Helpful Rules of Thumb

DOE-STD-1134-99

Helpful Rules of Thumb

When the analysis depends upon multiple controls on a single parameter, the reviewer should

assure himself that the controls are independent (i.e., no common mode failures) and that the

failure of each control is an unlikely event. When the safety evaluation credits the results of

sampling of solutions, one needs to consider the findings of NSTR 016-97, "Review of the

Criticality Safety of Bottle Storage and Handling," which evaluated the failure mode of the

sampling system. It is important that analyzed contingencies not credit the same sample result.

Certain controls are more vulnerable to operational error, and must be explained if they are used.

The reviewer should consider the control in the context of the proposed work to verify that the

control is an effective barrier to an unlikely event. Examples of controls that deserve extra

scrutiny include:

Failure to properly signoff a procedure or checklist

Failure to properly second check a procedure or checklist

Failure of administrative spacing

Failure of administrative mass controls leading to a minor overbatch

Failure to administratively maintain a planar array of containers

Failure to administratively control the number of items

Failure to administratively control the number of containers

Failure to administratively control volumes of containers

Examples of control failure or events that will, in general, qualify as unlikely events (i.e.

contingencies) by themselves include:

Fires (which lead to sprinkler activation)

Earthquakes and seismic events

Floods including room and glovebox floods

Failure of criticality drains

In general, failure of a single administrative control by itself does not constitute a

contingency. However, if two independent administrative controls must fail concurrently before

criticality becomes possible, then the combination of the two would probably constitute a valid

contingency (e.g., a signoff that valves are aligned properly followed by an independent check

and signoff at a different time by a different person, provided that the second person is at least as

qualified as the first person).