U.S. Nuclear Regulatory Commission
Enforcement Guidance Concerning "Substantial Potential" for Overexposure or Release ....
Title: Enforcement Guidance Concerning "Substantial
Potential" for Overexposure or Release ....
See the memorandum from L. J. Cunningham to J. Liberman
dated May 15, 1991. An event presents a substantial
potential when it was fortuitous that the resulting
exposure or release did not exceed the limits of 10 CFR
Part 20. If it is possible to construct a reasonable
scenario in which a minor alteration of circumstances would
have resulted in a violation of Part 20 limits, enforcement
action should be considered due to the substantial
potential for overexposure.
Enclosure 1 provides the final draft of enforcement
guidance on what constitutes a "substantial potential" for
overexposure, as used in C.4 of Supplement IV to 10 CFR 2,
Appendix C. This input to the Enforcement Manual was
provided following several enforcement actions where
Regions applied a narrow interpretation of "substantial
potential." The Severity Level III examples of Section C.4
of Supplement IV involve situations that present a
"substantial potential for an exposure or release in excess
of 10 CFR 20 whether or not such an exposure or release
An event presents a substantial potential when it was
fortuitous that the resulting exposure or release did not
exceed the limits of 10 CFR 20. The concern is not the
significance of the resulting, or potential, exposure
(Example C.1 of Supplement IV addresses exposures in excess
of Part 20 limits), but whether the licensee provided
adequate controls over the situation, as required, to
prevent exceeding the Part 20 limits. No credit is given
for luck. When taking escalated enforcement action for
this example consider if it is possible to construct a
reasonable scenario in which a minor alteration of
circumstances would have resulted in a violation of the
Part 20 limits. The following circumstances should be
1. Timing - Could the exposure period have reasonably
An individual in the proximity of an unknown source of
radiation receives an unplanned excessive exposure.
Because of the duration of the exposure, no limits were
exceeded; however, the individual could have reasonably
stayed in the proximity of the source long enough to be
2. Source Strength - Could the radiation source have
reasonably been stronger?
An inadvertent release results from a worker venting the
wrong waste gas decay tank. Although the release did not
exceed Part 20 limits, the same mistake could have resulted
in venting a decay tank with enough activity to exceed the
3. Distance - Could the person have reasonably been
closer to the source?
In example (1) above, the individual could have been
overexposed by standing closer to the source of the
4. Shielding - Could some unintended shielding have
been reasonably removed?
A radioactive source was accidently left in an office area.
Shielding afforded by a desk prevented the overexposure of
an individual worker in the office. However, nothing
prevented the source from being left in an area of the
office, that would not have been shielded by the desk,
where the individual would likely have been overexposed.
Regions were solicited for comments and they were
incorporated in this final draft, with the exception of two
comments in Enclosure 2 to this memorandum. The responses
to these two comments were as follows.
1. Supplement IV clearly refers to the exposure and
release limits in 10 CFR 20, not the 24-hour reporting
requirements of 10 CFR 20.403 (b) [or "new" 10 CFR 20.2202
2. A Severity Level III violation does not have to
present the risk of a serious violation of Part 20; there
is no reference to serious violations in example C.1 of
Supplement IV. An event meets the "substantial potential"
test if the licensee's controls were not effective in
preventing a violation of Part 20 and the consequences of
the event were a matter of chance.
Regulatory references: 10 CFR 2
Subject codes: 12.7