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

SSEM/2011/4730 June 2011the time of the visit may be important. Furthermore, in August 2009, the Evolution 2 detectionsystem was replaced with the Synergy system with its better capability for detecting itemscontaining either pure beta emitters or mainly alpha emitters by their low energy gammaemission.Table 2.3. Beach find rates 2006-2010 (particles and stones)MonitoringFind rate (finds per hectare)area 2006/07 2007/08 2008/09 2009/10St Bees – 0.214 0.077 0.059Braystones 0.334 0.158 0.115 1.043Sellafield 1.671 4.003 1.747 2.181Seascale – 0.209 0.188 0.176Drigg – 0.254 0.051 0.000All 0.835 1.725 0.692 0.6812.3.3 Find sizesItems recovered from the beach range in size, from tens of microns to large stones. Prior tothe 2008/9 programme, any finds recovered from the beaches surrounding Sellafield weredescribed as either stones, particles or pebbles (i.e. rounded stones). Deciding whether afind was a pebble or a stone was open to interpretation so from the 2008/9 monitoringprogramme the pebble classification was removed. At the same time, the standard sedimentclassification system was applied to the beach finds; anything less than 2 mm in diameter(upper limit for sand grains) was classed as a particle and anything larger than or equal to 2mm as a stone. This classification allows a foundation on which to judge the potential for a“particle” to be ingested, inhaled or adhere to the skin. However, this is based on a visualassessment following coarse separation and there will always be some ambiguity for findsaround 2 mm in size unless they are sent for detailed analysis.Contaminated stones have mainly been found within a few hundred metres north of theSellafield pipeline. The furthest a stone has been recovered from the pipeline isapproximately 2.5 km at the northern end of Sellafield beach. Two stones have been foundon Seascale beach, the furthest south being approximately 2.5 km south of the pipeline.Table 2.4. Numbers of Particles and Stones recovered 2006-2010MonitoringareaNumber of finds2006/07 2007/08 2008/09 2009/10Particles Stones Particles Stones Particles Stones Particles StonesSt Bees – – 6 0 3 0 4 0Braystones 3 0 2 0 4 0 68 0Sellafield 4 5 129 204 79 141 102 50Seascale – – 7 0 10 3 17 0Drigg – – 5 0 2 0 0 0Allonby – – – – 1 0 – –Workington – – – – 1 0 – –All 7 5 149 204 100 144 191 50© Nuclear Decommissioning Authority 2011. 11