Technical Bases for Yucca Mountain Standards (1995) / Chapter Skim
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APPENDIX D - THE SUBSISTENCE-FARMER CRITICAL GROUP
APPENDIX D - THE SUBSISTENCE-FARMER CRITICAL GROUP
Pages 153-160
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From page 153... ...
The risk measure recommended in Chapter 2 is the expected value of the consequences, determined by integrating the probabilistic distribution of consequences over the entire range of estimated consequences. The conceptual approach to analyzing risks to future individuals from a geologic repository will be illustrateci here for undisturbed performance (e.g., not including human intrusion, meteoric impact, etc.~.
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From page 154... ...
or by Monte CarIo/Latin Hypercube sampling of a smaller number of data combinations, as used by the WIPP anti Yucca Mountain Projects (Wilson et al., ~ 994~. Semianalytical adjoins techniques that help create probabilistic distributions from the discretized results are also available.
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From page 155... ...
In the era of temporal-maximum concentration, the concentrations at a given location vary little over a human lifetime, so the ground-water concentration can be assumed constant in calculating lifetime closes and risks for that critical group. The critical assumption in this model, then, is that a subsistence farmer extracts water from the location of maximum concentration of radionuclides in the aquifer, provided that no natural geologic feature precludes drilling for water at that location.
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From page 156... ...
Here, one can rely on scientific data for the typical soil conditions and for the kinds of foods assumed for this analysis. For a given food chain and for drinking, the amount of radioactivity ingested in a given time, or over a human lifetime, 2 There is a current proposal for commercial withdrawal of ground water Tom the aquifer near Yucca Mountain.
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From page 157... ...
Because the grounci-water concentrations vary little over a human lifetime, it is necessary only to sum the close commitments for a human who uses that contaminated water over his/her lifetime. The result is a probabilistic distribution of lifetime dose commitments, easily converted to lifetime average annual close commitments.
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From page 158... ...
To this risk from the ground-water pathways are to be added other calculated risks for the subsistence farmer, who is the individual at maximum risk within the critical group. To obtain the risk to the average member of the critical group, for compliance determination, it can be arbitrarily assumed for simplicity that there is a uniform distribution of inclividual risk within that group.4 Because {CRP's homogeneity criterion specifies that the critical group should have no more than a tenfold variation in inclividual dose, and because large departures from the linear dose-response theory are not expected for this calculation, the expected value of the risk to the average individual will be about ore-half that ofthe maximally exposed subsistence farmer.S The expected value of risk to the average individual within the subsistence-farmer critical group is to be compared with the risk limit that is to be selected for compliance.
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From page 159... ...
APPENDIX D -THE SUBSISTENCE-FARMER CRITICAL GROUP 159 or above the specified risk limit the calculated risk must be for compliance clecision.6 6 UK's NRPB specifies the calculation of a 95°/0 confidence interval for the expected or central value of risk. The upper value of this confidence interval is what is compared with a regulatory limit [Barraclough et al., 19921.
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