05000369/LER-2005-003

LER-2005-003, Containment Closure Requirements Not Met During Core Alterations

Docket Number
Event date:	9-20-2005
Report date:	11-15-2005
3692005003R00 - NRC Website

BACKGROUND

Applicable Energy Industry Identification (EIIS) system and component codes are enclosed within brackets. McGuire unique system and component identifiers are contained within parentheses.

The ice condenser [COND](NF) is an insulated cold storage area in which ice is maintained in an array of vertical cylindrical columns in the form of perforated metal baskets. The spaces between the ice baskets form the flow channels for steam and air. The ice condenser is contained in the annulus formed by the containment vessel wall and the crane wall over a 300 degree arc. The ice condenser's primary function is the absorption of thermal energy released abruptly in the event of a loss of coolant accident (LOCA) or a secondary line break for the purpose of limiting the initial peak pressure in containment.

The purpose of the ice conveyor subsystem [BC](NF) is to transport new ice from the auxiliary building to the ice condenser for ice basket replenishment during refueling outages. An ice delivery valve feeds ice into a stream of chilled compressed air produced by a blower [BLO] which transports the ice through a temporarily erected hose and a containment penetration to the ice condenser area. A ball valve [ISV] is also installed at the penetration which is manually closed when the ice blowing process is not in operation.

The purpose of the Containment Purge Ventilation System [VA](VP) is to reduce the airborne radioactivity levels in Containment by purging the containment atmosphere to the environment via the unit vent during refueling when periods of personnel access are required. Two carbon filter units [FLT](HEPA) are included in the system to aid in reducing the airborne radioactivity levels. The VP system helps to mitigate the consequences of a fuel handling accident (FHA) in the containment but is not required to be in operation provided the containment penetrations are closed.

Technical Specification (TS) 3.9.4, Refueling Operations, Containment Penetrations requires in part that during core alterations or movement of irradiated fuel assemblies within containment, each penetration providing direct access from the containment atmosphere to the outside atmosphere either be closed by a manual or automatic isolation valve, blind flange, or equivalent, or exhausting through an operable Containment Purge Exhaust System HEPA filter and carbon adsorber.

EVENT DESCRIPTION

At the time this historical condition was identified, McGuire Unit 1 was in Mode 5, cold shutdown, and Unit 2 was in Mode 1 at 100% power. No systems, structures, or components were out of service at the time of this event which contributed to this event.

In September 2005, the historical practice of re-filling the Ice Condenser ice baskets by blowing ice through a containment penetration during refueling outages was reviewed as a transportability corrective action from Problem Investigation Process (PIP) M-05-1608. This practice started in 1989 on both McGuire Units. PIP M-05-1608 documents LER 370/2005-03 and the cause for the operation of the Containment Air Release and Addition system during fuel movement event (containment closure requirements not met during core alterations).

The review was performed to determine if the ice blowing practice was also an operation prohibited by TS 3.9.4 if performed during core alterations or fuel movement. The ice delivery valve and the blower were attempted to be qualified as an "equivalent isolation method" as currently allowed by TS 3.9.4 (material boundary). The blower produces a low pressure, cold air stream which transports the ice to containment. The rotary air lock valve feeds ice into the cold air stream. These two components are basically a solid material with the exception of close tolerances for the rotating components. But a bypass line was discovered between the blower discharge and the open suction which was used for pressure control and to cool the blower. This line would represent an unblocked atmospheric opening from containment back to the auxiliary building. Therefore, it was concluded that the ice blowing practice did not meet. TS 3.9.4 LCO requirements when performed during core alterations or, fuel movement and thus represented an operation prohibited by McGuire's Technical Specifications. TS 3.9.4 only allows VP system penetrations to provide direct access from the containment atmosphere to the outside atmosphere during core alterations or fuel movement.

In 1989, the maintenance procedure revision to allow ice blowing into containment during core alterations and fuel movement was developed and supported by a safety evaluation as documented in calculation MCC-1503.13­ 00-0201. This evaluation relied on the positive pressure of the ice delivery blower or closure of a ball valve at the penetration as a contingency to maintain containment integrity. It was stated that as long as this process exhausted through the VP exhaust system, TS 3.9.4 LCO was met. With the ball valve at the penetration closed, TS 3.9.4 LCO was also fully satisfied. The Fuel Handling Accident (FHA) in Containment dose analysis was reviewed and was determined to be unaffected by this evolution.

TS 3.9.4 in 1989 was the pre-"Improved Tech Specs" (ITS) version but was basically the same as the current Technical Specification with the exception of the expanded and highly detailed Bases section. Without any detailed clarifications or interpretations in the pre-ITS TS 3.9.4 Bases, it was assumed that a containment penetration could be open as long as no air exhausted through that penetration AND the VP exhaust system was in operation.

As stated above, the current LCO for TS 3.9.4 is very similar to the pre-ITS version but the new Bases provide extensive detail as to how to interpret the LCO and Surveillances. The Bases Background discusses VP system operation during fuel movement and then goes on to state: "The other containment penetrations that provide direct access from containment atmosphere to outside atmosphere must be isolated on at least one side.

This is currently interpreted at McGuire that only the VP penetrations can provide direct access from the containment atmosphere to the outside atmosphere during core alterations or fuel movement. The current dose analysis for an FHA in Containment assumes the VP System is in operation and credits the VP filters to limit radioactivity. All other atmospheric penetrations are assumed to be closed. The act of closing the ball valve at the Containment penetration as the contingency also does not meet the Tech Spec LCO or the Surveillances.

CAUSAL FACTORS

The cause for this historical condition was the use of a non-conservative interpretation of TS 3.9.4 in the 1989 safety evaluation for the ice blowing evolution. McGuire's current interpretation of TS 3.9.4 LCO is that only the VP penetrations can provide direct access from the containment atmosphere to the outside atmosphere during core alterations or fuel movement.

CORRECTIVE ACTIONS

1. The Containment Closure and Integrity procedures, PT/1&2/A/4200/002C, were revised to prohibit opening this penetration during core alterations or fuel movement.

2. The Installation and Operation of Ice Blowing Equipment and Penetration procedure, MP/0/A/7150/092, was revised to prohibit ice blowing during core alterations or fuel movement.

Note: The 10 CFR 50.59 process at McGuire has fundamentally changed and improved since the 1989 safety evaluation (50.59) was performed. Therefore, the corrective actions associated with this cause were focused on barrier actions versus 10 CFR 50.59 process and training improvements.

SAFETY ANALYSIS

From a Probabilistic Risk Assessment (PRA) perspective, shutdown risk assessments focus on a loss of decay heat removal. Although a loss of decay heat removal did not occur, it was considered in concert with the ice blowing process to assess how the event affects public health risk. The occurrence of a loss of decay heat removal during the ice blowing process does not represent a significant increase in risk. Isolating the penetration would not have been time critical during refueling operations due to the extended period of time to core boiling and uncovery with greater than 23 feet of water above the Reactor Vessel flange. Also, the risk of a loss of decay heat removal accident while this penetration was open was low.

The penetration was capable of manual isolation during this time period.

The penetration could be closed using the ball valve or by disconnecting the ice delivery system and installing a blind flange. Adequate time was available to perform either evolution due to the extended period of time to core boiling and uncovery as a result of a loss of decay heat removal.

VP system filtration is credited in the current McGuire Design Basis Fuel Handling Accident Radiological Analysis reflected in UFSAR Chapter 15. In the event of a fuel handling accident in containment during the ice blowing process, initial releases would be made through the filtered VP system as has been modeled in the current analysis. These results are below the regulatory limits and the plant did not operate outside its design or licensing basis.

Therefore, there was no impact to the health and safety of the public or plant personnel.

ADDITIONAL INFORMATION

As previously stated, a similar condition was reported by McGuire LER 370/2005-03 dated May 26, 2005 regarding a containment air release during core alterations. This ice blowing condition was discovered as a result of corrective actions from the event reported in May 2005. No other occurrences of containment closure issues have been identified.

Corrective Action 11 from PIP M-05-1608 documents a complete review of the Containment Closure and Integrity procedures, PT/1&2/A/4200/002C, for potential conflicts with TS 3.9.4. No other issues were identified with the exception of this ice blowing containment penetration.