Repository for storing hazardous material in a subterranean formation

A hazardous material storage repository, comprising:

• a drillhole extending into the Earth and comprising an entry at least proximate a terranean surface, the drillhole comprising a substantially vertical drillhole portion, a transition drillhole portion coupled to the substantially vertical drillhole portion, and a hazardous material storage drillhole portion coupled to the transition drillhole portion, the hazardous material storage drillhole portion located below a self-healing geological formation, the hazardous material storage drillhole portion vertically isolated, by the self-healing geological formation, from a subterranean zone that comprises mobile water, at least one of the transition drillhole portion or the hazardous material storage drillhole portion comprising an isolation drillhole portion that is directed vertically toward the terranean surface and away from an intersection between the substantially vertical drillhole portion and the transition drillhole portion;
• a storage canister positioned in the hazardous material storage drillhole portion, the storage canister sized to fit from the drillhole entry through the substantially vertical drillhole portion, the transition drillhole portion, and into the hazardous material storage drillhole portion of the drillhole, the storage canister comprising an inner cavity sized enclose hazardous material;
• and
• a seal positioned in the drillhole, the seal isolating the hazardous material storage drillhole portion of the drillhole from the entry of the drillhole.