I worked a Thorium Overpack project in the 90s. A warehouse with 5777 deteriorating 55-gallon drums of thorium from an old reactor fuels effort were packaged for shipment to NTS. The drums were handled by a remotely controlled forklift and placed into an inverted container, the base was only a few inched and the lid made up the main volume of the container. No one was allowed in the warehouse when moving drums. A bank of HEPAs were attached to the warehouse mainly to provide a negative pressure in the warehouse during operations but after a weekend with them shutdown the Thoron levels rose to seven working levels. Filters from the CAMS would read one Rad when removed and we would have to let them decay to a mRad before sending for gammaspec. We ran a floor scrubber daily to keep the thorium levels down to a thousand or two dpm/100cm2 but even with that we would get elevated airborne thorium levels when running a forklift across the floor, entries were with PAPRs. Removing the containers were complicated by the thoron that masked thorium contamination. We wiped down the containers moving them through an airlock to a buffer zone to allow the thoron to decay before sampling. Another interesting fact was that to avoid having to post the storage areas was spacing of the containers that would read up to 70 mr/hr. By placing them far enough apart we avoided the cumulative dose that exceeded 100 mr/hr.
Sorry old retired nukeworker being nostalgic.
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