Event Notification Report for October 18, 2000

FAILURE OF VAPORIZE LEVEL PROBE IN "3A" VAPORIZER

NRC BULLETIN 91-01 24 HOUR NOTIFICATION

Periodic testing of the condensate level detection system in the 3A vaporizer steam chest determined that the system could not perform its intended function due to blockage in the system by loose debris. Further investigation determined that paint flaked from the recently processed cylinder and collected in the bottom of the vaporizer. However, the debris did not block the main condensate removal drain which allowed condensate to be removed from the vaporizer, so there was no condensate accumulation.

The vaporizer bottom was cleaned and the level detection system was checked. The system responded correctly.

SAFETY SIGNIFICANCE OF EVENTS:

No contingency occurred. No accumulation of water in the bottom of the vaporizer occurred. No SNM was involved.

CONTROLLED PARAMETER:

Mass and moderator are the controlled parameters for the vaporizer.

ESTIMATED AMOUNT, ENRICHMENT, FORM of LICENSED MATERIAL:

Cylinders heated in the vaporizer contain uranium hexafluoride gas with a uranium-235 enrichment less than 5.0 weight percent. No SNM was involved in this incident since uranium hexafluoride was contained at all times within the uranium hexafluoride piping system.

NUCLEAR CRITICALITY SAFETY CONTROL(s) OR CONTROLLED SYSTEM(s) AND DESCRIPTION OF THE FAILURES OR DEFICIENCIES:

The condensate level detection system in the 3A vaporizer was rendered inoperable as a result of a drain line that was blocked by debris which came from the most recently processed cylinder.

CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEMS AND WHEN EACH WAS IMPLEMENTED:

The debris in the 3A vaporizer was removed and proper functioning of the level detection system was verified. The 3A vaporizer was released for restart on October 19, 2000 at 0730 hours. Other vaporizers not in use at the time of the incident were checked for proper functioning of the level detection system; each system responded correctly. Other vaporizers in use at the time were subject to increased-frequency checks to verify proper functioning of the condensate removal system; all vaporizers were draining properly. In addition, the condensate level detection system for in-use vaporizers will be function-tested immediately after the uranium hexafluoride cylinder currently being processed is removed.


* * * UPDATE ON 10/23/00 @ 1210 BY HEATH TO GOULD * * *

Reason for submitting supplemental information:

Supplemental information is submitted to provide further information on the as found condition and to clarify the safety significance of the event.

Double Contingency Protection:

30B UF6 cylinders are heated in the vaporizers with saturated steam. The steam is removed via a condensate removal system. Double contingency protection for the vaporizers is based on mass and moderator control. Mass control consists of controls to prevent and detect an uncontrolled release of UF6 inside the vaporizer. Moderator control consists of controls to detect accumulation of moderator (specifically condensate) and prevent the accumulation of moderator in the bottom of the vaporizer.

As Found Condition:

Two drains are present in the bottom of each vaporizer which allow steam to enter the condensate removal system. Each drain has an individual drain screen. A larger removable debris screen rests in the bottom of the vaporizer above the two individual drain screens. One drain flows through a pot in which reside the high and high-high level probes. The second drain proceeds directly to the condensate system. In this event the screen which covers the drain which flows to the level pot was obstructed with paint residue, thereby isolating the level probes. As a result of the isolation of the level probes, the ability to detect high level was lost. However, at no time was the condensate removal path closed. There was no accumulation of water in the vaporizer and no SNM was present.

The cylinder from which the paint residue came was provided by Urenco. Urenco has been advised by this facility of the situation. Prior to processing, the paint showed no indication of being defective. The paint was not chipped, peeling, bubbling from the surface, discolored, or otherwise distinguishable as flawed.

It is also very likely that the plugging of the drain occurred as a result of the functional test which detected it. The functional test of the vaporizer level probes is performed by filling the bottom of the empty vaporizer with water from a hose. During steady state operation the expected flow rate of condensate through a vaporizer is on the order of 1.48 gallons per hour. As was described earlier, the larger debris screen rests above the two drains. The seal along the bottom perimeter of the debris screen is not air or water tight and need not be due to the fact that it sees a low flow rate of steam and not a flow of liquid. During the functional test, it is likely the paint debris was sluiced underneath the debris screen by the relatively high flow rate of water which is used for the test. Notification was nevertheless made due to the fact that there is a small possibility that the vaporizer was operated in this condition.


Conclusions related to safety significance:

* Loss of double contingency protection may have occurred.
* No UF6 leaks occurred in the vaporizer. No failure of mass controls occurred. No SNM was involved.
* The condensate flow path from the vaporizer was not blocked. No moderator accumulated in the vaporizer
* At no time was there any risk to the health or safety of any employee or member of the public. No exposure to hazardous material was involved.
* The safety significance of this event is evaluated to be low.


The Reg 2 RDO(Belise) and the MNSS EO(Schnieder) were notified

UNIT EXPERIENCED A MOMENTARY GRID DISTURBANCE RENDERING SEVERAL SAFETY-RELATED RADIATION MONITORS INOPERABLE

"At 1437CDT on 10/18/00, River Bend Station experienced an electrical perturbation in the Baton Rouge area. Line 758 [138 kV] was lost which feeds a local refinery and this loss resulted in a momentary grid undervoltage condition. This undervoltage condition lasted less than one (1) second. As a result of this undervoltage condition, power to selected radiation monitor sample pumps was lost. Specifically, the Control Room Fresh air intake radiation monitors on both Division I and Division II lost sample pump power and this resulted in these monitors being inoperable for approximately three (3) minutes. The monitors were subsequently restarted. As a result of this condition, the radiation monitors would have been unable to initiate the Control Room Fresh Air Filter trains upon receipt of a high radiation signal. This signal is required to be operable when handling irradiated fuel; modes 1, 2, 3 and/or performing operations with the potential to drain the reactor vessel. No fuel handling or reactor vessel drain activities were in progress. This condition also existed for the Fuel Building ventilation radiation monitors. This condition is conservatively being reported as a loss of safety function for the Control Room Fresh Air System. Further evaluation if this condition is in progress."

The licensee informed the NRC resident inspector.

* * * RETRACTION 1111 11/10/2000 FROM HUSTON TAKEN BY STRANSKY * * *

"At 1746 on October 18. 2000 River Bend Station (RBS) reported a loss of power to radiation monitors in accordance with 10 CFR 50.72(b)(2)(iii)(D). Both divisions lost power for approximately 3 minutes until the units were restored due to operator action.

"A review indicated a concern for two safety functions related to charcoal filtration. One was related to control room fresh air and one related to the fuel building, specifically related to fuel handling accidents.

"The radiation monitors sensed low voltage during the grid transient and correctly shut down. They restarted automatically when voltage was restored: however, the sample pump must be restarted by the operator. The radiation monitors operated correctly per design for the conditions they sensed.

"Review of the event by RBS Engineering and Licensing personnel indicate that the loss of both divisions of radiation monitors for Control Room Fresh Air (CRFA) is covered by technical specifications. The allowed outage time in technical specifications was met when the radiation monitor sample pumps were restored within about three minutes. Additionally, plant procedures account for operator action to ensure the safety related monitors are operating and restarting the sample pumps is considered non-heroic, assessed action. Therefore this occurrence is not reportable.

"A review of the alarm history for the fuel building radiation monitors indicated that one division did not lose the sample pump and remained operable throughout the transient. Therefore, there was no loss of safety function for the fuel handling accident.

"Based on this information, RBS concluded that the loss of the radiation monitor sample pumps is not reportable and the previous report is retracted."

OFFSITE NOTIFICATION TO LOCAL FIRE DEPARTMENT FOR FIRE ON OWNER CONTROLLED POPERTY

"REFERENCE NUREG [1022 - SECTION] 3.3.7:

NOTIFICATION OF CONTACT OF ST. LUCIE '911' (FIRE) TO REQUEST OFFSITE FIRE DEPARTMENT TO EXTINGUISH A SMALL GRASS FIRE EAST OF PLANT BETWEEN DUNE LINE AND MANGROVES, IN A GRASS COVERED PARKING AREA. TOTAL TIME FROM DISCOVERY UNTIL NOTIFICATION OF 'FIRE IS OUT' WAS 38 MINUTES. NO E-PLAN ACTIVATION WAS REQUIRED. FIRE [WAS] NOT ON PLANT SITE."

THE LICENSEE INFORMED THE NRC RESIDENT INSPECTOR AND LOCAL AUTHORITIES.

OFFSITE AGENCIES NOTIFIED OF INADVERTENT ACTUATION OF OFFSITE SIRENS DURING "SILENT TEST"

"At approximately, 1200 on 10/18/2000, the Prompt Notification System (PNS) sirens were inadvertently actuated during a 'Silent Test' of the PNS system by the Hamilton County Emergency Management Agency (HCEMA). The Corporate Emergency Planning (EP) personnel were in contact with the HCEMA and Tennessee Emergency Management Agency (TEMA) Staff at the time of the test and immediately canceled the activation of PNS system at approximately 1201. The Corporate Operations Duty Specialist (ODS) notified the Sequoyah Operations Shift Manager at approximately 1205. Tennessee Valley Authority (TVA) Public Information personnel notified the media. Due to heightened public and media interest and notifications, this incident is being reported under 10CFR 50.72(b)(2)(vi)."

The licensee informed state/local agencies, local media and the NRC resident inspector.

LICENSEE IDENTIFIED DURING SURVEILLANCE TESTING THAT THE CONTAINMENT LEAK RATE EXCEEDS THE ALLOWABLE LEAK RATE

"PRIMARY CONTAINMENT AS-FOUND MINIMUM PATHWAY LEAK RATE EXCEEDED THE ALLOWABLE LEAK RATE OF 1.5%/DAY DURING REFUELING OUTAGE 14. THE MAJOR CONTRIBUTOR TO TOTAL CONTAINMENT LEAKAGE WAS THE 'D' MAIN STEAM LINE WHOSE LEAK RATE WAS NOT ABLE TO BE QUANTIFIED."

THE LICENSEE HAS APPROXIMATELY 35 ADDITIONAL COMPONENTS TO EVALUATE PRIOR TO COMPLETING LEAK RATE TESTING.

THE LICENSEE INFORMED THE NRC RESIDENT INSPECTOR.

10 CFR PART 21 NOTIFICATION FOR DISCREPANT WEIGHT OF SPENT FUEL RACKS

Spent fuel racks removed from Byron Nuclear Power Plant were discovered to have as-found weights ranging from approximately 8,200 to 10,500 lbs more than the weights used in the analyses supporting the original design and licensing of these racks and in the design of the lifting equipment used to lift the racks. The analyses related to seismic loadings, bearing pad design, spent fuel pool liner fatigue, and possibly others used to design and license these racks may no longer be conservative when the additional weight is considered. The actual impact on these analyses has not, to our knowledge, been evaluated. The impact on the design of the lifting equipment is that the design safety factors for the lifting equipment, while still above 1.0, may not meet the minimum safety factors in NUREG-0612 and associated reference documents.

Braidwood Nuclear Station has four similarly designed racks provided by the same supplier.


* * * UPDATE ON 1/5/01 @ 0946 BY GUTHERMAN TO GOULD * * *

The manufacturer of the spent fuel racks reported in the initial reports was Joseph Oat Co of Camden, NJ.