ML20246C088
| ML20246C088 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 06/21/1989 |
| From: | Sterud C CONTROL COMPONENTS, INC. |
| To: | Salvo J YANKEE ATOMIC ELECTRIC CO. |
| References | |
| REF-PT21-89 NUDOCS 8907100238 | |
| Download: ML20246C088 (2) | |
Text
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N 21833 June 21, 1989 TIMii_(fen Mr. Jce Salvo sr. Mechanical Engineer Yankee Atomic Electric Co.
580 Main' Street Bolton, Mass.
01740
Subject:
Atmospheric Dump Valves at Seabrook (NHPEL)
$/N 21274-6 & lo potential Signiff. cant Deficiency Under 10CFR-21 Dear Mr. Salvos i
We are hereby notifying you of e. potential significant deficiency tha.t may be reportable under the recp.tirements of 10CFR-21.
We are not re-porting this directly to the Nu: lear Regulatory Commission (NRC).
We at CCI do not have the systers expertise that would permit us to de-cide if this is a significant deficiency.
However, because of the NRC's interest and their prior contact for information regarding plants with a similar design, we have sent a copy to Rich Label of the Events Assessments group in Washington D.C.
ccI has completed it's analysis of the Atmospheric Dump Valves for
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your site.
This analysis wan prompted per your telecon with H.L.
Miller on 5/26/89.
The analysis has been aimed at calculating a worst case bonnet pres-sure after the pilot valve has bean cpened.
If the leakage by the piston ring is larger than the ab!.11ty of the pilot plug to drain the bonnet, excessive pressure remaint; in the bonnet.
If the pressure is g
too high, the actuator cannot overcone the f orces holding the main plug on the seat.
Our calculation indicates that the atnespheric dump valves at your site may fail to open.
The cause of the failure is speculative.
But i
high bonnet pressure results, which does not permit the actuator to open the valve.
That is; the actuator force with the current air pressure supply available is not large enough to overcome the pressure force holding the plug closed, j
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2,' 2 Mr. Jos salvo
.*-.Y4nkee Atomic Electric Co.
As noted above, the cause of failure is not known.
not be made to occur on denand. and in fact appears randomly.
Our The condition can-piston ring cavity and preventspeculation is that pipe scale and other dirt p the ring from sealing.
Until the re-cessive bonnet pressure existed. cent testing in March 1989, we have been The resolution to th% problen is to increase the pilot valve capac-ity.
This requires and a new stem tc :aal the pilot valve when closed..vork of the plug to enlarg A second change is to use a two (2) piece wedge style piston ring te assure a good seal.
This changt the pilot capacity but adds extra margin.is not as significant as increasing In addition to the changes of valve tri:t, the actuator spring _ lead should be reduced.
Currently with the valve plug on the seat.the actuators spring is 2800 lb load The spring has. a 190#/ inch rate.
We proximate 160#/ inch rate.weuld change the spring load to 1520 lb load on the extra margin on actuator differential pressure required to openThe valve.
the The analysis indicates that the vulve an in, will open with 66 psi ac-tuator differential pressure if the pinten ring is sealing within de-sign.
If the piston ring leak:s significantly as in the worst case
- scenario, the actuator differe ntial would be 149 psi to open the valve.
Please contact myself, Ron Adams, Larry Stratton or Herbert Miller at if you should have any queuuions or need any additional informa-CCI tion.
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Sincerely, CONTROL COMPONENTS INC.
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