05000269/LER-2007-002
| Oconee Nuclear Station | |
| Event date: | |
|---|---|
| Report date: | |
| Initial Reporting | |
| ENS 43660 | 10 CFR 72.74, Reports of Accidental Criticality Or Loss of Special Nuclear Material |
| 2692007002R00 - NRC Website | |
EVALUATION:
BACKGROUND
This event is being reported per 10 CFR 71.95(b) as "instances in which the conditions in the certificate of compliance of a spent fuel shipping cask were not followed during a shipment. 10 CFR 71.95 does not contain a "statute of limitations" clause relative to old events; therefore, this event is reportable following discovery even though the applicable shipments occurred twenty years ago. This is being reported as an Oconee Nuclear Station (ONS) event because ONS initiated the shipment.
followed in the fall of 1973 and Unit 3 in 1974. The initial cores for each of the three ONS units included two Americium-Beryllium- Curium (A-B-C) neutron emitters as sources of neutrons to facilitate initial start-up. In various documents these sources are described as "primary sources", "startup sources" and "neutron sources." This report uses the term "neutron sources." These neutron sources do not qualify as special nuclear materials (SNM) or "source material" as defined in the regulations.
Problem Investigation Process (PIP) G-95-0896, written on 11/15/95, identified potential weaknesses in ONS tracking of the specific location of these sources. A search of various documents, such as completed ONS procedures, was performed to determine the fuel assemblies which contained the neutron sources in the early ONS reactor cores.
The documents did not conclusively give the final location of the neutron sources. They indicated that two assemblies, possibly and 2 spent fuel pool and that the neutron sources from Unit 2 may have been installed in fuel assemblies 2C40 and 2C52, which were shipped to the McGuire Nuclear Station (MNS) spent fuel pool in 1987. (Due to limitations in the capacity for fuel storage at ONS, Duke Energy Carolinas, LLC (Duke) shipped spent fuel from ONS to MNS over a period of several years.) ■ Revision 13 of the Certificate of Compliance (CofC) for the TN-8L shipping cask, which was used for shipping the two assemblies to MNS, contains the following condition:
"7. PWR assemblies may be shipped either with or without burnable poison rod, thimble plug, or control rod assemblies.
EVENT DESCRIPTION
On 07/19/2006, PIP 0-06-4569 was written primarily to address issues related to the two assemblies in the ONS Unit 1/2 spent fuel pool suspected to contain Unit 3 neutron sources. However, corrective actions were created to develop appropriate tooling and procedures in order to physically inspect the assemblies in the ONS and MNS spent fuel pools to confirm the presence of primary sources.
On 9/24/07, a tool was inserted into the fuel assembly guide tubes of 2C40 and 2C52, the two assemblies in the MNS spent fuel pool suspected to contain ONS Unit 2 neutron sources, to determine if there were obstructions consistent with occupancy by a neutron source. Obstructions were confirmed in one guide tube in each of the two assemblies. While the primary sources were not visually confirmed, Duke personnel have high confidence that the obstructions are due to the presence of the sources.
Upon concluding that the neutron sources were present, the MNS personnel initiated PIP M-07-5072 to document the condition and made a one hour notification, on 9/24/07 (event number 43660), as loss/discovery of SNM. This event notification was subsequently retracted on 9/25/07 because these sources do not meet the definition of SNM.
However, as a part of the reportability review for this condition, Duke concluded that the shipments of these two fuel assemblies to MNS in 1987 may not be in full compliance with the CofC for the shipping casks used. As quoted in the Background section above,'- Condition 7 of the CofC appears to specifically limit the radioactive material associated with a fuel assembly allowed to be included in a shipment to the listed items, which do not include neutron sources.
Therefore this event is being reported per 10 CFR 71.95(b) as "instances in which the conditions in the certificate of compliance were not followed during a shipment.
10 CFR 71.95(c)(2) specifies the narrative description must include the following specific information as appropriate for the particular event:
(i)Status of components or systems that were inoperable at .the start of the event and that contributed to the event; Not Applicable - This event did not involve inoperable components or systems.
(ii)Dates and approximate times of occurrences; Fuel assemblies 2C40 and 2C52, including the neutron sources, were irradiated in the ONS Unit 2 reactor, cycles 1, 2, and 3 from December 1973 to November 1978.
Fuel assembly 2C40 was shipped from ONS to MNS on 8/17/87.
Fuel assembly 2C52 was shipped from ONS to MNS on 9/24/87.
(iii)The cause of each component or system failure or personnel error, if known; There were no component or system failures involved in this event. The issue is believed to be the result of a programmatic deficiency rather than a personnel error by any individual. See section vii below.
(iv)The failure mode, mechanism, and effect of each failed component, if known; Not Applicable - This event did not involve inoperable components or systems.
(v) A list of systems or secondary functions that were also affected for failures of components with multiple functions; Not Applicable - This event did not involve inoperable components or systems.
(vi) The method of discovery of each component or system failure or procedural error; To summarize the event description given above:
In 2006, Duke identified that the locations of the primary sources could not be positively ascertained based on available records. It was determined that attempts should be made to verify, to the extent practicable, the locations of these sources. A task was generated to inspect those assemblies.
Following generation of appropriate procedures and tooling, on 9/24/07 a tool was inserted into the guide tubes of two assemblies stored at MNS to determine if there were .
obstructions consistent with occupancy by a neutron source.
Obstructions were confirmed in one guide tube in each of the two assemblies. Therefore, Duke personnel have high confidence that the obstructions are due to the presence of the sources.
Following this inspection, in evaluating the reportability of the event, Duke personnel concluded that the presence of the sources during shipment would constitute "instances in which the conditions in the certificate of compliance were not followed during a shipment.
(vii) For ,each human performance-related root cause, a discussion of the cause(s) and circumstances; The inappropriate action is that; historically, the specific locations of the neutron sources-were not adequately tracked.
Thus, the personnel involved in processing the actual shipments apparently had no indication that these two assemblies contained primary sources.
This is a legacy issue, and due to the elapsed time involved, the reason that the sources were not tracked cannot be positively determined. The issue is considered a programmatic issue rather than a human performance issue.
The apparent cause of this event is a lack of programmatic guidance to track all radioactive materials and components related to fuel assemblies.
- In accordance with NRC regulations, the location of SNM, including the fuel assemblies themselves, has always been tracked. However, in the early years at ONS, associated components (control rods, orifice rods, etc.) were not always tracked. The ONS neutron sources were. apparently overlooked when the requirements to track associated components (including neutron sources at the other Duke nuclear sites) were added to the Duke program.
The SNM database has been updated to reflect the locations in associated fuel assemblies in the MNS spent fuel pool. While these sources are not SNM, the SNM database is being used as the tracking mechanism for convenience since the sources are currently associated with fuel assemblies.
(viii)The manufacturer and model number (or other identification) of each component that failed during the event; and No component failed during the events. However, the involved sources were:
Component: A-B-C Source Manufacturer: General Electric Serial numbers: could not be determined The involved shipping casks were:
Component: spent fuel shipping cask Model: TN-8L Manufacturer: Transnuclear, Inc, Columbia, Md.
Applicable Certificate of Compliance: No. 9015, revision 13 (ix)For events occurring during use of a packaging, the quantities and chemical and physical form(s) of the package contents.
Chemical form of the material, as manufactured: Americium beryllium pellets (Am02-Be mixed powder); approximately 0.35 lbs Physical form: Americium-beryllium pellets in a sealed stainless steel capsule. The capsule is then housed in a "neutron source shroud tube assembly", which is positioned in a fuel assembly guide tube. The fuel assemblies are Babcock & Wilcox 15x15 design.
CORRECTIVE ACTIONS
Immediate:
None: The affected fuel shipments were completed approximately twenty years prior to discovery of the event.
Subsequent:
The Duke database for tracking SNM has been modified to include various control components, now including these neutron sources.
While the locations of these sources have not been absolutely confirmed, Duke is highly confident that the inspected assemblies in'the MNS spent fuel pool do contain the two sources, and the database has been updated to reflect these locations.
Planned:
None: All corrective actions have been taken and the sources are acceptable for storage in the MNS spent-fuel pool.
These corrective actions are not considered NRC Commitment items.
There are no.NRC Commitment items contained in this LER.
SAFETY ANALYSIS
In 1998, Duke Nuclear Fuels Management personnel in the Duke General Office evaluated the sources and concluded that the neutron sources present no radiological, thermal or criticality concerns.
Therefore, there was no actual impact on the health and safety of the public due to this event.
ADDITIONAL INFORMATION
There were no releases of radioactive materials, radiation exposures or personnel injuries associated with this event.
This event is not considered reportable under the Equipment Performance and Information Exchange (EPIX) program.