Radionuclide contaminated land scenarios at UK nuclear legacy sites

1. Radionuclide contaminatedland scenarios at UKnuclear legacy sites C.L. Thorpe G.L. Law, I.T. Burke, J.R. Lloyd and K. Morris DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

2. The Project • Project summary • Model site: • Sellafield nuclear facility • Cumbria, UK. • Focus: • The treatment of co-contaminants strontium and technetium in a variety of conditions including high nitrate and low pH. • Scenarios: • Bio-stimulation by electron donor addition in high nitrate/ low pH sediment • Nano-scale/micro-scale Zero Valent Iron addition Figure 1: www.visitcumbria.com DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

3. Geochemical Conditions • Nuclear facility conditions • pH range (~5.5-10) • High nitrate (0->100 mM) • Localised high bicarbonate concentrations • Contamination of problematic radionuclides • Technetium-99 • Strontium-90 • Uranium • (Rifle, CO, US; Sellafield, UK; Naturita, CO, US; ORFRC, US; Hanford, US; Dounreay, UK; Drigg, UK) DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

4. My Project Outline • Aim: to investigate the potential methods for remediation of strontium and technetium contamination in the “far field” at a range of pH and potentially high nitrate. • The effect of nitrate as a co-contaminant on terminal electron accepting processes (TEAPs) • The potential co-treatment of strontium and technetium with nano-scale zero valent iron (nZVI) • The effect of nZVI on the microbial community and progression of TEAPs DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

5. Nitrate Co-contamination • Question: What is the effect of high nitrate (100 mM) on the progression of terminal electron accepting processes (TEAP’s) in Sellafield sediments? • Nitrate is present at nuclear facilities due to the use of nitric acid in the nuclear fuel cycle • Nitrate can inhibit TEAPs as it competes with metals and radionuclides as an electron acceptor in anaerobic respiration. • Previous studies show that metal/radionuclide reduction does not take place until nitrate reduction is complete DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

6. Experimental Methods • Monitoring progression of TEAPs • Spectrophotometrically: • nitrite, • Mn • Fe(II) • % Fe(II)/Fe(III) in sediments (acid extraction) • Ion Chromatography: • Nitrate • Sulphate • Probe: • Eh • pH Microcosms Headspace gas Argon Sellafield representative groundwater (Wilkins et al. 2006) 100 ml Sellafield sediment 10g DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

7. Nitrate Scenarios Microcosm work: the effect of 100 mM nitrate on terminal electron accepting processes (TEAP’s) in Sellafield Sediment at pH 5.5 and pH 7. DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

8. Results T=30 days Iron reducing Iron reducing sulphate reducing sulphate reducing nitrate reducing nitrate reducing pH 7 100 mM nitrate pH 5.5 0.3 mM nitrate pH 5.5 2 mM nitrate pH 5.5 10 mM nitrate pH 5.5 100 mM nitrate pH 7 0.3 mM nitrate DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

9. Results – 10 mM nitrate, pH 5.5 % Fe (II) in sediment pH Eh Nitrite (mM) DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

10. Results – 100 mM nitrate, pH 7 % Fe (II) sediment pH Nitrite (mM) Eh DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

11. Discussion – pH 5.5 (0.3, 2, 10 and 100 mM nitrate) • Iron reduction did not commence until nitrate reduction had reached completion and all nitrite was reduced. • Results at pH 5.5 • In microcosms containing 0.3, 2 and 10 mM nitrate TEAP’s progressed to iron reduction within 25 days. In microcosms containing 100 mM nitrate, nitrate reduction is ongoing at 80 days • A rise in pH was observed in all microcosms, the extent of pH rise was dependent on initial nitrate concentration but 10 mM was sufficient for pH to rise from 5.5 to 7 during production of nitrite. DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

12. Discussion – pH 7 (0.3 mM and 100 mM nitrate) • Iron reduction did not commence until nitrate reduction had reached completion and all nitrite was reduced • Results at pH 7 • Microcosms containing 0.3 and 100 mM nitrate progressed to iron reduction within 15 and 60 days respectively. • In sediment containing 100mM nitrate pH rose to 9.4 during nitrate reduction and a darkening of the pore water was observed thought to be leaching of organic matter. DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

13. Microbial Analysis DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

14. Future Questions Further work- scenarios to treat strontium and technetium co-contaminants: Question: What is the optimum pH for Sr sorption to Sellafield sediment? Question: How does nZVI affect the pH and Eh of a system when it is initially added and over time? Question: What effect does nZVI addition have on iron mineral phases and on Sr Sorption and mobility? Question: What effect does nZVI addition have on the microbial community? Can hydrogen production act as an electron donor? DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

15. Rationale for nZVI Work Fe0 + 2H2O--- Fe2+ + H2 + 2OH- • nZVI reduces everything indiscriminately so will affect nitrate, Mn and Fe species as well as redox sensitive radionuclides Tc and U. • OH‾ produced during iron corrosion may raise the pH and aid bioreduction. Increased pH aids strontium sorption and co-precipitation with Ca minerals. • Hydrogen production may stimulate the in situ microbial community and help maintain reducing conditions. DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal

16. Eventual Aim • 24 month aim: to design “flow through columns” suitable for use with Tc and Sr to demonstrate bioremediation scenarios: • Electron donor addition • pH neutralisation • Zero valent iron addition • Combinations of the above Magga et al. 2008- column to measure pesticide contaminate spread DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal