ML20056H645

Safety Evaluation Permitting Use of 1989 Edition of ASME Code Section XI,IWA-5250(a)(2) Until End of Current Fuel Cycle for Removal of Bolting from Flanged Joint

ML20056H645
Person / Time
Site:	Limerick
Issue date:	09/07/1993
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20056H638	List: ML20056H637 ML20056H645
References
NUDOCS 9309100248
Download: ML20056H645 (2)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO BOLT REMOVAL ON A LEAKING RHR FLANGE - RELIEF RE0 VEST RR-20 LIMERICK GENERATING STATION. UNIT 1 PHILADELPHIA ELECTRIC COMPANY DOCKET NO. 50-352

1.0 INTRODUCTION

The licensee has identified leakage at the bolted connection joining the shell to the channel head of the residual heat removal (RHR) Heat Exchanger (IBE205) during an American Society of Mechanical Engineers (ASME)Section XI system hydrotest. The 1986 Edition of the ASME code is the code of record for the Limerick Generating Station and requires that all of the bolting be removed from the leaking flange and be visually examined. The way this flange is  !

designed,16 of the 64 studs cannot be removed for visual inspection without '

complete disassembly of the heat exchanger. Disassembly of the heat exchanger ,

would require cutting at two 20-inch diameter safety related pipes. '

The heat exchanger shell flange to tube sheet and channel head flange contains sixty-four 1-1/8 inch diameter studs located around a bolt circle that is 58-5/8 inches in dian.eter. The studs are fully threaded from top to .

bottom. The studs are made according to SA-193-B7 and the nuts are made according to SA-194-2H. Every fourth stud around the bolt circle is locked in place by a threaded washer located inside the flanged joint for a total of 16 locked studs. Removal of these 16 studs requires complete disassembly of the triple flanged joint.

The remaining 48 studs were removed and examined using VT-1 examination. The load bearing threads on each end of the studs showed no evidence of degradation. The non-load bearing areas of these studs showed corrosion product build-up making VT-1 examination not possible. Attempts to remove the  ;

corrosion products raised radiological concerns; so, the licensee decided to

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replace these studs. One stud was cleaned and no adverse surface conditions i were noted. The material loss in the non-load bearing areas was predominantly from ths major diameter with superficial loss from the minor diameter.

The licensee analyzed the effect of not replacing the 16 locked studs on the integrity of the flanged joint and determined that the structural integrity of the joint would not be compromised.

The licensee has committed to disassemble this flanged joint during the fifth refueling outage scheduled for the first quarter of 1994. The 16 locked studs will be removed and examined at that time. The joint is being disassembled for a tube bundle replacement.

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The licensee reported that leakage below the technical specifications limit  !

continues at this bolted connection. The licensee has a monitoring program in place to determine the rate and nature of the leakage. l 2.0 CODE CONSIDERATIONS The licensee at the Limerick Generating Station has requested relief from the 1986 Edition of the ASME Code Section XI requirements, IWA-5250(a)(2) which require that all bolting be removed and VT-3 examined for corrosion and i evaluated in accordance with IWA-3100 if leakage of the joint occurs. The  :

1989 Edition of the ASME Code Section XI, IWA-5250(a)(2) was revised and  ;

requires that only the bolt closest to the source of the leak be removed, VT-3  ;

examined, and evaluated in accordance with IWA-3100. Title 10 of the Code of  !

Federal Regulations (10 CFR) 50.55a(g)(4)(iv) permits the use of portions of later editions of Section XI of the ASME Code provided that all related ,

requirements of the respective editions or addenda are met and subject to I approval by the NRC. i 3.0 DISCUSSION The licensee at Limerick Generating Station has done more than the minimum l requirements of the 1989 Edition of the ASME Code Section XI, IWA-5250(a)(2)  !

by removing 48 studs and by examining the studs using a VT-1 visual i examination rather than the code required VT-3 examination. The licensee has '

also examined the structural integrity of the bolted joint and has determined '

that the structural integrity of the joint is not compromised if the remaining i l 16 studs are not removed. There are no related requirements in the 1989 l Edition of the ASME Code. The staff concurs that the licensee's examination I of this joint and the structural analysis of the joint indicate that the joint l will continue to operate safely until the end of the current fuel cycle.

4.0 CONCLUSION

Based on a review of the information provided, the staff has concluded that i the examination of the RHR heat exchanger joint and the structural analysis will provide for continued safe operation of this flanged joint.

The staff concludes that permitting the use of the 1989 Edition of the ASME i Code Section XI, IWA-5250(a)(2) until the end of the current fuel cycle is l l acceptable in accordance with 10 CFR 55.55a(g)(4)(iv). l 1

l l Principal Contributor: J. A. Davis l Date: September 7, 1993 i

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