Information Notice 1985-38, Loose Parts Obstruct Control Rod Drive Mechanism
| ML031180406 | |
| Person / Time | |
|---|---|
| Issue date: | 05/21/1985 |
| From: | Jordan E NRC/IE |
| To: | |
| References | |
| IN-85-038, NUDOCS 8505200168 | |
| Download: ML031180406 (3) | |
SSINS No.: 6835 IN 85-38 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555 May 21, 1985 IE INFORMATION NOTICE NO. 85-38: LOOSE PARTS OBSTRUCT CONTROL ROD DRIVE
MECHANISM
Addressees
All utilities with pressurized water reactor (PWR) nuclear power facilities
designed by Babcock & Wilcox (B&W) and holding an operating license (OL) or a
construction permit (CP).
Purpose
This information notice is provided to alert recipients of a potentially
significant problem pertaining to loose parts that can obstruct and prevent
motion inside of control rod drive mechanisms . It is expected that recipients
will review the information for applicability to their facilities and consider
actions, if appropriate, to preclude a similar problem occurring at their
facilities. However, suggestions contained in this information notice do not
constitute NRC requirements; therefore, no specific action or written response
is required.
Description of Circumstances
In 1981 at the Davis-Besse Nuclear Plant, a locking spring broke in a control
rod drive mechanism (CRDM) in core location C-7 and became wedged against the
control rod, preventing it from operating. The cause was not determined at
that time. During the 1984 outage, the locking springs were inspected and none
appeared broken or in the wrong position. On March 16, 1985, the control rod
in core location E-3 would not drop into the core on demand and had to be
driven downward by control room personnel. This control rod was tested during
an outage on March 21, 1985, and jammed after three cycles of operation.
Inside of this CRDM were foreign objects and a broken locking spring. The
foreign objects were pieces of a set screw from the handling tool used during
the 1984 outage that had lodged in the CRDM and prevented the drive screws from
being disengaged. The locking spring (a flat tee-shaped device with a riveted
tab) was broken at the tee and the upper rivet hole. The upper portion of the
broken spring was not found and is believed to be inside of the CRDM.
Further examination of all of the mechanisms revealed a broken locking spring
in core location M-5. In addition, four springs were not in their normal locking
position. During operation there is no means of detecting broken springs or
foreign objects in the CRDM. Exercising the control rod will allow loose pieces
to move.
8505200168
IN 85-38 May 21, 1985 The most likely cause of the spring failures is that the unit went into service
with some of the locking springs not in their correct position. The present
assembly procedure has the maintenance technician determining that the spring
is in the correct position by "feel" through a long handling tool. If this
process is not successful, the reactor will be placed in operation with the
spring out of position. When the control rod is fully withdrawn, an out-of- position spring will hit the inside of the torque tube cap and snap when
sufficiently loaded. This was confirmed by the appearance of the spring
failures which were brittle, intergranular fractures. In addition, examination
of the inside of the cap showed a gouge in the tapered portion near the bottom
and an indentation on the bottom surface.
Spring failures are considered to be a potential common mode failure that could
affect the reactor trip function because (1) four springs at Davis Besse were
found not to be in their normal position and two others were broken; (2) the
likelihood for out-of-position springs to be broken when the control rod is
fully withdrawn; and (3) the potential for a broken spring to cause the control
rod to jam.
The corrective action by Davis-Besse Nuclear Plant was to replace all of the
out-of-position spring assemblies and to verify by visual examination that the
springs were in their correct positions. Consideration is being given to
adding this verification as a regular part of the maintenance procedures. The
B&W-Owners-Group-has notified their members that- there were-fa-iled locking
springs at Davis-Besse in the control rod drive mechanisms.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edwar6~ Jordan, Director
Divis n of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact:
P. Cortland, IE
301-492-4175 Attachment: List of Recently Issued IE Information Notices
Attachment 1 I . .
IN 85-38 May 21, 1985 LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information Date of
Notice No. Subject Issue Issued to
85-37 Chemical Cleaning Of Steam 5/14/85 All pressure water
Generator At Milestone 2 reactor facilities
84-55 Seal Table Leaks At PWRs 5/14/85 All power reactor
Sup. 1 facilities holding
85-20 Motor-Operated Valve Failures 5/14/85 All power reactor
Sup. 1 Due To Hammering Effect facilities holding
85-36 Malfunction Of A Dry-Storage, 5/9/85 All licensees
Panoramic, Gamma Exposure possessing gamma
Irradiator irradiators
84-52 Inadequate Material 5/8/85 All power reactor
Sup. 1 Procurement Controls On facilities holding
The Part Of Licensees And an OL or CP ( ,
Vendors
85-35 Failure Of Air Check Valves 4/30/85 All power reactor
To Seat facilities holding
85-34 Heat Tracing Contributes To 4/30/85 All power reactor
Corrosion Failure Of Stainless facilities holding
84-84 Deficiencies In Ferro- 4/24/85 All power reactor
Rev. 1 Resonant Transformers facilities holding
85-33 Undersized Nozzle-To-Shell 4/22/85 All power reactor
Welded Joints In Tanks And facilities holding
Heat Exchangers Constructed an OL or CP
Under The Rules Of The ASME
Boiler And Pressure Vessel
Code
85-32 Recent Engine Failures Of 4/22/85 All power reactor
Emergency Diesel Generators facilities holding
OL = Operating License
CP = Construction Permit