05000397/LER-2007-002
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber ' No 0500 | |
| Event date: | 0-4-2007 |
|---|---|
| Report date: | 05-31-2007 |
| Initial Reporting | |
| ENS 43344 | 10 CFR 20.2201(a)(1)(ii) |
| 3972007002R00 - NRC Website | |
Plant Conditions
On April 4, 2007, Columbia Generating Station (Columbia) was operating in Mode 1 (Power Operation) at 97 percent of rated power when a small amount of licensed material in the form of special nuclear material (SNM) was identified as potentially missing. There were no structures, systems, or components (SSCs) inoperable at the time of the event that contributed to the event.
Event Description
During preparations for an NRC inspection of Columbia's SNM Control and Accounting Program (April 16-19, 2007), documentation concerning the recovery of two pieces of a broken fuel rod was obtained. The documentation revealed the existence of potential fuel particles estimated to be less than 1 gram, in aggregate, located in the spent fuel pool.
The particles were created during a 1990 refueling outage while inspecting a leaking fuel bundle. To identify the leaking rod, the bundle was disassembled and rod-by-rod electronic sorting performed.
During the process of inspecting the failed rod, the rod bent and snapped while being guided through a fuel inspection funnel. A procedure was approved and successfully executed to recover the broken rod sections. Following the recovery, an inspection was performed with an underwater camera to determine if any fuel pellets had been released as part of the evolution. No fuel pellets were identified; however, a small dark particle of material, surrounded by smaller black particles, was observed in a stainless steel bucket which had been positioned under the broken fuel rod pieces.
The bucket containing the particles was suspended off the west wall of the spent fuel pool. The location of the particles within the bucket was viewed as a temporary storage location; however, no corrective actions were established to ensure a suitable long-term storage location. Statements from station personnel indicate that during the next refueling outage the bucket containing the fuel particles was dislodged from this location and its contents are believed to have spilled into the spent fuel pool.
This observed condition was not entered into the corrective action program at the time.
The contents of the bucket have been described by the individuals involved in the broken rod recovery as a small particle of material roughly the size of a fingernail clipping surrounded by a few black particles the size of ground pepper. The material is suspected to be a small portion of an irradiated fuel pellet, i.e., ceramic Uranium Dioxide (UO2) containing irradiated Uranium-235 (U235), small amounts of Plutonium generated during reactor operation, and embedded fission products. An underwater survey performed at the time indicated a radiation level of greater than 400 Rad per hour on contact for the largest particle: Due to radioactive decay, the dose rate of this particle today is estimated to be 40 Rad per hour with an activity of less than 0.4 Curies. The total amount of material is estimated to be considerably less than 10 percent of a single pellet's worth of material, and therefore, less than 1 gram.
On May 4, 2007, Energy Northwest informed the NRC of a potential loss of positive control and accounting of these fuel particles pursuant to 10 CFR 20.2201(a)(1)(ii) (Event Notification #43344).
26158 R3 Energy Northwest is continuing to investigate this event. This report is submitted pursuant to 10 CFR 20.2201(b) as the location of these particles of licensed material cannot be positively identified at this time.
Immediate Corrective Action Upon the identification of missing licensed material, Energy Northwest promptly initiated an investigation of the circumstances surrounding the issue. This investigation was discussed with NRC personnel inspecting Columbia's SNM Control and Accounting program on April 16, 2007.
Cause of Event
The apparent cause of the missing licensed material is a lack of programmatic guidance for action and issue tracking at the time the loose fuel particles were generated. This was further compounded by a lack of understanding that SNM tracking requirements apply to small amounts of material, i.e., less than one gram.
Contributing to this event was the initial decision to inspect the failed fuel rod, which ultimately created the condition under which the loose SNM was generated. This inspection was performed without an adequate contingency plan and long-term storage solution in the event loose SNM was generated.
Assessment of Safety Consequences
This event does not pose a threat to the health and safety of the public or plant personnel.
Statements from plant personnel indicate that in 1991, the bucket used to capture the fuel particles was observed to be lying upside down on the floor of the spent fuel without contents. As such, it is believed that the fuel particles were spilled into the spent fuel pool. The spent fuel pool is an ideal location to safely contain SNM, and therefore, no threat to the health and safety of the public or plant personnel would exist.
The only credible path for the particles to be removed from the spent fuel pool would be through the vacuuming of the pool floor with a Tri-Nuc vacuum. The general area where the spill of the bucket occurred was vacuumed in November 2006, as part of a spent fuel pool cleanup campaign. The two Tri-Nuc filters associated with this vacuuming currently remain in the spent fuel pool. These filters have been surveyed at less than 1 Rad per hour indicating that it is unlikely that they contain fuel particles. No specific records of vacuuming the pool floor in the area of interest exist prior to this point; however, the possibility that a previous vacuuming of this area occurred between 1991 and 2006 cannot be ruled out. Should this have occurred, the Tri-Nuc filters would have been surveyed and shipped to the US Ecology commercial disposal site for long-term storage.
In summary, the location of the licensed material is most likely on the floor of the spent fuel pool (or suspended on some other structure internal to the pool) or contained within Tri-Nuc filters that have 26158 R3 been sent to a site licensed to receive radioactive material for long-term storage. Given the disposition of the material, there is no significant potential that this licensed material has resulted, or will result, in any exposure to radiation for plant personnel. Furthermore, as the licensed material is located in either the spent fuel pool or buried at a facility licensed to receive and store radioactive material, there is no potential for exposure of persons located in unrestricted areas.
Further Corrective Actions Energy Northwest is pursuing corrective actions to both address the missing fuel particles and to prevent future recurrence of a loss of control and accountability of licensed material.
Energy Northwest is planning to perform a survey with an underwater camera in the area where the fuel particles were believed to have been spilled.
At the time the particles were generated, the corrective action culture at Columbia was not as robust as it is today. This was manifest by a lack of programmatic guidance for action and issue tracking and was compounded by a lack of understanding of tracking requirements for small amounts of SNM.
Since that time, the corrective action program and associated culture at Columbia has matured and specific guidance has been incorporated into the plant procedure governing control of SNM (PPM 9.2.1,"Special Nuclear Material Control"). This procedure was revised in 1998 to clarify that the 1 gram threshold for the requirement to report SNM transfers is not a threshold for control and accountability purposes. Therefore, there is a high degree of confidence that Energy Northwest would address this event in a more focused manner today than 17 years ago.
Additional corrective actions being pursued to preclude recurrence include:
Procedure SWP-NFM-01, "Nuclear Fuel Reliability," will be revised to require contingency planning when removing an irradiated fuel pin from its bundle for inspection purposes. The contingency plan would address the potential for fuel pin separation or other damage and the associated potential for generation of loose SNM.
Procedure SWP-NFM-01 will also be revised to direct the use of suitable temporary and long-term storage devices for the capture and storage of any loose SNM generated during fuel inspection activities.
Procedure PPM 9.3.32, "Fuel Integrity Monitoring," will be revised to address balancing the risk of generating loose SNM during handling of individual failed rods for inspections, against the need for information to support failed fuel root cause evaluations.
Energy Northwest will evaluate the availability of reliable storage canisters for loose SNM (pellets and fragments). Such canisters would be of sufficient size, capable of being handled underwater using appropriate refueling tools, capable of being covered and sealed with a tamper proof seal to meet accountability requirements, and have requisite criticality and cooling analyses.
26158 R3 NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001) Columbia Generating Station 05000397 1 _ Similar Events There have been no other events associated with the loss of control and accounting of loose SNM at Columbia.
26158 R3