Appendix CRF - Part 3 - Northamptonshire County Council

3 RADIATION RISKS FROM ACCIDENTS
The following reasonably foreseeable incidents/accidents have been identified:
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VERSION 3, 14 July 2009
3.1 The delivery of waste containing unexpectedly high levels of radioactivity
The likelihood of receiving waste that is more radioactive than expected is limited by the strict
pre-acceptance criteria and associated procedures that are to be put in place. In addition, it is
expected that incoming consignments will be monitored, and a dose rate acceptance test
applied. Thus any radiation exposures from this scenario, should be limited to a brief external
exposure to increased dose rates at the receiving stage. Even if the dose rate is 10x the
acceptance criteria, the resulting doses to workers from the monitoring and subsequent
quarantine of the consignment would be expected to be negligible.
3.2 Dropping or otherwise damaging a container of waste and spilling the contents
The “dropped bag” scenario is specifically considered in the RSA93 application using a
pessimistic dispersion model to estimate the radiation doses (from dust inhalation) to workers
and persons off-site. This assessment is principally concerned with the exposure of workers,
in particular those that may be involved in cleaning up any spills. Consequently, for this risk
assessment the following general “spillage” scenario is assumed:
either type of waste container (drum or bag) could be damaged;
contaminated dust is released producing a localised dust loading of 10 mg/m 3 , which
is considered a pessimistic assumption for an accident outdoors;
workers remain in the above dust loading for a total of 4 hours (to allow for any cleanup).
the worker breathing rate is 1.2 m 3 /h and no respiratory protective equipment (RPE)
is worn; and
dust is inadvertently ingested (e.g. during the clean-up) at a rate of 3.45 x 10 -5 kg/h
(the same rate as assumed in the RSA application for excavation scenarios)
The above assumptions produce an inhaled dust mass of 48 mg, and an ingested dust mass
of 138 mg. ICRP dose coefficients for inhalation and ingestion (the same as those used in
the RSA93 application) are given in the Appendix to this risk assessment. Combining these
with the mass of dust inhaled and ingested, and an activity concentration of 200 Bq/g (i.e. a
worst case assumption) gives the following (rounded) internal doses:
Radionuclide
Estimated internal dose from a single spillage (mSv)
Inhalation Ingestion Total
Ac-227 5 5
Th-229 2 2
Th-230,232
Pa-231
Pu-238, 239, 240, 242
Am-241
Ra-228, Th-228
U-232, Np-237
Cm-243, 244
All other radionuclides