Electrical, civil, and mechanical risks when creating new wall penetrations

core drill

Routing a new conduit through a wall? Need to make a new penetration? There are hidden risks you need to know about, especially if you the responsible engineer for a mod package . . . .

If you need to route new conduit through a wall, that means you will probably need to create a new penetration. Here are a few of the major risks you should consider.

Electrical – There may be embedded conduits in the wall. You need to locate an embedded-conduit drawing and find out. The conduits may be PVC instead of metal. If they are PVC, that means that the core drill’s usual failsafe for protecting embedded conduit — drill interrupters that detect grounded metal and shut the drill off — won’t work; PVC conduits will be invisible to the drill. If possible, identify the conduits and cables in the vicinity to put the craft on alert. If the cables are safety-related, and there are no reliable means to detect the conduits, the penetration may need to be relocated because the risk of a plant trip or LCO could be too high.

Also, don’t forget about conduit identification. Any conduit or conduit sleeve that you install in the wall will probably have to be given a unique name and tracked in a plant cable-and-raceway-management database.

Civil – Civil will probably have to update penetration drawings. These drawings are different from conduit and raceway drawings because they typically show a wall’s elevation view and any interferences installed on or near them, like panels and HVAC ductwork. The civil engineer may have to specify what kind of fill to use to seal up the hole (like certain kinds of grout). They may have to evaluate the wall for structural integrity, meaning there could be associated calculations that need to be reviewed and updated. This is especially true if there is a need to cut any embedded rebar. Civil drawings may also need to be updated with details like hole dimensions and precise horizontal and vertical coordinates.

One way to detect embedded interferences is to use ground-penetrating radar. These scans can be sub-contracted to companies who specialize in that kind of work. It may seem pricey up front, but it can certainly be worth it if it means avoiding a plant trip.

Mechanical – Some walls may be fire barriers. If so, their ability to continue to act as a fire barrier following the sealing of the new penetration must be evaluated. If the wall is a fire barrier, then appropriate penetration and conduit seals must be specified. Sometimes a plant has a stock catalog of details to pick from.

There is probably a fire-barrier penetration log that must be updated, either in some kind of database format or drawing format. If that’s the case, the new holes must be given new penetration numbers. If there are already too many penetrations in a particular fire barrier, you may have to choose a different wall instead (or else perform some kind of 86-10 evaluation).

A final risk to consider is whether the wall is what the NRC calls a “hazard barrier.” They define it this way:

Hazard barriers are plant features or structures that are credited with protecting plant equipment from external and internal hazards such as flooding, tornado missiles, turbine missiles, and the effects of design basis events such as a loss-of-coolant accident (LOCA) or a high energy line break (HELB).

Basically, these barriers separate any mild environment from one that can become harsh following a high-energy line break or LOCA (in terms of temperature and pressure, not radiation). If you penetrate any wall that acts as a hazard barrier, there needs to be some discussion about how these barriers should be controlled during implementation when they are temporarily punctured. Adequate compensatory measures should be put in place.

2 thoughts on “Electrical, civil, and mechanical risks when creating new wall penetrations

  1. many walls are atmospheric pressure walls ie: Control Room Boundary
    ,where the envelope is required to be maintained at a positive pressure. Penetrations can effect this requirement and should be considered in the design phase.