Technetium Inventory, Distribution, and Speciation in Hanford Tanks

Abstract

The purpose of this report is three fold: 1) assemble the available information regarding technetium (Tc) inventory, distribution between phases, and speciation in Hanford's 177 storage tanks into a single, detailed, comprehensive assessment; 2) discuss the fate (distribution/speciation) of Tc once retrieved from the storage tanks and processed into a final waste form; and 3) discuss/document in less detail the available data on the inventory of Tc in other "pools" such as the vadose zone below inactive cribs and trenches, below single-shell tanks (SSTs) that have leaked, and in the groundwater below the Hanford Site.

Retention of99mTc at Ultra-trace Levels in Flowing Column Experiments – Insights into Bioreduction and Biomineralization for Remediation at Nuclear Facilities

“…In the sulfate reduction column the presence of FeS lead to the fastest rates of 99m Tc immobilization. The results are the first to show the variable but significant retention of 99m Tc at ultra-trace levels relevant to conditions at many nuclear sites in a range of biostimulated sediment columns and present a positive outlook for the treatment of Introduction Technetium-99 contaminated groundwater is present at many nuclear sites including the Sellafield nuclear facility, UK (Beals and Hayes 1995;Serne and Rapko 2014;Stamper et al 2014). Due to its long half-life (2.1 £ 10 5 years) 99 Tc is a key risk-driving radionuclide in many safety case scenarios and the behavior of 99 Tc in subsurface environments is of interest from both a radioactively contaminated land and radioactive waste management perspective.…”

In Situ Quantification of [Re(CO)3]+ by Fluorescence Spectroscopy in Simulated Hanford Tank Waste

“…99 Tc accounts for ∼100% of all Tc isotopes sources. The total 99 Tc content at the Hanford Site approximates to 2000 kg (∼36 000 Ci), of which ∼4% has been lost to the environment . Although 99 Tc exhibits only a weak β – decay (0.292 keV), it is of environmental concern for two reasons: (1) It has a half-life of 2.13 × 10 5 years and (2) its most abundant environmental species, pertechnetate, TcO 4 – , migrates quickly with groundwater .…”

“…Under tank conditions, the tricarbonyl species is expected to react with constituents within the waste, forming a [Tc­(CO) 3 (L) 3 ] n − complex, where (L) 3 represents a multidentate ligand binding to the metal center, such as citrate, oxalate, and gluconate. The presence of the nonpertechnetate species (which has been found in select Hanford tank supernatants at concentrations in the range of 2–60% of total Tc) has hampered the selective movement of Tc high level waste streams prior to immobilization . It is also believed that the [Tc­(CO) 3 (L) 3 ] n − species have the potential to leak from the tanks into the underlying vadose zone and groundwater.…”

Rhenium volatilization in waste glasses

“…In addition, 99 Tc is highly mobile in subsurface environments [2,3] and volatile at elevated temperatures [4]. Over 1.28 Â 10 3 TBq of 99 Tc (>1900 kg) was produced at the Hanford Site during nuclear fuel reprocessing for plutonium production between 1944 and 1989, of which $9.8 Â 10 2 TBq ($1560 kg) survives in 177 underground tanks of nuclear waste [5]. Hanford Tank Waste Treatment and Immobilization Plant, which is currently under construction, will separate tank waste into high-level waste (HLW) and low-activity waste (LAW) and immobilize both into durable borosilicate glasses.…”

“…Hanford Tank Waste Treatment and Immobilization Plant, which is currently under construction, will separate tank waste into high-level waste (HLW) and low-activity waste (LAW) and immobilize both into durable borosilicate glasses. Over 90% of the 99 Tc will be disposed in LAW glass at the Hanford Site in the Integrated Disposal Facility, where 99 Tc, though at a concentration below 0.001 mass%, will be the primary dose contributor over the period of tens of thousands of years [4,5].…”