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

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K.1 THERMAL CRITERIA<br />

K.1<br />

APPENDIX K<br />

GEOLOGIC REPOSITORY DESIGN CONSIDERATIONS<br />

A major factor in geologic isolation <strong>of</strong> radioactive waste is the heat generated by<br />

high-level waste (HLW) or spent fuel assemblies. This heat flows from the waste, through<br />

the emplaced canister and other protective material, into the host rock formation, through<br />

the rock surrounding or overlying this formation, and eventually out into the atmosphere.<br />

The heat can have definite impacts on:<br />

* the integrity and recoverability <strong>of</strong> the waste canisters<br />

* room and pillar stability<br />

* integrity <strong>of</strong> the waste form over long periods <strong>of</strong> time<br />

* the integrity <strong>of</strong> the host rock and the surrounding rock units<br />

* any overlying aquifers and buoyancy effects on ground-water flow<br />

* long-term uplift and subsidence <strong>of</strong> overlying rock.<br />

To assure that the impact <strong>of</strong> the heat on these factors will not be detrimental to<br />

waste isolation objectives, a systematic determination <strong>of</strong> the repository design thermal<br />

loads is required that includes:<br />

* establishment <strong>of</strong> limits for conditions affected by heat<br />

* determination <strong>of</strong> acceptable thermal loads that will not bring about conditions<br />

beyond the assigned limits<br />

* development <strong>of</strong> repository design thermal loads, taking into account safety, engi-<br />

neering and operational requirements.<br />

Design limits for the repository can be specified in terms <strong>of</strong> temperature and thermo-<br />

mechanical criteria. Preliminary estimates <strong>of</strong> acceptable thermal conditions are summarized<br />

in Table K.1.1 and discussed below.<br />

* Maximum Uplift Over Repository<br />

Uplift over the repository centerline was chosen as a measure <strong>of</strong> the far-field struc-<br />

tural consequences <strong>of</strong> repository thermal loading. The 1.2 to 1.5 m <strong>of</strong> maximum uplift,<br />

neglecting subsidence, is based on the assumption that rock-mass movements caused by uplift<br />

may be no worse than movements caused by subsidence over mines in sedimentary rocks, which<br />

are sometimes more than twice the stated limit. Far-field effects are currently being<br />

studied to determine whether 1.2 to 1.5 m <strong>of</strong> uplift is reasonable. This tentative limit<br />

may change as more information is developed. In any case, this limit must be reevaluated<br />

for each site so that the effects <strong>of</strong> rock-mass movement on the hydrological regime and long-<br />

term safety may be assessed.

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