A history of Hanford tank waste, implications for waste treatment, and disposal

Abstract

More than 40 years of plutonium processing have left almost 56 million gallons of mixed radioactive waste sequestered in 177 underground tanks on the Hanford Site. Three different processing technologies were employed for plutonium purification in addition to uranium scavenging and fission product removal from the tank waste. All of these chemical processes have contributed to a complex waste stream that varies from tank to tank that presents downstream processing challenges to render the waste into a safe form for long‐term storage. The current disposition pathway for Hanford tank waste is vitrification. To maximize waste loading and minimize the number of high‐level waste canisters stored in a geologic repository, pretreatment of the waste is required. Both pretreatment and vitrification operations are impacted by the waste composition.

Light‐Driven Oxidation of Pu(IV) to Pu(VI) Enables Green and Efficient Pu Recovery

“…The separation of Pu(IV)/Th(IV) usually requires valence adjustment of Pu(IV) by adding chemical reductant or oxidant. [ 25‐26 ] In this work, we directly irradiated a Th‐Pu mixed HNO 3 solution with UV light and then performed extraction by an amide extractant N,N,N',N',N”,N” ‐hexaoctylnitrilotriacetamide (NTAamide( n ‐Oct)), which has been found to exhibit high selectivity to Th(IV) over U(VI). [ 27‐28 ] As shown in Figure 3a, through one single stage extraction, Th(IV) was preferably extracted into the organic phase ( D Th = 12.6) while most of the oxidized Pu in the form of PuO 2 2+ remained in the aqueous phase ( D Pu = 0.127), achieving a high Th/Pu separation factor ( SF Th/Pu ) of 100 as compared to only 5 if without light irradiation.…”

Photon-In/Photon-Out X-ray Free-Electron Laser Studies of Radiolysis

“…The salt cake consists of water-soluble oxyanion and halide salts. The sludge consists primarily of insoluble Al oxides and oxyhydroxides, such as gibbsite (Al(OH) 3 ), or amorphous agglomerates of varying sizes and morphologies, all of which serve to complicate retrieval and processing [58,59].…”

Strontium/strontium‐90 removal from c helate‐bearing Hanford tank waste using crystalline silicotitanate

“…1 At the Hanford site, three stages of radiological tank waste treatment are planned: (1) vitrification of liquid and dissolved salt cake wastes (low activity waste to be buried on site), (2) vitrification of sludge (high-level waste for disposal in a geologic repository), and (3) stabilization of additional liquid and salt waste by grouting, vitrification, or steam reforming. 2 The most prevalent radionuclide in the salt cake is 137 Cs followed by 99 Tc. Only the former needs to be removed for the stabilized salt (e.g., glass) to be buried on site.…”

“…Gluconate and HEDTA were below the detection limits even though both species were added to the waste during processing at Hanford's B Plant. 2,32 All of the chelates slowly degrade via hydrolysis and radiolysis over time, [33][34][35][36][37][38] which likely explains why gluconate and HEDTA were not detected by Urie et al 25 Organic degradation products oxalate and the carbonate have accumulated in the solids at the bottom of tank AN-102. 39 There has likely been additional chelate degradation since the year 2002, but still significant quantities remain given the large concentration of dissolved 90 Sr recently observed in tank AN-102 supernatant.…”