05000275/LER-2002-006
| Event date: | |
|---|---|
| Report date: | |
| 2752002006R00 - NRC Website | |
I. Plant Conditions
Unit 1 was in Mode 6 (Refueling), with the reactor core offloaded to the spent fuel pool, during the described condition.
II. Description of Problem
A. Background
Technical Specification (TS) 3.7.17.2, "Spent Fuel Assembly Storage - Region 2," [DF][RK] requires that the combination of initial enrichment, fuel pellet diameter and burnup of each spent fuel assembly stored in Region 2 shall be within the acceptable area of Figure 3.7.17-2 (combination of initial enrichment and burnup), or the fuel assembly is stored in a checker board pattern with water cells or cells containing non-fissile material.
Surveillance Requirement SR 3.7.17.2.1 requires verification by administrative means that the fuel assembly characteristics and its expected storage location are in accordance with LCO 3.7.17.2 prior to each fuel assembly move, when the assembly will be stored in Region 2.
TS 3.7.16, "Spent Fuel Pool Boron Concentration," requires that the spent fuel pool boron concentration shall be >2000 ppm, when fuel assemblies are stored in the spent fuel pool.
It should be noted that since this event TS 3.7.16, TS 3.7.17.1 and TS 3.7.17.2 have been revised to remove region designations and analytically credit soluble boron in the spent fuel pool.
B. Event Description
On May 5, 2002, at 0022 PDT during the Unit 1 eleventh refueling outage (1R11) core offload, fuel assembly DD14 was placed in spent fuel pool location K-11.
On May 6, 2002, at 1025 PDT fuel assembly J55 was placed in spent fuel pool location L-11, adjacent to location K-11. Fuel assembly J55 met the TS requirements to be placed in any Region 2 location. Fuel assembly 'DD14, in location K-11, should have remained in a checkerboard pattern with water cells, however, following the J55 move adjacent to DD14, it did not, resulting in a violation of TS 3.7.17.2.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I) DOCKET NUMBER (2) -LER NUMBER (6) OF 2002 Diablo Canyon Unit 1 5 3 6 0 5 7 2 0 0 5 0 0 0 0 0 On May 11, 2002, at 1534 PDT fuel assembly DD14 was removed from spent fuel pool location K-11 during the core reload.
On September 27, 2002, a utility engineer discovered the nonconforming condition while updating a new fuel-tracking software package.
C. Inoperable Structures, Systems, or Components that Contributed to the
Event
None.
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
On September 27, 2002, a utility engineer identified the nonconforming condition while updating a new fuel-tracking software package.
F. Operator Actions
None.
G. Safety System Responses
None.
Ill. � Cause of the Problem
A. Immediate Cause
The preparer of the core offload sequence plan failed to recognize the relationship between fuel assemblies DD14 and J55.
B. Root Cause
The root cause of the event was personnel error by utility engineers that prepared, reviewed, and approved the core offload sequence. The cause of this error was skill and/or rule based, in that the preparer, reviewer, and approver had done this preparation multiple times but never with the spent fuel pool density as high as it was at that time.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I) DOCKET NUMBER (2) LER NUMBER (6) OF 2002 5 7 2 0 0 0 5 0 Diablo Canyon Unit 1 5 4 0 0 6 0 0
IV. Assessment of Safety Consequences
The Diablo Canyon Power Plant (DCPP) criticality analysis in effect at the time of the event for the Region 2 racks with up to 5% enriched fuel was examined. The analysis calculations demonstrate that a misplaced fuel assembly (fresh assembly of 5.0% enrichment accidentally loaded into a Region 2 cell) results in a KEFF of 0.978 (without uncertainties) with all other cells filled with fuel of the maximum permissible reactivity. To assure a maximum calculated KEFF below 0.95 the spent fuel pool would require an estimated 400 ppm soluble boron.
TS 3.7.16 at the time of the event required that the spent fuel pool boron concentration be >2000 ppm. Therefore at the time of the event the boron concentration exceeded the 400 ppm required to ensure KEFF is below 0.95 and DCPP was within the analysis for spent fuel pool storage.
There were no safety consequences involved in this event because the spent fuel pool storage is demonstrated to have sufficient margin to ensure safety.
Therefore the event did not adversely affect the health and safety of the public.
V. Corrective Actions
A. � Immediate Corrective Actions 1. On May 11, 2002, at 1534 PDT fuel assembly DD14 was removed from spent fuel pool location K-11 during the core reload.
2. The spent fuel pool storage configuration for the past five years was reviewed. PG&E verified there was no similar event during these previous core offloads.
3. The personnel involved with this event identified the condition and actively participated in the problem investigation.
B. � Corrective Actions to Prevent Recurrence 1. PG&E will revise procedures to incorporate a checklist outlining the key areas of focus when preparing, reviewing, and approving the core offload sequence to assure compliance with TS requirements.
2. PG&E will use a new fuel-tracking software program to help plan fuel movements. Use of this program will provide warnings of planned moves that would be in violation of TS requirements.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I) DOCKET NUMBER (2) LER NUMBER (6) OF 2002 5 Diablo Canyon Unit 1 5 5 6 0 0 5 7 2 0 0 0 0 0 0 VI. A Additional Information
A. Failed Components
None.
B. Previous Similar Events
None.