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

SSEM/2011/4730 June 2011Particle and stone finds are further sub-divided initially into an alpha-rich or beta-richcategories during recovery using count rate and dose rate measurements. The alpharichand beta-rich find categories are expanded to include 60 Co-rich and excess beta-richcategories when the high resolution gamma scan results are available. The definitions forthese categories are as follows: Alpha-rich: Finds with positive 241 Am activity greater than 137 Cs activity. Beta rich: Finds with positive 137 Cs activity greater than 241 Am activity and NOT 60 Corich.60 Co-rich: Finds with positive 60 Co activity greater than 137 Cs activity.Excess beta-rich: Finds with a contact beta-gamma dose rate divided by the 137 Csactivity greater than 15 mSv/h per Bq 137 Cs AND NOT Alpha-rich AND NOT 60 Co-rich.Note that finds in this category are potential candidates for a high energy beta emittersuch as 90 Sr.An assessment of the 1233 finds found up to 31 st March 2011 shows that most alpha-richfinds have little beta radionuclide activity and most beta rich-finds have little actinide activity.Similarly, 60 Co-rich finds have mainly 60 Co activity and the excess beta-rich finds are alsomainly beta-rich. Exceptions to these general rules are rare (i.e. 3 unusual alpha-rich findsout of 514 alpha-rich finds in total; see below for other categories). Table 3.6 below gives asummary of the numbers of finds in each category and their average and maximum activities.The data is split between monitoring techniques with Groundhog TM Evolution 2 employedbetween November 2006 and August 2009 and Groundhog TM Synergy employed betweenAugust 2009 and the end of the reporting period (i.e. 31 st March 2011).Table 3.6. Find numbers and activities by category and monitoring techniqueAlpha-rich Activity summary 1 Evolution 2 SynergyTotal number 63 457No. of particles 60 454No. of stones 3 3Particle Mean 241 Am 7.69E+04 Bq 2.95E+04 BqParticle Max. 241 Am 6.34E+05 Bq 2.52E+05 BqParticle Min. 241 Am 3.23E+03 Bq 2.20E+03 BqStone Mean 241 Am 1.74E+04 Bq 2.40E+05 BqStone Max. 241 Am 3.54E+04 Bq 6.18E+05 BqStone Min. 241 Am 7.60E+03 Bq 5.13E+04 BqParticle Mean 137 Cs 2.50E+01 Bq 2.93E+01 BqParticle Max. 137 Cs 9.03E+01 Bq 6.23E+01 BqParticle Min. 137 Cs 1.18E+01 Bq 1.90E+01 BqStone Mean 137 Cs 4.70E+03 Bq 3.64E+01 BqStone Max. 137 Cs 7.20E+03 Bq 5.46E+01 BqStone Min. 137 Cs 1.80E+01 Bq 2.62E+01 Bq© Nuclear Decommissioning Authority 2011. 35