ML20198B860
| ML20198B860 | |
| Person / Time | |
|---|---|
| Issue date: | 10/23/1985 |
| From: | Barrett R Office of Nuclear Reactor Regulation |
| To: | Rosztoczy Z Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20197K240 | List: |
| References | |
| FOIA-85-781 NUDOCS 8511070321 | |
| Download: ML20198B860 (5) | |
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, DCT 2 31!85 MEMORANDUM FOR: Zoltan R. Rosztoczy, Chief Research and Standards Coordination Branch Division of Safety Technology FROM: Richard J..Barrett Reactor Systems Branch Division of Systems Integration
SUBJECT:
IDCOR ASSESSMENT OF UNCERTAINTIES IN OFFSITE CONSEQUENCE CALCULATIONS
References:
- 1. G. D. Kaiser et al., "IDCOR Subtask 18.1:
Evaluate Atmospheric and Liquid Pathway Dose", NUS-4378 (October 1984)
- 2. G. D. Kaiser, "The Implications of Reduced Source Terms for Ex-Plant Consequence Modelling", Presented at the ANS Executive Conference on the Ramifications of the Source Term, Charleston, South Carolina (March 1985)
In my memo of September 3,1985, I comented on the IDCOR uncertainty analysis related to containment response and fission product behavior. At that time, I stated that IDCOR had not yet documented their analysis of the variations in calculated risk due to uncertainties in calculation of offsite consequences. Jim Carter of Energex Corporation has informed me that the final report for IDCOR Subtask 18.1 (Reference 1) contains a discussion of-sensitivities and uncertainties related to offsite consequences. A more complete description of this analysis is contained in Reference 2. The purpose of this memorandum is to coment on those results.
Effect of Fission Product Release Fractions on Risk References 1 and 2 examine the sensitivity of offsite consequences to the fraction of volatile fission products released to the environment. The
. assessment is based on a well documented sample of CRAC calculations performed by groups other than IDCOR. This type of information is useful insofar as it enables one to convert source term uncertainties, which are not useful in themselves, to variations in offsite consequences. It will be important for NRP to develop similar information based in part on the IDCOR work.
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. The assessment shows that early fatalities approach zero for volatile release fractions much below 10*. Above 10%, the conditional mean early fatalities can be as high as 104, with wide variations due to population densities, warning times, evacuation assumptions and other factors (Figure 10 from Reference 1, enclosed).
Figure 12 (enclosed) from Reference 1 shows a much more gradual variation of latent fatality risk with fission product release fraction.
- Effect of Consequence Calculation on Risk There are two types of uncertainties in the consequence calculations which can cause variations in estimated risk; model uncertainties, and input data uncertainties. A comprehensive discussion of these uncertainties may be-found in the final environmental statement for the Limerick Generating Station (NUREG-0974, p.5 - 112ff). Uncertainties in models, including atmospheric transport, plume rise, deposition, age-dependent dosimetry including effects of high LET radiation, and dose-effect response including effectiveness of medical treatment, are not discussed in the IDCOR -
documentation. Future IDCOR uncertainty analyses should treat these and other effects. . Input data uncertainties are due mainly to the warning time, 4
fission product release duration and energy, evacuation velocity, delay before evacuation, and fraction of people who do not evacuate. These input.
parameters are not believed to have a significant effect on latent cancer fatalities, but they can greatly effect estimates of early fatalities.
The IDCOR base case calculations presented in the Technical Status Report yield zero early fatalities for all sequences for the four reference plants. In most cases, this result is due to calculated fission product release fractions below the threshold for early fatalities. Accounting for the uncertainties in fission product releases would place many of these sequences in the range where early fatalities are possible (Figure 10).
However, the calculated release fractions for the ATWS sequence without containment venting, TC(NV), are above the thre-hold for early fatalities;
- yet no early fatalities are predicted. IDCOR attributes this result to the long warning time (4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />), the long release time for fission products i (10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />), and the assumption of 100% participation in the evacuation.
i IDCOR~ calculations assuming only 95% participation in the evacuation yielded i non-zero estimates of early fatalities. It is reasonable to assume that l variations in the assumed warning time, fission product release duration and
. energy, the availability and effectiveness of medical treatment and effects of high LET radionuclides in the non-volatile groups would result in significant variations in calculated mean early fatalities.
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. Summary The IDCOR approach to estimating the sensitivity of risk to variations in fission product release fractions appears to be useful and accurate. NRC should evaluate this method for possible use in our analyses.
At the September 26, 1985, NRC/IDCOR technical exchange meeting, the IDCOR contractors stated their intention to seek approval from their Steering Committee to conduct a comprehensive severe accident uncertainty analysis.
At that meeting we presented our recommendations concerning their treatment of uncertainties in containment response and fission product behavior. With respect to uncertainties in consequence analysis, I would make the following recommendations:
For the ATWS sequence without venting, TC(NV), the uncertainty in mean early fatalities due to shorter warning times, longer delay times, ~and more rapid and energetic fission product release from containment should be quantified.
Uncertainties in fission product release fractions, including those for high LET lanthanide radionuclides, should be analyzed with respect to their impact on latent and early fatalities, using the sensitivities cescribed in References 1 and 2. The impact on early fatalities should be coupled with the effect of variations in warning time and release time.
The uncertainties due to models and assumptions in the CRAC code are believed to be large. These uncertainties should be estimated and included in the IDCOR results.
Richard J. Barrett Reactor Systems Branch Division of Systems Integration i
Enclosures:
Distribution As Stated . Central. File RSCB Rdg cc: T. Spe'is R. Barrett R. Bernero R. Houston B. Sheron F. Coffman A. Buslik J. Rosenthal G. Marino M.-Cugingham omeet ..RSB:DSI g.gg g '.. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .
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'F gg TECHNICAL TECHNICAL CONSULTANTS ASSOCIATES ON ENERGY & TH D le G. Bridenbaugh 1723 Hamdton Avenue-Suite K Richard B. Hubbard San Jose. Cahtomia 95125 Gregory C. Minor Phone: (408) 266-2716 November 22, 1985 FHtti.juM OF INFORMAllON Mr. J. M. Felton, Director Division of Rules and Records ACT REQUEST Office of Administration U.S. Nuclear Regulatory Commission
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Washington, D.C. 20555 #d M-dh MS !
Dear Mr. Felton:
Pursuant to the Freedom of Information Act, please make available at the Commission's Washington, D.C., Public Document '
Room copies of records in the following categories:
A. All internal NRC staff and national laboratory comments, criticisms, evaluations, etc., concerning the American Nuclear Society's report on source terms.
B. All internal NRC staff and national laboratory comments, criticisms, evaluations, etc., concerning reports by the IDCOR Program on source terms.
C. All internal NRC staff and national laboratory comments, criticisms, evaluations, etc., concerning the EPRI report on a source term analysis of the Surry Nuclear Power Plant.
If there are any questions regarding this requet.t, please do not hesitate to contact me directly by telephone at (408) 266-2716. Your attention to this request is appreciated.
Sincerdly, C-Steven C. Sholly r i
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