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

SSEM/2011/4730 June 20112.3.4 Find classificationAll finds are recovered and returned to Sellafield site for analysis in the laboratory usinggamma spectrometry. This measures the key radionuclides that are detected by theEvolution/Synergy system ( 137 Cs and 241 Am) and any other significant radionuclides (e.g.60 Co, 106 Ru). Finds with positive analytical results are broadly classified into alpha- or betarich:Finds with 241 Am activity greater than 137 Cs activity are classified as “alpha-rich”;Finds with 137 Cs activity greater than 241 Am activity are classified as “beta-rich”.Following the introduction of the Synergy monitoring system during the 2009/10 monitoringprogramme, which is more effective at detecting low energy alpha and pure beta emittersthan Evolution 2, the number of “alpha-rich” finds being recovered, particularly from Sellafieldand Braystones beaches, increased.A comparison of finds detected by the Synergy system (NaI detectors plus FIDLER probes)and those that would have detected using the Evolution 2 system (i.e. NaI detectors only)revealed that there would have been 55 fewer beach finds during 2009/10 if Synergy had notbeen introduced in August 2009 (D’Souza, 2010). The vast majority of the extra 55 findswhich Synergy detected were characterised as alpha-rich, reflecting the capability of Synergyto detect lower energy finds. Interpretation of this improvement is complicated because theSynergy system also introduced a carbon fibre detection box which also appears to havemade the NaI detectors more efficient.The number of beta-rich finds recovered has decreased from 322 in 2007/8, to 220 in 2008/9and 94 in 2009/10 despite the same total area being monitored (approximately 250 ha). Thecontinued reduction in 2009/10 is even more significant because of the use of more sensitivedetection equipment (Synergy). In addition to the alpha and beta rich find classification, a total of 12 finds have beenallocated a 60 Co rich classification since 2006. A 60 Co rich find is defined as a particle orstone where the 60 Co activity is positive and greater than the 137 Cs activity (but notnecessarily greater than 241 Am).Generally, 60 Co activity in the nuclear industry is associated with neutron activation of steelcomponents of the reactor fuel or its support structure. Superficially, this might appear tooffer an easier route for identifying the time and source of the release into the environment.In reality, however, the complexity of fuel handling and reprocessing operations together withsubsequent effluent treatment makes a definitive assessment very difficult.Table 2.5. Numbers of alpha-rich, beta-rich and 60 Co rich Particles recovered 2006-2010ClassificationNumber of Particles2006/07 2007/08 2008/09 2009/10Alpha-rich 1 31 24 140Beta-rich 6 117 74 4660 Co rich 0 5 2 5© Nuclear Decommissioning Authority 2011. 12