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

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Draft p. 3.1.55<br />

Issue<br />

276<br />

MULTIBARRIERS FOR DISPOSAL<br />

The correlation between leaching <strong>of</strong> Zircaloy-clad fuel elements and referenced leach<br />

rates <strong>of</strong> unclad U0 2 pellets is very misleading. Explain why no credit is given to<br />

containers. (181)<br />

Response<br />

When full safety analyses are made, credit is usually given to the container by assum-<br />

ing that a certain time period elapses before the onset <strong>of</strong> leaching. The time period varies<br />

depending upon the scenario being studied. But, to be conservative, when leaching begins<br />

it is assumed that the cladding has "disappeared", i.e., no credit is taken for the protec-<br />

tion provided by residual intact portions <strong>of</strong> cladding.<br />

Draft p. 3.1.56<br />

Issue<br />

There is a discussion <strong>of</strong> the behavior <strong>of</strong> glass in hydrothermal environments which<br />

appears to ignore the potential for simply eliminating the problem by reduced waste loadings<br />

rather than extensive research studies. (198)<br />

Response<br />

Repository and waste package designs will be technically conservative to the extent<br />

that hydrothermal conditions will not occur under normal, anticipated repository conditions.<br />

Studies are underway to define abnormal scenarios that could lead to hydrothermal conditions<br />

if indeed they are possible. If so, the potential risk must be assessed and evaluated rela-<br />

tive to trade-<strong>of</strong>fs such as reduced waste loadings, improved waste form development, further<br />

aging <strong>of</strong> the waste prior to disposal, etc. The resultant decision must consider the impact<br />

on the total waste management system.<br />

Draft, p. 3.1.56<br />

Issue<br />

Has the Eh-pH dependency <strong>of</strong> the waste form been investigated? The waste itself, having<br />

muliple oxidation states, will have different solubilities with differing Eh-pH. Can we<br />

adequately characterize the Eh-pH <strong>of</strong> groundwater after they have reacted to some extent with<br />

well rocks? We are not talking <strong>of</strong> a hypothetical distilled water interaction. Appendix I<br />

does not seem to consider water quality. (43)

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