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

SSEM/2011/4730 June 2011Log Am241 Activity Histogram of Separate Evolution 2 and Synergy Particle Data706050Frequency4030201003 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6Log to base 10 of Am241 ActivityEvolutionSynergyFigure 3.13. Histogram of Log Normally Transposed Alpha Rich Particle 241 Am Activities forseparate Evolution 2 and Synergy Monitoring Periods.Further work with the statistical techniques advised in the first statistics report (Scott andTyler, 2011a) should provide evidence that can confirm or deny this hypothesis.A report on the assessment of the potential sources of alpha-rich finds, commissioned by theParticle Sources & Pathways Working Group (PSPWG), was completed in June 2010(Hackney ., 2010). The report used 238 Pu and 241 Am data on 51 alpha-rich finds that wereavailable at the end of March 2009. It identified that the bulk of these finds had their origins indistinct Magnox or Oxide fuel types. Since March 2009 a further 43 results have becomeavailable. These 43 finds have been categorised using the factors developed in the report,and are shown in Table 3.7 below.Table 3.7. Alpha-rich sub-group numbersAlpha-rich sub category Original Report New dataMagnox 25 3Oxide 23 27Unresolved 3 13When compared to the original data, the new data shows a marked increase in the Oxidegroup numbers and a drop in Magnox group numbers. This observation is consistent with thelower mean alpha activity for particles found since the introduction of the Synergy monitoringsystem in August 2009. That is, the mean 241 Am activity of all 50 Oxide finds (i.e. 6.31E+04Bq) is less than 50% of the mean activity for the 30 Magnox finds (i.e. 1.34E+05 Bq); so theOxide subgroup might be expected to be more prevalent in lower activity finds found bySynergy than the Magnox subgroup.© Nuclear Decommissioning Authority 2011. 40