A hazardous waste repository includes a drillhole formed from a terranean surface into a subterranean formation, the drillhole including an entry at the terranean surface and an access portion that extends from the entry toward a storage portion within the subterranean formation; a plurality of hazardous waste canisters emplaced within the storage portion of the drillhole, each of the hazardous waste canisters enclosing hazardous waste; and a granular material installed in a volume of the drillhole between a casing and the plurality of canisters and between adjacent canisters of the plurality of canisters, the granular material configured to support at least a portion of a weight of each of the plurality of canisters.