ML20029B600

LER 91-004-00:on 910205,leakage Found During Local Leak Rate Testing for Four Containment Isolation Valves.Caused by Improper Valve Seating.Valve Removed from Svc & Sent to Mfg for overhaul.W/910307 Ltr

ML20029B600
Person / Time
Site:	Millstone
Issue date:	03/07/1991
From:	Lyons T, Scace S NORTHEAST NUCLEAR ENERGY CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-004, LER-91-4, MP-91-213, NUDOCS 9103130095
Download: ML20029B600 (5)

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<go m es.sooo Re: 10CFR50.73(a)(2)(i)

March 7, 1991 MP-91-213 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20. 55

Reference:

Facility Operating License No. NPF-49 Docket No. 50-423 Licensee Event Report 91-004-00 Gentlemen:

This letter forwards Licensee Event Report 91-004-00 required to be submitted within thirty (30) days pursuant to 10CFR50.73(a)(2)(i), any operation or condition prohibited

-by the plant's Technical Specifications.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY 4 vcN St E. cace irector, Millstone Station SES/TWL:mo

Attachment:

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, While shutdown in Modes 5 (Cold Shutdown) and 6 (Refueling) during the performance of Local Leak Rate Testing (LLRT), the "as found" leak rates for four Containment Isolauon Yalves exceeded the Techmcal Specification Type C and Dypass leakage limits of 0.6 La and 0.04: L. .

The LLRT failures ccurred on February 5,1991 at 1331 (for 3RHS'MY6702A), February 7,1991 at 2200 (for 3RSS*V6), Fe' tary 10.1091 at 0 00 (for 3CDS'CTV91D), and February 19,1991 at 1330 (for 3RSS'MOY23B). o immediate action was required.

Leakage par 3RHS'MV6700A is beheved to be due to debris or bonc acid crystals on the seating surface.

The penetrauon was flushed with water and retested successfully. Leakage past 3RSS*V6 was due to improper seaung caused by banc acid crystal precipitation on the seating surface. The valve seat was cleaned and an "as-left" LLRT was satisfactonly performed. Leakage past 3CDS*CTV91B was due to failure of an elastomer T-nng which had partiali) rolled out of its retaining poose. The T-ring was replaced and an as-left LLRT will be performed nnor to startup. Leakage past 3RSS'MOY23D was caused by separation of the vulcanized rubber seat from the valve body mounung surface. The valve was removed from the system and has been sent'to the manufacturer for oserhaul. It will be reinstalled anti retested prior to startup.

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l. Descrmtion of Event On February 5,1991 at 1331, while at Orc power in hiode ! (Cold Shutdown), during the third refueling outage. 40 psia and 95 degrees Fahrenheit, dunny the performance of Local Leak Rate Tesung (LLRT),

3RHS'h1V8702A had excesure leakage which prevented the desired test pressure from being reached.

This *as found" undetermined leak rate exceeded the Technical Specihcation hmit of 0.6 L ,

3RHS'h1VS700A is the outside contamment Reactor Coolant System recirculrion suction isolation valve to the "B" Residual Heat Removal Pump. No immediate action was required since the plant was shutdown.

On February 7,1991 at 2200, while in hiode f. at atmosphene pressure and 101 degrees Fahrenheit, 3RSS*V6 had excessive leakage which prevented the desired test pressure from being reached.- This "as found" un6etermined leak rate exceeded the Technical Specihcation hmit of 0.6 L., 3RSS*V6 is the Containment Rectreulation System f RS$1 inside containment discharge check valve to the RSS Spray Header from the

• B" RSS Pump. No immediate action was required since the plant was shutdown.

On February 10.1991 at 2200. in hiode 5, at atmospheric pressure and 100 degrees Fahrenheit.

3CDS'CTV918 had excesshe leakage which prevented the desired test pressure from being reached.

This "as found" undetermined leak rate exceeded the Technical Specihcation bypass leakare hmtt of 0.042 L., 3CDS*CTV91B is the inside containment Re ctor Plant Chilled Water System *B" Train isolation vahe. No immediate action was required since the plant was shutdown.

On February 19,1991 at 1330, in hiode 6 (Refueling), et atmospheric pressure and 96 degrees Fahrenheit. 3RSS'hlOV23B had excessive leakage which prevented the desired test pressure from tring reached. This "as found" undetermined leak rate exceeded the Technical Specification hmit of e.o L..

3RSS'h10V23B is the outside containment suction valve to the "B" RSS Pump. No immediate action was required since the plant was shutdown. i

11. Cause of Event The root cause of the 3RHS'h1V6702A leakage was improper valve seating prior to the LLRT (possibly due to debris or bonc acid crystals on the seaung surface). 3RHS*h1V6702A is a 12 inch Westmphouse motor-operated gate valve.

The root cause of the 3RSS*V6 leakage was improper vahe seating prior to the LLRT (due to piccipitation of boric acid crystals on the seating surface). 3RSS'Y6 is a 10 inch Walworth swing check valve.

The root cause of the leakage observed at 3CDS*CTY91B was failure of an c!astomer T-ring which had partially rolled out of its retaining groove, apparently due to normal wear. 3CDS'CTV91B is a 10 mch Fisher Controls air-operated butterfly valve.

The root cause of the 3RSS'h!OV23B leakage was separation of the vuP . aired rubber seat-from the valve body mountmg surface. 3RS$'h!OY23B is a 12 inch Henry Pratt mo& operated butterfly valve.

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In the hrst event, containment miernty was maintamed by senlying that the inside contamment isolati9n valve, 3RHS*NtV67028. was operable and leak ught as serified by a satisfactory LLRT.

In the second esent, containment integnty was maintained by verifying . hat the outside containment isolation valve, 3RSS'hlOY20D, was operable and leak tight as venfie6 oy a sausfactory LLRT.

In the third event, containment intepnt) was maintamed by serifymg that the outside containment iulation valve, 3CDS*CTV3BA, was operable and leak tight as verified by a saustactory LLRT.

In the fourth event, containment integrity was maintamed by the RSS System piping, The RSS System is a closed loop in which the RSS Pumn takes suction from the Containment Sump and discharges back to containment. 3RSS*h10Y23B, the "D" pump suction isolation valve, is a normally open valve which remaire open during accident conditions, 11 does not serve as a containment boundary under accident conditions. The integnty of the RSS System piping was venhed by conducting a sausfactory LLRT of the "B" RSS pump piping from the suction up to the discharge isolation valve, 3RS$'h10Y208.

Based on the previous discu',sion, these events posed no significant safety considerations.

IV. Corrective Action No immediate corrective action was required by plant operators since the plant was shutdown, As corrective action for the 3RHS'h1V6702A leakage, the penetrauon was flushed with water and retested. This subsequent LLRT was successful. The Bushing apparently dislodged -the debris or boric acid which was preventmp proper valve seating, Because of the satisfactory test, valve disast.embly and inspection were deemed unnecessary, it should be noted that this piping had been drained, and that no problems were or have previously been identihed on similar valves.

As corrective action for the 3RSS'Y6 leakage, the valve was opened and inspected. The inspection resuhs showed a boric acid buildup on the calve seat which prevented full disc-to-seat contact. The seat was cleaned, the valve reassembled, and an *as-left" LLRT was satisfactorily performed. Investigation into the cause of the boric acid buildup is still under way, As corrective action for the 3CDS'CTV91 A leakage, the valve was opened and inspected. The j inspection results showed a failure of an elastomer T-ring, whic' had partially rolled out of its retaining proose, apparently due to normal wear. The T-nq wcs replat.d, the valve reassembled using the revised mamtenance procedures, and an *as left" i W uill be performed prior to startup. Investigation into several alternauves for action to prevent recurrenes is currently ongoing.

As correcuve action for the 3RSS'h10V23D leakage, the vahe was opened and inspected. The inspection results shcwed a detachment of the vulcanized rubber seat from the valve body mounting surf ace. The rubber seat apparently has a hmited installed life when used in an apphcation where it is not constantly wetted. The valve was removed from the system and will be sent to the manufacturer for overhauh it will be subsequently reinstalled and retested prior to startup. Investigation into several alternatives for action to present recurrence is ongoing.

Final valve inspection and ietest results as well as any additional RF03 LLRT failures will be provided as required in a supplemental report by hlay 15. 1991.

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ol5lololol4l2l3 9l1 0l 0l 4 0l0 0l 4 OF 0l4 i it xi of mv. .m. is <.w.c us. .etow Nec sem mA u nn j Y. Addinnnnl Information Leks87-043. 89-011, and 89-012 discuwed similar events of containment leakage in excess of hmits due to valve leakage.

LERs87-043 and 89-011 involved failures of 3CDS'CTV91B and 3CDS'CTV40B (respectisely) which are sister valves to 3CDS'CTVVI A. The previous event root causes were also identihed as failure of elastomer T-nnps which had rolled out of their retaining grooves. These events resulted m AIMntenance procedure changes requinng detailed and exact mstalianon procedures, bench stroking pnor to Installation, and valve cychng post-maintenance to ensure correct T-nng installation pnor to retest.

Neither of these previous failures exactly duplicated the mechanism of the current problem. The 87-043 esent was the result of inadequate overhaul practices, and the 89-011 event was specihcally attributed to a defect on the valve disc. The root cause of the current event appears to be normal wear on the T-nng surface.

LER 89-012 involved a failure of 3RSS'h10V23A wluch is a sister valve to 3RSS'h10V03B. The previous esent root cause was also identihed as a failure of the elastomer valve seating surf ace.

A review of the NPRDS data base identihed eight other Fisher failures and five other Pratt failures similar to those in question. Failures of Fisher and Pratt butterfly containment isolauon valve seating surfaces are not uncommon it, the industry.

EIIS Codes Systems Chilled Water System - Kh1 Residual Heat Removal / Low Pressure Safety injection System - BP Containment Recirculation System - DE Comrionents isolauon Valve - ISV Check Valve - V Vendon l Fisher Controls - F130 Henry Pratt - P340 l

Walworth Valves - WO30 Westinghouse - W351

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