Devices, systems, and methods for closure of deep geological nuclear waste disposal repository

A method of sealing a waste repository from upwards migration of waste located within the waste repository from migration past a modified cap-zone located above the waste repository, wherein the method comprises steps of:

• (a) installing at least one lower-plug within at least one wellbore at a location that is below at least one cap-zone and above the waste repository;
• wherein the at least one lower-plug completely blocks an interior portion of the at least one wellbore at that location, wherein the at least one wellbore runs from a terrestrial surface through the at least one cap-zone and into a deep geologic formation, wherein the waste repository is located within the deep geologic formation;
• (b) forming at least one radial-hole within the at least one cap-zone from the at least one wellbore using jet drilling equipment;
• (c) removing rock material from the at least one cap-zone in an outward radial direction from a portion of the at least one wellbore that is passing through the at least one cap-zone, wherein an output of this step (c) removal is a region of void-volume located within the at least one cap-zone;
• (d) landing a downhole in-well heater into the void volume;
• (e) filling the void-volume around the downhole in-well heater with crushed rock until the downhole in-well heater is completely covered by the crushed rock;
• (f) melting rock within a melt-zone by energizing the downhole in-well heater, wherein the melt-zone comprises the crushed rock within the void-volume and native intact rock of the at least one cap-zone that is interfacing and adjacent to the crushed rock within the void-volume;
• and
• (g) cooling the melt-zone, such that an output of the step (g) cooling is the modified cap-zone, wherein the modified cap-zone comprises the crushed rock within the void-volume and the native intact rock of the at least one cap-zone that were formerly melted during the step (f) and that are now resolidified and recrystallized, wherein an exterior radial boundary of the modified cap-zone is welded and fused to the at least one cap-zone, wherein the modified cap-zone is configured to prevent the upwards migration of the waste and fluids located within the waste repository from getting past the modified cap-zone.