05000445/LER-2004-001
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4452004001R00 - NRC Website | |
I. DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any operation or condition prohibited by the plant's Technical Specifications.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On March 3, 2004, Comanche Peak Steam Electric Station (CPSES) Unit 1 was in Mode 1, Power Operation, operating at 100 percent power and CPSES Unit 2 was in Mode 1, Power Operation, operating at 99.1 percent power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED
TO THE EVENT
There were no inoperable structures, systems, or components that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
In November 1992, at end of Unit 1 Cycle 2, fuel assembly C45 was off-loaded and stored in the Spent Fuel Pool (SFP). In April 1998, fuel assembly C45 was reloaded in the Unit 1 core as a center assembly for Cycle 7. From the BURNUP code, the fuel assembly burnup at the beginning of this cycle was 16275 MWD/MTU. BURNUP is the approved source of fuel assembly burnup. BURNUP is run monthly and at the end of each cycle and uses flux map information along with other data to calculate fuel assembly burnup.
Facility Name (1) LER Number (6) Page(3) 001 � 00 Docket 05000445 COMANCHE PEAK STEAM ELECTRIC STATION UNIT 1 Year Sequential � Revision Number � Number Enclosure to I XX-U4U8U In April 1998, CPSES procured and adopted the ABB Combustion Engineering Nuclear Fuel Accountability System (NFAS) to support tracking fuel and other Special Nuclear Materials components, providing a historical repository for fuel-related movement and isotopic data, and generating the NRC Form 741, NRC Form 742, and NRC Form 742C report(s). NFAS uses the fuel assembly bumups and isotopic concentrations calculated by the BURNUP code as input in addition to the historical data stored in an important electronic file, PRIOR_BURNUP. NFAS was tested at the ABB Windsor site to validate all modifications made to the software for customization and to validate the initialization (i.e, database loading from TXU files) of the database. However, it is unclear from validation documentation if the PRIOR_BURNUP values were populated and tested.
Upon receipt and in accordance with approved software Quality Assurance procedures, TXU personnel executed the Function Test Procedure provided by the vendor to ensure that the software performed as expected. However, the Functional Test Procedures would not have validated the integrity of the PRIOR_BURNUP data file. It is believed that the PRIOR BURNUP data file was incorrectly populated.
In October 1999, fuel assembly C45 was discharged from Unit 1 Cycle 7 and stored in the SFP low density rack. From BURNUP, the correct burnup at the end of the cycle was 35102 MWD/MTU.
In April 2000, a Special Condition Surveillance was performed by Core Performance engineering personnel (utility, non-licensed) for preparation of a fuel shuffle into the Region II racks. A NFAS "Fuel Assembly/ICA Isotopic Inventory" report was used for initial U-235 enrichment and fuel assembly burnup. The NFAS code functioned as designed. However, because the electronic file PRIOR_ BURNUP had been incorrectly populated during the original implementation of NFAS, the code calculated and reported an incorrect bumup value (51377 MWD/MTU) for fuel assembly C45. The isotopic quantities and enrichments were correct. An independent review of the surveillance was performed, but the erroneous burnup value was not identified. There was no specific procedural guidance for preparing, reviewing, and conducting the Special Condition Surveillance.
In May 2001, a Special Condition Surveillance was performed using the validated computer code HDSL (High Density Storage Location). This code package was developed "in-house" to track the implementation of the new TS 3.7.17 requirements associated with the installation of new spent fuel pool storage racks, and used the fuel assembly burnup from NFAS as an input. No documented verification of the HDSL input or results has been found. Based on the incorrect NFAS bumup of 51377 MWD/MTU, HDSL indicated that fuel assembly C45 was allowed in a "4 out of 4" storage configuration.
On June 25, 2001, fuel assembly C45 was moved into a "4 out of 4" storage configuration. The data base error from 1998 went undetected throughout this, and all subsequent, surveillances until 2004.
On March 2, 2004, Core Performance Engineering personnel were reviewing discharged fuel assembly inventory to identify candidates for use in future core designs and noticed discrepancies between informal engineering notes and the electronic files which were being reviewed. Errors in the electronic data files were identified.
On March 3, 2004, Core Performance Engineering performed a complete verification of fuel assembly configurations in the SFP. At 1110, Core Performance Engineering personnel (utility, non-licensed) discovered that fuel assembly C45 was stored in an unacceptable "4 out of 4" configuration which violated TS 3.7.17 and notified the control room. At 1516, Shift Operations (utility, licensed) moved the fuel assembly to an acceptable configuration. The LCO was exited on March 3, 2004 at 1516.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM
FAILURE, OR PROCEDURAL OR PERSONNEL ERROR
While reviewing discharged fuel assembly inventory to identify candidates for use in future core designs, errors in electronic data files were identified. Core Performance Engineering personnel (utility, non-licensed) performed a complete verification of fuel assembly configurations in the SFP and discovered that fuel assembly C45 was stored in an unacceptable "4 out of 4" configuration.
II. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED
COMPONENT
Not applicable — No component failures were identified during this event.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable — No component or system failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY
FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable — No component failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable — No component failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable — No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable — No safety system train inoperability occurred as a result of this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS
CPSES has a common Fuel Building for storage and transfer of new and spent fuel.
Two pools are provided for CPSES spent fuel storage. Each pool has Region I and Region II storage positions. The storage configurations of Region II (i.e., High Density) racks are restricted based on the fuel assembly initial enrichment and discharge burnup.
Region II racks can accommodate fuel in "1 out of 4", "2 out of 4", "3 out of 4" and "4 out of 4" storage configurations (i.e., checkerboard patterns). Soluble boron is credited for maintaining the reactivity of the array of stored spent fuel assemblies within licensing limits when spent fuel assemblies are stored in the "3 out of 4" and "4 out of 4" configurations. Upon discovery of fuel assembly C45 in an incorrect (4 out of 4) storage configuration, immediate steps were taken to move the assembly to an acceptable configuration, as required by the Action Statements in TS 3.7.17.
The event is bounded by the analyzed accident scenario of a single fresh assembly misloaded at maximum allowable enrichment into a cell for which the restriction on location, enrichment, or burnup is not satisfied. The analysis determined that a total of 1900 ppm soluble boron would be sufficient to meet the Ken-licensing limit of 0.95 (described in FSAR Sections 3.1.6.3 and 4.3.1.5, as well as the Bases for Technical Specifications 3.7.16 and 3.7.17). During the time in which assembly C45 was incorrectly stored, the spent fuel pool boron concentration remained above the required limit of 2000 ppm specified in Technical Specification 3.7.16. There were no safety system functional failures associated with this event.
Based on the above, it is concluded that the event of March 3, 2004, did not adversely affect the safe operation of CPSES or the health and safety of the public.
IV. CAUSE OF THE EVENT
In April 1998, CPSES procured and adopted ABB Combustion Engineering Nuclear Fuel Accountability System (NFAS) to support Core Performance in tracking fuel and other Special Nuclear Materials components, providing a historical repository for fuel-related movement and isotopic data, and generating the NRC Form 741, NRC Form 742, and NRC Form 742C report(s).
NFAS was tested at the ABB Windsor site to validate all modifications made to the software for customization and to validate the initialization (i.e., database loading from CPSES files) of the database. Functional Test Procedures provided by the vendor, and executed with the CPSES installation were used to conclude that the CPSES installed version of NFAS had been demonstrated to function properly and provide accurate results. However, TXU Energy believes that during the NFAS implementation, the PRIOR BURNUP data file was not correctly populated. The Functional Test Procedures would not have detected this error.
Hence, NFAS incorrectly reported the fuel assembly C45 discharge burnup which was used in determining the Region II allowable storage configuration. In addition, procedural guidance on preparing, reviewing and conducting the TS 3.7.17 surveillance was not established.
V. CORRECTIVE ACTIONS
Upon discovery, Shift Operations immediately initiated actions in accordance with TS Action Statements to move fuel assembly C45 from the Region II "4 out of 4" configuration to the Region I racks where TS 3.7.17 is not applicable.
Core Performance Engineering performed a complete verification of fuel assembly configurations in the Spent Fuel Pools using approved and validated data sources independent of HDSL and NFAS. During this effort, several discrepancies in fuel assemblies other than fuel assembly C45 were identified. Core Performance Engineering reviewed TS 3.7.17 criteria with the correct values and concluded that the affected fuel assemblies, other than C45, were acceptable in their existing storage configuration.
In accordance with approved software Quality Assurance procedures, Core Performance Engineering will develop and implement a plan to validate critical data bases used in the control of SPF storage. In addition, procedural guidance on preparing, reviewing and conducting the surveillance for TS 3.7.17 will be developed and will require independent verification checks.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar events where fuel assemblies have been stored in the incorrect location within the spent fuel pool.