ML20058K493

Informs That Isolation Valves Installed in Main Steam Line of BWR to Assure That Any Significant Release of Fission Products Retained within Containment Sys in Event of DBA, Particularly,Loca

ML20058K493
Person / Time
Site:	Millstone, Monticello, Dresden, Oyster Creek, Pilgrim, Quad Cities
Issue date:	04/03/1973
From:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
To:	Dienhart A NORTHERN STATES POWER CO.
References
NUDOCS 9102110322
Download: ML20058K493 (10)

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l TocEet,4s UNITED STATES j

ATOMIC ENERGY COMMISSION

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April 3, 1973 L

Docket No. 50-263 I

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Northern States Power Company ATTN:

Mr. Arthur V. Dienhart i

Vice President of Engineering 1

414 Nicollet Mall 4

Minneapolis, Minnesota 55401 Centlemen:

To assure that any significant release of fission products is retained within the containment system in the event of a design basis accident such as a loss-of-coolant accident, isolation valves have been installed in the main steam line of boiling water reactors (BWR). To achieve high reliability of containment isolation, two valves are installed in series in each steam line.

7 Proper closure of either of the two valves will prevent release of fission products by this route from exceeding 10 CFR 100 guidelines in the event of an accident. To achieve the required s

high reliability, it is necessary that each valve have a high reliability.

A review of the reliability to close on demand of the main steam isolation valves (M51Vs) for the larger BWRs has been conducted.

It is concluded that supplemental action is requirad to improve -

the reliability of the MSIVs to close on demand.

i A summary of the failures of the MSIVs is included in Attachment A.

Experience at the four older BWRs *s not included because of the significant differences in valve configuration. A review of the sixteen reported failures to close shows that in all cases, except one, the f ailures were caused by a sticking pilot valve in the MSIV pneumatic control system. Events have also been reported of slow MSIV closure and malfunctions during exercising which have been caused by sticking pilot valves. It is our understanding that the sticking pilot valves are all of the same design and provided by one vendor. Based on the reported experience, correction of.the cause of pilot valve sticking should be a first priority item in improving MSIV closure reliability.

(for distribution and concurrence see central file' copy)

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9102110322 730403 CF ADOCK 05000263 CF a

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1 i April 3,1973 Corrective action has been taken at some reactors to eliminate some of the causes of pilot valve failure.

During 1970 and early 1971, Dresden 2 sustained nine occurrences of MSIV failure to close. The corrective actions taken at Dresden 2 and 3 are described in detail in Attachment B.

In summary the following actions were implemented:

1.

The clearances between the piston and the cylinder walls of the pilot valve were increased.

2.

The operating gas was changed from air to nitrogen on both the inboard and outboard valves to compensate for the higher leakage of gas into the drywell caused by item 1.

Changes were made in the gas handling system to improve gas quality. The pilot valve temperature environment was found to be in excess of the design temperature and was corrected.

In addition, a change was made at Dresden 2 and 3 to the MSIV slow closure system such that the fast closure pilot was exercised during _.

each twice-weekly exercising of the MSIVs. In the two-year interval since the above changes, no failures of the MSIVs to close have been reported.

Based on information provided by telephone, all but one of the large operating BWRs have pistons in the pilot valve with increased clearances, and all but two have converted the operating gas, on at least the inboard valves, to nitrogen. It may be noteworthy that all four of the most recent failures were of outboard valves which were operated by air.

We conclude from the experience to date that poor quality operating gas is the most probable cause of most of the MSIV f ailures to close. A temperature environment higher than the design rating of-the pilot valve cannot be climinated as a possible contributing cause. Based on the experience to date, we conclude that design improvements to eliminate pilot valve sticking are necessary at most BWRs to assure that MSIV valve closure reliability is improved to the level required by the safety function of this equipment.

It is requested that you provide a description of any changes planned for your reactor to upgrade the reliability of MSIV closure. If no changes are planned, provide a discussion of the features of your system which you believe causes it to be more reliable than is indicated by the general experience of Attachment A.

l 3-April 3, 1973 l

To aid in our current and future evaluation of MSIV performance, the

- following information is requested:

The minimum clearance between the pilot valve piston and a.-

the pilot valve cylinder.

b.

The specifications for the cleanliness of the MSIV operating gas (es), a description of the means for achieving these specifications including the particle size rating of particulate filters, and the nearts used to monitor that the specifications are being achieved.

The temperature environment of the MSIV pilot valves.

c.

d.

A description of the preventive maintenance program for the MSIV pneumatic control system.

r The above information is requested in 90 da'ys and should be submitted as 1 original'and 39 additional copies'.

Sincerely, j

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,,Donald y'Skovholt Assistant Director for Operating Reactors Directorate of Licensing' 1

Enclosure:

1.

Attachment A - MSIV Failure-To-Close Experience 2.

Attachment B - Corrective Actions J' to Assure MSIV Operability cc: See next page I

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Cerald Charnoff l

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Shaw, Pittman, Potts, Trowbridge & Madden 910 - 17th Street, N. W.

Washington, D. C.

20006 1

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" Howard J. Vogel, Esquire Knittle & Vogel 814 Flour Exchange Building l

j Minneapolis, Minnesota

$5415 i

Steve Cadler, P. E.

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2120 Carter Avenue St. Paul, Minnesota 55108 i

Harriett Lansing; Esquire Assistant City Attorney l

City of St. Paul 638 City Hall i

St. Paul, Minnesota 55102 1

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j Ken Dzugan i

Minnesota Pollution Control Agency l

717 Delaware Street, S. E.

4 Minneapolis, Minnesota 55440 4

Warren R. Lawson, M. D.

Secretary & Executive Officer State Department of Health i

717 Delaware Street, S. E.

Minneapolis, Minnesota 55440

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1 Environmental Library of Minnesota i

1222 S.E. 4th Street i

Minneapolis, Minnesota 55414 l

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i ATTACRMEhT A MAIN STEAM ISOLATION VALVE FAILURE-TO-CIASE EXPERIENCE Date Reactor Number of Failures Component. Failure i

5/8/70 Dresden 2 4

Pilot valves 12/4/70 Dresden 2 4

Pilot valves t

1/22/71 Dresden 2 1

. Pilot valve f 8/1/71 Millstonet 1

Pilot valve 11/16/71 Oyster Creek 1

Dash pot 5/13/72 Monticello 1

Pilot valve 11/15/72 Quad-Citiesi 1

Pilot valve 11/29/72 Pilgrim 1

Pilot valve 12/3/72 Oyster Creek 1

Pilot valve 12/29/72 Oyster Creek 1

Pilot valve e

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ATTACHMENT B I

REPORT NO. 7 CORRECTIVE ACTIONS TO ASSURE MAIN STEAM LINE ISOLATION VALVE OPERABILITY March 17, 1971 f

Commonwealth Edison Company

l D-2 REPORT NO. 7 l

COMMENT A detailed report of corrective actions taken to assure main steam line isolation valve operability.

Background

i On several occasions between April 30, 1970 and February 1,1971 tte main steam isolation valves (MSLIV's) installed in the Dresden 2 '

Nuclear Power Plant failed to operate due to sticking of the pneu-matic valves which control the flow of air to a cylinder operator to open and close the MSLIV's.

The pneumatic valves in use during April and May 1970 had small clearances and were highly sensitive to contaminated air and exces-sive heat. Test thermocouples installed on the outside of the pneumatic valve housings showed that in operation the valves installed in the drywell reached approximately 129*F and valves in the steam tunnel reached 175*F.

Inspection of the valves showed the lands of the spools were significantly discolored and coated with a varnish-like substance. All spools were very sticky in the sleeve.

When the spools were washed in solvent and cleaned up, they freed up considerably, but not as free as manufacturer repre-sentatives recommended for a nonnal spool and sleeve. Therefore, it was concluded that two problems were being encountered. First, there was contamination getting into the valve in sufficient quantity to cause the spools and sleeves to stick and bind.

In addition, some of the spools and sleeves were binding mechanically because of the heat.

Either one of the two problems would render a valve of the type used at that time inoperative. As discussed in the Special Report on the June 5 incident, Supplementary Informa-tion, steps were taken to replace all the pneumtic valves with higher clearance type valves and also additional air conditioning equipment was added to the steam tunnel to reduce temperatures in the area of the valves.

In early December 1970 four main steam isolation valves failed to close and one closed out of tolerance <!uring a schedule surveillance test. Upon inspection of be relot valves the same sort of contamin-ation on the spnol caused the sticking. The source of the contamin-ation has been traced to the air supply compressors. These are oil lubricated compressors. After a significant period of operation the oil leaks into the air supply.

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D-2 rep 0RT NO. 7 I

Corrective Action a

The following corrective actions will be taker. to eliminate the MSLIV actuation problems:

1.

The clearance between the sleeve and spool has been increased I

and additional air cooling has been installed in the steam tunnel to eliminate binding caused by high temperature.

2.

The instrument air system for both Dresden 2 and 3 has been thoroughly cleaned to avoid entrainment of dirt and oil.

I' 3.

Ihree different plans of action are being undertaken to ensure oil and other contamination are not introduced back into the MSLIV pneumatic supply, a.

The valves inside the drywell will take their suoply from a pumpback system. This system consists of two air com-pressors, filters, separator and dryer, a 250 gallon receiver, and associated piping, valves, controls and instrumentation. The drywell pneumatic supply system takes suction from the drywell atmosphere, compresses and cleans the gas and stores it in the 250 gallon receiver at a nominal 100 psig. The receiver discharges to' the equipment in the drywell which require motive gas. -This system provides'a source of clean gas for use in all pneumatic equipment thus limiting the effects of dirt and oil on the operation of MSLIV's. This system is being installed during the current outage. The system will be connected to the presently installed pneumatic system to supply all the equipment within the drywell requiring motive gas. The back up supply is nitrogen from the Drywell Atmosphere Make-Up System. A copy of the P&ID for the Drywell Pneumatic Supply System is attached.

I b.

As an interim solution the MSLIV valves located.inside the steam tunnel will take their motive supply from four liquid nitrogen storage tanks. The liquid nitrogen system provides j

a constant regulated pressure of 115 psig to the supply system. The system is capable of continuous delivery of 800 scfh or 1850 scfh for si. ort periods at pressures up to 150 psig.

Each station comprises of:

1) filter, 2) a fin air vaporizer, 3) console with controls, 4) appropriate valves and pressure regulator, 5) liquid nitrogen tanks each having 3650 scfh capacity, and 6) pressure switch and low pressure annunciator in the control room.

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0-2 REPORT NO. 7 i

l This system will be replaced by an oil-free non-lubricated compressor.

The instrument air will be separated from the service air compressors and two non-lubricated compressors, redundant filters, dryers, air

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receivers, installed into the instrument air supply to form a com-pletely separated oil-free system. The Dresden 2 and 3 instrument -

air supplies will be identical and " cross-tied" to provide redundant systems for both plants (each system has the capacity to supply both units). As the source of oil was being introduced into the system by the oil lubricated compressor, the installation of the new com-pressors will eliminate the source of contamination..

It is concluded that the corrective action described above will'elim-inate any further MSLIV problems. This conclusion is substantiated by the number of BWR's in operation with this type of valve without any actuator problems. The only difference between the successfully operating valves in these BWR's and Dresden is the air supply system.

After the completion of the corrective action described above, the plant will return to a normal technical specification surveillance program.

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