ML19347C800

AO 50-219/74/4:on 740116,while Reactor Shut Down for Maint Work W/Mode Switch in Refuel,Msiv NS03B Failed to Close on Manual Signal.Caused by Pilot Valve Design & Oxide Residue on Valve Spools & Sleeves

ML19347C800
Person / Time
Site:	Oyster Creek
Issue date:	01/25/1974
From:	JERSEY CENTRAL POWER & LIGHT CO.
To:
References
AO-50-219-74-4, NUDOCS 8103040576
Download: ML19347C800 (4)

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OYSTER CREEK NUCLEAR GENERATING STATION i FORKED RIVER, NEW JERSEY 08731 l Abnormal Occurrence Report No. 50-219/74/4 Report Date:

January 25, 1974 Occurrence Date:

January 16, 1974 Identification of Occurrence:

Failure of Main Steam Isolation Valve NS03E to close upon receiving a manual signal to close. This event is considered to be an abnormal oc-currence as defined in the Technical Specifications, paragraphs 1.1SD 6 E.

Conditions Prior to Occurrence:

The reactor was in the shutdown condition with the mode switch in " Refuel".

Reactor coolant temperature was less than 212*F with the reactor head vented.

Description of Occurrence:

In order to minimize airborne radioactivity in the drywell during the plant shutdown while maintenance work was in progress on several relief valves, a negative pressure had been impressed on the reactor vessel via the mechanical vacuum pump through Main Steam Isolation Valves NS03B and NSO4B. At that time, a complete inspection and cleaning of the " spool" valves used in the control scheme for Main Steam Isolation Valves NS03A.

and NSO4A was in progress which necessitated these valves being closed.

After the inspection / cleaning was completed, steps were taken to open these valves and close valves NS03B and NSO4B so that the same preventive maintenance steps could be performed on their associated spool valves.

When the close signal was impressed on NS03B, the valve did not respond.

Subsequent attempts were made to close the valve and on the third try the valve closed. An operator located in the drywell noted that the sulenoid valves which operate the power valve appeared to be functioning properly.

It should be noted that this valve had previously been cycled properly on January 12, 1974 during the plant shutdown at approximately 270 MWe during the full closure test and again later in preparation for a MSIV leak rate test. In both of these cases, valve operation was satisfactory.

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Abnormal Occurrence Report No. 50-219/74/4 Page 2 Apparent Cause of Occurrence:

Pilot valve design is a major factor contributing to the cause of this e c t. euring operation, the operators for both MSIV NS03A and NS03B are supplied by the nitrogen system. However, when shut down, the valve operators are supplied by the station air system due to the drywell being purged and open for access. Prior failures have been experienced with the outside MSIVs which are continuously supplied by the station air system. Past inspections have revealed an oxide / powder film or residue on the valve spools and sleeves. Inspection of this valve revealed the same conditions.

Analysis of Occurrence:

The Main Steam Isolation Valves are intended to provide a means of minimizing fission product release under design bases conditions. Since the redundant valve NSO4B closed in the proper manner, this function would have been performed. This consideration is only important had the valve failed to close during power operation. Since the plant was shut down, the safaty significance of this particular event is minimal.

Since the first instance of valve maloperation in December 1972, all of the pneumatic pilot valves have been inspected and cleaned when plant availability has been such that inspection and cleaning has been possible.

This practice will be continued until such time that the pilot operated valves can be replaced with ones of a different design. It s'iould be recognized that this pilot valve failure was the first of its type for a valve operator normally supplied by N2 It is presumed, therefore, that the nitrogen environment is superior to that supplied by the station air system.

Corrective Action:

The spool valve was disassembled, inspected and cleaned. The valve spcol assembly was observed to operate freely both before and after reassembly.

It was com:1uded that, based upon valve history of operation and use of N2 '

as an operating medium on the inside valves, there was no safety significance with regard to returning the plant to power. The General Office Review Board (GORB) concurred with this conclusion provided the following steps were taken:

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1. Ensure that nitrogen is up to het main pilot valves of the inner MSIV and ensure the spools are free and operable on nitrogen. Before startup, ensure all valves cycle properly.

2. During the six-week cycling test of valves, carefully observe control room response with respect to timing, pressure control, and other pertinent parameters. Consider corrective action and inform GORB should any abnormal conditions occur in testing.

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Abncrmal Occurrence Report No. 50-219/74/4 f Page 3

3. GORB also recommended that Jersey Central Power 6 Light Company continue to proceed with design, procurement of equipment, engineer-ing, and safety evaluation necessary to make system modifications i before the'end of the Spring refueling outage. These modifications are:

(a) Change the valves in the control system.

(b) Change the outside valves from air to nitrogen (unless change of control system obviates need for nitrogen instead of air.

Failure Data:

Manufacturer: Numatics Inc. - Valve Division Type: Pilot Operated Power Valve Nodel: Print Reference No. 917470 and modified by General Electric Company FDI #322/91700.

See Attachment 1.

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, e NEUMATIC PIIDT VALVES ,

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NS03A NS03B NSO4A NSO4B =o

. Cleaned 6 Failure Cleaned 6 Failure Cleaned 6 Failure Cleaned 6 Inspected Failure bh Date Inspected Occurred Inspected Occurred Inspected Occurred Occurred  !-

N/A N/A X Failed to

-eg j 12/30/72 X X N/A X Close - g

12/29/72 g Cause

g Main Pilot ,

Valve .g e 0

N/A X N/A "

4/28/73 X N/A X N/A X 2:

5/31/73 X N/A X N/A X Failed to X N/A Open - g 5/31/73 L Cause. .

Main Pilot b Valve R u

9/11/73 X N/A - - X N/A X N/A 9/30/73 X N/A X N/A - - - -

12/18/73 - - - - X Overtravel - -

reduced load Replaced during slow

<451, for speed clo-maintenance sure test.

Cause:

Test Pilot Valve 1/15-16/74 X N/A X Failed to X N/A X N/A Test Pilot Close Required 1/15/74*

Cleaning

• Found both main and test pilot valve spools free to move in their respective sleeves. NS03B was not inspected in a failed condition, however, because subsequent attempts to close NS03B succeeded; therefore, above results -

of inspection nay be misleading.