Waste rock. Barren or submarginal rock or ore that has been mined, but is not of sufficient value to warrant treatment and is therefore removed ahead of the milling processes.

Working level. Any combination of short-lived radon daughters in 1 liter of air that will result in the ultimate emission of 1.3 × 105 MeV of potential alpha particle energy.

Working level month. An exposure to 1 working level for 170 hours (2,000 working hours per year/12 months per year = approximately 170 hours per month).

Yellowcake. Concentrated, high-purity (75-85%) uranium oxide (U3O8), which is used as the raw material for nuclear fuel fabrication.

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