ML20059C241
| ML20059C241 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 10/05/1993 |
| From: | Beall J, Durr J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20059C243 | List: |
| References | |
| 50-271-93-81, NUDOCS 9311010065 | |
| Download: ML20059C241 (20) | |
See also: IR 05000271/1993081
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.U.S. NUCLEAR REGULATORY COMMISSION
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REGION I
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Docket No.
50-271
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Report No.
50-271/93-81
License No.
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Facility Name:
Vermont Yankee Nuclear Power Plant
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Inspection At:
Vernon, Vermont
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Inspection Conducted:
September 10-14, 1993
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inspectors:
G. West, Jr., Engineering Psychologist, NRR
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T. Shedlosky, Project Engineer, DRP
P. Harris, Resident inspector, DRP
A. Burritt, Operations Engineer, DRS
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Observer:
W. Sherman, State of Vermont
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Team Leader:
J.
Beall, Team Leader
D' ate -
ineering Branch, DRS
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Approved By:
/A,p 8m hb
g/f-
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Dafe
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J. P. gurr, Chief,
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Engineering Branch, DRS
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Inspection Summary:
See Executive Summary
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9311010065 931021
ADOCK 05000271'
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TABLE OF CONTENTS
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EXECUTIVE SUMMARY
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1.0
INTRODUCTION
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1.1
AIT Scope and Obj ectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I
1.2
AIT Process
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2.0
DESCRIPTION OF THE EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3.0
PERSONNEL PERFORMANCE AND REFUELING OVERSIGHT
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3.1
Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1.1 Operator Training Prior to September 3,1993 . . . . . . . . . . . . . 3
3.1.2 Reactor Engineer Training Prior to September 3,1993 . . . . . . . . 4
3.1.3 Operator / Reactor Engineer Training rollowing the
September 3,1993 . . . . . . .
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3.2
Fuel Handling Procedure . . . . . . . . .
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3.2.1 Procedure Adequacy . . . . . .
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3.2.2 Fuel Handling Steps
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3.3
Personnel Performance . . . . . .
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3.3.1 Reactor Engineers
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3.3.2 Refueling Platform Operators . .
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3.3.3 Senior Reactor Operators .
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3.4
Management Oversight . . .
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3.4.1 Procedure Usage
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3.4.2 Communications
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3.4.3 Fuel Movement Briefings . .
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3.4.4 Schedule
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3.4.5 Refuel Staffing and Overtime .
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3.4.6 Management Oversight of Fuel Handling
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4.0
REFUELING BRIDGE FUEL HANDLING EQUIPMENT DESIGN
CHANGES
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4.1
Fuel Grapple Replacement . . . . . . . . . . .
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4.2
Refuel Platform Upgrade
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4.3
Refueling Platform Hoist Interlock Modification
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MAINTENANCE AND TROUBLESHOOTING OF REFUELING
EQUIPM ENT . . . . . . . . . . . . . . . . . . .
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Table of Contents
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6.0
HUMAN FACTORS REVIEW
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6.1
Human-System Interfaces
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Human Factors Weaknesses . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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6.3
Conclusion
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7.0
LICENSEE CORRECTIVE ACTIONS
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8.0
S AFETY SIGNIFICANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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C O N CLU S I ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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10.0 M AN AG EMENT MEETING S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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ATTACHMENT 1 - NRC Augmented Inspection Team Charter
A'ITACHMENT 2 - Persons Contacted
ATTACHMENT 3 - Sequence of Events for the Vermont Yankee Refueling Incidents
ATTACHMENT 4 - Human Factors Weaknesses
ATTACHMENT 5 - September 3,1993: Post-Event Radiological Summary
ATTACHMENT 6 - Slides Presented at September 21,1993 Public Exit Meeting
FIGURE 1 - Grapple Up and Down Control
FIGURE 2 - Refueling Bridge Control. Console
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EXECLTf1VE SUMMARY
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On September 3,1993, at about 12:30 p.m., Vermont Yankee personnel inadvertently
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dropped a fuel assembly approximately eight feet back into its reactor core location during
fuel handling activities. At the time, the plant was shutdown in a refueling outage with about
one-third of the planned fuel moves already completed. On September 7,1993, the licensee
resumed fuel handling activities after completion of troubleshooting, implementation of
corrective actions, and discussions with tne NRC. On September 9,1993, a second fuel
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handling incident occurred when operators inadvertently lowered a fuel assembly onto a core
component. After the second incident was reported, the licensee suspended further fuel
handling.
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An Augmented Inspection Team (AIT) was dispatched by the NRC to determine the
circumstances that led to the events, their causes, safety significance and generic
implicaGons. The AIT began its assessments on September 10,1993, completed its onsite -
review on September 14,1993, and presented its preliminary findings in a public exit
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meeting on September 21,1993.
Errors by operators were the immediate causes of the events. The preponderance of the
physical evidence indicated that the grapple had not properly closed on the fuel assembly
handle and that the grapple light had not energized resulting in the drop of the assembly on
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September 3,1993. The September 9,1993, event was an inadvertent operator performance
error. Human factors weaknesses contributed to the error in lowering rather than raising the
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fuel assembly. The team concluded that the fuel handling incidents had been appropriately
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mitigated by the systems operable and the existing plant configuration, and were,
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independently, of minor safety significance.
The team concluded that the root cause of the dropped fuel assembly event was a significant
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weakness in management oversight of fuel handling activities. Weak management oversight
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had allowed many of the measures intended to prevent a fuel handling accident to become
degraded. The AIT found that design changes were not transmitted to allow timely and
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accurate training on the modifications; training was not effective in that operators were not
aware of certain key procedure steps; procedures were not used and were not adhered to; and
supervisors did not ensure that procedures were followed. Management did not communicate
expectations and provide proper oversight of fuel handling activities.
The decision by the senior reactor operator to continue the planned move of the assembly
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which had, on September 9,1993, inadvertently been lowered onto a core component was
not in compliance with the licensee's fuel handling procedure. This procedure compliance
error was not identified by licensee line management or by the licensee's event investigation.
This was indicative of a weakness in corrective actions to the September 3,1993, incident
and a continued weakness in management oversight of fuel handling activities.
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DETAILS
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1.0
INTRODUCTION
Upon being informed of the fuel handling incidents on September 3 and 9,1993, at the
Vermont Yankee Nuclear Power Station, the NRC Region I Regional Administrator and
senior management from the Office of Nuclear Reactor Regulation (NRR) and the Office for
Analysis and Evaluation of Operational Data (AEOD) determined that an augmented
inspection team (AIT) should be formed to review the circumstances and evaluate the
significance of the events. The bases for the determination were the need for the NRC to
fully understand the causes of the events and to determine if these were associated with
generic issues which required further NRC action. Accordingly, an AIT was selected,
briefed, and dispatched to the site on September 9,1993.
1.1
AIT Scope and Objectives
The charter for the AIT (Attachment 1) was finalized on September 9,1993. The charter
directed the team to conduct an inspection and to accomplish the following general
objectives:
Develop a detailed sequence of events related to both events, from September 3
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through 9.
b.
Determine the specific circumstances and causes of the apparent operator errors that
occurred during refueling operations on September 3 and 9,1993.
Determine and evaluate any changes (specifically Plant Design Change 92-11
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implemented in Spring 1993) made in the design, maintenance, testing, or operation
of the refueling bridge including hoist, grapple, and operator controls. Also, included
was associated training for such modifications.
d.
Evaluate the human factors aspects of both events, including: 1) command ano
control, and communications; 2) human performance factors, such as staffing,
overtime, and schedule; and 3) human-systems interfaces, such as with console
design.
Assess the safety significance, including existing damage to the affected fuel
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assemblies.
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Determine the adequacy of Vermont Yankee's maintenance and troubleshooting
practices for refueling equipment, including vendor interface and control.
Evaluate Vermont Yankee's corrective actions and management controls following the
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September 3rd event, as they relate to the second September 9th event, particularly
on-the-job training.
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AIT Process
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During the period September 10 - 14, 1993, the AIT conducted an independent inspection,
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review, and evaluation of the conditions and circumstances associated with the events. The
team inspected fuel handling, equipment, and controls; held discussions and formal
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interviews both with personnel involved in the event and others performing the same duties;
reviewed relevant records, including operator logs, modification packages, and training
documents; and evaluated the adequacy of established procedures, personnel training, and
management oversight. Attachment 2 is a list of personnel contacted by the AIT.
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2.0
DESCRIPTION OF TIIE EVENTS
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On August 27,1993, the licensee initiated a reactor shutdown and entered a refueling outage.
On Septen'ber 1,1993, the licensee commenced the first of (about) 700 planned movements
of fuel assemblies necessary to refuel the reactor. On September 3,1993, during fuel move
number 233, one fuel assembly became detached from the grapple while being lifted out of
the reactor core. The assembly fell an estimated 8 feet back into its original location. Some
assembly damage and a small radioactive release occurred.
The licensee suspended fuel handling, notified the NRC, and investigated the event. After
the licensee completed their investigation and implemented certain corrective actions, fuel
handling was resumed with NRC concurrence.
On September 9,1993, during fuel mon number 388, a fuel assembly was inadvertently
lowered, instead of raised, resulting in an apparent impact with another assembly or
component in the core. The potentially damaged assembly was then moved to a fuel sipping
can, as originally planned. The licensee reported the event, suspended fuel handling
activities, and the NRC dispatched an AIT to investigate the fuel handling incidents.
A chronology associated with the fuel handling incidents is contained in Attachment 3.
3.0
PERSONNEL PERFORMANCE AND REFUELING OVERSIGIIT
The AIT assessed the preparation, performance and practices associated with core
alterations / fuel movement prior to, between and after the two refueling events. The findings
of the team are grouped into four categories: Training, Procedures, Personnel Performance
and Management Oversight.
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3.1
Training
3.1.1 Operator Training Prior to September 3,1993
Prior to the refueling event on September 3,1993, all operations personnel received specific
refueling training as a part of the normally scheduled continuing training cycle. The training
was provided to licensed operators and non-licensed Auxiliary Operators. The training,
conducted during the six week period between June 29,1993 and August 6,1993 was one
and a half hours in length. All operations personnel attended the normally scheduled training
except for two who completed a read and sign package on refueling operations as a make-up.
An outline in lesson plan LOT-00-234H, Revision 8 (06/93), was used to guide the training
provided on refueling. The outline specified a discussion of vessel disassembly, refuel
outage tests, planned modifications to the refuel bridge along with a review of the listed
licensed operator objectives. Although, one of the objectives required the use and/or
understanding of procedure 1101, the objective did not provide clear performance
expectations regarding the level of understanding. The lesson plan included a memorandum
on the scope of PDCR 92-011, " Refuel Platform Upgrades." The memorandum stated that
the main hoist controls would be replaced but did not provide any details about the new
controls. The figure of the main hoist controls in the lesson plan was not the same as the
controls installed at the beginning of the outage. The training occurred prior to the controls
being replaced.
Based on interview data, procedure 1101, " Management of Refuel Activities and Fuel
Assembly Movement" was discussed in class with emphasis on the administrative limits and
duties and responsibilities sections. The body of the procedure was briefly reviewed with
particular attention to notes and cautions. The instructor did not specifically discuss the
procedure steps or procedural adherence.
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Instruction provided to cover the objectives for requalification training, by practice is left to
the discretion of the instructor. Although the training provided was generally considered to
be adequate based on interviews, there was no documentation of what was covered in class
as well as no assurance that the same information was presented from one class to the next.
On The Job Training (OJT) by either demonstration or hands on practice was not provided
prior to the September 3,1993 event. This training was not considered on the basis that it
had not been done in the past for requalification training. Although the personnel involved
in refuelling generally had a significant amount of fuel movement experience, some
individuals interviewed felt hands on practice was necessary. Since core alteration fuel
movements are done infrequently, the team concluded that it would be a good practice to
renew manipulative skills under non-safety significant conditions, particularly following the
modification of equipment, indications and controls.
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Training practices prior to the September 3,1993, event were weak. This assessment is
based on the absence of OJT prior to refueling and the results ofinterviews. Through
interviews, the AIT determined that most of the operators were not aware of certain
important procedural requirements and routinely had not performed all the required steps
during fuel movement operation.
3.1.2 Reactor Engineer Training Prior to September 3,1993
Prior to the refuel outage the reactor engineers were provided a number of training sessions.
One of these sessions was given using an informal 5 page briefing sheet. The intent of this
training was to review refueling goals, various procedural requirements along with refuel
contingency plans with the reactor engineers providing fuel movement support. The " Things
to remember when moving fuel" section contained a specific discussion that the reactor
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engineer should verify the grapple close light to be on prior to lifting a fuel bundle.
The AIT did not review all the training and documentation for the instructional briefings
provided to the reactor engineers, but the team did confirm that the expectations to verify
grapple closure were clearly addressed.
3.1.3 Operator / Reactor Engineer Training Following the September 3,1993
Training immediately following the September 3,1993 event was performed as a part of the
facility corrective actions. The training consisted of a classroom session, a read and sign
package, and handsen OJT for the operators and reactor engineers.
The classroom training included a review and discussions of procedure 1101, " Management
of Refuel Activities and Fuel Assembly Movement," Revision 21, in detail. Although the
lesson plan had no specific objectives, it did clearly document the key points to be
emphasized and appeared appropriate for the circumstances. The training took approximately
3/4 of an hour to perform and was done prior to the OJT portion.
The read and sign package was provided to operations personnel on the revised procedure
1101, " Management of Refuel Activities and Fuel Assembly Movement," Revision 23.
The OJT consisted of moving the bridge and trolley to coordinates provided in the spent fuel
pool, grappling the bundle, performing the grapple engagement verifications including the
rotation check under load. All members of the refuel teams performed in their normal
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positions while practicing the direction and communications required.
Training provided following the September 3,1993, event was adequate. The team noted,
however, that although the controls were operated during the OJT portion of the training, the
changes in hoist speed and the effective reversal of switch motion compared to hoist direction
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were not addressed.
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3.2
Fuel llandling Procedure
3.2.1 Procedure Adequacy
The AIT reviewed procedure 1101, " Management of Refuel Activities and Fuel Assembly
Movement," Revisions 21,22, and 23. Although a number of enhancements were made in
each of the successive revisions, the team determined Revision 21 of the procedure to be
adequate for fuel movement with the main hoist.
The procedure provided expectations that the reactor engineer and the SRO were required to
visually verify grapple closure. Additionally, the reactor engineer and SRO verification step
was imbedded in the step to close the grapple. The procedure, Revision 23, required a more
directed evolution by the SRO as well as establishing additional verifications to ensure proper
grappling of a fuel bundle. The additional procedural barriers consisted of SRO verification
of proper grapple head orientation prior to engaging the grapple and redundant checks by the
reactor engineer and SRO to verify the grapple light was energized following grapple
closure.
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The procedure, Revision 21, ZZ axis (refueling hoist depth) counter reference values were
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incorrect. These reference points provide approximate relative height for key components
within the spent fuel pool and reactor core. The values had changed based on the installation
of a new ZZ axis indication system prior to the refuel outage. Although these levels
provided valuable operator informationf additional operator aids were in place, updated daily
and effectively ensured that the operator had the most up to date reference values.
The AIT identified specific weaknesses with procedure 1101, " Management of Refuel
Activities and Fuel Assembly Movement," Revision 21, but concluded that these weaknesses
did not significantly contribute to the September 3,1993 event. Further, Revision 23 of this -
procedure was assessed as adequate to perform fuel movements with the main hoist and
therefore was not a contributing factor in the September 9,1993 event.
3.2.2 Fuel IIandling Steps
Procedure 1101, Revision 23, directed operators withdrawing a peripheral fuel assembly to
withdraw it "to just above the core, move toward the center-core area, then fully raise" the
assembly. The licensee chose this method over the alternative, raising the assembly fully and
then moving toward the center, to reduce radiation levels in the drywell when handling fuel.
This allowed fewer restrictions on personnel access to the drywell; such restrictions could
increase the time to complete scheduled outage work.
Operators interviewed stated that it was their general practice to move all assemblies using
the method directed for peripheral assemblies. Most facilities similar to Vermont Yankee
restrict access as necessary and use the " full lift then move to center" approach for moving
fuel. The team did not conclude that the licensee's fuel handling steps were inadequate, but
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did note that the approach used significantly increased the chance that an inadvertent operator
error, such as occurred on September 9,1993, would result in a fuel assembly impacting a
core component. Using the more common fuel handling steps, an operator would have over
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30 feet of clearance to correct a mistake rather than the two to three feet (or four to six
seconds) available to operators.
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3.3
Personnel Performance
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3.3.1 Reactor Engineers
During the September 3,1993, dropped fuel assembly event, the reactor engineer was off the
bridge of the refueling platform performing other duties on the refueling platform floor.
Therefore, the reactor engineer did not follow the facilities Operating Procedure No,1101,
Revision 21, and verify grapple closure which stated: " Move the Grapple Open/Close
Switch to the CLOSE position, the SRO and the Reactor Engineering representative visually
verify grapple closure."
Operating Procedure 1101, Revision 21, indicated that the reactor engineer shall:
a.
watch for and notify the Senior Licensed Operator of any occurrence which may
potentially jeopardize safe refueling,
b.
ensure compliance with the Fuel: Loading Schedule,
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maintain tag boards on the refuel floor and place target tags on boards for operator
reference,
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assist the Senior Licensed Operator on the refuel floor,
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maintain the Refueling I.og (DP 0420).
The above duties placed conflicting organizational expectations by management on the reactor
engineer. When only one reactor engineer was assigned to a refueling shift crew, the
individual had duties that were both on the refueling platform bridge and on the refueling
platform floor. This conflict was a contributing factor to the dropped fuel assembly event.
The team concluded that, prior to the September 3,1993, event; the reactor engineers should
have been aware of all assigned responsibilities and identified conflicting duties to their
supervision.
Reactor engineer performance was good during the September 9,1993, inadvertent lowering
of the fuel assembly event. The reactor engineer quickly observed that the fuel bundle was
being lowered rather than raised, called to the refueling platform operator to stop, which
probably mitigated the consequences ~of the event,
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3.3.2 Refueling Platform Operators
The refueling platform operator involved in the dropped fuel assembly event reported that he
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verified grapple closure (i.e., observed that the grapple closed-light was on). Moreover,' the -
operator noted that he observed the change in state of the grapple closed light. The report
and observation by the operator were inconsistent with the preponderance of physical
evidence, which indicated that the grapple was not closed when raised. The team assessed
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the performance of the refueling platform operators to be poor prior to the
September 3,1993, event; the operators generally were not aware of the requirement to
perform a rotational check, which ensured proper engagement, after grapple closure. That :
rotational check, not done for the dropped assembly, was intended to detect improper
grappling and may have prevented the September 3,1993, event.
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The refueling platform operator engaged in the inadvertent lowering of the fuel bundle event
committed an error resulting principally from two reasons. First, the human factors aspect.
of the change to the main crane controls, a " joystick," was a contributing factor (see Section
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3.1.1). The operator had received no training on how to use the new joystick. The -
relationship between the motion of the joystick and control of the grapple was inconsistent
with his past experience and reversed the direction of control used in the previous outage.
Second, the way the licereee moved fuel, that is, initially raising each assembly 2-3 feet
above the core, next moving the bundle to the center of the core, and finally taking the
assembly full up, was also a contributor. This pattern provided an additional opportunity to
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commit an error of this type (see Section 3.2.2).
3.3.3 Senior Reactor Operators
The SRO's performance (specifically, command and control) during the dropped fuel
assembly event was unsatisfactory for several reasons. The senior reactor operator failed to
verify grapple closure and did not ensure that the reactor engineer, who was off the refueling
platform bridge, verified grapple closure. Operating Procedure 1101, Revision No. 21,
required the senior reactor operator and the reactor engineer to visually verify grapple
closure. Further, the senior reactor operator did not comply with the following step of the
subject procedure: " Verify the fuel assembly is grappled by: 1) attempting to carefully
rotate the control console one way then the other..." Thus, the senior reactor operator
lacked command and control not only because he failed to follow procedure, but also because
he did not require the shift crew to follow procedure.
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The SRO's performance regarding command and control was also unsatisfactory during the
inadvertent lowering of the fuel bundle event. After the fuel bundle was inadvertently
lowered, the SRO continued with the movement of the fuel bundle to the spent fuel pool.
This action was contrary to Operating Procedure 1101, Revision No. 23, which stated:
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If any off-normal condition or evidence of interference or binding of components in
the core develops, further operation in that area of the core shall be immediately
stopped and the problem investigated and corrected.
Fuel bundles not properly seated may be rescated. However, no fuel movement or
core alteratio;s shall be made to correct a damaged, mistoaded or misoriented bundle
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in the reactor until the R/CE Manager has been notified.
Halt any activity in the event of an unusual or abnormal occurrence. Once any
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activity has been halted, it may only be re-initiated by the Shift Supervisor after
receiving concurrence from the Operations Manager.
3.4
Management Oversight
3.4.1 Procedure Usage
The facility did not have an administrative procedure or guideline that dictated the level o,f
use required for procedures. Based on interviews, the team was unclear on what the
management expectations were for use of procedure 1101, " Management of Refuel Activities-
and Fuel Assembly Movement." Prior to the September 9,1993, event, operators did not
use procedure 1101 during fuel handling, did not have it on the fuel bridge for reference
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purposes, and did not know it it was available on the refuel floor. Some operators thought it
was appropriate to have the procedure available on the refuel bridge for either step by step
referral or to reference it as needed, since there was a lot of information to remember.
However, the majority of personnel interviewed thought this was not necessary due to the
repetitive nature of fuel movement and due to housekeeping concerns while over the vessel
and spent fuel pool.
The AIT determined that clear management expectations did not exist for the required level
of use of refuel procedures. The team was concerned that lack of clear management
expectations may have created an environment in which refuel procedures routinely were not
used.
3.4.2 Communications
During interviews, the AIT determined that the SRO used a hand-held phone to maintain
communication with the control room during fuel movement within the core. Additionally,
the operator would use binoculars to observe fuel assembly placement. These two factors
would challenge the ability to hold and use the procedure. The team considered
communications to have been adequate, but noted that the current practice could inhibit
future in-hand procedure use on the refuel bridge.
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3.4.3 Fuel Movement Briefings
During interviews, the AIT determined that pre-job or pre-shift briefs had not been
conducted prior to fuel movements. The FSAR stated that "All supervisors shall hold
instructional briefings with members of their staffs prior to executing a refuel procedure in
the interest of safety and good power station practice," (FSAR Section 13.9.3). The failure
of shift supervisors or the refuel floor SROs to perform the briefings, represents a missed
opportunity to review and verify the understanding of key administrative and procedural
requirements to ensure safe refuelling practices. Based on interviews, the team concluded
that cognizant licensee managers had not been aware of the FSAR commitment.
3.4.4 Schedule
Based on interviews, the AIT determined that the refuel teams had felt no undue sense of
urgency or pressure from management related to fuel movement. All personnel interviewed
stated that there was a clear emphasis on "doing things right and safely." Additionally, there
appeared to be no competition between shifts that potentially could have compromised safety.
3.4.5 Refuel Staffing and Overtime
The AIT reviewed the plant staffing assigned to refueling activities and concluded that the
refuel staff size was appropriate for the conduct of safe refueling operations. A good
initiative was demonstrated by VY to atigment the number of senior licensed operators with
two individuals from the Training Department. However, the team concluded that the
staffing for refueling was inadequate during occasions when only one of the two reactor
engineers were on the refuel floor. During these occasions, the remaining engineer was
challenged to effectively perform all assigned duties and responsibilities because the
engineer's attention was divided between administrative requirements (maintenance of the
status board and refuel log) and refuel activities (grapple, hoist, and bridge operation). This
conflict contributed to the dropped fuel assembly event (see Section 3.3.1). Following the
event, two engineers were assigned to the refuel floor during refueling.
The team reviewed the hours of work for control room and refueling operators and
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concluded that the use of overtime was within licensee requirements and NRC guidance and
did not contribute to either event. The team verified that operators had received at least 8-
hours off between shifts and noted that 12-hour breaks were normally scheduled. Operators
interviewed by the team stated that they had had adequate rest and the team concluded that
there was no evidence that fatigue had contributed to either event. Based on a myiew of
time and attendance records, the team concluded that the licensee had effectively
administered operator hours.
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3.4.6 Management Oversight of Fuel IIandling
The team concluded that there had been little or no management oversight of fuel movement.
Operations management stated that there had been no management observations of fuel
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movement during the current outage. The quality assurance organization had not performed
any fuel movement surveillance since 1987.
4.0
REFUELING BRIDGE FUEL IIANDLING EQUIPMENT DESIGN CIIANGES
The team reviewed the details of design changes made to the refueling platform fuel handling
equipment over the past five years. During that period, the licensee completed three separate
activities intended to improve the performance of this equipment. The fuel grapple was
replaced in 1988 with an improved design with two independent hooks to carry the fuel
assembly. This year, modifications were made to improve the overall reliability of the
equipment by replacing the hoist and its controls and the other associated components such as
the refueling hoist depth (ZZ axis) monitoring and display. Following the
September 3,1993, dropped fuel assembly event, an interlock was added to the hoist upward
control circuit.
Modifications to the handling equipment controls had also occurred. Earlier training
illustrations depicted a " joystick" control on the operator console to control trolley movement
left and right, a second joystick for platform forward and reverse motion and a third for fuel
grapple hoist raise and lower. These three vertical joysticks were replaced with three
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horizontal rotary lever controls. These were operated, for example, by rotating the lever
clockwise toward the operator to raise the hoist and counter clockwise away from the
operator to lower the load.
4.1
Fuel Grapple Replacement
The original fuel grapple was replaced with a grapple of improved design in
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April - May 1988. The new grapple had redundant hooks that carried the fuel assembly
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handle. The two hooks operated independently, each actuated by its own air cylinder.
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Separate position sensing switches were operated by each of the two hooks. The switch was
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operated when its associated hook was fully engaged under the fuel assembly hand.Ie. The
switches were wired in series such that both had to be closed to illuminate the grapple closed
lamp located on the hoist operator's console.
The team reviewed the documentation for the grapple replacement contained in Plant Design
Change Request (PDCR) No. 87-03, " Fuel Grapple Replacement," and General Electric
Company Service Information Letter (SIL) No.181, " Redundant Hook Grapple Head." The
safety evaluation accompanying the design changes reasoned that the redundant hook grapple
had two hooks each with a factor of safety equal to or greater than the original single hook.
Also, the position sensing microswitches of the new grapple were believed to be more
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reliable than the proximity switch used in the original design.
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The team discussed the grapple design with vendor representatives. The redundant grapple
was designed such that a single component failure would not result in dropping a fuel bundle.
In regard to load safety factors, under normal conditions, the entire grapple assembly had a
safety factor of three, the primary hook a safety factor of 12, the secondary of 8.5 and the
shaft on which the hooks pivoted has a safety factor of 21. The redundant hooks were
configured such that it should not be possible for both to simultaneously hang up on a fuel
bundle. For example, one of the two hooks was 3/16 inch shorter that the other.
Additionally, the opening in the grapple head that accepted the fuel assembly bale handle had
been machined to provide 1/4-inch clearance across the handle width and 1/8-inch across its
thickness. When seated on the fuel assembly handle, the grapple hooks passed under the
handle with approximately 0.5 inch clearance. Additionally, the configuration of the grapple
closure sensing microswitches and their associated grapple hooks provided a positive
indication of grapple closure that was relatively insensitive to changes in switch position
adjustment. The team concluded that the grapple design provided a close tolerance fit with
the fuel assembly handle, and that the redundant hooks and their associated microswitches
provided good assurance of positive grapple operation.
During the 1988 installation, the licensee exercised an option and changed the vendor
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recommended design not to install an electrical interlock involving hoist upward motion.
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The design, as proposed by the vendor in SIL 181, provided an interlock to prevent upward
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hoist motion when loaded to approximately 480 pounds unless both grapple hook position
switches were closed indicating that the hooks were fully positioned under the fuel assembly
handle. During the design change review process, the licensee decided not to include this
electrical interlock because of their experience and the poor performance of the proximity
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switch in the old grapple. The interlock was not installed because of their concern that the
grapple might become inoperable if a microswitch failed.
4.2
Refuel Platform Upgrade
The licensee began the first phase of modifications intended to upgrade the reliability of the
refuel platform with PDCR 92-11. The work associated with this change was performed in
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the period of June 25 through August 19, 1993. The scope of these modifications was
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determined by a task force formed to review past problems with the platform and provide
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recommendations to improve reliability and performance. The equipment replaced included
the main hoist including the motor, drum, brakes, cable and controls, a new depth indicator
including a digital encoder and display, new electronic load cells and display with
programmable interlock modules, new air hoses and reels, a new air dryer and stainless steel
air lines, a new main power cable, a new access ladder and a new remote readout assembly
for the digital displays.
The team reviewed the design change documents including the safety evaluation, the design
change review comments, the completed procedure for shop tests of the hoist and controls,
and the installation and test procedure. The design change was routed within the licensee
staff for review and comment. Included on the routing were the operations and training
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departments. These documents described the various aspects of the modifications including
their operator interface aspects such as the type and location of new digital displays for main
hoist depth and main hoist load. The new hoist and its motor speed controller and associated
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joystick control were selected to provide the operator with better fine control of hoist motion.
The hoist was replaced primarily due to limitations on obtaining spare parts for the old hoist
mechanism.
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The design change document did not address the hoist direction in relation to joystick
movement, nor did it address the difference in control when replacing the rotary motion
controller with the joystick and the resultant differences to operations personnel. The
installation and test procedure for PDCR 92-11, Step 7.24.2, required operation of the main
hoist joystick and verification that the hoist rotated in the proper direction. It was necessary
to reverse motor leads to complete this requirement. Proper hoist operation was an attribute
that was verified as a third party quality control inspection.
The team concluded that the refuel platform modifcations resulted in an overall improvement
in the reliability of fuel handling equipment. However, the licensee did not seek design input
from operations personnel concerning modification of the operator interface components 'such
as controls and indication. The team also noted that the modification work was not
scheduled for completion early enough before the current refueling outage to allow hands-on
training of personnel prior to fuel movement.
4.3
Refueling Platform Holst Interlock Modification
The control circuit for the refueling platform main hoist was modified on September 6,1993,
by the licensee in response to the September 3,1993, event. The modification added an
electrical interlock that prevents upward movement of the hoist when loaded to greater than
approximately 450 pounds if both fuel grapple hooks are not fully closed. The installation
was accomplished as Temporary Modification (TM)93-053, and done under Work Order
No. 93-07052-04. The interlock installed was similar to that recommended by the vendor for
incorporation with the redundant hook fuel grapple (see Section 4.2).
The licensee modified the vendor recommended circuit after finding that a resistor in series
with the close grapple relay coil did not allow the relay to pick-up. A "b" contact in the
same relay was used to bypass the resistor and, therefore, allowed enough current to pass for
the relay to operate. The team concluded that the modification should be transparent to the
operator under normal circumstances. The grapple closed indicator lamp and main hoist load
cell operated in the same manner as before the rnodification.
5.0
MAINTENANCE AND TROUBLESHOOTING OF REFUELING EQUIPMENT
The team reviewed records of work requests and work orders for plant refueling equipment.
The team found that the licensee had been performing preventive and corrective maintenance,
applying appropriate priority to these activities.
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Under Work Order 93-07019-00, an inspection was made of the grapple, its hooks, and their
air cylinder operators and position indicating switches on September 5,1993, two days after
the dropped fuel assembly event. Other than air cylinder leaks, all components were
determined to be functioning properly. A small air leak was found at the lower air
connection to a cylinder, the other was found filled with water. The second cylinder was
replaced. The grapple hook position microswitches were found to be set to open with slight
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outward motion of the grapple hooks. In that condition, the grapple closed light would go
out as the main hoist mast was rotated to verify proper engagement with a fuel assembly
handle. The AIT was unable to determine the extent, if any, that the leaking air cylinders
contributed to the dropped fuel assembly; however, the licensee's investigation findings
discounted any contribution by the condition of the air cylinders to the event.
Work Order 93-07133-00 was written to adjust the microswitches and eliminate the
intermittent loss of grapple closure indication. This was performed on September 8,1993.
Although the team did not identify any concerns with technician performance, the team noted
that the work was accomplished without the benefit of a written procedure.
The licensee was unable to reproduce an incomplete grapple configuration with the grapple
light energized. The team concluded that the preponderance of the physical evidence
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indicated that the grapple light had not been energized during the September 3,1993, event.
The team noted, however, that the incomplete grapple configurations tested by the licensee
on smooth bar stock had not demonstrated sufficient gripping or pinching force to allow a
partial lift of a fuel assembly. The licensee stated that the assembly handle geometry, which
had a chamfered underlip. would have allowed more lift force to be transferred. The team
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considered the licensee's troubleshooting, completed about one week before the AIT
investigation, to have been adequate.
6.0
IIUMAN FACTORS REVIEW
The AIT reviewed the human factors aspects of both events regarding (a) human-system
interfaces with the refueling platform console and (b) human performance, including
ccmmand and control. In addition, human engineering deficiencies relative to the refueling
platform console that were not necessarily related to the two events were also identified.
6.1
Iluman-System Interfaces
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During the previous outage the control for the grapple was a lever switch. To raise the
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grapple, the lever switch would be pushed forward (see Figure 1). Prior to the current
outage (during August 1993), the lever switch was changed to a joystick. Although training
received information on this design change No. 92-11 (June 1993), refueling platform
operators (RPOs) received no training on how to use the new joystick. Funher, the
classroom training that was taught in preparation for the outage used a figure that
erroneously depicted the lever switch as the control for the grapple.
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The licensee indicated that the joystick was installed based on Occupational Safety and Health
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Administration (OSHA), American Society of Mechanical Engineers (ASME), and Crane
Manufacturers Association of America (CMAA) guidelines. OSHA 1910.179 section 3(iv)
states: " As far as practicable, the movement of each controller handle shall be in the same
general directions as the resultant movements of the load." CMAA Specification 70-1988,
Section 5.7.3, states: "The movement of each master switch handle should be in the same
general direction as the resultant movement of the load, except as shown in Figures 5.7.3a
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and 5.7.3b, unless otherwise specified." ASME B30.2-1990, Section 2-1.13.3(d), states:
"The movement of each manual controller or master switch handle should be in the same
general direction as the resultant movement of the load, except as shown in Figs. 6 and 7."
The licensee interpreted the above guidelines as a control panel in the horizontal plane. The
licensee considered the control console (shown in Figure 2) for the refueling platform to be
an incline plane design (i.e., about 30 degrees). Thus, the licensee installed and labelled the
joystick with the resultant load in the direction that would be appropriate for a fully vertical
plane design (i.e., forward motion is up and backward motion is down, as shown in
Figure 1). An alternate rationale would be to consider forty-five degrees to be the dividing
line for deciding whether guidelines should be applied for horizontal or vertical plane design.
In either case refueling platform operators should have been trained regarding the control
change for the refueling platform grapple.
6.2
Human Factors Weaknesses
The walkthrough, interview results, and desk top review of photographs relative to the
operation of the refueling platform console identified several additional human factors
weaknesses to the guidelines of Section 6 of NUREG-0700. The weaknesses are presented in
Attachment 4.
6.3
Conclusion
The team concluded that the human factors weakness associated with the joystick controls
change was a significant contributor to the September 9,1993, fuel assembly inadvertent
lowering event. The licensee stated at the September 21,1993, public exit that the joystick
controls had been changed as one of the licensee's corrective actions. The licensee indicated
that forward motion was now "down" and backward motion was "up" as appropriate for a
control panel in the horizontal plane.
7.0
LICENSEE CORRECTIVE ACTIONS
Following the September 3,1993 event, the licensee conducted maintenance and
troubleshooting of the hardware involved (see Section 5.0), conducted additional training (see
Section 3.1.3), and revised the fuel handling procedure (see Section 3.2). The licensee also
added a grapple interlock (see Section 4.3) and required oversight by QA during the
supplemental training sessions.
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8.0
SAFETY SIGNIFICANCE
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The team reviewed the radiation surveys, air sample records, and chemistry results following
both fuel handling incidents. No evidence was found of any increases following the
September 9,1993 event. Some small increases were identified to have occurred after the
September 3,1993 event. These increases are summarized in Attachment 5. The team
concluded that the radiological safety significance of the events was low. The team noted,
however, that the observed gaseous activity increases suggested some damage probably
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occurred to one or more fuel rods.
The team reviewed the videotapes taken of the two assemblies involved in the events and the
central core structures potentially impacted during the September 9,1993 event. There was
no indication of any damage other than to the two assemblies, but the full extent of damage
from the September 3,1993 event could not be assessed without removing the dropped
assembly. The damage visible in the videotapes was of low safety significance.
A fuel handling accident is a design basis accident and, as such, is addressed in Section
14.6.4 of the Vermont Yankee FSAR. Secondary containment integrity and operability of
key ventilation systems are prerequisites for handling fuel and were confirmed by the team to
have been in place during both events. The team concluded that the fuel handling incidents
had been appropriately mitigated by the systems operable and the existing plant
configuration, and were of minor safety significance separately.
The team was concerned, however, tiikt the weaknesses in management oversight had
allowed many of the measures intended to prevent a fue' handling accident to become
degraded. Design changes were not properly transmitted to allow timely and accurate
training on the modifications. Training was not effective in that operators were not aware of
certain key procedure steps. Procedures were not used and were not adhered to.
Supervisors did not ensure that procedures were followed. Management did not effectively
communicate expectations and provide proper oversight of fuel handling activities.
9.0
CONCLUSION
The AIT concluded that the preponderance of the evidence indicated that the
September 3,1993, event resulted from operator error. An improperly grappled fuel
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assembly became detached and fell about eight feet back to its original location with some
minor damage to the assembly. The root cause of the event was a weakness in management
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oversight of fuel handling activities as evidenced by lack of knowledge of and adherence to
the fuel handling procedure by operators, engineers, and supervisors.
The team concluded that mistaken lowering of a fuel assembly onto another core component
on September 9,1993, was an inadvertent operator performance error caused, in part, by
human factors weaknesses. The continuance of movement of the affected assembly was a
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precedure compliance error. This procedure compliance error was not identified by licensee
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line management or by the licensee's event investigation. This was indicative of a weakness
in corrective actions to the September 3,1993, incident and a continued weakness in
management oversight of fuel handling activities.
10.0
MANAGEMENT MEETINGS
Licensee management was informed of the scope of this AIT during an entrance meeting on
September 10, 1993. The team briefed licensee mam.gement of the team's observations
routinely and at the conclusion of onsite review on Sepkmber 14, 1993.
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A public exit meeting was conducted on September 21,1993, at 10:00 a.m., at the Vernon,
Vermont, town hall with licensee representatives identified in Attachment 2 to discuss the
preliminary inspection findings. The slides presented at the public exit meeting are contained
in Attachment 6. The licensee acknowledged the inspection findings and provided the results
of their assessment of the event and the short term and long term corrective actions.