United States Nuclear Regulatory Commission - Protecting People and the Environment

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


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

Page Last Reviewed/Updated Thursday, March 29, 2012