ML19309A217
| ML19309A217 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/19/1974 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19309A214 | List: |
| References | |
| NUDOCS 8003260920 | |
| Download: ML19309A217 (2) | |
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8,4RAMENTO MUNICIPAL UTluTY f'iTRICT U 8201 S Street Box 15430. Sacr-Mnt2, Califomia 95813: (916) 452 32tt
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I June 19, 1974
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f Mr. R. E. Engelken 7
Directorate of Regulatory Operations 3
Region V U. S. Atomic Energy Commission Post Office Box 1515 Berkeley, California 94701 Rancho Seco Nuclear Generating Stiation No.1 Heat System Stop C..ack Valves DHS-015 and DHS-016 s
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Dear Mr. Engelken:
1 During the hot functional t'esting (HFT) program at Rancho Seco Nuclear Generating Station No. 1, the decay heat system stop 1
l check valves DHS-015 and DHS-016 stuck in the closed position. The j
valves would not open using normal operating procedures.
In accord-ance with our Quality Assurance procedures, this nonconformance has j
been reviewed and has been determined te be a reportable "signifi-
. cant deficiency" as defined liy 10CFR50.55(e).
Description of Deficiency:- The stop check valves are ten inch, 1500#, 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 j
have a twenty inch closing handwheel for manual operation. The internal plug has a notch seating surface which is at a 16, degree N
slope from the vertical position. The valve seat was. cut at.t 10 l
degree angle from the yertical. With this type seatitig arrangement, I
it was possible to overtorque the plug via the closing handwheel or by downstream eystem pressure. The plug tended.to wadge (cork) into the valve seat with a force greater than the decay heat pump could overcome.
Investigation of Deficiency: The Rancho Seco personnel 1
conducted a two-phase p ogram to determine the cause of this discrep-ancy.
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Phase one was to use a torque wrench to apply a known i
force to close the internal plug. At 150 foot pounds 1
applied to the vcive handwheel nut, the plug would not come out of the seat using the available pressure (275 psis) from the decay heat pumps.
j-i 177 a
AN ELECTRIC SYSTE M S E RVIN G MORE THAN 600.000 IN T H'E HEART OF C ALIFO R N I A N
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Mr. R' E. Engelken f June 18, 1974 I
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Phase two w'as to apply primary system pressure to the b
internal plug. Pressure was then bled off and the decay heat pump pressure was applied to the bottom of the plug to determine if this would unseat the internal
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plug.
The valve opened satisfactorily with 1,000 psig
. primary system pressure, but stuck closed at 2,150 psig primary system pressure.
This two-phase test program described above verified that'the existing valve design is unacceptable for use at the Rancho Seco Nuclear Gen-ersting Station, Unit No. 1.
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k Corrective Action.This problem has been thoroughly analyzed by the vendor's design engineer and a decision made to change these i
valves to a flat seating surface configuration.
A flat seating sur-face has been machined on the valve body and internal plug of both
- valves, The surfaces have been " lapped-in" to insure adequate leak t
tightness.
I' With this modified design there is no wedging (corking) action and therefore, the internal plug cannot stick closed.
i Should any additional information be needed on this problem or if we can be of further assistance, do not hesitate to call.
Sincerely yours, J.
. Mattimoe-b Assistant General Manager
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and Chief Engineer r
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