Graphite waste classification and disposal cost estimation for high temperature gas and salt reactors

As high-temperature reactor designs progress to demonstration, managing the radioactive wastes from these systems presents unique challenges. This work explores the irradiated graphite source term produced by three reactor designs: The Modular High Temperature Gas reactor (MHTGR), a pebble-bed High Temperature Gas Reactor (pb-HTGR), and a Fluoride-cooled High-temperature Reactor (FHR). We predicted a C-14 concentration of 4.3 Ci/m³ for the MHTGR, 1.2 Ci/m³ for the pebble bed HTGR, and 2.5 Ci/m³ for the gFHR after 20 years of operation. The final C-14 concentration highly depended on the graphite nitrogen impurity, a major precursor for C-14. The C-14 concentration in all reactor types exceeded the 0.8 Ci/m3 threshold, resulting in a Class C waste classification. The costs associated with accepting the graphite after 20 years in a low-level waste disposal facility were projected to be 255 dollars per kWe for the MHTGR, 248 dollars per kWe for the pb-HTGR, and 56.8 dollars per kWe for the FHR.. Authors: Hines, Liam [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)] (ORCID:0000000215704540); Shirvan, Koroush [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)]; Peterson, Per [University of California, Berkeley, CA (United States)]; Snead, Lance [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Stony Brook Univ., NY (United States)]. DOE Contract: NE0009294. Subjects: 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; Fluoride-cooled high-temperature reactor; High temperature gas reactor; Irradiated graphite; Low level radioactive waste; Waste management