05000316/LER-2003-004
| Donald C. Cook Nuclear Plant Unit 2 | |
| Event date: | 04-26-2003 |
|---|---|
| Report date: | 06-25-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3162003004R00 - NRC Website | |
17. TEXT (if more space is required, use additional copies of NRC Form (366A) Conditions Prior to Event Unit 1, MODE 4 Unit 2, MODE 4
Description of Event
On April 26, 2003, Donald C. Cook Nuclear Plant (CNP), during the performance of a routine inspection of the ice bed within the Unit 2 ice condenser, identified that ice basket 11-7-1 weighed 1125 pounds (lbs.). Technical Specification (TS) 3.6.5.1d requires that the ice bed shall be OPERABLE with each ice basket containing at least 1144 lbs. of ice (end-of-cycle). Therefore, the weight of ice basket 11-7-1 did not meet the minimum required weight specified in TS 3.6.5.1d.
Based upon these TS requirements, the discrepant basket and the 20 additional representative baskets were evaluated. This evaluation was performed in accordance with the requirements of 12-EHP-4030-010-262, "Ice Condenser Surveillance and Operability Evaluation," Revision 1. The representative sample of 20 additional baskets were from the same bay and were adjacent to the discrepant basket in order to be representative of the discrepant basket. The result of this data collection revealed the average weight of the 21 ice baskets was 1423 lbs. and the standard deviation was 92.92 lbs. The 95% level of confidence was calculated to be 1388 lbs. This 95% level of confidence value is greater than the 1144 lbs./basket required by TS Surveillance Requirement 4.6.5.1.b.2.
Ice basket 11-7-1 was filled prior to restart of Unit 2 in June 2000. The original weight of the ice in this basket in April 2000 was 1518 lbs. The as-found weight during the Unit 2 2002 refueling outage (U2C13) was 1525 lbs. The as-left weight in January 2002 was 1518 lbs. The as-found weight in the Unit 2 2003 refueling outage (U2C14) was 1125 lbs.
Baskets in row 1 of this part of the ice condenser typically range between losing a maximum of ten pounds to gaining a maximum of fifteen pounds during a cycle. In this case, the basket lost 393 pounds, which is highly unusual. Obtaining an Improper weight or some unknown loss of ice could cause this. The surrounding baskets performed as expected without any unexpected results. During U2C13, 13 of the 27 baskets refurbished were row 1 ice baskets from which ice was removed and the baskets re-weighed, including ice basket 11-7-1.
Ice basket 11-7-1 was subsequently emptied, inspected and found undamaged, and refilled in accordance with 12-MHP-5021-010-002, "Ice Condenser Ice Removal and Filling," Revision 1, and ISP-5021-010-005, "Ice Condenser Ice Baskets Removal, Inspection, Repair and Installation." The U2C14 as-left weight of ice basket 11-7-1 was 1484 lbs.
- 1004 00 2003 17. TEXT (If more space is required use additional copies of NRC Form (366A) Concerns associated with the weight of ice basket 11-7-1 were first identified on April 26, 2003. At that time, CNP considered the weight, as measured, to be suspect. The rate of ice loss due to sublimation appeared excessive. CNP had planned to re-weigh the basket; however, the basket was emptied prior to the request for re-weighing being issued. The causal evaluation for this concern was completed in early June of 2003. Upon completion of the causal evaluation, CNP determined the suspect weight of ice basket 11-7-1 was reportable and the reportability process was entered.
During the extent of condition evaluation for this event, CNP discovered that during the Unit 1 2002 refueling outage, ice basket 24-1-7 fell below the minimum TS weight limit. Ice basket 24-1-7 was emptied and refilled, at that time, with 1445 lbs. of ice. This condition was not recognized as being reportable at that time. This event will be reported to the Nuclear Regulatory Commission in been entered into the CNP corrective action program.
Cause of Event
The apparent cause of the loss of 393 lbs. of ice from ice basket 11-7-1 cannot be definitively explained. The most likely cause is an error in the weighing process.
This event is considered an isolated case.
Analysis of Event
The safety functions associated with this condition are:
1. The ability to absorb thermal energy resulting from a loss of coolant accident or a main steam line break to limit containment pressure rise to less than design pressure immediately following an accident, and to support longer term heat removal (until the ice bed has completely melted).
2. Remove iodine from the containment atmosphere.
3. Provide an inventory source for the containment recirculation sump to support sump recirculation level requirements, sump pH, and sump boron requirements.
There is no safety significance consequence of the condition. The representative sample of 20 additional ice baskets in the same bay revealed the 95% level of confidence weight was 1388 lbs. of ice, which is greater than the minimum of 1144 lbs. The ice condenser would have performed all of its safety functions. The overall mass of ice met the needs of each of the safety functions.
Corrective Actions
Ice basket 11-7-1 was emptied, inspected for damage, and refilled with 1484 lbs. of borated ice.
—1004 00 2003 17. TEXT (If more space is required, use additional copies of NRC For ► (366A) In accordance with TS 4.6.5.1.b.2, upon discovery of the low weight in ice basket 11-7-1, an additional 20 ice baskets within the same bay were weighed. The average weight of the 20 additional ice baskets and the discrepant basket (ice basket 11-7-1), was greater than 1144 lbs.
Procedure 12-EHP-4030-010-262, "Ice Condenser Surveillance and Operability Evaluation," will be revised. This revision will incorporate an engineering verification to ensure as-found weights are consistent with previous as-left weights prior to actions being implemented to correct discrepant conditions.
Previous Similar Events
- LER 50-315/98-007-01, Ice Condenser Weights Used to Determine Technical Specification Compliance Not Representative
- LER 50-315/98-015-01, Ice Weight Requirements Potentially Not Met Due To Nonconservative Assumptions In Software Program
- LER 50-315/98-026-00, T/S Surveillance Requirement 4.6.5.1.b.2 Not Met Due To Failure To Accurately Transfer Requirements Into Plant Procedures
- LER 50-315/2002-008-00, Weight of Ice Basket Below Minimum Allowed in Technical Specification 3.6.5.1 CNP has reviewed the above docketed LERs and has determined that the events associated with the identified LERs were sufficiently different. Therefore, the corrective actions associated with these events would not be expected to prevent the event being reported in LER 50-316/2003-004-00.
During the 2002 Unit 1 refueling outage, CNP identified ice basket 24-1-7 did not meet the minimum weight requirements of TS 3.6.5.1d. This condition was not recognized to be reportable at the time of discovery, but is now considered as a failure to comply with TS 3.6.5.1d and was included in LER 50-315/2002-008-00 to meet the reporting criteria of 10 CFR 50.73(a)(2)(i)(B). The discrepant condition was corrected at the time of discovery.