Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 22, 1994
NRC INFORMATION NOTICE 94-13: UNANTICIPATED AND UNINTENDED MOVEMENT OF FUEL
ASSEMBLIES AND OTHER COMPONENTS DUE TO
IMPROPER OPERATION OF REFUELING EQUIPMENT
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to potential problems resulting from inadequate
oversight of refueling operations and inadequate performance on the part of
refueling personnel. It is expected that recipients will review the
information for applicability to their facilities and consider actions, as
appropriate, to avoid similar problems. However, suggestions contained in
this information notice are not NRC requirements; therefore, no specific
action or written response is required.
Description of Circumstances
Vermont Yankee Events
The Vermont Yankee facility was in a refueling outage with fuel movement in
progress on September 3, 1993, when an irradiated fuel assembly became
detached from the grapple after being lifted out of its position in the
reactor core. The assembly fell approximately 2.4 m [8 ft] back into its
original location in the reactor core. The licensee suspended fuel handling
and investigated the event. The licensee determined that the grapple had not
properly engaged the lifting bail on the fuel assembly and that the personnel
performing the fuel handling activities had failed to verify proper grapple
engagement. After completing the investigation and taking corrective actions,
the licensee resumed fuel handling activities on September 7, 1993.
On September 9, 1993, a fuel assembly that was being moved to a fuel sipping
can was inadvertently lowered, instead of raised, striking another core
component. The potentially damaged fuel assembly was then moved to the fuel
sipping can and the licensee again suspended fuel handling activities. The
NRC dispatched an augmented inspection team (AIT) on September 9, 1993, to
investigate the fuel handling incidents.
The AIT documented its findings in NRC Inspection Report 50-271/93-81, issued
October 21, 1993. The AIT concluded that mistakes made by refueling personnel
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were the immediate causes of both events. In addition, weaknesses in the
human factors aspects of the controls for the fuel handling equipment
contributed to the event in which a fuel assembly was lowered rather than
raised. The controls for the fuel handling equipment had been modified
shortly before this event occurred. The team concluded that the root cause of
the events was a significant weakness in management oversight of fuel handling
activities. Weak management oversight had allowed many of the measures
intended to prevent a fuel handling accident to be neglected. The AIT found
that (1) design changes were not transmitted to allow timely and accurate
training on modifications to the refueling bridge, (2) procedures were not
always used and, when they were used, they were not always adhered to, and
(3) supervisors did not ensure that procedures were followed. In addition,
the AIT found that training was not effective in that operators were not aware
of certain key procedure steps in most instances. Specifically, the personnel
monitoring the fuel handling activities were not aware of the requirement to
visually verify grapple closure when engaging and lifting fuel assemblies.
The AIT found that management did not communicate expectations and provide
proper oversight of fuel handling activities.
Peach Bottom Events
With Unit 3 shut down for refueling on September 23, 1993, a fuel assembly
could not be fully inserted into its spent fuel rack cell. It was thought
that the fuel assembly had swelled due to irradiation in the core, and the
fuel assembly was successfully placed in a different cell. It was further
postulated that there might be some debris in the cell, and that the cell
should be checked at some future date. On September 24, 1993, another fuel
assembly became stuck in its spent fuel rack cell. The licensee evaluated the
material condition of the fuel assembly, calculated an allowable lifting
force, and conferred with the fuel vendor. The licensee increased the load
limit of the refueling hoist and the fuel assembly was freed from the rack
with no damage to the fuel assembly. Subsequent examinations revealed that
sections of local power range monitor instrument strings that had previously
been cut up were in the bottoms of three cells in the rack, including the two
cells with which difficulties were experienced. The licensee believes that
the debris may have fallen into the cells during a fuel pool cleanup effort
conducted during the previous summer.
The licensee is currently investigating why the debris was in the spent fuel
pool and why the refueling personnel did not ensure that the spent fuel rack
cells did not contain any debris prior to inserting the fuel assemblies.
Susquehanna Events
The Susquehanna Steam Electric Station Unit 1 was shut down with defueling in
progress on October 6, 1993, when the personnel performing the fuel handling
activities removed an incorrect fuel assembly from a peripheral location in
the core. The personnel involved realized they had removed the wrong assembly
and they inappropriately decided to return the assembly to its prior position
in the core. The appropriate action, per licensee procedures, would have been
to place the bundle in the spent fuel pool and secure fuel handling activities
until the cause of the error was determined and corrected.
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On October 26, 1993, while lowering a fuel assembly into the core during
refueling, an unexpected drop of 25 to 38 cm [10 to 15 in] of one of the
sections of the fuel handling mast occurred. The fuel assembly was not
released and it did not strike the vessel internals. Subsequent testing
reproduced mechanical binding of the mast, and a bend in the mast was
observed. The binding temporarily restrained one section of the mast while a
lower section extended. Eventually weight or motion caused the bound section
to release and drop down a limited distance. The licensee subsequently
determined that the mast had been bent by an impact with the flange protector
for the reactor vessel while traversing through the "cattle chute" between the
core and fuel pool, because the mast was not raised high enough. The Unit 2
refueling bridge was transferred to Unit 1 and, after satisfactory completion
of surveillance testing, refueling was resumed.
On October 27, 1993, while transferring a double blade guide to the spent fuel
pool, the blade guide hit the side of the reactor vessel because it was not
raised high enough to clear the vessel. The licensee suspended refueling
activities, revised the associated procedure, and inspected the mast. The
core reload was resumed after surveillances on the fuel handling equipment
were successfully conducted. On October 28, 1993, while attempting to grapple
a new fuel assembly in the fuel pool, the personnel performing the fuel
handling activities heard two loud bangs and observed bubbles in the pool for
5 to 10 seconds. Subsequent inspection revealed that one section of the mast
from Unit 2 was bent. The licensee believes that the mast was weakened by the
impact with the reactor vessel that occurred during the October 27 event.
On October 29, 1993, the NRC dispatched an AIT to the site to review the
events. The AIT documented its findings in Inspection Report 50-387/93-80,
issued on December 21, 1993. The AIT concluded that facility management did
not maintain proper oversight of refuel floor activities and that inadequate
corrective actions were implemented in the past for problems with the fuel
handling equipment. The AIT also concluded that the licensee fuel handling
procedures were adequate for the proper completion of the fuel handling
activities, although certain improvements could be made to increase the
awareness of the operators concerning potential problems.
Nine Mile Point Event
Nine Mile Point Unit 2 was shut down with refueling in progress on
November 1, 1993, when a blade guide was moved from the core into the spent
fuel pool. The contractor refueling operator disengaged the grapple and
observed the correct light indication on the bridge. There was no procedural
requirement to visually verify disengagement or for the Senior Reactor
Operator Limited to Fuel Handling (LSRO) or the spotter to verify
disengagement. The refueling operator noticed increased drag after the
refueling bridge crane had been moved approximately 23 cm [9 in] toward the
next location. At that time, licensee personnel determined that the blade
guide was still engaged on the grapple. The bridge was returned to its
previous position, the blade guide was lowered and disengaged (positive
verification was obtained this time), and the operator proceeded to move the
next component, which was a fuel assembly. While lowering that fuel assembly
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into the core, the refueling operator noticed that the mast was binding. At
this point, the LSRO became involved and directed that the fuel assembly be
returned to the fuel pool. While lowering the fuel assembly into the rack in
the fuel pool, the inner section of the mast dropped between 61 and 76 cm [24
and 30 in]. However, the fuel assembly was not released. After the fuel
assembly was lowered, the grapple was disengaged and the LSRO halted further
fuel movement. The licensee subsequently determined that the mast was bent
and that the blade guide was not damaged. After the licensee reviewed the
event, modified the procedure, and repaired the fuel handling equipment, fuel
movements were resumed on November 4, 1993.
The licensee determined that there were several personnel performance issues
that needed to be addressed. The refueling operator had been trained to
verify disengagement after releasing each component, although the procedure
only required verification of ungrappling when handling fuel assemblies.
Disengagement was to be verified by raising and rotating the mast. The
refueling operator did not verify disengagement after releasing the blade
guide. In addition, the refueling operator did not notify the LSRO of the
unanticipated equipment response (remaining connected to the blade guide while
traversing the bridge). Also contributing to the event was the fact that the
LSRO was observing a refueling bridge trolley bearing about which he was
concerned, rather than the handling of the blade guide. Licensee review
determined that management expectations regarding the supervision of refueling
activities had not been clearly expressed to the LSROs.
Discussion
Refueling activities are safety-significant operations that are not conducted
on a routine basis. In addition, fuel handling activities are often performed
by contractor personnel under the supervision of licensee personnel. As a
result, fuel handling personnel may not be familiar with the fuel handling
equipment or may feel that their experience in fuel handling operations
permits them to ignore some requirements for procedural use and adherence.
Either of these situations could require increased management attention and
oversight by the licensee to ensure proper and safe performance of fuel
handling activities.
Appendix B to Part 50 of Title 10 of the Code of Federal Regulations
(10 CFR 50) requires licensees to have appropriate procedures to control
activities affecting quality (such as the actions to be taken during operation
of refueling equipment), and that the procedures are used and followed. In
addition, 10 CFR 50.120 requires licensees to implement a training program for
various categories of nuclear power plant personnel to ensure that those
personnel have the necessary knowledge, skills, and abilities to perform their
assigned jobs competently. This rule applies to the personnel (including
contractors) who operate or supervise the operation of the refueling
equipment. The cases discussed in this notice include situations in which the
licensees failed to conduct appropriate training in the use of their refueling
equipment, particularly with respect to design modifications made to the
controls for the fuel mast. These events also demonstrated that the fuel
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handling personnel involved in certain instances were variously not aware that
management expected them to identify deviations from expected results, cease
operations when an unexpected or abnormal condition is encountered, and notify
operations and/or plant management of unexpected or abnormal conditions.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below, or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
ORIGINAL SIGNED BY
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts: P. L. Eng, NRR E. M. Kelly, RI
(301) 504-1837 (215) 337-5183
J. R. White, RI L. E. Nicholson, RI
(215) 337-5114 (215) 337-5128
Attachment:
List of Recently Issued NRC Information Notices
