ML20024D227
| ML20024D227 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 07/20/1983 |
| From: | WASHINGTON PUBLIC POWER SUPPLY SYSTEM |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML20024D218 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8308030337 | |
| Download: ML20024D227 (3) | |
Text
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Attachment I WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PROJECT N0. 2 DOCKET NO. 50-397 LICENSE N0. CPPR-93 10CFR50.55(e) CONDITION #49 OPERATION OF STANDBY GAS TREATMENT SYSTEM DAMPER INTERIM REPORT Description of Deficiency The Standby Gac Treatnent System (SGTS) contains redundant trains consisting of two 100% capacity fans per loop'for a total of four 100% capacity fans.
To maintain a 1/4" water gauge negative pressure within the Reactor Building in the event of a LOCA, only one fan is required.
As shown on the attached flow diagra'm, there exists electrically operated dam-pers to control the mode of operation of each train (e.g., isolation, recircula-tion or exhaust). Also depicted on the attached diagram is the source of power for each motor operated damper and fan.
It may be postulated that due to the system design which provides power from two redundant electrical divisions to dampers in each fan train, both Standby Gas Treatment System loops from a single event may be made non-functional.
Safety Implication The Standby Gas Treatment Systems function is to collect and process the leak-age of radioactive materials from the Primary Containment into the Secondary Containment or Reactor Building following a LOCA.
It also enables purging of the Primary Containment through the SGTS filters when airborne radiation levels within the drywell are too high to permit purging through the Reactor Building Exhaust System. The system has redundant trains with electrical damper control circuits for each train within a given electrical division routed in a common enclosure or cable tray. A fault-generated fire in the common tray could damage adjacent control cables and cause spurious signals to be generated. This could cause the dampers powered from that single division to close in both SGTS trains thus making the system unable to perform its intended function (see attached
. sketch). This condition is. considered to be a reportable deficiency.
Cause of-the Deficiency The condition exists due to an initial failure by the Architect Engineer (AE) to adequately apply single failure criteria where a single system process loop depends upon proper functioning of redundant division equipment.
Corrective Action The AE has issued PED-218-E-B137 a'nd others to reroute the circuits for the various dampers on each SGTS unit. This was done so a single event could not disable both trains. This will, tin effect, provide separation within an electri-cal division between the control circuits for the damper operators on each train.
The work is in progress and scheduled to be completed before fuel load.
All other safety related systems will be reviewed to assure that similar condit-.
' '30 dn not exist requiring separation within a division.
B PDR UUl 830720'
~
S DCK 05000397 PDR
Attaciument I Page 2 of 3 1
Action to Prevent Recurrence The Electrical Separation Practices for WNP-2, Engineering Criteria Document, Appendix 3 (Paragraph II.B.4), has been revised to identify the systems presently known to require separation within an electrical division in order to preserve functional. integrity. At the completion of.the study identified above, the criteria document will _ be further amended if appropriate.
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