05000327/LER-2009-009
| Docket Numbersequential Revmonth Day . Year Year Month Day . Year ,Number No. Sqn Unit 2 05000328 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3272009009R01 - NRC Website | |
I. PLANT CONDITION(S)
Units 1 and 2 were operating at approximately 100 percent power at the time the probable maximum flood (PMF) calculation was issued.
II. DESCRIPTION OF EVENT
A. Event:
On December 30, 2009, the Tennessee Valley Authority (TVA) issued an updated calculation titled "PMF Determination for Tennessee River Watershed" that increased the SQN design basis PMF level from Elevation 719.6 feet to Elevation 722.0 feet. The increase in calculated PMF elevation resulted from several calculational changes including better flood modeling and changes in river and reservoir operating policies. A previous change had decreased the SQN PMF elevation from 722.6 feet to 719.6 feet.
However, SQN remains designed for Elevation 722.6 feet with the current exception of the diesel generator sets (EDS code EK) and spent fuel pool cooling pumps (EllS code DA). No actual flooding occurred; however, because of the unanalyzed condition, the ,potential existed for SON to exceed its design basis PMF level and adversely affect plant safety.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
Date � Description March 19, 2008� The Nuclear Regulatory Commission (NRC) issued an inspection report and notice of violation on implementation of the quality assurance program governing the hydrology code for TVA's Bellefonte Nuclear Plant combined license application.
February 3, 2009 � Based upon preliminary updated calculations indicating an increase in PMF elevation, SON issued a standing order requiring contingency measures to protect the diesel generator sets and spent fuel pool cooling pumps during a PMF event.
December 30, 2009 Updated PMF calculation increased the design basis PMF elevation from 719.6 feet to 722.0 feet.
D. Other Systems or Secondary Functions Affected:
No other systems or secondary functions were affected by this event.
E. Method of Discovery:
The implementation of the quality assurance program governing TVA's 'PMF calculation for the Bellefonte Nuclear Plant combined license application was questioned by the NRC resulting in the issuance of an updated calculation titled "PMF Determination for Tennessee River Watershed" that increased the SQN design basis PMF level from Elevation 719.6 feet to Elevation 722.0 feet.
F. Operator Actions:
SQN Operations issued a standing order requiring contingency measures to protect the diesel generator sets and spent fuel pool cooling pumps during a PMF event.
G. Safety System Responses:
No safety system activation occurred. Contingency measures were put into place to protect the diesel generator sets and spent fuel pool cooling pumps.
CAUSE OF THE EVENT
A. Immediate Cause:
The immediate cause of this event was river system operational changes and incorrect assumptions regarding PMF calculations.
B. Root Cause:
The root cause of this event was determined to be the failure to establish a PMF procedure or process that could be used to train personnel to perform, revise, and maintain accurate PMF calculations. A second root cause was organizational and programmatic deficiencies caused by organizational breakdowns and inadequate communication between TVA organizations.
C. Contributing Factor:
Contributing factors were inadequate information and training, and incorrect assumptions regarding PMF calculations.
IV. ANALYSIS OF THE EVENT
On December 30, 2009, the issuance of an updated PMF calculation revealed that the PMF elevation had increased from Elevation 719.6 feet to Elevation 722.0 feet. Earlier preliminary calculations had indicated an increase in PMF elevation, and contingency measures to protect the diesel generator sets and spent fuel pool cooling pumps during a PMF event had already been put in place. These contingency measures required advance notification be given to SQN Operations of any rainfall conditions that would require implementation of contingency protection measures. Although no flooding occurred, because of the unanalyzed condition the potential existed for SQN to exceed its PMF design basis and adversely impact plant safety.
V. ASSESSMENT OF SAFETY CONSEQUENCES
Based on the above "Analysis of The Event," this event did not adversely affect the health and safety of plant personnel or the general public.
VI. CORRECTIVE ACTIONS
A. Immediate Corrective Actions:
SQN entered the information into the Corrective Action Program and issued a standing order requiring contingency measures to protect the diesel generator sets and spent fuel pool cooling pumps during a PMF event.
B. Corrective Actions to Prevent Recurrence:
The corrective actions are being managed by the TVA and Sequoyah Nuclear Plant Corrective Action Program.
Corrective actions consist of developing a PMF evaluation process that will include interface reviews between impacted TVA organizations, define ownership, roles and responsibilities of impacted TVA organizations, include a periodic review of critical PMF inputs, and provide training on management of the PMF process. Applicable plant procedures are being revised to incorporate the contingency measures during a PMF event. A design change has been initiated to permanently protect the diesel generator sets and spent fuel pool cooling pumps based on the increased PMF elevation.
VII.�ADDITIONAL INFORMATION
A. Failed Components:
None.
B. Previous LERs on Similar Events:
A review of previous reportable events within the last three years did not identify any previous similar events.
C. Additional Information:
None.
D. Safety System Functional Failure:
This event did not result in a safety system functional failure in accordance with 10 CFR 50.73(a)(2)(v).
E. Unplanned Scram with Complications:
This condition did not result in an unplanned scram with complications.
VIII. COMMITMENTS
None.