Information Notice No. 85-52: Errors in Dose Assessment Computer Codes and Reporting Requirements under 10 CFR Part 21
SSINS No.: 6835
IN 85-52
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 10, 1985
Information Notice No. 85-52: ERRORS IN DOSE ASSESSMENT COMPUTER CODES
AND REPORTING REQUIREMENTS UNDER 10 CFR
PART 21
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
The purposes of this information notice are to alert licensees (1) of errors
in a dose assessment computer code supplied by a vendor, and (2) that, in
general, computer codes can be considered basic components under the
requirements of Part 21, and errors that can lead to substantial radiation
exposures would be considered reportable under 10 CFR 21. It is expected
that recipients will review the information for applicability to their
facilities and consider actions, if appropriate, to preclude a problem at
their facilities. Licensees are also encouraged to share this information
with their vendors. However, suggestions contained in this information
notice do not constitute NRC requirements; therefore, no specific action or
response is required.
Description of Circumstances:
The NRC staff recently evaluated an event where errors were found in
computer software supplied by Nuclear Data, Inc. (ND) for predicting offsite
doses at San Onofre. Attachment 1 provides further details of the San Onofre
event, including the cause and effect of the computer error. Although
notification was made via INPO's electronic "notepad", this information was
prepared to ensure that all potentially affected licensees are aware of the
problem.
In the past, licensees and vendors appear to have been diligent in reporting
non-conservative errors in computer software used to perform design
calculations. However, NRC staff conversations with licensees in regard to
the San Onofre problem have indicated that some licensees believe, in
general, that errors in vendor supplied computer software used for offsite
dose assessments are not reportable under 10 CFR 21. However, such errors
may be reportable in some circumstances. This particular error was not
reportable under 10 CFR Part 21 because the error led to substantially
overestimating calculated offsite doses. However, if the error had been
non-conservative and caused significant underestimation of offsite doses,
then this could have (theoretically) led to
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IN 85-52
July 10, 1985
Page 2 of 2
radiation exposures exceeding the guidelines found in NUREG-0302 (Rev. 1)
regarding the exposure levels associated with substantial safety hazards.
Attachment 2 repeats the pertinent guidelines (NUREG-0302, Rev. 1) for
determining when a substantial safety hazard exists.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: J. E. Wigginton, IE
(301) 492-4967
R. L. Pedersen, IE
(301) 492-9425
Attachments:
1. Description of San Onofre Event
2. Guidelines For Determining Whether a Substantial Safety Hazard Exists
3. List of Recently Issued IE Information Notices
.
Attachment 1
IN 85-52
July 10, 1985
DESCRIPTION OF SAN ONOFRE EVENT
During a recent emergency preparedness exercise at San Onofre, NRC Region V
personnel noted large differences between the results of the offsite dose
calculations made by the licensee and the region. With the licensee and
Region V using the same input parameters (radiological source term and
meteorological conditions), offsite doses calculated by the region were an
order of magnitude less than the licensee's estimations. The NRC staff
recognizes that there is no "standard code" for calculating offsite doses.
Because of modeling assumptions and complexities, large differences in
resultant doses can exist when comparing two codes with both codes still
correctly considered to be error-free. However, when they examined their
code for internal accuracy, the licensee noted the problems discussed below.
The licensee found errors in the dose assessment computer programs, supplied
by ND, used to estimate environmental doses for both routine operations and
emergency operations. Coordinating with ND, the licensee corrected these
errors and notified other licensees via INPO's electronic "notepad." The
vendor-supplied computer program DISP (main program for calculating
atmospheric dispersion) had an inherent error, which led to predicting less
atmospheric dispersion (dilution) than the code should have calculated,
hence leading to an overestimation of the effect of a radioactive gaseous
release (by a factor of approximately 10 for emergency doses).
During an emergency situation, overestimating or underestimating the dose
due to code errors could lead to potential confusion. During an emergency
situation protective action decision making would be based principally on
plant conditions. However, dose projection calculations do influence such
decisions . Therefore, the calculations need to meet accuracy expectations
to be useful. Given the levels of real-time technical oversight and review
by local govern mental authorities and Federal agencies, including
independent dose estimations, it is not likely that a protective actions
decision by the local authorities would be based solely on the licensee dose
projection.
Staff discussions with the San Onofre licensee and another licensee
indicated that some licensees believe such software errors are simply not
reportable. However, NRC staff maintains that such errors are reportable in
some circumstances as a material defect.
If errors result in substantially underestimating or overestimating offsite
doses, it could possibly result in inappropriate protective actions. An
error that substantially underpredicts offsite doses (non-conservative)
would certainly be reportable under 10 CFR 21. This underestimation could
possibly cause a delay or deferral of a protective action which could
clearly lead to the unnecessary exposure to a person in an unprotected-area,
thereby creating a "substantial safety hazard." An error that substantially
overpredicts (conservative) is not strictly reportable under 10 CFR 21,
since it is very unlikely that such an overestimation could result in
personnel radiation exposures exceeding the referenced guidelines. However,
given the potential non-radiological negative impact from unnecessary
protective actions that could result from overly conservative dose
estimates, licensees should continue to cooperate with vendors and share
information concerning common problems with generic computer codes.
Staff guidance on the amount of radiation exposure that can be considered to
represent a substantial safety hazard is provided in NUREG-0302 (Rev. 1)
(see Attachment 2).
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Attachment 2
IN 85-52
July 10, 1985
Guidelines For Determining Whether A "Substantial Safety
Hazard" Exists*
1. A substantial safety hazard means the loss of a safety function to the
extent there is a major reduction in the degree of protection provided
to public health and safety. Note that the term "public health 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:
o Greater than 25 rem wholebody (or its equivalent to other
body parts) to occupationally exposed workers
o Exposure of 0.5 rem wholebody (or its equivalent to other
body parts) to an individual in an unrestricted area
b. Guidelines for determining what "...release of, licensed
material." means:
o Release of materials in amounts reportable under the
provisions of 10 CFR Part 20, *******20.403(b)(2)
*Taken from NUREG-0302 (Rev.l), "Remarks Presented (Questions/Answers Dis-
cussed) at Public Regional Meeting To Discuss Regulations (10 CFR Part 21)
for Reporting of Defects and Noncompliance," October 1977.
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