ML19261B621

LER 78-038/03X-2 on 780527:temp Average Dropped Below 541 F. Caused by Lifting of Code Safety Valve

ML19261B621
Person / Time
Site:	Farley
Issue date:	02/22/1979
From:	Hairston W ALABAMA POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19261B612	List: ML19261B611 ML19261B621 ML19261B625 ML19261B630
References
LER-78-038-03X, LER-78-38-3X, NUDOCS 7902280292
Download: ML19261B621 (3)

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[ o l 4 l lthan/ equal to 541 F. Tavg was restored to within T/S limits at 0405. The code safetvl o 5 iv alve failed to rescat after the unit was brought on line, and an attempt was made to l O c l gag the valve to rescat it. T/S 3.7.1.1 requires all main steam line code safety l o 7 l valves be operable. At 0538 unit tripped (high S/G level) and was cooled down to o a Ireplace valve. T/S requirements were met. llealth/ safety of public not affected. I 7 8 9 60 SYSTEY CAUSE CAUSE COMP. VALVE CODE CODE SUBCODI COMPONENT CODE SUBCODE SUSCODE O 9 Ic I cl@ LFjh [pjh I V l A l L l V I E l Y lh [X_lh [3] h 19 20 7 8 9 10 11 12 13 18 SE QUENTI AL OCCURRENCE HEPORT REVISION

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ALABAMA POWER COMPANY JOSEPH M. FARLEY NUCLEAR PLANT DOCKET NO. 50-348 ATTACHNENT TO LER 78-038/03X-2 Facility: Joseph M. Farley Unit 1 Report Date: (Update Report - Previous Report Date 6/26/78)

Event Date: 5/27/78 Identification of Event:

Tavg decreased below technical specification limit of 541F; main steam line code safety valve failed to reseat after lifting.

Conditions Prior to Event:

The unit was in Mode 1 at approximately 8% of . full power. A routine startup operation was in progress. The unit was not on-line.

Description of Event:

At 0400 on 5/27/78, while transferring from turbine throttle v lve control to governor valve control during a unit startup, a pressure transient caused one main steam line code safety valve (Q2N1' !D11A) associated with the B steam generator to lift. The effective increase in load resulted in the Tavg decreasing below 541F. Technical Specification 3.1.1.5 requires that the reactor coolant system lowest operating loop temperature Tavg be greater than or equal to 541F. The Tavg was returned to within the technical specification limits at 0405.

After lifting, the code safety valve failed to rescat. The Emergency Director was notified, and plant personnel were prepared to take the-necessary emergency tion if plant conditions required. The unit was brought on line and the load increased to approximately 20% in order to decrease main steam pressure enough to cause the valve to shut, and also to orevent an uncontrolled cooldown. When this attempt failed, it was decided to gag the valve. Plant conditions were being maintained at 20%

power while gagging the valve when a steam generator level transient resulted in a high-high steam generator level turbine trip-reactor trip.

The unit war cooled down and placed in Mode 5 in order to replace the valve.

The valve was replaced, the valve setpoint was verified, and the unit was returned on-line at 0231 on 5/30/78.

Designation of Apparent Cause:

Decrease in Tavg was due to lifting of main steam line code safety valve. Failure of code safety valve to rescat was due to broken lower adjusting ring locking pin. This allowed the lower adjusting ring to mo e upward and prevent the valve from rescating. The pin was subsequently determined to have failed due to fatigue. The vendor has stated that it

78-038/03X-2 is highly probable that localized stresses were created during machining of the pin which were not apparent during the surface inspection of the pin subsequent to machining. These stresses greatly multiplied the effects of the relatively low applied stresses on the pin during valve operation, and eventually resulted in failure of the pin.

Analysis of Event:

The Tavg was returned to within its limit within the time period specified in Teclnical Specitication 3.1.1.5.

i The code safety valve lifted at its set pressure, 1075 psig + 1%. The requirements of Technical Specification 3.7.1.1 were complied with.

The vendor considers the failure of the pin to be a random failure peculiar only to the Farley Plant and that there is an extremely low probability of a similar failure occurring. Should a similar failure occur, it would not affect the setpoint or the ability of the valve to lift and relieve overpressure. There is a potential for the valve not to seat (similar to the failure which occurred).

This occurrence did not affect the health and safety of the public.

Effect on Plant:

This occurrence resulted in a unit shutdown. The unit was off-line for approximately 69 hours7.986111e-4 days <br />0.0192 hours <br />1.140873e-4 weeks <br />2.62545e-5 months <br />.

Corrective Action:

Reactor power was increased to increase Tavg.

klaut the code safety valve could not be scated, the unit was cooled down, <nd the valve was replaced.

The vendor has modified his inspection procedure to preclude the possibility of a similar failure. The vendor feels that the probability that other pins installed at Farley have similar stresses is extremely remote; however, the existing ring pins will be replaced during the refueling outage.

Failure Data:

Q1N11V0llA is a type 3707RA-RT22, 6 inch safety valve manufactured by the Dresser Industrial Valve and Instrument Division. Dresser has stated that this is the first failure of a ring pin on a 3700 Series Valve.