ML17252A867

Letter Regarding a 04/26/1973 Occurrence Concerning the Failure of Number 22 Main Steam Line Isolation Valve to Close in Response to a Manual Signal Initiated by the Control Room Operator - Indian Point Unit No. 2

ML17252A867
Person / Time
Site:	Indian Point
Issue date:	05/04/1973
From:	Zarakas P Consolidated Edison Co of New York
To:	O'Leary J US Atomic Energy Commission (AEC)
References
Download: ML17252A867 (3)

Text

.... ' . \ William E. Caldwell, J

• Vice President Consolidated Edison Company of NewYork. Inc. 4 Irving Place. New York.NY 10003 * ' Regulatory . --__ :_--::---..::7-

--Telephone (212) 460-5181 Mr. John F. O'Leary, Director Directorate of Licensing U. S. Atomic Energy Commission Washington, D. c. 20545

Dear Mr. O'Leary f May 4,

1973 Re: Indian Point Unit No. 2 Docket No. 50-247 This report of an Abnormal Occurrence is submitted in accord-ance the requirements

• of Section 6.6.1 of the Unit No. 2 Technical Specifications:

On April 26, 1973 at approximately 8:30 A.M., Number 22 Main Steam Line Isolation Valve_ failed to close in response to a manual signal initiated by the Control Room Operator.

The signal was initiated for the purpose of testing valve closure time. At the time of the occurrence,*

the reactor was shutdown with all control rods inserted.

The Reactor coolant System pressure and temperature were 2235 psig ttnd 525°F, ively, and the reactor coolant boron concentration was 1790 ppm. With this concentration of boron and all control rods fully inserted, the reactor was subcritical by at least 10 percent delta k/k. Initial investigation of the occurrence revealed that both of the solenoid-operated air cylinder exhaust valves (two in parallel) failed to open. The remaining three Main Stearn Line Isolation Valves were also tested and these results were found to be satisfactory.

Howeve:i:-, it was ... noted that only one of the two air exhaust solenoids associated with Nos. 23 and 24 Main Steam Line .Isola.tion Valves functioned.

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• Mr. John F. O'Leary May 4, 1973 ' -; .; *I Description and Evaluation -of Safety Implications Each of the steam generators is equipped with an isolatio.n valve in its main*steam line. These valves contain a free swinging disc which is normally held up *out of the main steam flow PC),th by an air piston. The isolation valves are automatically closed upon receipt of a signal from the steam line break protection system as described in 'section 7 of the FSAR. They may also be closed by manual action. The safety implications of this occurrence stem primarily from the fact that four out of sixteen solenoid valves failed to properly, and not the fact that one isolation valve failed to close. This is so because: (1) there was no actual *steam break, and it was, therefore, not essential that the isolation valve close, (2) the safety presented in Section 14.2.5 of .the*FSAR shc:iws that the cor:<e is protected*

even if one of the four isolation valves should fail to close, and (3) a repeat failure of four solenoids, in a certain combination, could result in two.steam line isolation valves* not closing in response to *an actual pipe rupture signal. If the postulated pipe rupture was a*large *one downstream of the isolation.

valves, the related safety effect eould be signifi<;ant.

Determi*nation of* cause Each of the four subject solenoid valves was thoroughly exam-. ined to determine the cause of its malfunctioning.

On the pasis of these examinations, it has been concluded that *the cause was the same in each case, and that each of the functions resulted from binding of the l.inkage connect:i,ng . the solenoid armature to the valve it is intended to operate. The binding was caused by a. combination of hardening of the lubricant used at the several points associated with each and *contamination of the 'lubricant through . .... .. long-term exposure to the dust-laden air commonly caused to exist at a site .*. Corrective Action to Prevent Recurrence As a means for preventing linkage associated with each of the four subject solenoids has *been thoroughly cleaned of all In addition,*

the lubricant is to be removed from the remaining twelve solenoid valves prior to initial criticality of the reactor.

, ** *J * .... . *;' * * .Mr. John F. O'Leary May 4, 1973 A reevaluation as_to the need for lubrication has been made, and we have concluded that none is required in this particular application.

The solenoid linkage will, fore, be left free of lubricant to prevent recurrence.

To assure that the potential for similar_malfunct:ions does not exist elsewhere within the Unit facility, we are currently reviewing the records to determine in what other applications this type of solen9id has been employed.

In any case where the same or similar solenoid is used, we will take steps to remove all traces of lubricant.

Each of the solenoid valves will be. thoroughly tested to insure its operability following the above described ive and preventive maintenance efforts. In addition, periodic inspection of solenoid valve linkage is to be incorporated in our preventive maintenance program. conclusion Although, as stated previously, a malfunction of four of the. sixteen solenoid valves associated with the Unit No. 2 main steam isolation valves carries with it safety implications, we do not believe the probability of recurrence is significant.

The cause of these particular malfunctions was identified, and the principal ingredient necessary to cause repetition, i.e., the lubricant, either has been eliminated or will be within the next several days. Our Nuclear Facilities Safety Committee reyiewed the circumstances relating to this abnormal occurrence and has approved the corrective measures instituted as a . result thereof. , ' '. , .. **Pet arakas Assistant Vice President