05000456/LER-2005-001
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| Event date: | |
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| Initial Reporting | |
| 4562005001R00 - NRC Website | |
A. Plant Condition Prior to Event:
These events may have occurred during three refuel outage conditions for both Units 1 and 2 within the past three years (Unit 1 10th refueling outage, Unit 2 10th refueling outage and Unit 1 11th refueling outage). The units were in Mode 6, Refuel Operations, at the time the plant configuration may have existed.
B. Description of Event:
There were no additional structures, systems or components inoperable at the beginning of the event that contributed to the severity of the event.
During the Byron Station Unit 1 refueling outage in March of 2005, an issue was raised with respect to Technical Specification (TS) 3.9.4, "Containment Penetrations," as to whether Byron was violating item "c" of the Limiting Condition for Operations (LCO) by causing direct access from containment atmosphere to the outside atmosphere during the performance of local leak rate tests (LLRT) on containment isolation valves while core alterations or movement of irradiated fuel within containment were in progress. Item "c" of the LCO requires that, during core alterations or movement of irradiated fuel within containment, each penetration providing direct access from containment atmosphere to the outside atmosphere be closed by a manual or automatic isolation valve, blind flange or equivalent. During a typical LLRT setup, the penetration piping is drained and a direct air path may exist for a short period of time from within containment to the auxiliary building through the open small diameter vent and drain valves. Based on the issue that was raised, it was believed an air path from containment to the auxiliary building was considered direct access to the outside atmosphere.
This position is contrary to how Braidwood and Byron Stations had historically applied this TS. Both Stations had always viewed this wording to mean those penetrations that have a direct air path from within containment to the outside atmosphere (i.e., not through an intermediate area or building such as the auxiliary building). Both Stations' application has been consistent since initial startup of the units.
Both Stations' original TS wording for TS 3.9.4 had identical wording as the now current Improved TS (ITS). The original Bases wording was silent on defining what "direct access from the containment atmosphere to the outside atmosphere" meant. Transition to the ITS in the 1999 timeframe indicated the new TS 3.9.4 was an equivalent change. The current ITS Bases wording also does not explicitly define "direct access from the containment atmosphere to the outside atmosphere." It does contain more details but nothing that contradicted the application of the TS.
On June 2, 2005, Braidwood Station decided to submit a voluntary LER due to the similarities in plant design and outage execution between Braidwood and Byron Stations.
(B. Description cont.) Braidwood Station's test records for the LLRTs do not have specific times that the direct path from within containment to the auxiliary building existed during each test in order to correlate it with the core alterations or movement of irradiated fuel logs. However, since several of these LLRTs were most likely started and finished within the core offload or reload schedule windows and with the absence of specific controls or coordination with fuel moves specified within the LLRT procedures, it is likely that at least once Braidwood Station had a direct path from within containment to the auxiliary building during core alterations or the movement of irradiated fuel with in containment.
Based on this likelihood, Braidwood Station believes it is prudent to submit a voluntary LER.
C. Cause of Event:
In retrospect, the original TS wording for TS 3.9.4 was issued and approved with the ambiguous wording "direct access to outside atmosphere" and was inadequately explained in its Bases section.
The cause of this ambiguous wording is unknown. The most probable cause is the authors and reviewers of the original TS and TS Bases wording inadvertently used imprecise language and failed to realize that the proposed wording and lack of detailed explanation could lead to a plausible alternate implementation of the TS 3.9.4.
D. Safety Analysis
An engineering evaluation was conducted at Byron to analyze the safety consequences of having a direct air path from within containment to the auxiliary building during a design basis fuel handling accident within containment. This evaluation concluded that there are no adverse safety consequences. This is based on available radiation monitoring and alarms to the operators and sufficient time for operator intervention to realign the auxiliary building ventilation to the charcoal filtration path to prevent exceeding 10CFR100 offsite dose limits.
E. Corrective Actions
The outage schedule for the April 2005 Braidwood Unit 2 refueling outage was rearranged to not allow the performance of LLRTs that provide direct access from containment to the auxiliary building during core alterations or movement of irradiated fuel within containment. Future outages will have the same restriction unless TS relief has been obtained via a license amendment request.
F. Previous Occurrences
There have been no previous occurrences of this nature.