05000458/LER-2020-003, Weep Holes Discovered in G-Tunnel Wall Result in Inoperable Safety Related Equipment

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Weep Holes Discovered in G-Tunnel Wall Result in Inoperable Safety Related Equipment
ML20300A577
Person / Time
Site: River Bend Entergy icon.png
Issue date: 10/26/2020
From: Vercelli S
Entergy Operations
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RGB-48052 LER 2020-003-00
Download: ML20300A577 (4)
v • d • e


LER-2020-003, Weep Holes Discovered in G-Tunnel Wall Result in Inoperable Safety Related Equipment
Event date:
Report date:
4582020003R00 - NRC Website
v • d • e

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Enclosure RBG-48052 Licensee Event Report 50-458 / 2020-03-00, Weep Holes Discovered in G-Tunnel Wall Result in Inoperable Safety Related Equipment

NRC FORM 366 (08-2020) 8.6. N8CLEAR REG8LA7OR< COMMI66ION LICEN6EE E9EN7 REPOR7 (LER)

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EVENT DESCRIPTION

On June 10, 2020, weep holes were identified in exterior wall of the HVAC Chamber located adjacent to the G-Tunnel.

The HVAC Chamber is a concrete duct which extends from El. 80¶-6' where air is admitted through a filter housing (HVY-FLT8) down to El. 66¶-3'. The bottom of the 30' x 30' ducting to the fan in the G-Tunnel is at 71¶-6'. Because the original construction had a simple grating at the top (this condition was corrected under MR 93-0086), this vertical shaft could collect precipitation in the bottom. As part of the design documentation four weep holes were to be drilled in the exterior wall at approximately El. 68¶ to allow standing water to drain to the environment. Only 2 weep holes (each 2 inches in diameter) were confirmed as drilled into the wall.

During a postulated PMP event, water would pond within the excavation area, for what would have been River Bend Unit 2, and would cover these weep holes. During this event, it would have been possible for water to have infiltrated this chamber and, as the water in the excavation area rose, water could have flowed into the ducting for the fan and into the G-Tunnel. A engineering analysis determined that water flow from the weep holes would exceed the capability of the three sump pumps located in the area. The G-Tunnel is interconnected principally with E and F Tunnels and these tunnels contain safety related equipment. As a result, that equipment could have been adversely impacted.

On June 22, 2020 the work was completed to plug the weep holes in accordance with an approved engineering design change.

SAFETY ASSESSMENT

There were no actual consequences to the general safety of the public, nuclear safety, industrial safety and radiological safety as a result of this discovery. A PRA analysis does not exist for external flooding events. Based on the non-mechanistic nature of the PMP, the rainfall amounts exceeding the maximum anticipated yearly rainfall in the Baton Rouge area of Louisiana and the short duration of the event the risk is considered to be low. Additionally, the risk significant equipment (Service Water motor operated valves) in the tunnel complex which would be exposed to this flooding are located several feet above floor level and would likely be in their required positions before seeing any impact from this low probability external flooding scenario.

EVENT CAUSE

The direct cause of this event was due to inadequate design for a ventilation opening.

CORRECTIVE ACTIONS

RBS took immediate actions to correct the identified conditions. These actions were:

Completed work order to plug the weep holes Revised drawing EC-057P to show the weep holes in the HVAC Chamber for HVY-FN8 as plugged

PREVIOUS SIMILAR EVENTS

None.

2 2

River Bend Station 458 2020 03 00

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