Event Notification Report for April 19, 2006

CONTRACT EMPLOYEE FAILED A RANDOM FITNESS FOR DUTY TEST

A non-licensed contract supervisor tested positive for a controlled substance during a random test. The individual's access to the plant has been terminated. Contact the Headquarters Operations Officer for additional details.

The licensee notified the NRC Resident Inspector.

RADIATION READING IN CONTAINMENT READ 100 TIMES ABOVE NORMAL LEVELS

"At 0225 hrs on April 19, 2006, a container storing in-core instrument pieces rose to the surface of the flooded reactor cavity under its own buoyancy, causing unexpected high radiation readings in the general vicinity of the reactor cavity for a few seconds before the container returned to the bottom of the reactor cavity. Emergency Action Level RU2.2 was promptly reviewed, and it was determined that the threshold for an unusual event was not exceeded, because the area radiation monitors rose by a factor of approximately 100 versus the EAL setpoint of 1000 over normal levels.

"Subsequently, at 1750 hrs, during post event investigation, it was discovered that dose rates indicated by an electronic dosimeter worn by an individual in the area at the time of the event may have exceeded the EAL setpoint of 1000 times the normal radiation levels for that area of containment for a few seconds. The total exposure received by the individual was less than 50 millirem. Therefore, this event is being reported in accordance with NUREG 1022, Revision 2, Section 3, 'Discussion' as a potential event discovered after-the fact."


The licensee notified the NRC Resident Inspector, and Al Svilpe, Emergency Management Office in Van Buren County, MI. There is also expected to be some media attention from this incident.

POTENTIALLY LOST DEPLETED URANIUM SHIPPING SAFES

The licensee recently performed a physical inventory of the depleted uranium "safes" used for shipment of Technetium-99m generators. These safes weigh about 45 lbs each and are used to provided shielding during the Tc99m shipments. Of approximately 3200 safes possessed by the licensee, 145 could not be located. The licensee is continuing its investigation and has expanded the search area within other buildings in the 20 acre facility. The licensee is also investigating possible inventory record keeping errors associated with the inventory tracking program.

The licensee has informed the NRC R3 (Gattone) of the missing safes.

THIS MATERIAL EVENT CONTAINS A "LESS THAN CAT 3" LEVEL OF RADIOACTIVE MATERIAL

Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks.

NON-CONSERVATIVE COLD OVERPRESSURE LIMIT CURVES DISCOVERED DURING ENGINEERING REVIEW

"Cold overpressure limit curve utilized in the EMG (Emergency Guidelines) network including EMG F-0, Critical Safety Function Status Trees is incorrect and non-conservative. This could have resulted in some instances where the operator may have diagnosed a green path (no challenge) when a yellow (potential challenge) or orange path (severe challenge) actually existed. The consequence would have been failure to implement the correct functional restoration procedure."

This problem was found during an Engineering review. The problem had existed since 1999.

The NRC Resident Inspector was notified of this event by the licensee.


* * * RETRACTION AT 1308 EDT ON 5/17/2006 FROM Lance Lane TO Steve Sandin * * *

"The purpose of this notification is to retract a previous report made on 4/19/06 at 1113 hours (EN# 42510). Further evaluation revealed that a green path would not have been diagnosed instead of an orange path. The evaluation also concluded that this condition does not prevent the fulfillment of a safety function."

The licensee informed the NRC Resident Inspector. Notified R4DO (Jones).

POSTULATED SCENARIO WHERE CONTAINMENT SPRAY SYSTEM MAY BE UNABLE TO FULFILL DESIGN SAFETY FUNCTION

"During a review of the operation of the plants emergency cooling system for the containment an unanalyzed single failure was discovered. The identified single failure scenario could result in the containment spray system being unable to fulfill its design safety functions.

"In the event of loss of offsite power occurring after the initiation of an accident signal, the 480V undervoltage relays serve to trip open containment spray pump breakers (as well as other ESF breakers) in order to prepare the breakers for resequencing after the diesel generator output breakers have closed onto their associated buses. The undervoltage trip bypass function performed by the sequencer timer relay contacts serves to prevent tripping ESF breakers due to inadvertent actuation of the undervoltage trip circuits and allows ESF breakers to trip only when sequencers have been reset by a loss of voltage at the 4160V bus level.

"In situations where a loss of power occurs at the 480 volt level without a coincident loss of power at the associated 4160 volt level, ESF loads supplied from the lost 480 volt bus, such as containment spray pumps, do not receive a trip signal due to the undervoltage blocking feature of the sequencing relays. For most ESF loads, this is not a problem and can be considered part of a single failure scenario affecting only one train of ESF equipment. In the case of containment spray pumps SI-3B and SI-3C, however, the failure of the associated breakers to trip during a single failure of bus 1B4B, results in the operation of a single spray pump, SI-3A with two containment spray valves open. This results in one pump operation to two containment spray headers.

"Operating the containment spray system in a one pump, two header configuration creates the possibility of inadequate system performance. This configuration may result in overloading the running pump (due to runout) and inadequate NPSH to the running pump. This condition was intended to be prevented by a modification which installed an interlock between spray pumps SI-3B and SI-3C and spray valve HCV-344. The modification apparently failed to consider the single failure of specific 480 Volt buses.

"Spray valve HCV-344 has been disabled in the closed position so that no external signals will allow the valve to be opened. Disabling this valve places the plant in a 24 hour LCO (Technical Specification 2.4.2.d) starting at 0950 CDT."

The licensee notified the NRC Resident Inspector.

* * * RETRACTION FROM MATZKE TO HUFFMAN AT 1439 EDT ON 6/01/06 * * *

"On April 19, 2006, Ft. Calhoun station reported that an unacceptable single failure scenario had been identified that could result in the containment spray system being unable to fulfill its design safety functions. The failure scenario required that there be a loss of power at the 480 volt AC level without a coincident loss of power at the associated 4160 volt AC level. This resulted in the potential for one pump operation to two containment spray headers.

"Following a review of failures that would cause this it was determined that of all the possible failure mechanisms that could impact the capability of affected 480 volt AC bus, such that both trains of containment spray pump could be adversely affected, the only failure mechanism that has unacceptable consequences is a failure of multiple phases of AC power failing in an open circuited manner without a fault occurring and, consequently, without supply breakers opening. This failure mechanism has been determined not to be credible. Therefore, it is not necessary to assume that this type of failure could occur as part of a design basis event. Therefore, no credible single failure could result in the failure of the containment spray system to perform its intended safety function. The report of April 19, 2006 is being retracted June 1, 2006."

The licensee notified the NRC Resident Inspector. R4DO (Spitzberg) notified.