05000331/LER-2007-002
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3312007002R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Duane Arnold Energy Center 05000331 YEAR
I. Description of Event:
Sometime on or about February 11, 2007, 3 eight inch penetrations were opened between the control room floor and the cable spreading room. The exact time that the 3 eight inch penetrations were opened is unclear. When this event was determined to be reportable, the temporary contract personnel who opened the penetrations were unavailable for interviews, since they had already left the plant site. The time they were opened has been estimated to be around midnight on February 11, 2007.
On February 12, 2007 at 0416, a test was performed to evaluate the impact of opening 2 four inch penetrations between the turbine building and the cable spreading room on control room positive pressure.
The initial value of the control room pressure for the test was 0.1 inch of water. This value was established with the 3 eight inch penetrations open. At the beginning of the test, data was stable and showed an acceptable value for the control building pressure. The test was completed on February 12, 2007 at 0519.
However, the final pressure measured from the test showed a value of 0.095 inches of water. During the performance of the test, controls were not in place to limit opening of doors to the control room, which would lower the measured pressure, and the conditions for performance of a surveillance test meeting the requirements of Technical Specification Surveillance Requirement 3.7.4.4 were not established.
Consequently, as a result of the final measured control room pressure and the uncertainty associated with the test conditions, the control building boundary was conservatively declared inoperable February 12, 2007 at 1052. The control building boundary had potentially been inoperable for as much as 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> and 52 minutes with Core Alterations in progress, a condition prohibited by Technical Specifications. Technical Specification 3.7.4, Condition F requires that Core Alterations be suspended immediately upon discovery of an inoperable control building boundary. Subsequent surveillance testing proved the ability of the Standby Filter Unit (SFU) System to fulfill its function to maintain a control room positive pressure of greater than or equal to 0.1 inches water gauge relative to the outside atmosphere during the isolation mode of operation.
There were no other structures, systems, or components inoperable at the start of the event that contributed to the event.
II. Assessment of Safety Consequences:
There was no adverse effect to the plant. Once the condition was identified, fuel movement was immediately suspended per the requirements of Technical Specification 3.7.4, Condition F.
Based on the testing completed, it is believed that the SFU System was available during the time period the control building boundary was declared inoperable and could have maintained the required positive pressure and, therefore, no loss of filtration occurred. Therefore, it is believed that control building habitability was maintained during the period that the penetrations were opened.
A quantitative assessment of the risk associated with this event was not performed since this event did not involve a loss of residual heat removal, a loss of offsite power or a loss of reactor inventory, and therefore had no effect on Core Damage Frequency (CDF) or Large Early Release Fraction (LERF). It is FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Duane Arnold Energy Center 05000331 YEAR NUMBER NUMBER believed that the SFU system would still mitigate those accidents for which it is designed to mitigate in the refueling mode, such as a fuel handling accident, with no effect on LERF.
By assessment of the control building design, it is believed air flows would have progressed from the control room to the cable spreading room. This is supported by the fact that the air supply to the control room is designed to maintain the control room at a higher pressure. Therefore, it is believed no inleakage from the cable spreading room to the control room will occur.
III. Cause of Event:
Previously, it was not understood that opening of penetrations within the control building envelope compartments could render the control building boundary inoperable. The control building at the Duane Arnold Energy Center (DAEC) is atypical in that the control room is not isolated from the rest of the control building. The control room proper is to be capable of being maintained at greater than or equal to 0.1 inches of water positive pressure with respect to the outside atmosphere. This assures that unfiltered air does not reach the control room in the isolation mode. Other areas of the control building that directly communicate with the control room via HVAC system ductwork or doors are also required to maintain a positive pressure relative to the adjacent areas outside the control building. This will assure that leakage is from the control building to the adjacent areas or outdoors.
The work order steps that opened the 3 eight inch penetrations between the control room floor and the cable spreading room were not followed properly, thereby creating a condition that the control room operators were not aware of. DAEC staff also did not understand that opening of penetrations within the control building envelope compartments could render the control building boundary inoperable.
Additionally, workers were not directly required to inform the control room operators that they were opening control building penetrations within the control building.
IV. Corrective Actions:
- Procedure ACP 1408.1, Work Orders, was updated to require that, in order to open any penetration in the control building envelope, a control building penetration control form be filled out and forwarded to the control room supervisor for signature prior to opening the penetration. This ensures that control room operators will be made aware of any plans to open control building penetrations and judge whether these plans are acceptable based on the current plant operating mode or other condition specified in the Technical Specification Applicability. (PCR045165)
- Plant personnel were coached on appropriate work controls with respect to control room operator notification prior to starting work.
- Operators will be briefed on this event and the administrative changes made to prevent recurrence during upcoming Operator Requal Training. (RFT045699) FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Duane Arnold Energy Center 05000331 YEAR
V. Additional Information:
Previous Similar Occurrences:
A review of LERs and operator logs at the DAEC over the last 5 years identified no LERs or other similar events with similar causes.
EIIS System and Component Codes:
Control Building/Control Complex Environmental Control System
VI
Reporting Requirements:
This report is being submitted under 10 CFR 50.73(a)(2)(i)(B).