ML19206A550
| ML19206A550 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 07/28/1976 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | |
| Shared Package | |
| ML19206A547 | List: |
| References | |
| IEC-76-1, NUDOCS 7904200130 | |
| Download: ML19206A550 (2) | |
Text
,g NUCLEAR REGULATCRY CC:0!ISSIO:i 0FFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 IE Circular 76-01 DATE: July 28, 1976 Page 1 of 2 CRANE HOIST CCSTROL - CIRCUIT MCDIFICATICNS DESCRIM ICN OF CIRCO! STANCES:
In r,sponse to NRC concerns about the potential for, and consequences of, dropping a spent fuel shipping cask or other heavy load, Cecconwealth Edison =odified the hois centrol systen for the fuel cask handling cranes at their Dresden Units 2 and 3 and Quad cities Units 1 and 2 to provide additional hoist redundancy and sicw speed hoist capability.
The original desi:n utilized a General Electric "nsgspeed" hoist control systen.
In :his system which includes two electro-mechanical brakes in series spring ferce holds the brakes engaged while DC solenoids, ener-gi:ed when the hois coccr i= energi:ed, disengage the brakec.
The =odificatica which added the sicw speed hois: capability included installing additional contactors in the brake solenoid pcwer circuit to energize the colencids when the low speed hoist motor was energized.
The original heist control systen design 2:ili:ed a single Size 2 DC contactor (two contacts in sert?C' in the sclercic circuit.
The desiga codifica ica added a circuit in parallal with the original DC contactor with utili:ed four AC rated Size 1 single contacts in a series-parallel array to distribute current carrying and interrupting burden.
Initial experience with the modified heist control system at Dresden showed that the circuit interrupting capacity of the series-para _lel array was targinal. On several occasions when the low speed notcr was stoppei in the lowering = ode, the solenoid circuit contacts arcud re-sulting in power being supplied to the solencids long enough so : hat the load dropped sc e distance before the brakes engaged. Over travel of as
=uch as 15 inches was reported, but no datage to hoist or load was found.
The crane anufacturer's representatives have advised the NRC that the proposed corrective action is to install a single Size 2 DC contactor (two centacts in series) with are suppressors. the same as originally provided in the General Electric design, in place of the added four AC rated contacts. The original contactor in the normal speed ccatrol circuit has shown satisfac:ory service since initial operation of the plant in 1969.
. #3 7904200/3G
.c.
IE Circular 76-01 DATE: July 23. 1476 Page 2 of 2 ACTION TO BE TAKES SY LICENSEE:
1.
Determine and report to this office within 90 days the following inf ormation:
(a)
Have you made, or do you plan to caka todificatiens to the hoist centrol for your installed cranes si=ilar to the described modifications?
(b)
If such codificaticas have been cade, or are planned, identify changes required in ske pcwer and control circuitry?
(c)
What steps have been taken or are planned, to pro-vide assurance that brake pcVer contactors are adequate for the service?
2.
If =adifications are planned, provide the schedule for cc=pletion and a brief description of your plan-for design review and functional testing.
Your respcnce should be submitted to the Director of this Office, with a copy to the Director, Division of Reactor Inspection Programs, Office of Inspection and Enforcement, U. S.
"uclear Regulatery Cc cissien, Washington, D. C.
20555.
Approval of MRC require ents for reports concerning possible generic problems has been obtained under 44 U. S. C.
3152 from the U. S. General Accounting Office.
(GAO Approval 3-180255 (RC072), expires 7/31/77).
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