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

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40St Bees30Residual cps2010040Seascale30Residual cps201003530Drigg25Residual cps20151050-50 500 1000 1500 2000 2500 3000Energy (keV)Figure 3.18: Average residual spectra for the beaches shown in figures 3.15-3.17.29
4. DISCUSSIONThe work reported here consists of two aspects related to airborne survey detection ofradioactive particles on the beaches around Sellafield, as a continuation of an earlier phase ofwork (Sanderson & Cresswell 2010). The earlier work used Monte Carlo simulationapproaches to determine detection limits for different survey parameters in natural radiationenvironments typical of the West Cumbrian coastline. The work reported here presentsassessments of the impact of dispersed 137 Cs backgrounds on detection limits, and theresponse to the particles already recovered from the beaches.4.1 137 Cs backgroundsPrevious airborne and ground based surveys have demonstrated that there are, in severalplaces, background levels of 137 Cs along the coastline of West Cumbria. On estuarine saltmarshes, where fine silt particles which readily sorb 137 Cs accumulate these backgroundlevels are very high. On sand and gravel beaches it is not expected that the 137 Cs containingsilts would accumulate, and background levels here are much lower. In some locations, inparticular in the vicinity of the Sellafield and Drigg sites, radiation originating from areasbehind the beach is a significant contribution to the 137 Cs background observed from anairborne survey.Detailed ground based surveys of the beaches of West Cumbria have shown that 137 Cs hasaccumulated in patches of several metre dimensions, and samples from these have typicallyshown activity concentrations of up to 50 Bq kg -1 . The form of the 137 Cs contamination isunknown, as is the depth profile of these patches of activity. For the purpose of this study, thedepth profile was assumed to be uniform to 30cm. The impact on detection limits forindividual patches of activity with concentrations of 50 Bq kg -1 , and areas where several suchpatches are present, have been determined along with uniform activity distributions.For activity distributions with uniform concentrations over areas that exceed 3-4 times thefield of view of the detector, and high density of patches of activity over similar areas, thelimits of detection for 137 Cs particles is only slightly increased by approximately the sameamount as observed in the previous phase of work with the change from a medium to highnatural background. The significance, defined as the ratio of net counts to the uncertainty, ofmeasurements over sources of different strengths and distributions have been calculated.Interpolation from these calculated values allows detection limits based on a significance ofeither 2 or 3 to be determined. This has been done for three survey parameters; a “rapid”survey at 75m ground clearance and 75 knots, a “low and slow” survey at 15m groundclearance and 15 knots, and a very slow survey at 15m and 4 knots. These are given in Table4.1 for the medium natural background and the highest 137 Cs background considered here.The earlier work noted that reducing the ground clearance below 15m would significantlyincrease full energy peak count rates, with a corresponding reduction in detection limits,although the full simulation of the spectra for these heights have not been conducted. Thesedetection limits assume a data analysis algorithm that can determine trends in the radiationsignal over time, such as the background change alarm criteria based on predicted signalsused by Nuvia or the filtered differential analysis approach (Cresswell & Sanderson 2009), orspatially using multiple measurements from different survey lines.For individual patches of activity of dimensions simulated here, the radiation observed from alow flying aircraft is indistinguishable from a single particle of similar total activity near the30
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Particles in the EnvironmentAnnual
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SSEM/2011/4730 June 2011ContentsPur
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SSEM/2011/4730 June 2011List of Tab
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SSEM/2011/4730 June 20111. Introduc
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SSEM/2011/4730 June 2011Figure 2.1.
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SSEM/2011/4730 June 2011In August 2
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SSEM/2011/4730 June 20112.3.4 Find
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SSEM/2011/4730 June 2011as well as
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SSEM/2011/4730 June 2011The monitor
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SSEM/2011/4730 June 2011(Field Inst
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SSEM/2011/4730 June 2011number of f
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SSEM/2011/4730 June 20114.5004.000F
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SSEM/2011/4730 June 2011Table 3.5.
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SSEM/2011/4730 June 20113.1.5 Risks
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SSEM/2011/4730 June 2011presence of
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SSEM/2011/4730 June 2011Beta-rich A
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SSEM/2011/4730 June 2011Find Popula
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SSEM/2011/4730 June 2011Log Am241 A
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SSEM/2011/4730 June 2011Beach Find
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SSEM/2011/4730 June 2011Log Pu239 A
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SSEM/2011/4730 June 2011Figure 3.22
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SSEM/2011/4730 June 2011Table 3.9.
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2.52.72.93.13.33.53.73.94.14.34.54.
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SSEM/2011/4730 June 2011In summary,
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SSEM/2011/4730 June 2011particles h
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SSEM/2011/4730 June 2011• Boron,
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SSEM/2011/4730 June 2011Table 3.15.
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SSEM/2011/4730 June 2011Recommendat
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SSEM/2011/4730 June 2011Recommendat
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SSEM/2011/4730 June 2011homogeneous
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SSEM/2011/4730 June 2011[the Sellaf
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SSEM/2011/4730 June 2011Figure 3.33
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SSEM/2011/4730 June 2011 © Nuclea
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SSEM/2011/4730 June 2011 © Nucle
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SSEM/2011/4730 June 2011The finding
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SSEM/2011/4730 June 2011Communicati
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SSEM/2011/4730 June 20115. Health R
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SSEM/2011/4730 June 2011The numbers
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SSEM/2011/4730 June 2011wear gloves
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SSEM/2011/4730 June 20116. Aims and
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SSEM/2011/4730 June 2011specificati
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SSEM/2011/4730 June 20116.5 Primary
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SSEM/2011/4730 June 20113. Where ar
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SSEM/2011/4730 June 20115. What is
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SSEM/2011/4730 June 2011Fundamental
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SSEM/2011/4730 June 2011size and wi
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SSEM/2011/4730 June 201130 May Drig
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SSEM/2011/4730 June 20117.2 Applica
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SSEM/2011/4730 June 20117.2.3 Consi
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SSEM/2011/4730 June 20117.3.2 DSRL
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SSEM/2011/4730 June 2011contract mo
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SSEM/2011/4730 June 2011From 2008/0
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ID WBS Task Name Duration Start Fin
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SSEM/2011/4730 June 2011Hackney PD,
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SSEM/2011/4730 June 2011Appendix 12
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Harrington monitoring extent and as
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Whitehaven North/Harbour monitoring
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Nethertown monitoring extent for 20
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Drigg monitoring extent and associa
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Contents1. Introduction ...........
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Figure 1 - Swath bathymetry of Scro
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Figures 4 to 6 show the same data w
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3.2 Options for acquiring new bathy
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3.3 Interpretation of gross geomorp
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Head, shows a marked northerly sedi
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of artefacts affecting the original
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Executive Summary
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Table of contents1 Introduction ...
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sinks and transport pathways of rad
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Bed shear stress exceedance - Sella
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Page 223 and 224: About usCefas is a multi-disciplina
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Page 227 and 228: SummaryThe response of large volume
Page 229 and 230: Contents1. INTRODUCTION ...........
Page 231 and 232: Figure 3.15: 137 Cs activity concen
Page 233 and 234: 2. MODEL PARAMETERISATIONThe approa
Page 235 and 236: Figure 2.2: Stripped 137 Cs count r
Page 237 and 238: 200150Number of finds1005000 5 10 1
Page 239 and 240: 1000 Bq kg -1SignificanceSignifican
Page 241 and 242: SignificanceSignificanceSignificanc
Page 243 and 244: 0 Bq kg -1SignificanceSignificanceS
Page 245 and 246: 40 Bq kg -13Significance21012.5 Bq
Page 249 and 250: 3.1.2.2 Detailed Small Area SurveyF
Page 253 and 254: 3.2 Patches of Enhanced 137 Cs acti
Page 255 and 256: 3020Stripped cps100-100 200 400 600
Page 257 and 258: Figure 3.15: 137 Cs activity concen
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Page 263 and 264: distribution. There appears to be n
Page 265 and 266: clearance reduce detection limits,
Page 267 and 268: Appendix A: Location and Activity D
Page 269 and 270: Position (BNG)Activity of recovered
Page 271 and 272: 11/09/2007 301521 503408 6 Sand 195
Page 273 and 274: 14/11/2007 301442 503457 4 Sand 255
Page 275 and 276: 10/01/2008 301694 503522 12 Sand 27
Page 277 and 278: 24/06/2008 301662 503500 4 Sand 263
Page 279 and 280: 27/10/2008 302058 503065 5 Sand 128
Page 281 and 282: 16/01/2009 301522 503320 7 Sand 367
Page 283 and 284: 22/09/2009 301787 503592 7 Pebbles
Page 285 and 286: 17/03/2010 301446 503542 2 Sand 26
Page 287 and 288: 31/08/2010 300219 505597 0 Sand 33
Page 291 and 292: 24/05/2010 299805 505799 3 Sand 30
Page 295 and 296: Activity of recoveredPosition (BNG)
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Page 299 and 300: Page 2 of 3provides useful informat
Page 301 and 302: Week StartingSoftrak Beach Monitori
Page 303 and 304: Additional justification of 2011/12
Page 305 and 306: In the context of the total monitor
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Annual Report for 2010/11 and Forward Programme - Sellafield Ltd

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