Decontamination of metals containing plutonium and americium

Abstract

Melc-slagging (melt-refining) techniques were evaluated as a decontamination and consolidation step for metals contaminated with oxides of plutonium and americium. Experiments were performed in which mild steel, stainless steel, and nickel contaminated with oxides of plutonium and americium were melted in the presence of silicate slags of various compositions. The metal products were low in contamination, with the plutonium and americium strongly fractionated to the slags. Partition coefficients (plutonium in slag/plutonium in steel) of 7 x 10^ were measured with borosilicate slag and of 3 x 10° with calcium, magnesium silicate slag. Decontamination of metals containing as much as 14 000 ppm plutonium appears to be as efficient as for metals with plutonium levels of 400 ppm. Staged extraction, that is, a remelting of processed metal with clean slag, results in further decontamination of the metal. The second extraction is effective with either resistance-furnace melting or electric-arc melting. Slag adhering to the metal ingots and in defects within the ingots is in the important contributors to plutonium retained in processed metals. If these sources of plutonium are controlled, the melt-refining process can be used on a large scale to convert highly contaminated metals to homogeneous and compact forms with very low concentrations of plutonium and americium. A conceptual design of a melt-refining process to decontaminate plutonium-and americium-contaminated metals is described. The process includes single-stage refining of contaminated metals to pr&uuce a metal product which would have less than 10 nCi/g of TRU-element contamination. Two plant sizes were considered. The smaller conceptual plant processes 77 kg of metal per 8-h period and may be portable. The larger one processes 140 kg of metal per 8-h period, is stationary, and may be near the maximum size that is practical for a metal decontamination process.

Decontamination of metals by melt refining/slagging. An annotated bibliography: Update on stainless steel and steel

“…The results showed similar volatility behavior to the stainless steel test work but analytical data was not yet available at the time of these publications. Industrial operation was quoted as Seitz (1979) 10 NiO 10 U 0.005 Nafiiger (1988) . , a. BI = Basicity Index = (wt,% basic oxides)(wt.% acidic oxides) b.…”

“…With respect to stainless steels the slags that achieved less than natural levels of uranium ( Table 3- A variety of slags have been successfully b e d to lower the plutonium content in both mild steels and stainless steels to plutonium concentrations less than one ppm. Borosilicate slags appear to be effective for steels, e.g., Seitz (1979) presents data showing plutonium removals over the range 0.001-032 ppm. Hobbick (1981) has demonstrated effective plutonium removal using borosilicate slags, high silica calcium-aluminum-silicate slags and fluoride containing basic calciumaluminum-silicate-ferrite slags.…”

“…Table 5-2. The ten radiologically most important radionuclides at different times for surface contamination for decommissioning waste Heshmatpour (1981a) 1.94 Heshmatpour (198la) uo2 Heshmatpour (1981a) u o 2 5.23 Heshmatpour (1981a) u o 2 1.08 Heshmatpour (1981a) 0.14 Heshmatpour (198la) 10 Pu 2.5 10 Pu 1 9 uo2 5.23 Heshmatpour (198la) 11 Pu 0.09-22.0 Seitz (1979) 10 Pu NA Seitz(1979) U L=583 Snyder (1991) Seitz (1979) 0.26 Uda (1985) 0.31 Heshmatpour (198la) .0019 Seitz (1979) 0.005-0.20 Seitz (1979) 0.017-0.22 Seitz (1979) Seitz (1979) 0.002403 Seitz (1979) 0.016 Seitz (1979) Seitz (1979) O.OOO2…”

Decontamination of metals by melt refinings/slagging: An annotated bibliography

“…With respect to stainless steels the slags that achieved less than natural levels of uranium (Table 3. A variety of slags have been successfully used to lower the plutonium content in both mild steels and stainless steels to plutonium concentrations less than one ppm. Borosilicate slags appear to be effective for steels, e.g., Seitz (1979) presents data showing plutonium removals over the range 0.001-0.32 ppm. Hobbick (1981) has demonstrated effective plutonium removal using borosilicate slags, high silica calcium-aluminum-silicate slags and fluoride containing basic calcium-aluminum-silicate-ferrite slags.…”

Technical assessment of processes to enable recycling of low-level contaminated metal waste

“…Melting without any flux at all reduced the U contaminationfrom 500 to 0.65 ppm,TM and between 85 and 100 ppm 25. The disparity in these values could be related to the method of applying the contaminationto the melt stock.Seitz, et al,16 Found that some of the slags were inhomogeneous, notably the borosilicateslags which sometimesexhibited a mottled or marbled appearance. Analyses disclosed higher Pu concentrationsin regions of higher alumina content; higher concentrationsof chromium were also found in the higher alumina phase.…”