Annual Report for 2010/11 and Forward Programme - Sellafield Ltd

SSEM/2011/4730 June 20112.3.5 Analysis of findsFollowing the initial analysis of the finds at the Sellafield Ltd analytical laboratory, threeseparate batches of finds have been sent to the National Physical Laboratory (NPL) fordetailed analysis. NPL provide more in-depth information about their chemical/mineralcomposition, associated dose rates, isotopic composition, structure and potential bioavailabilityof the associated radioisotopes upon ingestion. Analysis methods have included:contact dose rates, gamma spectrometry, Scanning Electron Microscopy/Energy DispersiveX-Ray Spectroscopy (SEM/EDX), dissolution and leaching behaviour in seawater andsimulated human gut fluid. Separate studies were also conducted by HPA to determine thelikely uptake of activity in the human gut following ingestion. The uptake fraction of 238 Pu,239 Pu / 240 Pu and 241 Am for ten alpha rich particles measured in rats has been used by theHPA in their assessment of overall risk (Brown and Etherington, 2011).The analysis carried out from 2006 to date is summarised in Table 2.6. The results havebeen used by the HPA to demonstrate that the overall risk posed by both the alpha and betarichparticles is acceptable (see Section 5 for a full explanation). The Plutonium andAmericium isotope analysis and physical and chemical properties have been used by the SLParticles Sources and Pathways Working Group (PSPWG) to determine a likely candidatesource process for the alpha-rich particles (see below).Table 2.6. Analyses carried out on particles since 2006 by NPLType of AnalysisParticle Numbers AnalysedAlpha rich Beta richGamma spectrometry* 154 293Instrument dose rates 20 60TLD dose rates 20 60Mass 27 59Volume 23 41Density 19 57Scanning Electron Microscopy 33 62Energy Dispersive X-Ray 33 62Dissolution 23 55Pu isotopes 23Sr-90 8 54Tc-99 8 19Metals 8*Includes several analyses originating from the same particle, e.g. initial characterisation,after a seawater leach, after simulated gut dissolution and total dissolution.2.4 Sources and Pathways of beach findsAn assessment of the source and pathway of alpha-rich finds was co-ordinated by specialistsfrom the Sellafield Ltd central Environmental Management team, utilising the operationalknowledge and experience of representatives from key production, legacy and wastemanagement facilities on the Sellafield site (e.g. Magnox, Thorp, liquid effluent treatmentplants etc.), through the formation of the Particle Source & Pathway Working Group in 2007.Alpha-rich finds which contained sufficient actinide isotope concentrations had their agesestimated based on the relative decay of 239 Pu and 241 Pu, burn-up and cooling assumptions© Nuclear Decommissioning Authority 2011. 13