Environmental Qualification

Environmental qualification has to do with Class 1E equipment installed in a harsh environment. But it may not be as intuitive as it at first appears . . . .

Every plant has an EQ program, and if you install new equipment that meets the criteria for inclusion in it then you’ll need to do extra work to make sure the proper reviewers are involved and any extra information that’s necessary is provided. “Environmental Qualification” is a specific term that refers to special categories of equipment. The term implies that equipment is compatible with (or qualified for) its installed environment.

While this is the case, this term isn’t used in the industry to describe general equipment qualifications. It is used specifically to describe electric equipment important to safety that is installed in a harsh environment. Environmental Qualification is described in 10 CFR 50.49, and here I’ll introduce the program and give a brief outline of its high points.

As just alluded, a dedicated program must be setup at each plant to track this equipment. The list must be maintained in an “auditable” form to “permit verification that each item of electric equipment [that] is important to safety meet the” NRC’s usage requirements. This equipment must be itemized and tracked in an EQ list. Each piece of equipment must also contain qualification data in a file that, first, shows what the worst-case environmental conditions are that it’s expected to operate under, and second, maintains paperwork (usually in the form of test reports) that demonstrates that the equipment will function properly during and after experiencing the conditions it is expected to encounter.

There are three categories of equipment that must be tracked in a plant’s EQ program:

  1. Class 1E equipment (safety-related electrical equipment)
  2. Non-Class 1E equipment that, should it fail, could hinder Class 1E equipment from accomplishing any of its three safety functions
  3. Some post-accident monitoring equipment that monitors and reports critical parameters to operators in the Control Room (like neutron flux, control rod position, reactor coolant system pressure, reactor vessel coolant level, containment pressure, and containment radiation levels).

Class 1E equipment located in a mild environment is not included in the EQ program. The NRC defines a mild environment as one in which its environmental conditions following an accident or other transient event remain practically the same as during normal operation. Conditions inside containment change dramatically between normal operation and during a loss-of-coolant accident; conditions in the control building probably won’t. Official plant documents will say for sure.

To give you an idea of the dramatic swings in environmental conditions, example graphs of pressure (Figure 1) and temperature (Figure 2) over time inside containment during and following a loss-of-coolant accident are shown below. They are general representations. Every plant is a little different, but the idea is the same.

pwr loca pressure


Figure 1 – Representative containment pressure LOCA profile for a pressurized water reactor

pwr loca temp


Figure 2 – Representative containment temperature LOCA profile for a pressurized water reactor