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

SSEM/2011/4730 June 2011accounted in assessing risk for the public. Controls and measures are applied for thesespecific operations to ensure suitable protection of the operators. In that operations to findand retrieve objects are on public beaches, a dose level of significance for workers is takenas 1 mSv per annum, corresponding to a 5x10 -5 overall fatal risk (ICRP, 2007).5.3.2 InhalationOnce a find is located by the Groundhog systems, the operator needs to remove materialsurrounding the object. Often conditions are inclement, windy, not always wet, and so thereis potential for material, e.g. sand, to become airborne. Calculations on size of respirablematerial show that potential radioactivity associated with the particulate size is low (i.e.approximately 0.1 Bq of actinide activity) and presents little hazard unless large numbers ofparticles are inhaled. For example, the inhalation of approximately 375 particles of averagerespirable size is required to give a dose of 1 mSv. This is corroborated by the HPA’sevaluation in their reports (Randles, 2010).A proportion of the particle finds are known to be potentially friable (Randles, 2010). Theseconsist of aggregations of smaller particles that are stable when wet but prone to fragment asthey dry out, particularly when handled directly. The smaller particles will have a range ofsizes with a proportion of them being of respirable size.For an acute inhalation intake, analysing for worst case fraction of particles that becomefriable and worst case release fraction around the highest alpha-rich find, the calculatedpotential uptake to the operator is an order of magnitude below the significant dose. Even atthis low dose level, several thousand particles would need to be present to ensure there aresufficient respirable particles available for inhalation.For chronic inhalation uptake, analysis follows average activities, friability and releasefractions and results indicate that there is potential for uptake via this route that couldmarginally exceed 1 mSv per annum. This worse case assumption requires that most, if notall, particles are friable and their recovery generates sufficient respirable-size particles toallow a small number to be inhaled.However, natural mitigation is that beach materials are often wet and it is unlikely that themajority of finds dry out during recovery. Operational mitigation includes the requirement towet the material around a find zone, to reduce the risk of friability and therefore significantlyreduce the risk of chronic inhalation. An internal dosimetry regime for operators is also inplace to monitor this potential (and any ingestion potentials detailed below). Environmentalchronic inhalation uptake for operators is calculated to be more than 3 orders of magnitudeless than significant dose (Randles, 2010).5.3.3 IngestionWhereas the HPA reports recognise a potential (albeit very unlikely) for inadvertent orintended ingestion of radioactive objects by some categories of the public, operators do notfall into these person categories. Nevertheless, operators spend more time on the beachesthan members of the public (around 1200 h per annum). Calculations of sand intake byoperators, just by being on the beaches and looking for particles, show that there is potentialfor an attributable dose uptake but at 3 to 4 orders of magnitude less than significant dose.Given the qualified and experienced nature of operators as health physics surveyors, anacute ingestion intake is not credible. For example, for a 1 mSv acute ingestion dose it isimplausible that the 5000 Bq particle required would not be detected and for a 1 mSv chronicingestion dose it is implausible that the 150 ingestion events would take place. Operators© Nuclear Decommissioning Authority 2011. 81