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
                           WASHINGTON, D.C. 20555

                                July 10, 1985

                                   AND REPORTING REQUIREMENTS UNDER 10 CFR 
                                   PART 21 


All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP). 


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 

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 


                                                              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

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

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). 

                                                              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 

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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