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

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179<br />

WASTE MANAGEMENT OPERATIONS<br />

*higher conductivity than the hard rocks and is surrounded by shale which is not a good con-<br />

ductor. We would like to correct this discrepancy between DOE and A. D. Little heat<br />

loading models. (113-EPA)<br />

Response<br />

Our reading <strong>of</strong> the A. D. Little report prepared for EPA (EPA 1977) indicates that the<br />

primary consideration relative to the repository heat loading in that study was the far-<br />

field effect <strong>of</strong> surface uplift. DOE's analysis did not find far-field effects to be the<br />

limiting factor for 5 to 10 year old waste except in the case <strong>of</strong> spent fuel disposal in<br />

salt. For all other cases, the thermal loading limit was set by near-field criteria, i.e.,<br />

rock stresses in the implacement region. To allow for uncertainties in the criteria and<br />

calculations, actual loadings used for the conceptual repositories were limited to two-<br />

thirds <strong>of</strong> the calculated allowable loading. All temperature pr<strong>of</strong>iles were recalculated and<br />

rechecked for the final Statement using an improved version <strong>of</strong> the computer code used in<br />

the draft Statement. The thermal criteria and temperature pr<strong>of</strong>iles can be found in<br />

Appendix K.<br />

Draft p. 3.1.106<br />

Issue<br />

No discussion is given <strong>of</strong> the air content <strong>of</strong> the repository following backfilling.<br />

The mobility <strong>of</strong> several significant radioelements, plutonium, neptunium, uranium, and tech-<br />

netium, are affected significantly by their oxidation state. (In some schemes for the in<br />

situ solution mining <strong>of</strong> uranium, air is used as the source <strong>of</strong> 02 and is the oxiding agent<br />

<strong>of</strong> the uranium.) The air content should be briefly discussed. (113-EPA)<br />

Response<br />

A room backfilled to within 0.6 m <strong>of</strong> the top will be slightly over 90% filled as rooms<br />

in the different host rocks range in height from 6.7 to 7.6 m. Since the backfill cannot<br />

be compacted to theoretical density, it is apparent that only some 70 to 80% <strong>of</strong> the room<br />

volume will be occuppied by solid matter. Thus, the remaining 20 to 30% will be air. How-<br />

ever, significant oxidation <strong>of</strong> the various radionuclides from this source <strong>of</strong> oxygen is not<br />

anticipated for several reasons.<br />

1. Air, alone, is not expected to corrode, erode, etc., or otherwise damage the<br />

waste package.<br />

2. Some <strong>of</strong> the air will dissolve in circulating water (ground water or brine) making<br />

ground waters somewhat more aggressive. The waste package will be designed to<br />

last 50 or more years at which time waste package temperatures will have passed<br />

their peaks and be declining. Consequently, the waste form will not be exposed<br />

simultaneously to its maximum temperature and an aggressive environment.

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