ENS 40165
ENS Event | |
|---|---|
13:43 Sep 17, 2003 | |
| Title | Post Alert Emergency Declaration Based on Calculated Rcs Inventory Loss |
| Event Description | The plant is currently in Mode 5 for a Refueling outage. Reactor Coolant System (RCS) level was being maintained just below the Reactor Vessel flange, 1012.33 feet, with Shutdown Cooling in service and Shutdown Cooling Purification in service. RCS temperature was 100F. At 0821 a lowering level was noted on the Control Room level indications LI-119 and LI-197. At 0824 Shutdown Cooling Purification was secured and the lowering level was stopped with an indicated RCS level 1010.33 feet. At 0843 it was determined that approximately 1350 gallons of RCS water was lost over the 3 minutes that the event lasted. It was determined that during that time conditions existed to enter EAL 1.4, RCS leak greater than 40 gpm. At no time was Shutdown Cooling lost and RCS temperature remained at 100F. At 0825 Abnormal Operating Procedure (AOP-19) was entered. Makeup to the RCS was initiated immediately and level was completely restored at 0842 with charging pumps secured. It has not been determined at this time where the inventory went. A walkdown of the Containment and Auxiliary Building has been completed.
At this time the plant is stable with an RCS level on 1012.5 feet. The licensee is conducting an investigation and will provide an update to this report. The licensee informed both the State of NE and IA and the NRC Resident Inspector.
The licensee is retracting this report based on the following: On September 17, 2003, the Fort Calhoun Station notified the NRC that conditions had existed, for about 3 minutes, to make an alert notification. No alert was declared as the time the station was in the condition was such, a limited time. The condition that required the notification was a reactor coolant system (RCS) leak of >40 GPM. The event occurred as follows: At approximately 0821 on September 17, 2003, Operations noted decreasing level in the reactor vessel. This was indicated on both of the shutdown RCS level indicators. Due to the uncontrolled (indicated) reduction in RCS level, AOP-19 was entered. Within minutes, the indicated level had dropped from 1012' 6" to 1010' 3". Shutdown cooling purification was isolated. The two (2) charging pumps running for shutdown purification were left in operation. After a few minutes, the charging pump's 80 gpm flow caused the RCS level to stop dropping and RCS level began to rise. During and immediately following this event, numerous walkdowns of containment and the auxiliary building were performed that ensured there was no loss of water from the RCS. No coolant leakage was noted during the walkdowns. The cause of the level change was small pressure in the head making the indication read higher than actual. Disconnecting the HJTC clamp allowed a positive vent which caused indicated level to fall. When interviewing the craft performing the work on the HJTC, it was noted that when removing the clamp front a HJTC, the craft noticed a small amount of water bubbling on the HJTC and when an attempt was made to lift the HJTC hub, air was heard in the vicinity of the HJTC. Additionally the craft stated there was some resistance felt from the HTJC when attempting removal. The craft then contacted radiation protection to determine what personnel protection was required. On the second attempt to lift the hub, the craft heard air flow in the vicinity again. When the clamp was finally lifted there was little resistance. It is suspected that the air at the HJTC was due to a pressure differential between the vessel and the containment atmosphere. The higher pressure in the reactor vessel caused level indications to read higher than actual level by approximately 2 feet. When the HJTC flange opened, the change in pressure caused a redistribution of water levels in the RCS. This caused the indicated RCS level change. There was never a leak of RCS coolant outside of the RCS. Therefore, this event notification is being retracted. The licensee informed the NRC Resident Inspector. Notified R4DO(Gody). |
| Where | |
|---|---|
Ft Calhoun  Nebraska (NRC Region 4) | |
| Reporting | |
| Emergency class: | Alert |
| 10 CFR 50.72(a) (1) (i), Emergency Class Declaration | |
| Time - Person (Reporting Time:+-3.23 h-0.135 days <br />-0.0192 weeks <br />-0.00442 months <br />) | |
| Opened: | Randall Cade 10:29 Sep 17, 2003 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Sep 19, 2003 |
| 40165 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Cold Shutdown (0 %) |
| After | Cold Shutdown (0 %) |
WEEKMONTHYEARENS 514392015-10-02T14:05:0002 October 2015 14:05:00
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