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

SSEM/2011/4730 June 2011Recommendations7 Standard statistical analyses (such as generallinear models, confidence intervals andhypothesis tests) be used to explore the beachfinds and where appropriate to draw inferencesconcerning the population distributions, factorswhich account for the variability in the finds andto summarise changes.8 For temporal comparability over monitoringcampaigns, time series of finds should beadjusted for monitoring effort and equipmentchanges (see also recommendation 3 and 5).9 To assess which beaches should have a highpriority from habit information. Monitoring ofthese beaches should have a substantiallygreater footprint (>50 %) consistently to providea better sample of the particle population onthese beaches at a frequency, which iscommensurate with the change in sedimentprofile height between monitoring events. Thischange in sediment height should becomparable to the detection capability for theparticle activities of concern (e.g. 100 kBq for137 Cs). Beaches with markedly lower particledensities and habit characteristics may bemonitored less frequently although morecomprehensively to provide a better estimate ofthe detectable particle population (see alsorecommendation 10).10 The particle density will be greatly influenced bythe depth over which number of particles isestimated. The target detection depth andmonitoring frequency should be designed toreflect the amount of sand and therefore depthof sand being exchanged with the offshoreenvironment (see also recommendation 9).11 Data layers exist for within window, backgroundcounts, detector height and beach height data.This provides the possibility of modeling andmapping detection capability (probability ofdetection and detection limit) for each locationon the beach, in a similar way as undertaken atDounreay (Tyler ., 2010). Such data shouldbe used to provide more particle specific insightinto the likely abundance of particles with depth(see also recommendations 3, 5 & 8).SL initial responseSome of these techniques have already beenemployed and will be expanded, as advised.See response to recommendation 3 and 5.Historically, the beach monitoring programmehas focused on high occupancy areas basedon the EA's habit reports. This has beencombined with monitoring of high find rateareas to give a balanced approach. It isjudged that the > 50% footprint has beenachieved for beta-rich finds containing 137 Csor 60 Co-rich finds as the 1E+05 Bq limit ofdetection for these radionuclides is 30 cm ormore. However, for 241 Am the 1E+05 Bq limitof detection is 5 cm making it impracticable toachieve a 50% footprint in the current beachareas over a period of a single tide. Thedefinition of footprint therefore needs to bedefined explicitly for Sellafield finds,recognising that it may be different from thatused at Dounreay. A request will be made tothe Environment Agency for the next HabitSurvey to provide more detailed habit datawith respect to the beach occupancy and use.The depth of sand on beaches between StBees and Drigg point is not explicitly known.Practical observations of the appearance anddisappearance of rocks on the Sellafieldbeach would suggest that an explicit sanddepth measurement over the 630 hectares ofbeach that can be monitored (or 1400hectares of total beach area) could not berealistically achieved. Consideration will begiven to a practical solution to this problem,such as, an assessment of beach depthbased on the additional data gathered duringthe more frequent visits to the main beachareas.To be considered for inclusion into statisticswork programme.© Nuclear Decommissioning Authority 2011. 61