ML17252A961

Letter Reporting Local Leak Rate Testing Revealing That Four Feedwater Check Valves, Two Main Steam Isolation Valves, One Reactor Head Cooling Check Valve and the Personnel Air Lock Had Leak Rates in Excess of Technical Specifications - Dre

ML17252A961
Person / Time
Site:	Dresden
Issue date:	06/20/1973
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
WPW Ltr. #468-73
Download: ML17252A961 (4)

Text

CommonwaA Edison One First Nati~aza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 Regulatory 50-249

. File ~*

WPW Ltr.#468-_7~---. Dresden Nuclear Power Station R. R. #l - ----- -*

Morris, Illinois 60450 June 20, 1973 Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing U. s. Atomic Energy Commission Washington, D. c. 20545

SUBJECT:

LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #

SECTION 6.6.C.l OF THE TECHN~CAL SPECIFICATIONS.

Dear Mr. Giambusso:

This letter reports a condition relating to the unit, in which local leak rate testing of the primarY containment revealed seven contain-ment penetrations with leakage]? in excess of Technical Specifications limits.

• INVESTIGATION AND CORRECTIVE ACTION The unit was shutdown for. a maintenance outage from March 3, 1973 to May 26, 1973. During that period, primary containment local l~ak rate tests were performed in accordance wt.th Technical Specifications Section

• 4.7.A.2.e. The tests revealed that four feedwater check valves, two main steam isolation valves, one reactor head cooling check valve and the personnel air lock had leak rat~s in excess of Technical Specifications Sec.tion 4. 7.A.f,. The Technical Specifications local leak rate limits are 5% Lto (48) or 2*9.3 _standard cubk feet per hour (scfh) for any one pene-tration or isolation valve and 11.5 scfh at 25 psig for any one main steam isolation valve.

A) Feedwater Check Valves Reference (P&ID M-347)

Initial testing of the feedwater check valves revealed the following leak rates:

Valve No. *Leak Rate ( scfh) 220-62A 1941.5 220-58A 4295.0 220-62B 3136.6 220-58B 144.7 5023

Mr. A. Giambusso June 20, 1973 . .:'

All* four valves;;_were disassembled and repa-i,red by machining the valve seating surfaces. The seat ring and disc were replaced on valve 220-62B because machining did not remove all the irregularities in its seating surfaces. These check valves have two seating areas: one consists of the valve disc and seat ring and the other is a seat ring to valve body seal. The majority of the leakage through the valves was determined to be via the seat ring to valve body seal. Because of similar problems with the Unit 2 feedwater check valves, a modification was performed on these valves whereby the stainless steel body to seat seal ring was replaced with a "Silastic" silicone rubber "O"ring. The stainless steel seal ring requir,es a large differential pressure across the check valve in order to provide a tight seal. Changing to the silicone rubber "O"ring produced a much better seal even at the low leak test pressure of 48 psig. Following the extensive rep~irs outlined above, the valves were reinstalled and retested satisfact-orily. The leak rates exhibited after repair of the valves were as follows:

Valve No. Leak Rate (scfh) 220-62A o.o 220-58A 20.0 220-62B 11.0 220-58B 6.1 I

As previously mentioned, these valves are designed to seal under a high differential pressure condition. Under operating conditions, the valves would experience this high differential in conjunction with a water seal on the valve seating surfaces thereby reducing leakage through the valves.

B) Main Steam Isolation Valves (Reference P*ID M-345 The initial leak test of MSIV 203-2C revealed a leakage throug~

the valve of 49.0 scfh. The valve was disassembled and its seating surfaces*

refinished under the supervision of the valve manufacturer's technical representative. After repair of the valve, a subsequent leak test showed the combined leakage through MSIV 203-2C and MSIV 203-lC to be only 1.6 scfn.

Valve 203-lC is located in the same steam line as 203-2C and is between the reactor vessel and MSIV 203-2C. Therefore, MSIV 203-lC would be the limiting leak rate in an accident situation and leakage through this valve was well within Technical Specifications limits.

Main Steam Isolation Valve 203-2B exhibited an initial leak rate of 29.224 scfh. This valve was repaired in the same manner as MSIV 203-2C.-

and retes_t_e_d.____TJ:u~. re t~s_t _showed the combined leakage through MSIV 203-2B and MSIV 203-lB to be 4. 847 scfh. Leakage through MsIV 203-.lB would be -the_

limiting leak rate for the "B" steam line in an accident situation.

C) Reactor Head Cooling Check Valve 205-2-7 (Reference P*ID M-357)

The initial leak test of reactor bead cooling check valve 205-2-7 showed a leak rate of 254.8 scfh. The valve was disassembled and repaired by lapping the disc. The valve was then reassembled and retested. The leak rate for valve 205-2-7 after repair was only 0.3 scfh.

Mr. A. Giambussa'!';

e -* June 20, 1973 A_s_ ~ith all ~~ck valves, Jhe *-~eactor'.'he~d __coQ_ling check valve is designed--to seal uridera high differential pressure'condition. Also, motor operated valve 205.-2-4 -.which is immediately downstream of_ the check valve exhibited no measurable :i_ea~age. * , ,:

D) -Personnel* Air Lock The initial leakage from the personnel air lock of 52.7 scfh was determined to be via the handwheel shaft seals. After tightening the seal packing glands, the lock was retested and showed no measurable leakage.

The packing in the air lock handwheel shaft seals will be replaced during the next unit shutdown. In addition, a suryeillance routine will be established to renew the packing in these seals each operating cycle so as to prevent a recurrence of this problem.

Sincerely,

• 1N-~ J. Vii\~

fl .n W. P. Worden

.f" '-Superintendent WPW:do

UNIT 3 PRIMARY.CONTAINMENT PENETRATIONS EXHIBITING EXCESSIVE LEAKAGE

INITIAL - LEAKAGE AFTER PENETRATION 11.EAKAGE (scfh) REP.AIR REPAIR (scfm) .

Personnel Air Lock 52. 771 Tightened Stem Seals o.o Main Steam Valve 203-2C 49.001 Lapped Seat. 1.615 Reactor He~d Cooling Valve 205-2-7 254.810 Lapped Disc 0.256 Feedwater Valve 220-62A 1941.550 Machined Seat " Disc 0.0 Feedwater Valve 220-62B 3136.600 Replaced Seat " Disc 10.999 Feedwater Valve 220-58A 4295.700 Machined seat-".Disc 20.0 Feedwater Valve 220-58B 144.700 Machined Seat *" Disc 6.057 Main Steam Valve

• 203-2B 29.224 Lapped Seat . 4. 847

1) Leak £ate limit for any one penetration or isolation valve is 5% Lto (48) or 29.3 scfh.

2) Leak rate limit for MSIV' s is 11. 5 scfh @ 25 psig for one valve.

3~, All four feedwater check valves were modified by replacing stainless steel seat to body seal ring with "silastic" silicone vubber "O"ring.