Patent Number: 
Section: claims

1. A method for forming a directional drillhole for hazardous waste storage, comprising:identifying a subterranean formation suitable to store hazardous waste;determining one or more faults that extend through the subterranean formation;forming a vertical drillhole from a terranean surface toward the subterranean formation; andforming a directional drillhole from the vertical drillhole that extends in or under the subterranean formation and parallel to at least one of the one or more faults, the directional drillhole comprising a hazardous waste repository configured to store the hazardous waste. 2. The method of claim 1, further comprising forming the directional drillhole perpendicular to a direction of maximum horizontal stress of the subterranean formation. 3. The method of claim 1, wherein the subterranean formation is located in an area of high risk of seismic activity. 4. The method of claim 3, wherein the seismic activity comprises earthquakes. 5. The method of claim 1, wherein the hazardous waste comprises radioactive or nuclear waste. 6. The method of claim 5, wherein the nuclear waste comprises spent nuclear fuel or high level waste. 7. The method of claim 1, wherein the subterranean formation comprises at least one of shale, clay, or salt. 8. The method of claim 1, wherein the one or more faults comprises at least two parallel faults, and forming the directional drillhole comprises forming the directional drillhole between and parallel to the at least two parallel faults. 9. The method of claim 1, wherein determining the one or more faults comprises determining the one or more faults based on at least one of:one or more seismic records;one or more seismic reflection surveys;a geologic mapping; orone or more electromagnetic (EM) surveys. 10. The method of claim 1, wherein the directional drillhole does not cross the one or more faults. 11. A hazardous waste repository system, comprising:a directional drillhole that extends from an entry proximate a terranean surface to a subterranean formation that comprises one or more faults that extend through the subterranean formation, the directional drillhole comprising:a substantially vertical portion coupled to the entry,a transition portion coupled to the substantially vertical portion, anda substantially horizontal portion that is coupled to the transition portion and is formed in or under the subterranean formation and parallel to at least one of the one or more faults;a hazardous waste repository formed in the substantially horizontal portion of the directional drillhole;a storage container positioned in the hazardous waste repository, the storage container comprising an inner volume sized to enclose hazardous waste material; anda seal positioned in the directional drillhole that isolates the hazardous waste repository from the entry. 12. The system of claim 11, wherein the directional drillhole extends perpendicular to a direction of maximum horizontal stress of the subterranean formation. 13. The system of claim 11, wherein the subterranean formation is located in an area of high risk of seismic activity. 14. The system of claim 13, wherein the seismic activity comprises earthquakes. 15. The system of claim 11, wherein the hazardous waste material comprises radioactive or nuclear waste. 16. The system of claim 15, wherein the nuclear waste comprises spent nuclear fuel or high level waste. 17. The system of claim 11, wherein the subterranean formation comprises at least one of shale, clay, or salt. 18. The system of claim 11, wherein the one or more faults comprises at least two parallel faults, and the directional drillhole extends between and parallel to the at least two parallel faults. 19. The system of claim 11, wherein the one or more faults are determined based on at least one of:one or more seismic records;one or more seismic reflection surveys;a geologic mapping; orone or more electromagnetic (EM) surveys. 20. The system of claim 11, wherein the directional drillhole does not cross the one or more faults.