ML19317G924
| ML19317G924 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/19/1974 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19317G917 | List: |
| References | |
| NUDOCS 8004020579 | |
| Download: ML19317G924 (2) | |
Text
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- MENTO MUNICIPAL UTIL~' DISTRICT - O 6201 S Stree!, Box 15830, " etmentr. Calif:rnia 95813: (916) 452-3211 1 hhtl.Yu f
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I June 19, 1974 e
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Mr. R.' H. Engelken.
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- ,[55 Directorate of Regulatory Operations Regien V
" ' En U. S. Atomic Energy Commission
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Post Office Box 1515
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Berkeley, California 94701 Rancho Seco Nt. clear Generating Station No.1 Heat System Stop Check Valves DHS-015 and DHS-016
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Decr Mr. Engelken:
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During the hot functional testing (HFT) program at Rancho Seco 'uclear Generating Station No.1, the decay heat system stop check valves DHS-015 and DHS-016 stuck in the closed position.
The valves would not open using normal operating procedures.
In accord-2;.;
ance with our Quality Assurance procedures, this nonconformance has
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been_ reviewed and has been determined to be a reportable "signifi-cant deficiency" as defined by 10CFR50.55(e).
Description of Defici v: The stop check valves are ten inch, 15000, stainless steel valves, Mark No. 127GS, manufactured-
.by Velan Engineering Limited, Montreal, Canada.
The internal plug is of the piston type with a spring closing action.
The valves also have a twenty inch closing handwheel for manual operation.
The internal plug has a notch seating surface which is at a 16 degree
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slope from t.Se vertical position. The valve seat was cut at a 10 degree angle from the vertical. With this type seating arrangement, it was possible to overtorque the plug via the closing handwheel or by downstream system pressure.
The plug tended.to wedge (cork) into the valve seat with a force greater than the decay heat pump could overcome.
Investigation of Deficiencv: Le Ranc}o Seco persc.inel conducted a 'two-phase program to determine the c
- of this discrep-ancy.
1.
Phase one was to use a torque wrench to apply a known force to close the internal plug. At 150 foot pcunds applied to the valve handwheel nut, the plug would not come out of the seat using the available pressure g.
(275 psig) from the decay heat pumps.
AN ELECTRIC SYSTEM S E R VIN G MORE THAN 600,000 IN THE HEART O F' C ALIFO R N I A w
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Mr. R. H. Eng21kan e
.c June 18, 1974
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Phase two was to apply primary system pressure to the I
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2.
internal plug. Pressure was then bled off and the
. {1 decay heat pump pressure was applied to the bottom of
.s the plug to determine if this would unseat the internal r.
plug. The valve opened satisfactorily with 1,000 psig primary.ystem pressure, but stuck closed at 2,150 psig 7'
~T primary system press'ure.
This two-phase test program described above verified that the existing velve design is unacceptable for use at the Rancho Seco Nuclear Gen-creting Station, Unit No. 1.
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Corrective Action This problem has been thoroughly analyzed i
by the vendor's design engineer and a decision made to change these valves to a flat seating surface configuration.
A flat seating sur-fece has been machined on the valve body and internal plug of both valves.
The surfaces have been " lapped-in" to insure adequate leak
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z tightness.
With thic modified design there is no wedging (corking) action and therefore, the internal plug cannot stick closed.
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g Should any additional information be needed on this problem
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or if we can be of further assistance, do not hesitate to call.
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Sincerely yours, J.
. Mattimoe Assistant General Manager km and Chief Engineer j
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