05000261/LER-2012-003

LER-2012-003, Plant Modification Interfered with the Operation of Containment Wide Range Level Indicator

Docket Number
Event date:
Report date:
2612012003R01 - NRC Website

I. DESCRIPTION OF EVENT

On January 19, 2012, at approximately 0557 hours0.00645 days <br />0.155 hours <br />9.209656e-4 weeks <br />2.119385e-4 months <br /> EST, while H. B. Robinson Unit 2 was shutdown in MODE 5, Condition Report (CR) 510240 was initiated documenting that an NRC inspector identified that the installation of the chain for the west half of the wall on the south side of the reactor [RCT] shield area was found to interfere with the path of the float for the Post Accident Containment Vessel [VSL] (CV) Water Level Transmitter (LT), LT-802E [LT]. The CV LT was inoperable because it could not indicate a flooded containment level of 375 inches required by the Critical Safety Function Status Trees. On March 7, 2012, work was completed which removed the obstruction.

CR 510240 also determined that LT-802E had been inoperable since October 15, 2005. Although LT- 802E would not have been able to provide an indicated flooded containment level of 375 inches, it would have been able to provide the indication of 354 inches required for placing the Reactor Coolant System (RCS) and Residual Heat Removal (RHR) on recirculation.

CR 530799 was initiated on April 16, 2012 to determine the root cause of the event.

II. CAUSE OF EVENT

The installation of LT-802E in 1981 was managed with Modification M-525. The closure of Modification M-525 did not adequately incorporate the changes from the modifications. Specifically, there was no labeling or identification of the level transmitters in the field and there was no drawing change requested to show the location of the installed level transmitters.

III. ANALYSIS OF EVENT

TS Table 3.3.3-1 requires two channels of Containment Sump Water Level (Wide range). Condition A of Limiting Condition for Operation (LCO) 3.3.3 requires the inoperable channel to be restored in 30 days. If not restored in 30 days, Condition B of the LCO requires immediate action in accordance with TS 5.6.6.

TS 5.6.6, Post Accident Monitoring (PAM) Instrumentation Report, states that a report shall be submitted within the following 14 days which outlines the preplanned alternate method of monitoring, cause of inoperability, and the plans and schedule for restoration of the channel.

The PAM Channel in question was determined to be inoperable for greater than 30 days and the required report was not made in 14 days; therefore this event is reportable pursuant to 10 CFR 50.73 (a)(2)(i)(B). The report due date is May 7, 2012, which is based on the date of the reportability determination date, March 8, 2012.

IV. SAFETY SIGNIFICANCE

This condition described above did not constitute an unanalyzed condition as LT-802E was available to provide the level indication of 354 inches used by the operators to determine switchover from injection to recirculation mode of operation. Therefore, the safety function of providing level indication for switchover was available even though the alarm function was not available. The containment flooding alarm is a secondary indication of containment flooding. The sources of water causing containment flooding and reaching the alarm setpoint of 375 inches are Fire Water, Service Water, Component Cooling Water, Primary Water, and Steam Generators. The associated alarms and actions are shown below:

Cause

Fire Water Service Water Component Cooling Water Primary Water Steam Generators [SG] Alarm Pump start Low flow alarms due to loss of water Surge tank low level Low primary water tank level Decreasing SG level Response Investigate cause of start/isolate if required Determine cause of low flow and isolate as required Determine cause of low surge tank level Determine cause of low tank level Determine path out of SG and isolate If any of the above conditions would have continued to exist, then LT-802E would have provided indication up to approximately 370 inches while Channel A, LT-801E (the redundant channel), would have continued to increase and alarm.

V. CORRECTIVE ACTIONS

Completed Corrective Actions:

• EC 84548 was approved, and on March 7, 2012, the chain was relocated using Work Order 2035875 so that no interaction exists between the chain and level instrumentation float for LT-802E.

Planned Corrective Actions:

• Labeling of LT-802E and other related instruments will be brought up to current plant standards including an exclusion zone. The applicable plant drawing will be updated to include LT-802E and the other related instruments.

VI. PREVIOUS SIMILAR EVENTS:

Licensee Event Reports (LERs) for HBRSEP, Unit No. 2, were reviewed from the past 5 years. There were no similar events found.