Presentation on theme: "Remediation of Hanford Plutonium Site Natalie Grenz Camille Azencott 9 th March 2007 University of Nottingham School of Civil Engineering Environmental."— Presentation transcript:
Remediation of Hanford Plutonium Site Natalie Grenz Camille Azencott 9 th March 2007 University of Nottingham School of Civil Engineering Environmental Geotechnology
Background Nuclear fission discovered in 1942 Control of splitting atoms Potential for unlimited power Cold War and Arms Race pushed for pursuit of military action. WARNING: Uncertainties in plutonium production
Hanford in History 105-B Reactor September 26, 1944: Reactor Operation Started July 16, 1945: Trinity Test in Alamogordo, New Mexico August 9, 1945: Bomb dropped on Nagasaki, Japan October 31, 1952: First Hydrogen bomb tested at Pacific Proving Grounds
Hanford Site Primary Site Functions: Fuel Manufacturing Fuel Irradiation Chemical Separation Plutonium Finishing 8 single pass reactors and 1 closed loop reactor located along the Columbia River. 4 chemical separation complexes on the interior plateau. Fuel Manufacturing adjacent to Columbia River above Richland.
Contamination Cooling water contaminated with radioactive and hazardous chemicals discharged to Columbia River from cooling towers. Contaminants include strontium-90, carbon-14, tritium, and hexavalent chromium. Contaminated solid wastes disposed of in burial grounds. Approximately 11 square miles of contaminated groundwater.
Contamination Effects While groundwater is NOT used for drinking water, it discharges into the Columbia River. Hexavalent chromium can cause increased risk of lung cancer, eye, nose, throat, and mucous membrane problems, nasal ulcers, dermatitis and skin ulcers. Strontium-90 increases cancer risk, especially bone cancer, tissue near the bone, and bone marrow.
Solutions dismissed Removal : advocated by stakeholders, but abandoned due to its high cost, poorly workability. Pump and Treat System. Cryogenic barrier. Soil Flushing.
Relevance of the Apatite barrier Impermeabilisation => Groundwater flow stopped =>Contaminant cannot move by advection. Apatite can trap Sr-90 by switching Ca with Sr. (same size and valence) Half life of Sr-90 (30 years) allows radioactive effluents to decay.
Alternative Apatite-forming technologies air injection of solid apatite abandoned. Hydrofracture grout curtain was abandoned, due to a high cost. Chosen technology : injection of the apatite-forming solution in a series of wells. Possible in a saturated media. Infiltration is also possible, because the contaminant is near the surface. Need to be done in a unsaturated soil.
Method step by step (1) Injection of Citrate in a well. Precipitation of apatite Apatite expands into pores => impermeabilisation => role of barrier, groundwater flow carrying the contaminant stopped.
Method step by step (2) Substitution of Sr in natural apatite, allowed by a similar size of atoms, and by an identical valence. Formation of strontiapite, which is stable, and even less soluble than apatite. Sr-90 decays, at a rate of 50% every 30 years.
Clean-Up Progress From 2003-04, 2300 tons of spent nuclear material removed. 5.9 million tons of contaminated soil and debris removed from site wastes since 1996 as of November 2006. Over 6.2 million liters of chromium-contaminated water and 1.1 billion liters of strontium-90 contaminated water removed as of June 2006.