Assessing the potential of phytoextraction to remediate land contaminated with 137Cs at nuclear power station sites

• Main Author: Watt, Nicholas Robin
• Published: University of the West of England, Bristol 2004
• Subjects: 628.55
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409444

The intended endpoint for Magnox Electric plc's reactor decommissioning strategy is site clearance and de-licensing, which may require remediation of any 137CS contaminated land on these sites. Phytoextraction might provide a practical and environmentally acceptable method of reducing radioactive waste volumes for disposal. Field trials conducted at Bradwell Nuclear Power Station, Essex, UK and experiments in controlled conditions, using Beta vulgaris, showed that soil-to-plant transfer factors increase as soil 137CS activity concentration decreases, implying that constant 137CS removal rates are possible during site remediation. It was shown that 133CS might be responsible for this effect. Short time-interval multiple croppings were not found to increase the rate of 137 Cs removal. For successful implementation of 137CS phytoextraction plant species need to be identified that can accumulate higher concentrations of 137 Cs than those identified at present. The large variation in 137CS uptake between species tested here suggests that extensive species screening programmes will be required. Soil amendments appear essential to the phytoextraction of aged 137CS and NH/, 133CS+ and K+ were shown to be capable of extracting up to 25 % of the 137CS from soil at a field site. In a 14 month simulated 137CS phytoextraction trial in controlled conditions, over 60 % of 137CS applied to an organic soil was removed using a 20 mg kg-1 CsCl soil amendment suggesting that, where 137CS is sufficiently plant available, phytoextraction might be a useful soil remediation technology. In a desk based BPEO study, composting was identified as the most appropriate option for conditioning the biomass arising from 137 Cs phytoextraction allowing it to be stored at the UK's LLW repository at Drigg, Cumbria. It was concluded that the risk associated with soil amendments of 137 Cs leaching off sites and the poor plant growth conditions likely to be found at field sites would require the use of a greenhouse with soil contained in lysimeters during phytoextraction.