IE Bulletin 76-07 and IE Circular 76-01 - Crane Hoist Control - Circuit Modifications
JUL 27 1976
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
J. P. O'Reilly, Director, Region I
N. C. Moseley, Director, Region II
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV
R. H. Engelken, Director, Region V
IE BULLETIN 76-07 and IE CIRCULAR 76-01 - CRANE HOIST CONTROL - CIRCUIT
The subject documents are transmitted for issuance by close of business July
28, 1976. The Bulletin should be issued to all holders of Power Reactor OLs.
The Circular should be issued to all holders of Power Reactor CPs. The text
is identical except for the response time. Also enclosed are draft copies of
Since the LER enclosure is not appropriate for remote typewriter
transmission, text transmission has been forwarded by express mail,
scheduled to arrive your office today, with issue date set accordingly.
Dudley Thompson, Acting Director
Division of Field Operations
Office of Inspection and
1. Bulletin 76-07
2. Circular 76-01
3. Licensee Event Report
dated 6/10/76, sep cov
(Transmittal letter for Circular 76-01 to each applicant for, or holder of a
The enclosed Circular, 76-01 is forwarded to you for information and action.
This is the first issue of an expanded system for communication from the
Office of Inspection and Enforcement to applicants and licensees, to
supplement the issuance of IE Bulletins.
Bulletins have been, and will continue to be, limited to subjects considered
to be of appropriate significance to require prompt response. Circulars will
cover subjects of lesser significance or immediacy for which a longer
response time appears appropriate. Circular 76-01 contains the same subject
matter as Bulletin 76-07, which is being issued concurrently. If you are
also the holder of a NRC Operating License, you will also receive a copy of
Bulletin 76-07 which will require a separate response. The only difference
between the two documents is the time allowed for response. Future IE
Circulars may be addressed to any class of NRC licensees, and may or may not
IE Circular 76:01
IE Circular 76-01 DATE:
CRANE HOIST CONTROL - CIRCUIT MODIFICATIONS
DESCRIPTION OF CIRCUMSTANCES:
In response to NRC concerns about the potential for, and consequences of,
dropping a spent fuel shipping cask or other heavy load, Commonwealth Edison
modified the hoist control system 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 slow speed hoist capability. The original design
utilized a General Electric "magspeed" hoist control system. In this system
which includes two electro-mechanical brakes in series, spring force holds
the brakes engaged while DC solenoids, energized when the hoist motor is
energized, disengage the brakes.
The modification which added the slow speed hoist capability included
installing additional contactors in the brake solenoid power circuit to
energize the solenoids when the low speed hoist motor was energized.
The original hoist control system design utilized a single Size 2 DC
contactor (two contacts in series) in the solenoid circuit. The design
modification added a circuit in parallel with the original DC contactor with
utilized four AC rated Size 1 single contacts in a series-parallel array to
distribute current carrying and interrupting burden.
Initial experience with the modified hoist control system at Dresden showed
that the circuit interrupting capacity of the series-parallel array was
marginal. On several occasions when the low speed motor was stopped in the
lowering mode, the solenoid circuit contacts arced resulting in power being
supplied to the solenoids long enough so that the load dropped some distance
before the brakes engaged. Over travel of as much as 15 inches was reported,
but no damage to hoist or load was found.
The crane manufacturer's representatives have advised the NRC that the
proposed corrective action is to install a single Size 2 DC contactor (two
contacts in series) with arc 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 control circuit has shown
satisfactory service since initial operation of the plant in 1969.
IE Circular 76-01 -2- DATE:
ACTION TO BE TAKEN BY LICENSEE:
1. Determine and report to this office within 90 days the following
(a) Have you made, or do you plan to make modifications to the hoist
control for your installed cranes similar to the described
(b) If such modifications have been made, or are planned, identify
changes required in brake power and control circuitry?
(c) What steps have been taken or are planned, to provide assurance
that brake power contactors are adequate for the service?
2. If modifications are planned, provide the schedule for completion and
a brief description of your plans for design review and functional
Your response 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. Nuclear Regulatory Commission, Washington,
D. C. 20555.
Approval of NRC requirements for reports concerning possible generic
problems has been obtained under 44 U. S. C. 3152 from the U. S. General
Accounting Office. (GAO Approval B-180255 (R0072), expires 7/31/77).
Licensee Event Report dated 6/10/76
Malfunction of the drive brakes on the Unit 2/3 reactor building crane
special slow-speed hoist caused the Unit 2 reactor vessel head to slip
vertically about 15 inches as it was being lowered into place. An attempt
to continue lowering resulted in a second 15 inch drop, and the slow-speed
drive was taken out of service. Operations were resumed using the
normal-speed drive. Since the special slow-speed hoist drive is a new piece
of equipment, no data on past performance exists. (50-237/1976-32)
Investigation revealed that the slow-speed hoist brakes, which were designed
to engage upon loss of power to a release solenoid, were fully engaging only
after a delay of 1-2 seconds. It was further discovered that the contactor
for the break release solenoid was undersized, which permitted arcing when
the contacts opened. This arcing caused the release solenoid to remain
partially energized, and prevented the immediate full engagement of the
hoist brakes in the slow-speed mode.
The hoist brakes, which are common to both the normal-speed and slow-
speed drives, are controlled by two similar circuits, one in each drive
system. Each circuit culminates in a single contactor. Since the slow-speed
drive had been selected, only the slow-speed circuit contactor was in
operation at the time of failure.
The normal-speed circuit contactor has proven its reliability; however,
representatives of the crane vendor (Whiting Crane Corp.) have been
consulted and have agreed that the slow-speed circuit contactor is indeed
undersized for its duty requirements. The entire slow-speed hoist drive
design is being reviewed for other improper component applications. The
slow-speed drive will remain out of service until appropriate modifications
have been completed.
Page Last Reviewed/Updated Tuesday, September 01, 2015