ML20032C665
| ML20032C665 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 10/30/1981 |
| From: | Parker W DUKE POWER CO. |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, SD-413-81-23, NUDOCS 8111100714 | |
| Download: ML20032C665 (3) | |
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Dear Mr. O' eilly:
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Report SD-413/81-23.
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CATAWBA NUCLEAR STATION REPORT: SD-413/81-23 REPORT DATE: October 30, 1981 FACILITY: Catawba Nuclear Station, Unit 1 IDENTIFICATION OF DEFICIENCY:
Nonconformance of welds on the Unit 1 spent fuel pool gates INITIAL REPORT:
On October 1,1981, Mr. A. Ignatonis of NRC Region II, Atlanta, GA was notified of this deficiency by Mr. W. O. Henry and Mr. J. H. Lanier of Duke Power Company,-
Charlotte, NC.
SUPPLIER AND/0R COMPONENT:
The spent fuel pool gates were designed and fabricated by the Presray Corporation of Pawling, New York, under Duke specification CNS-ll44.28-00-0001.
DESCRIPTION OF DEFICIENCY:
Twelve horizontal stiffeners are welded to the main gate plate at two foot intervals. One quarter inch continuous fillet welds on both sides of the stiffener are used for the stiffener to plate connection. These welds were cut and exposed in section when one edge of the gate was cut for width modification.
It was discovered that there was a partial lack of fusion on the gate plate leg of the welds. This condition was observed on all the stiffeners. Without the stiffeners, the main gate plate would be overstressed when water is retained on one side of the gate.
ANALYSIS OF SAFETY IMPLICATIONS:
Two safety implications were possible in the event these defects had gone undetected and the fuei pool gates had failed:
a.
The first possible implication relating to a possible gate failure is the lowering of the water level in the fuel pool belaw the acceptable minimum cover over the spent fuel assemblies. Assume both gates are in place and that the transfer canal and the cask pit are unwatered.
If both gates should fail, water from the fuel pool would fill the transfer canal and cask pit until an equilibrium level for all three areas is attained. The equilibrium water level is calculated assuming no makeup capability. The normal operating water elevation in the fuel pool is 598'+4 3/4" which corresponds to water volume of 87,872 cubic feet.
Distribution of this volume to the transfer canal and cask pit yields an equilibrium elevation of 593'+0".
The top of the fuel racks is at elevation 573'+0".
With the water elevation at 593'+0", a cover of 20 feet of water would exist over the stored fuel.
The Catawba FSAR states that a minimum of 10' feet of water is required
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to limit the direct gamma dose. The water level is above this minimum elevation with failure of both gates. This condition would not adversely affect the safety of operation or create a substantial safety hazard, b.
The second condition involves the ability to unwater the cask pit separately from the fuel pool, in the event of a cask drop accident.
The postulated accident is that a fuel cask may be dropped in the cask pit and possibly rupture the cask pit liner. Contaminated water may than have a path through the concrete to the adjacent outside environment.
The cask pit gate would be used to isolate the fuel pool from the cask pit so that the cask pit could be unwatered to prevent significant leakage of contaminated water. Failure of the cask pit gate would allow leakage to continue through the postulated liner rupture. The minimum level of water cover on spent fuel in the fuel pool would not be affected because tha makeup capability for the fuel pool water is greater than any leakage which might occur through the ruptured liner plate.
Performance of the cask pit gate as designed is necessary in order to prevent significant leakage from the cask pit in the event of a rupture of the cask pit liner.
CORRECTIVE ACTION:
In order for the fuel pool gates to inerform as designed, stiffeners are required.
Since the Unit 1 gates have been shown to have defective welds on the stiffeners, additional stiffeners will be welded to the other side of the main gate plate to correct this deficiency. The new stiffeners will be the same in size, number, and material as the original stiffeners and will be fabricated and installed by Duke Construction personnel. Weld inspection will be by Duke QA personnel using the approved NDE inspection procedures. One hundred percent of the welds will be inspected.
The Unit 2 gates are currently in fabrication at the Presray shop in Pawling, New York. One hundred percent weld testing will be performed on all gate welds with a Duke QA inspector present to witness the tests.
The additional stiffeners on the Unit 1 gates and the testing and inspection on the Unit 2 gates will assure that the deficiency has been corrected and prevented for the Catawba gates.
Similar gates manufactured by the Presray Corporation are employed at Duke's McGuire Nuclear Station, Units 1 and 2.
All the gates at McGuire have been tested under Test Procedure TP-1-A-1550-03N (Unit 1), TP-2-A-1550-03N (Unit 2),
Weir Gate Placement and Seal Testing. As part of this procedure both the cask pit and transfer canal are unwatered using the respective gates to hold back the fuel pool water. All gates performed structurally in a satisfactory manner with no detrimental effects observed on any gate. From this testing it is concluded that the McGuire gates are adequate to perform their requested function with no danger to public safety.