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

SSEM/2011/4730 June 20114.5004.000Find Rate (finds per ha)3.5003.0002.5002.0001.5001.0002006/072007/082008/092009/102010/110.5000.000St Bees Nethertown Braystones Sellafield Seascale DriggMonitoring AreaFigure 3.6. Changes in year on year find rate at beaches closest to SellafieldThe key radionuclides detected by the Groundhog TM Synergy monitoring are 137 Cs and241 Am. Consequently, initial characterisation of each find recovered via the monitoringprogramme concentrates on these isotopes, such that, for positive analytical results; 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”.Finds with positive 60 Co activity and greater than the 137 Cs activity are classified as“Cobalt-rich”When Synergy was introduced in 2009, its greater capability for detecting low energy alphaand pure beta emitters resulted in a significant change in the find profile. In the latter half ofthe 2009/10 programme the number of finds classified as “alpha-rich” increased notably andthis trend continued throughout the 2010/11 annual beach monitoring programme (Table3.4). Over 84% of all finds were classified as alpha-rich and were detected on most beachesthat were surveyed (Table 3.5, Figure 3.8). The majority of beta-rich and a significantproportion of alpha-rich finds were recovered at Sellafield and Braystones (Figure 3.9).The number of finds classified as beta-rich continued to decline (down 36% compared to2009/10) even with the large increase in the total number of finds recovered throughout theprogramme. This trend is consistent with previous monitoring reports and suggests that theactive particles/stones are being removed (by the monitoring/retrieval programme) fasterthan they are becoming available in the beach environment. Furthermore, over 80% of betarichfinds were recovered from Sellafield beach which is also consistent with previousmonitoring programmes.© Nuclear Decommissioning Authority 2011. 26