PA 19464 l This LER is being submitted pursuant to the requirements of l 10 CFR 50.73(a)(2)(1)(B) and 10 CFR 50.73 (a)(2)(v)(C).

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u' b WAR:aj cci W. T. Russell, Administrator, Region I, USNRC T. J. Kenny, USilRC Senior Resident Inspector, LGS 9001170419 90o13o

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On December 12, 1989, the 'A' Standby Gas Treatment System (SGTS)

Charcoal Filter was discovered to be in a degraded condition with possible bypass leakage paths through the charcoal filter bed.

This condition provided the potential for SGTS Filter bypass leakage 'to be g: eater than the Technical Specifications (TS) surveillance allowable limit of 0.05% and could have prevented the SGTS from fulfilling its intended safety function. Several charcoal f\1ter assembly welds failed, creating openings (holes) at the bottom of the outer (downstream) screen of the filter assembly. On the 'A' SGTS Filter, approximately 2.5 cubic feet of charcoal had leaked out and the level of charcoal was lower

! than the normal full condition. On December 18, 1989, a similar degraded condition of the 'B' SGTS Charcoal' Filter was discovered l with approximately 0.1 cubic feet of charcoal having leaked out, but the level of charcoal remained at the normal full condition.

After a thorough inspection, the damaged filter screens were repaired, charcoal replaced, and the SGTS returned to operable status. We are continuing to evaluate the cause of the weld failures. As an augmented surveillance activity, each SGTS Charcoal Filter bed will be inspected monthly, following the TS required system flow test.

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Unit Conditions Prior to the Event: -

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Unit 1 Unit 2 ',  ;

dperating Condition: 1 (Power Operation)* 4 (Cold Shutdown) f.

Reactor-Power: 100% 0% i i

These Operating Conditions existed immediately prior to discovery of the degraded condition of the Standby Gas Treatment System L

(SGTS)(EIIStBH) Charcoal Filters. However both units have '

operated at various reactor power levels since January 19, 1989, >

when the 'A' and.'B' SGTS Charcoal Filters were last inspected ~

during routine surveillance testing. In addition, operability of the SGTS was required to support Refuel Floor. Secondary Containment opert.bility from February 8, 1989 to March 30, 1989 ,

and from November 8, 1989 to December 9, 1989.

Description of the Events ,

During a routine maintenance activity, the SGTS Charcoal Filters were discovered to be daraged with possible bypass leakage paths '

through the charcoal filter bed. This condition provided the potential for SGTS Filter bypass leakage to be greater than the

!' Technical Specifications (TS) allowable limit of 0.05% and could have prevented the SGTS from fulfilling its intended Safety function to limit the release of radioactive material.

On December- 11, 1989, the 'A' SGTS Charcoal Filter was opened for a routine inspection and scheduled replacement of the filter bed charcoal. Approximately 2.5 cubic feet of a total of . ,

approximately 80 cubic feet of charcoal was discovered on the filter housing floor and the level of charcoal in the 8 inch thick filter bed was lower than the normal full condition. On December 12, all of the charcoal was removed from the filter bed o

as planned. A thorough inspection of the filter assembly revealed the source of loose charcoal to be from three openings (holes) at the bottom of the outer (downstream) screen of the filter assembly. An engineering evaluation of the filter screen holes determined that they were caused by failure of several small spot welds connecting the screen to the filter mounting frame. On December 13, at 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br />, station personnel concluded that degradation of the screen and the lower than normal level of charcoal in the filter bed could have created a y,._ .

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bypass leakage path exceeding the TS surveillance allowable -

bypass leakage limit of 0.05%. Following screen' repairs, loading i new charcoal in the filter bed and performing required  :

SGTS was returned to operable status

' surveillance tests, the 'A' at 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> on December 16, 1989. The 'A' SGTS was out of

' service for 134.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> total for the scheduled filter charcoal replacement and correction of the deficiency.

After discovery of the failed welds on the 'A' SGTS filter bed, station management decided to inspect the redundant 'B' SGTS filter bed for indications of a similar degradation. On December 14, 1989 with the 'B'.SGTS in operable status, a boroscope was -

used to inspect the 'B' SGTS Charcoal Filter. Approximately '

three quarters of the charcoal bed was inspected and no evidence of similar filter degradation was. observed. The inspection was .

not complete because the entire filter screen surface area was not accessible with the boroscope. Since no problems were identified by the inspection, station management concluded that i the 'B' SGTS was operable and would be fully inspected after the

'A' SGTS was returned to service.

, After completion of repairs to the 'A' SGTS filter bed, the 'B'  ;

l SGTS was removed from service on December 18, and a complete visual inspection of the 'B' Charcoal Filter was conducted.

Approximately 0.1 cubic feet of loose charcoal was discovered on the filter housing floor in the area not accessible during the boroscope inspection. Similar to the 'A' filter, this charcoal H was due to a small opening of the filter bed outer screen where it was spot welded to the filter mounting frame. Although some charcoal leaked out, the charcoal filter bed was still filled above the screen height and there was no evidence of voids or potential bypass leakage paths. The 'B' SGTS was not considered inoperable as a result of this condition. However, station management conservatively concluded that the 'B' SGTS may have been in a condition that could have prevented the 'B' SGTS f rom 1

performing its intended function. Following the charcoal unloading, screen repair, loading of new charcoal in the filter l bed and performing required surveillance tests, the 'B' SGTS was i returned to operable status at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br /> or. December 21. The

'B' SGTS was out of service 70.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> total for the filter

! charcoal replacement and corrections of the deficiency.

A four (4) hour. notification was made to the NRC on December 13, 1989, at 0947 hours0.011 days <br />0.263 hours <br />0.00157 weeks <br />3.603335e-4 months <br /> in accordance with 10 CFR 50.72 (b)(2)(iii)(C) because the event could have prevented the SGTS from performing its intended function to limit the release of radioactive material. A follow-up notification was made to the NRC on December 18, 1989 at 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />, when it was discovered that the 'B' SGTS filter had a similar, although less significant 3on. u.,

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s degradation. Accordingly, this report is being submitted in

• accordance with 10 CFR 50.73 (a)(2)(v)(C). This condition may  ;

have existed since January 19, 1989 when the 'A' and 'B' filters t

I were last inspected for routine surveillance. Therefore this:

Jeport is also being submitted in accordance with 10 CFR 50.73 ,

L (a)(2)(1)(B), "Any Operation or Conditiod Prohibited by the  ;

Plants Technical Specifications," because the significant bypass leakage path discovered on the 'A' SGTS Charcoal Filter was s

assumed to be greater than the TS Surveillance 4.6.5.3 allowable limit of 0.05% and the required TS remedial actions were not

.taken.

Consequences of the Event

• The consequences of tnis event were minimal. There was no release of radioactive material to the environment and the system

'a' degradation was discovered as a result of the established '

surveillance and preventive maintenance programs. The exact duration this degraded condition existed is not known. However i it did not exist on January 19, 1989 when the 'A' and 'B' filters -

were last-inspected for routine surveillance.

l There were, however, greater potential consequences of this l condition. Normal SGTS lineup is with both the 'A' and 'B' SGTS '

I Filter trains aligned in the automatic start mode. Had the SGTS been required to limit the release of radioactive material in response to a Loss of Coolant Accident (LOCA) or Refueling Accident, both the 'A' and 'B' SGTS trains would have initiated.

Due to the discovered condition of the 'A' and 'B' SGTS Filters, the SGTS would not have performed its design function to remove 99.0% of all radioactive iodine from secondary containment effluent' gases as assumed in the Design Basis Accident (DBA) safety analyses. -

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sna w . u. ,, u a enc u au.am Cause of the Event: -

This event was. caused by holes in the SGTS charcoal filter ,

assemblies-created by failure of spot welds which connected the outer (downctream) screen to the filter mounting frame. The holes allowed charcoal to leak from the filter bed and increased the potential for' untreated filter bypass air flow. The exact cause of the spot weld failures is not known, but does not appear to be the result of operations, surveillance or maintenance activities.

The design of these charcoal filters is unique to the SGTS at Limerick Generating Station.

Corrective Actions:

1 Following discovery of the 'A' SGTS Charcoal Filter screen problem, on December 13, a Nonconformance Report (NCR) was issued and Engineering Department personnel initiated an investig,c.lon and. analysis of the problem. A second NCR was issued on December 19, when.a similar problem was discovered on the 'B' SGTS Charcoal Filter screen. Both the 'A' and 'B' filter outer screens were repaired using a silver solder, brazing procedure.

The affected areas (openings) of the screens were re-fitted and securely attached to the filter mounting frame. The filter manufacturer was consulted and concurred with the repair procedure used. Both filters were refilled with new charcoal and were tested to demonstrate acceptable bypass leakage before they were declared operable and returned to service.

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Actions Taken to Prevent Recurrence:

With the charcoal removed, each of the filter screens were examined completely for evidence of degradation (attachment weld failures). The only problems identified were on the outer (downstream) screen, where it connected to the lower mounting frame. The affected areas were limited to three welds on the 'A' filter and one weld on the 'B' filter. This failure was reported on the Nuclear Plant Reliability Data System.

The Engineering department is continuing its evaluation of the weld failures to determine the reason for their failure. As an goeu un

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f augmented surveillance. activity, a complete inspection of each .

j SGTS. Charcoal, Filter bed.will'be performed monthly, following the 'j TS required system flow test. Results of the engineering  ;

evaluation of the weld failures will be provided in a supplement i to this report by May 15, 1990.- 1 g.

Previous Similar Occurrences:

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Cause~ Codes B -

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