ML20217Q704

Safety Evaluation Accepting Util Request to Leave Leak Chase Channels Plugged During Performance of Containment ILRT

ML20217Q704
Person / Time
Site:	LaSalle
Issue date:	05/04/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217Q702	List: ML20217Q700 ML20217Q704
References
NUDOCS 9805110011
Download: ML20217Q704 (3)

Text

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! p k UNITED STATES g j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20886-0001 i l  % >

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l

l RELATED TO THE ACCEPTABILITY OF PERFORMING CONTAINMENT INTEGRATED LEAK RATE TESTS WITHOUT VENTING THE LEAK CHASE j COMMONWEALTH EDISON COMPANY l

l LASALLE COUNTY STATION. UNITS 1 AND 2 DOCKET NOS. 50-373 AND 50 374 i

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1.0 INTRODUCTION

By letter 6ted November 26,1997, as supplemented on February 20 and April 7,1998, l Commor wself h Edison Company (Comed, the licensee) submitted for staff review its justification j for leaving i se leak chase channel plugs installed during the performance of containment j

, integrated Is ik rate tests (ILRT). This practice was identified in an NRC inspection report l 50-373/78-3S dated January 19,1979. Comed submitted its justification of the practice to the ,

! NRC in 1981. The NRC closed out this issue in inspection Report 50-373/81-28 stating the j j position that the ILRT had to be performed with the liner channel plugs removed or an exemption  !

obtained from NRC. Without further correspondence from the NRC, Comed continued to J l perform the ILRTs on both units with the leak chase channel plugs installed. The lack of i l acknowledgment from the NRC was not recognized until August 18,1997, and a License Event Report (LER 50-373/97-030) was issued. li was subsequently determined that an exemption is l not required because Comed determined that its practice satisfies the requirements of 10 CFR l Part 50, Appendix J. The November 26,1997, letter provides Comed's justification for this position.-

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- 2.0 EVALUATION

!- The main purpose of performing a containment ILRT is to monitor the leak rate of the contain-

! ment for leaks which are most likely to occur through penetrations and hatches. The liner welds

( shou!d be leaktight. Venting the leak chase channels subjects the containment liner welds to the l leak test. The butt welds joining two liner plates define the pressure boundary. However,if the  :

leak chase channels are unvented, the fillet welds attaching the channel to the liner plate i become the primary pressure boundary. The quality of these welds should be equal to or better than that of the liner welds. The leak chase channel, originally intended to provide an enclosure for pressure testing of liner welds, thus, becomes part of the containment liner and its structural integrity should be ensured. The strength of the channel box and its welds should be able to .

resist all loads and load combinations including the test loads, operating loads and postulated I accident loads. The design of the leak chase channel and its welds should meet the I p requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure 1 Vessel Code (Code) Section ill, Division 2, or American Institute of Steel Construction (AISC)

Manual of Steel Construction. The structuralintegrity of the leak chase channels as well as the containment liner should be evaluated as a part of the concrete containment.

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2-The staff has reviewed the information provided by Comed in the justification of its position. The information is contained in 11 attachments to Comed's letter to NRC dated November 26,1997.

The contents of these attachments consist of information about the location and details of the leak chase channels, welding procedure, welder certification, leak test system, penetration details, loads and load combinations used, and design calculations for the leak chase channels.

Comed claims that: (1) the channel welds are qualitatively equivalent to or better than those for the primary containment liner welds, and (2) the channels will maintain their integrity when subjected to the loading conditions of a postulated design basis accident as well as during normal operation.

According to Comed, the design, fabrication and erection of the liner followed the requirements of ASME Section lil,1971 Code, Subsection NE, Winter 1972 Addenda for class MC components. The same welding procedure and weld rod material used for the butt welds of the liner plates were used for the fillet welds of the leak chase channels to the liner. The welders were qualified for both the butt welds ar'd the fillet welds. Therefore, the quality of the material  !

and workmanship of the leak chase channel fillet welds is essentially the same as that of the liner I plate butt welds.

The liner seam butt welds were tested by partial radiography and 100 percent liquid penetrant or magnetic particle test. The leak chase channel fillet welds to the liner were tested by 100 percent liquid penetrant or magnetic particle test. The leaktightness of the leak chase and the liner welds was established during construction by pressure testing to the containment design pressure prior to pouring the containment concrete.

The containment liner and the attached leak chase channels are provided mainly to maintain the leaktight integrity of the concrete containment and are generally not considered to contribute any f j

structural strength to the containment. The strength of the contallment depends principally on i the concrete and reinforcing steel or prestressing steel. However, the leak chase channel should j be strong enough to resist any of the potentialloads and load combinations without jeopardizing i the integrity of the liner system, which includes the liner, its anchors and the leak chase l

channels. Comed provided the information on the loads and load combinations considered in  :

the design of the containment as a whole and also on the loads acting on the leak chase I channels located in the suppression pool. As indicated above, the design of the liner system  !

conforms to the criteria of the 1971 ASME Section til Subsection NE Code. The staff reviewed l the design procedure of the leak chase channels and their welds to the liner and found it to be i reasonable. Stainless steelleak chase channels (made of American Society for Testing and {

Materials (ASTM) A-240, A-276 Type 304 materials) are used on the stainless liner in the j suppression pool and channels of A-36 steel are used in the dryweel. The allowable stresses 1 used either follow the 1969 AISC or are judiciously established, considering the loading conditions. The results of the analyses for various loads and load combinations indicate the design of the leak chase channels and their weld connections to the liner meet the established criteria. However, by a letter dated February 20,1998, Comed informed the staff that there were 18 specific leak chase channels in each unit that are in direct contact with pool water and could not be demonstrated to maintain their integrity during postulated design basis accidents (DBA) due to their location with respect to the dynamic effects of the pressure suppression pool (PSP) water inventory during the postulated event. For those 18 leak chase channels on each unit, the plugs are to be permanently removed. For Unit 1, the 18 leak chase channel plugs have been permanently removed and a successful local leak rate test of each leak chase channel has been

, ,s l 3-performed. For Unit 2, the same will be done prior to the startup from the current refuel outage, L2RO7.

3.0 CONCLUSION

With the exception of the eighteen (18) specific leak channels located in the pressure suppression pool of each unit which are shown to be incapable of resisting the hydrooynamic effects and where the plugs are to be removed permanently, the following conclusion is applied to leak chase channels where the leak chase plugs are not removed during ILRT.

The staff has reviewed the information provided by Comed to justify its position for performing the containment ILRT without removing the leak chase channel plugs, thus, effectively making the leak chase channels and their welds to the liner the containment pressure boundary. Comed '

has demonstrated with the information provided that (1) the channel welds are qualitatively at least as leak resistant as the liner welds, and (2) the channels would maintain their structural integrity when subjected to containment design loads. The staff concurs with Comed's justification. However, before performing Type A containment IRLT, in addition to the visual inspection of the outside and inside surfaces of the containment as required by Appendix J, Option A, item V, the venting plugs and the leak chase channels should also be inspected, to .

ensure the structuralintegrity of the containment liner system and the concrete. '

. Principle Contributor C.P. Tan Dated: May 4, 1998