ML17309A439
| ML17309A439 | |
| Person / Time | |
|---|---|
| Site: | Ginna, Point Beach  |
| Issue date: | 04/18/1989 |
| From: | Mazumdar S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML17309A437 | List: |
| References | |
| TASK-AE, TASK-T904 AEOD-T904, NUDOCS 9002150206 | |
| Download: ML17309A439 (4) | |
Text
AEOD TECHNICAL REVIEW REPORT UNIT:
DOCKET NO.:
LICENSEE:
NSSS/AE:
Point Beach 1
50-266
'isconsin E1ectric Power Co.
Westinghouse TR REPORT KO.'EOD/T904 DATEAPR I5 889 EVALUATOR/CONTACT:
S. Hazumdar
SUBJECT:
DESIGN DEFICIENCY OF SAFETY INJECTION BLOCK SWITCH EVENT DATE:
August 19, 1989
SUMMARY
The Point Beach Nuclear Plant, Unit 1, has only one block/unblock manual selector switch controlling automatic safety injection (SI) circuits of both trains.
On August 19, 1988 a Licensee investigation established that a single failure of this selector switch in "block" position would make automatic SI of both trains partially inoperative.
As a consequence of this finding, the licensee has decided to replace this selector switch by two separate
- switches, one for each train.
We have discussed this issue with Westinghouse, Pittsburgh.
They concur with the Licensee's findings and have agreed to appraise all Licensees in the USA that may have similar design deficiency.
DESCRIPTION OF THE DESIGN DEFICIENCY On September 16, 1988 the Licensee issued LER 88-007 detailing the design deficiency they have found in the existing safety injection system.
The exist-ing safety injection system has a single "block/unblock" manually operated selector switch for automatic SI of both trains energized by the low steam line pressure SI signals from either steam line (Loop A or Loop B) and the low pressurizer pressure signal.
This selector switch is provided to manually block the automatic SI to permit normal cooldown and depressurization during "Hot Shutdown to Cold Shutdown."
This selector switch is a Westinghouse OT2V6 three position, cam operated, and spring return to neutral selector switch with four Westinghouse OT2A contact blocks; two blocks, one for blocking each train of SI are on top and two
- blocks, one for unblocking each train of SI are underneath.
The bottom contact blocks are operated by the top contact block plunger and therefore a
fai lure of the bottom contact blocks in stuck position would not affect the top contact blocks and a failure of a single bottom contact block will affect only one SI train.
This selector switch can fail in one of the following three modes:
a)
The spring can break in which case it will be apparent to the operator when he selects the switch position.
b)
The block contacts can get stuck.
c)
The unblock contacts can get stuck.
c 9002150206 900202 PDR ADOCK 05000244 8
The failure of unblock contacts is not a problem because the automatic SI block signal is automatically unblocked if the pressurizer pressure increases above 1775 psig and two of the three pressurizer pressure bistables deenergize.
This automatic unblocking features is single failure prof, and is mechanically and electr i ca 1 ly independent for the two S I tra ins.
The problem is when the top contacts get stuck in block position.
This will prevent automatic SI of both trains due to low steam line pressure or low pressurizer pressure.
- However, an automatic SI actuation on high containment pressure would still be available.
Furthermore, the SI master relay will energize SI independent annunicator lights "SI Blocked Train A" and "SI Blocked Train B" and will alert the operators who can respond with manual SI actuation, following Emergency Operating Procedure EOP-O, "Reactor Trip or Safety Injection."
Me have discussed this problem with Westinghouse, Pittsburgh.
They have studied the whole problem and concur with the Licensee's findings and have agreed to identify all the Licensees in the USA that may have similar deficiency and inform them.
CONCLUSION A single failure of the Westinghouse selector switch will make automatic operation of SI partially inoperative.
Westinghouse has initiated necessary procedure to identify the licensees that would be affected by this deficiency and inform them.
No further AEOD action is required though we will keep ourselves abreast on close-out of this issue.
Rs
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