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Management of Commercially Generated Radioactive Waste - U.S. ...

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Draft p. 1.18<br />

Issue<br />

63<br />

CONSEQUENCE ANALYSIS<br />

One commenter requested that the basis for the frequency <strong>of</strong> stream invasion <strong>of</strong> a repos-<br />

itory should be presented. (218-DOI)<br />

Response<br />

The total probability <strong>of</strong> release <strong>of</strong> waste materials from a repository via stream inva-<br />

sion is 4 x 10-15 (for one year). This figure is the product <strong>of</strong> the following:<br />

- A fault intersection in the repository-4 x 10- 1 1 /yr<br />

-2<br />

- A failure <strong>of</strong> a waste container-10-2/yr<br />

- Chance <strong>of</strong> aquifer intersection which leads to biosphere-10-2/yr<br />

The value <strong>of</strong> 4 x 1 /yr is taken from H.D. Clairborne and F. Gera, 1974, Potential Con-<br />

tainment Failure Mechanisms and Their Consequences at a <strong>Radioactive</strong> <strong>Waste</strong> Repository in<br />

Bedded Salt in New Mexico: Oak Ridge National Laboratory, ORNL-TM-4639.<br />

A more conservative value <strong>of</strong> 2 x 10 13 /yr for the probability <strong>of</strong> release <strong>of</strong> waste via<br />

stream invasion (versus 4 x 10-15/yr) was chosen for illustrative purposes in the draft.<br />

Because it is believed that such a value may not be defensible over millenia, a value <strong>of</strong><br />

4 x 10-l /yr was used in this final Statement to assure conservatism.<br />

Draft p. 1.19<br />

Issue<br />

The chemical nature <strong>of</strong> waste and <strong>of</strong> the geosphere appears to be largely ignored. 'Much<br />

<strong>of</strong> the reduction <strong>of</strong> radiation dose appears to occur as a result <strong>of</strong> the delay <strong>of</strong> radionuclides<br />

by sorption from the groundwater. The sorption <strong>of</strong> radionuclides depends on several factors,<br />

including the oxidation-reduction state <strong>of</strong> the nuclide, the presence or absence <strong>of</strong> complexing<br />

or chelating agents, and the nature <strong>of</strong> the specific geological materials present. In some<br />

cases, particularly if large and rather exotic containment canisters are postulated, the ion<br />

exchange requirements <strong>of</strong> the canister materials may be quite significant and might overload<br />

the exchange capacity <strong>of</strong> the media in which the waste was emplaced. (113-EPA)<br />

Response<br />

In some accident scenarios ingestion and use <strong>of</strong> ground water would contribute to the<br />

maximum individual dose. In those cases these pathways were analyzed.<br />

The chemical nature <strong>of</strong> the waste geosphere is not ignored. Retardation .<strong>of</strong> radionuc-<br />

lides is dependent upon several factors. However, with respect to transport modeling <strong>of</strong><br />

radionuclides, this Statement utilizes generally accepted modeling techniques. Of course

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