U-603225, Provides Closure of Util Commitments Re Ci Cv Noted in Previous Ltr to Nrc.Basis for Expecting Valves to Remain in leak-tight Condition Throughout Operating Cycle & Basis That Justifies Not Performing mid-cycle Leak Testing,Encl

Provides Closure of Util Commitments Re Ci Cv Noted in Previous Ltr to Nrc.Basis for Expecting Valves to Remain in leak-tight Condition Throughout Operating Cycle & Basis That Justifies Not Performing mid-cycle Leak Testing,Encl

ML20212E547
Person / Time
Site:	Clinton
Issue date:	09/20/1999
From:	Mcelwain J ILLINOIS POWER CO.
To:	Dyer J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
U-603225, NUDOCS 9909270035
Download: ML20212E547 (7)

Text

e lilinois Power Company P.O. Box G78 Chnton. IL 61727 Tel 217 935-8881 x3900

. Fax 217 935-4632 John P. McElwain Chael Nuclear Officer ILLINSIS POWER m 3225 1 A.120 An llunova Company September 20, 1999 Docket No. 50-461 Mr. James E. Dyer Regional Administrator Region III U.S. Nuclear Regulatory Commission 801 Warrenville Rd.

Lisle, IL 60532-4351

Subject:

Clinton Power Station Closure of Commitments Regarding Leak Testing / Leak Tightness of the Feedwater System Containment Isolation Check Valves ,

Dear Mr. Dyer:

After obtaining unacceptable leak rate test results for the feedwater system containment isolation check valves at the beginning of the Clinton's recent extended plant outage (RF-6), Illinois Power (IP) committed to provide a letter to the NRC explaining why, following reworking or modifying the valves to return them to a leak-tight condition, the check valves can be expected to remain leak tight for the duration of an operating cycle. In addition, and notwithstanding that commitment, IP also In' committed to perform leak testing of the check valves during the mid-cycle outage (PO-8) anticipated for Operating Cycle 7. These conunitments were prompted by the fact that unacceptable as-found leak-rate test results had been previously obtained for these valves. .

In light of the significant modifications that were made to the feedwater check , g0) valves and the resultant improved leakage performance that was subsequently demonstrated during the extended plant outage, this letter is submitted for closure of IP's commitments. Pursuant to the first commitment, IP's basis for expecting the valves to remain in a leak-tight condition throughout an operating cycle is provided in the attachment to this letter. With regard to the second commitment, a basis is also provided (in the attachment) that justifies not performing mid-cycle leak testing of the check valves, thus closing this commitment on that basis.

9909270035 990920 PDR ADOCK 05000461 G PDR

r. .

. U-603225

. Page 2

. i It should be noted that in addition to the significant improvements made to the l feedwa'ter check valves during RF-6, an extensive plant modification and associated new licensing basis for the feedwater system containment penetrations was also pursued during

the outage. Specifically, IP installed a feedwater leakage control system (FWLCS) that is l designed to provide a water seal for the feedwater penetrations under accident conditions. l l

The license amendment request to support use of the new FWLCS, however, is currently being reviewed by the NRC. Until the FWLCS is released for operation (after NRC approval of the associated license amendment), the feedwater check valves continue to l provide the required containment isolation capability for the feedwater penetrations per ]

the current licensing basis for CPS. j l

Sincerely yours, I l i l

l ohn P. McElwam ChiefNuclear Officer l

TBFJkrk l

cc: NRC Clinton Licensing Project Manager NRC Document Control Desk NRC Resident Office, V-690 .

D. Zemel, T-31Z l l

I

'i

'Q i

[;;

r

' Auachment

. to U-603225 Page 1 of 5 Background-During the initial ten years of plant operation at Clinton Power Station (CPS), periodic leak testing of the containmcnt isolation check valves in the feedwater lines at CPS yielded repeated unacceptable as-found results. That is, although acceptable as-left air leak test rates could be consistently cbtained prior to restart from each plant outage, acceptable as-found test results could not always be obtained during each subsequent outage.

Consequently, IP continually pursued improvements to the valves' leakage performance.

Several modifications to the valves, as well as improvements in the reworking techniques and leak testing methodology, were implemented over the course of several outages, leading up to the most significant actions taken during the recent, extended plant outage at CPS (RF-6).

As further explained below, modifications implemented for the feedwater check valves during RF-6 have improved the leakage performance of these valves such that the leakage performance issue with these valves is considered resolved. However, prior to completion of the modifications but immediately after unacceptable as-found leak test results were obtained at the beginning of the outsge, the NRC expressed concerns about the valves' capability to achieve repeated, acceptable, as-found leak test results. In response to those concerns, and on the basis of the modifications being implemented for the valves and the consequent improvements in leakage performance expected to be gained, IP committed

_(per References 1 and 2) to provide a letter to the NRC to provide assurance that the valves' leakage performance will not significantly degrade during the forthcoming (i.e.,

current) operating cycle (Operating Cycle 7). Further, and notwithstanding this commitment and its basis, IP also committed (per References 2 and 3) to perform leak l

. testing of the check valves during the mid-cycle outage (PO-8) anticipated for Oprating {

Cycle 7. The information below is provided to address and close these commitments. '

Actions Taken to Assure Leak Tinhtness of Feedwater System Containment Isolation Check Valves l

At CPS, the feedwater lines are part of the reactor coolant pressure boundary as they penetrate the containment and drywell and connect to the reactor pressure vessel. Each of the two feedwater line containment penetrations incorporates three containment isolation valves in series. The isolation valve inside the drywell is a simple check valve

- [lB21-F010A(B)] located as close as practicable to the drywell wall. Out:ide the primary containment is an air-assisted check valve [lB21-F032A(B)] located as close as practicable to the containment wall.' Farther away from the primary containment is a motor-operated gate valve [lB21-F065A(B)]. This arrangement is designed such that, should a break occur in the feedwater line, the check valves prevent a significant loss of reactor coolant inventory and offer immediate isolation.

' Each air-assisted check valve is " power-assisted" closed. Such closure is capable of being initiated (manually or automatically) cia the containment and reactor vessel isolation control system (CRVICS).

This " power assist" is not designed to overcome feedwater flow through the valve since it is desirable to

' maintain reactor coolant makeup from the feedwater system when available and required.

FL

, Anachment

' to U-603225 L , ,

Page 2 of 5 l During a postulated loss-of-coolant accident, it is desirable to maintain reactor coolant makeup from all sources of supply, including the feedwater system. For this reason, the ,

outermost valve [i.e.,1B21-F065A(B)] does not automatically isolate upon a signal from the protection system. However, this valve is capable of being remotely closed from the

, control room to provide long-term leakage protection when continued makeup from the feedwater source is unavailable or unnecessary.

. The current CPS licensing basis requires the feedwater penetrations to be subject to a Type C leak test (air test performed at 2 P.) pursuant to Technical Specification Surveillance Requirement 3.6.1.3.8 and 10CFR50, Appendix J. In addition, since the feedwater lines traverse secondary containment without terminating, leakage through l these penetrations is considered to be secondary containment bypass leakage for purposes of primary containment leakage accounting. The combined leakage rate for all secondary containment bypass leakage paths is required to be less than or equal to 0.08 L.. Thus the feedwater containment isolation valves are subject to stringent leak rate acceptance '

criteria.

l As discussed in LER 96-013, Rev.1, the four feedwater containment isolation check valves [lB21-F010A(B) and IB21-F032A(B)] did not pass the required local leak rate testing that was performed at the beginning of the most recent refueling outage. The subsequent troubleshooting, maintenance, and modification activities that were completed during the extended outage resulted in a better understanding of the critical failure mechanisms involved and a substantially improved material condition of the valves.

The inboard feedwater containment isolation check valves [lB21-F010A and i: IB21-F010B] are 18-inch non-slam type tilting disc check valves manufactured by the

' Anchor / Darling Valve Company. These two valves are provided with a resilient seat to improve their leak tightness at low differential pressures.

Following the above mentioned testing failures, the operational, maintenance, failure, and design histories for the IB21-F010A and IB21-F010B valves were reviewed. From this investigation, it was determined that the major failure mechanism involved with the unsuccessful local leak rate testing was the temperature and pressure stressors that occurred during the extended period of time (during the operating cycle preceding the current shutdown period) for which the reactor remained hot and pressurized, without

. flow through the feedwater lines. These stressors led to the premature failure of the resilient seats of these valves. The rework of the inboard check valves consisted of replacing the resilient seats. Actions to preclude recurrence of similar events included revising plant procedures to ensure that, following certain plant transients, the resilient seats for these valves will be evaluated to determine if early replacement is warranted.

t l

t

('

Attachment to U-603225 Page 3 of 5 L The ou'tboard feedwater containment isolation check valves [1B21-F032A and IB21-l F032B] are 20-inch non-slam type tilting disc check valves and were also manufactured by

the Anchor / Darling Valve Company. These valves have metal-to-metal seating and are provided with an actuator assembly that utilizes air pressure to assist valve closure upon receipt of a containment isolation signal.

'As noted above, during the recent extended refueling outage an extensive troubleshooting

and modification program was performed for these valves. These activities resulted in a complete redesign of the outboard feedwater check valves such that only the valve body

and the basic disc geometry were not changed. The number of actuators was increased l from one per valve to two per valve. The number of air cylinders was increased from one l per valve to four per valve. The actuating air pressure applied to the air cylinders was i increased from 75 to 100 pounds per square inch. To improve disc-to-body seat alignment, each actuator shaft is now one solid piece instead of a two-piece design. The

disc now rotates on the shaft instead of the shaft rotating in the body bushing. This also improves the disc-to-body seat alignment. Actuator torque is now delivered on both i sides of the disc instead of only one side, and it is applied directly to the disc web through l

two " dog ears" on each disc bushing. The new " dog ear" design eliminates the excessive mechanical clearances inherent to the previous single key-to-shaft configuration.

Collectively, these changes represent a substantial improvement in the disc closing force delivered by the actuator and in the ability to achieve repeatable disc-to-body seat alignment. Prototype testing as well as post-installation testing proved that the disc responded well to the new actuator system. The as-left local leak rata test results were also very good. The intrusiveness of the testing program and the scope of the actuator redesign provide assurance that the root cause of the repetitive failures of IB21-F032A and IB21-F032B has been adequately addressed.

Additional assurance of repeatable performance is gained by a comparison to a similar valve installation. A survey ofindustry information identified a Region 3, BWR-5/ Mark H plant with an almost identical outboard feedwater check valve configuration. This utility uses Anchor / Darling tilting disc check valves very similar to the ones installed at CPS.

Their valves also use a single piece actuator shaft design and drive the disc with a large air-powered actuator on each side of the valve. The outboard feedwater check valves for this plant have a good local leak rate testing history. This m' formation supports the assertion that the improvements during the most recent refueling outage will improve the long-term leak rate testing performance of IB21-F032A and 1B21-F032B.

Local leak rate testing was successfully performed on all four of the feedwater check valves following the maintenance activities described above. This testing was completed in January and March of 1997. Following these modifications and repairs the feedwater lines were returned to normal operating status consistent with the plant shutdown conditions. This included using the feedwater lines in the RHR shutdown cooling mode flow retum path to the reactor pressure vessel.

l l

4

' Attachment

, to U-603225

, Page 4 of 5

,The feedwater lines (including the four containment isolation check valves) continued to

. be used in this manner for approximately the next 18 months. In September and November of 1998 the local leak rate testing for the feedwater containment isolation check valves was re-performed to keep the Surveillance Requirement interval current and also as part of the post-modification testing requirements associated with the installation of the feedwater leakage control system modification. All four check valves passed this testing. The long period of operation (approximately 18 months) and the successful testing that followed demonstrated that the repairs and modifications performed earlier .

- during the shutdown period were successful.

. The activities described above constitute major improvements to the material condition of the feedwater penetration isolation check valves and a greater understanding of the failure mechanisms responsible for previous leak rate testing failures. As a result, satisfactory isolation capability of the feedwater penetrations has been sufficiently demonstrated to support continued plant operation.

Notwithstanding the recent advances and improved performance of the feedwater penetration isolation valves, IP has elected to pursue the next step toward an even greater enhancement of the isolation capability of the primary containment feedwater penetrations.

This is being accomplished by the installation of a modification (the feedwater leakage control system (FWLCS)] that provides a means to eliminate post-accident containment

. atmosphere leakage through the feedwater penetrations by sealing the isolation valves with water. All of the necessary piping, valves, and equipment to support this water-sealing

- function were installed and satisfactorily tested during the most recent outage period.

Given that changes to the Technical Speci6 cations are needed as a result of the FWLCS, IP submitted an application for amendment of the CPS Operating License on October 23, 1998. As such, operability ofthe FWLCS, and thus the associated improvement to the isolation capability of the feedwater penetration isolation valves, is currently pending NRC approval of the associated license amendment request.

l Based 'on the improvements made during the most recent shutdown period, and the 1 expectation that the FWLCS license amendment request will be approved by the NRC in the near future, IP no longer intends to perform leak-rate testing of the feedwater penetration isolation valves during the mid-cycle outage (currently scheduled for April of 2000).-

References }

1. . IP Letter U-602670 dated December 9,1996 (

Subject:

Clinton Power Station  ;

Startup Readiness Action Plan).

{

l

2. IP Letter U-602752 dated July 2,1997 (

Subject:

Response to Confirmatory Action Letter dated January 9,1997). {

4 I

i

e.

f --

l-..

l

, Attachment

.. to U-603225 i Page 5 of 5

.3, 'IP Letter U-602768 dated July 24,1997 (

Subject:

Clinton Power Station-Unit 1, l Licensee Event Report No. 1996-013-01).

l.

I-l l

f l

a i

l 1

I l

p

,s. -

?

l-