Monitoring a hazardous waste repository

A method for monitoring hazardous waste, comprising:

• identifying a hazardous waste drillhole formed from a terranean surface into one or more subterranean formations, the hazardous waste drillhole comprising an entry sized to receive a plurality of hazardous waste canisters that enclose radioactive hazardous waste into and through the entry, and a hazardous waste storage area formed in a storage subterranean formation and sized to receive the plurality of hazardous waste canisters;
• identifying a probe borehole formed from the terranean surface into the one or more subterranean formations adjacent the hazardous waste drillhole, the probe borehole having a diameter less than a diameter of each of the plurality of hazardous waste canisters;
• and
• measuring, with at least one radiation measurement instrument of a plurality of radiation measurement instruments positioned in the probe borehole near the hazardous waste storage area, at least one parameter associated with the hazardous waste;
• while measuring, impeding movement of radiation within the probe borehole between adjacent radiation measurement instruments with at least on radiation shield positioned in the probe borehole between the adjacent radiation measurement instruments, wherein
• the probe borehole is separated from the hazardous waste drillhole by a predetermined distance in the storage subterranean formation that defines a closest approach distance between the hazardous waste drillhole and the probe borehole, the closest approach distance defining an amount of attenuation of radiation from the radioactive hazardous waste between the hazardous waste drillhole and the probe borehole based on the storage subterranean formation.

A hazardous waste repository monitoring system, comprising:

• a hazardous waste drillhole formed from a terranean surface into one or more subterranean formations, the hazardous waste drillhole comprising an entry sized between 28 inches and 60 inches to receive a plurality of hazardous waste canisters that enclose hazardous waste into and through the entry, and a hazardous waste storage area formed in a storage subterranean formation and sized to receive the plurality of hazardous waste canisters, the hazardous waste comprising radioactive waste;
• a probe borehole formed from the terranean surface into the one or more subterranean formations adjacent the hazardous waste drillhole, the probe borehole having a diameter of between 4 inches and 8 inches and less than a diameter of each of the plurality of hazardous waste canisters, the probe borehole separated from the hazardous waste drillhole by a distance of between 1 and 3 meters at which a radiation level from the radioactive waste by at least one measurement instrument is attenuated by a portion of the one or more subterranean formations between the hazardous waste drillhole and the probe borehole to be insufficient to damage the at least one measurement device over a particular time duration;
• and
• the at least one measurement instrument positioned in the probe borehole near the hazardous waste storage area and configured to measure at least one parameter associated with the hazardous waste.