10 C.F.R. § 707.9
When there is an occurrence which is required to be reported to DOE by the contractor, under contract provisions incorporating applicable DOE Orders, rules, and regulations, it may be necessary to test individuals in testing designated positions, or individuals with unescorted access to the control areas of the DOE reactors listed in § 707.7(c) , for the use of illegal drugs, if such individuals could have caused or contributed to the conditions which caused the occurrence. For an occurrence requiring immediate notification or reporting as required by applicable DOE Orders, rules, and regulations, the contractor will require testing as soon as possible after the occurrence but within 24 hours of the occurrence, unless DOE determines that it is not feasible to do so. For other occurrences requiring notifications to DOE as required by applicable DOE Orders, rules, and regulations, the contractor may require testing.
10 C.F.R. §707.9