ML20052G305

LER 82-029/03L-0:on 820407,crack Found on Main Steam Safety/ Relief Valve S/N 303,2B21-F013E.Probably Caused by Fatigue Due to Tube Vibration.Valve Body Replaced W/Modified Version.All Valves Will Be So Modified at Refueling Outage

ML20052G305
Person / Time
Site:	Hatch
Issue date:	05/06/1982
From:	Sumner H GEORGIA POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20052G299	List: ML20052G298 ML20052G305
References
LER-82-029-03L, LER-82-29-3L, NUDOCS 8205180237
Download: ML20052G305 (3)

Text

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PIRC FORM 366 ' U. S. RUCLE AR REGULATORY COMMISSION j (7 77)

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7 8 60 61 DOCKET NUMBER 68 EVENT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h

! 10121 l Wi th Uni t 2 in refueling. an inspection of oilnt conting tiihn e rin n n r t I i

i lo 13I l welds on all main steam safety / relief valves was Derformed Der LER No. I i

in i4; l50-366/1982-023. A crack was found for body S/N 303, 2B21-F013E. No sig-l jo isi i nificant occurrence took place as a result of this event. Unit 1~has in-l I 10161 i stalled valves of the same design. This is a non-repetitive event. Thist l l0 l7l [ event posed no threat to public health or safety. Welds on all other l 1

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h

,, go [The cause of this event was probably fatigue due to tube vibration. The i g , valve body has been replaced with a body that was modified by the vendor; i

i 2 lThis modification will be made on all valves during the next refueling i

! ,,,,,, outages on both units. l i l1 l4l l l 7 8 9 80 A S  % POWER OTHER ST ATUS DIS O R DISCOVERY DESCRIPTION

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.LER #: 50-366/1982-29 Licensee: . Georgia Power Company Facility Name: Edwin I. Hatch Docket #: 50-366 Narrat.i ve' R eport for LER 50-366/1982-29 4

With Unit 2 in the refueling mode, an inspection of the pilot sensing tube support welds on the main steam safety / relief valves was performed per a . commitment made in LER No.

50-366/1982-023, Rev. O. A crack was found in the Heat-Affected Zone (HAZ) between the valve body wall and the tube support plate-to-body weld on valve body S/N 303. The affected support plate is on the pilot sassembly side of the sensing tube. This valve had been installed as 2B21-F013E and is a Target Rock model 7567F safety / relief valve.

The p il ot sensing tube is welded in between two small plates which are, in turn, welded to the inside wall of the valve body. The purpose of this tube is to provi'de a true pressure to the pilot assembly during valve actuation. At this time, the static pressure in the valve is reduced due to steam flowing through the open valve. The absense of this tube will cause the valve to rescat at a higher pressure but will not affect the actuation setpoint. When the tube came out of body S/N 312, it was swept down the discharge line into the tee-quencher in the torus. The A/E has stated that, due to the small size of the tube, its passage down the discharge line should have caused no damage to the line or to the tec-c uencher. The A/E has postulated a failure mode in which the lottom end of the tube becomes loose at the support and the top end becomes stuck in its boring in the body wall, causing the tube to crimp. If this were to occur, the pilot assembly would not be able to receive. the steam pressure signal, and the pressure relief function of the valve would be inoperable. The vendor analyzed this postulated failure mode and responded- by stating that the probability of occurrence is no greater than the probability of tube blockage by any other means.

LER No. 50-366/1982-023, Rev. O described the failure of tube support welds on valve body S/N 312. As a result of this failure, tube support welds on all Unit 2 valves of this desi gn were inspected. The only failure discovered by this inspection was on ~ valve body S/N 303. Tube support welds on all other Unit 2 valves were found to be acceptable. The vendor stated that, prior to the failure of body S/N 312, only one instance of a pilot sensing tube coming loose had occured. This f ailure was in n Japanese Reactor. The absence of this tube does not affect the manual or automatic air

actuation functions of the valve. Plant Technical Spec i fi ca t i ons section 3/4.4.2 requires nine of the eleven relief valves to be operable. No significant occurrence took place as a result of this event. Unit I has, installed eleven relief valves of the same model. This event posed no threat to public health or safety. .

The vendor has stated that the failure of the tube support welds was probably due to fatigue induceu by lateral vibration of the upper end of the tube. The vendor has proposed a desi gn mod i fi ca ti on in which the two support plates are replaced with a single U-shaped strap welded to the tube and to the valve wall. In additi on, the upper end of the tube is to be tack-welded to the valve wall in order to prevent tube i vibration. The A/E has reviewed and approved this new design. These modifications have been made by the vendor on valve body S/N 312. This body was installed as 2B21-F013E after body S/N 303 was removed. All of these valve bodies will he modified during the next refueling outages for both units.

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