U.S. Nuclear Regulatory Commission
Errors in Dose Assessment Computer Codes and Reporting Requirements Under 1 0 CFR Part 21
HPPOS-041 PDR-9111210186
Title: Errors in Dose Assessment Computer Codes and
Reporting Requirements Under 10 CFR Part 21
See IE Information Notice No. 85-52 entitled as above and
dated July 10, 1985. This notice alerts licensees to: (1)
errors in a dose assessment computer code supplied by a
vendor, and (2) in general, computer codes can be
considered basic components under the requirements of Part
21, and non-conservative errors leading to substantial
underestimation of radiation exposures would be considered
reportable under 10 CFR 21. The health physics position
was written in terms of 10 CFR 20.403, but it also applies
to "new" 10 CFR 20.2202.
IEIN-85-52 was issued following an evaluation by NRC staff
of an event where errors were found in the prediction of
offsite doses using computer software supplied by Nuclear
Data, Inc. In the incident, a large discrepancy between
the result of the offsite dose calculations made by the
licensee and the regional office during an emergency
preparedness exercise was noted. The licensee and Region V
office used the same input parameters (radiological source
term and meteorological conditions); however, the offsite
calculated dose determined by the Region V office was an
order of magnitude less than the licensee's estimation.
The licensee found errors in the dose assessment computer
programs that were used to estimate environmental doses for
both routine and emergency operation supplied by Nuclear
Data, Inc. In coordination with Nuclear Data, the licensee
corrected the errors and notified other licensees via
INPO's electronic "notepad" of the inherent program error
that led to predicting less atmospheric dispersion than the
code should have calculated.
If errors result in substantially underestimating or
overestimating offsite doses, it could result in
inappropriate protective measures. An error that
substantially underpredicts offsite doses
(non-conservative) would be reportable under 10 CFR 21.
The underestimation could cause a delay or deferral of
protective action leading to unnecessary exposure to a
person in an unprotected area, thereby creating a
"substantial safety hazard." An error that substantially
over predicts (conservative) is not strictly reportable
under 10 CFR 21, since it is unlikely that such an
overestimation could result in personnel radiation
exposures exceeding the referenced guidelines. However,
because of potential non-radiological negative impact from
unnecessary protective actions resulting from overly
conservative dose estimates, licensees should continue to
cooperate with vendors and share information concerning
common problems with generic computer codes.
The following NRC staff guidance on the amount of radiation
exposure that can be considered to represent a "substantial
safety hazard" is taken from NUREG-0302 (Rev.1):
1. A substantial safety hazard means the loss of a
safety function to the extent that there is a major
reduction in the degree of protection provided to public
health and safety. Note that the term "public heath and
safety" includes both members of the public and licensee
workers / employees.
2. From a radiological perspective, a criterion for
determining whether substantial safety hazard exists
includes "moderate exposure to, or release of, licensed
material."
a. Guidelines for determining what "moderate exposure
to ..." means: greater than 25 rem to the whole body (or
its equivalent to other body parts) to occupationally
exposed workers; or exposure of 0.5 rem to the whole body
(or its equivalent to other body parts) to an individual in
an unrestricted area. b. Guidelines for determining
what "... release of, licensed material" means: release of
materials in amounts reportable under the provisions of 10
CFR 20.403 (b) (2) [or 10 CFR 20.2202 (b) (2)].
Regulatory references: 10 CFR 21, NUREG-0302
Subject codes: 2.2, 7.3, 12.12
Applicability: Reactors
