Tutorial Question 6: Worker Dose at a Fuel Fabrication Plant

Q: A worker at a UO $_2$ fuel fabrication plant spends an average of 3 hours per day at 1.5 m from a fuel assembly over a 230-day working year. The dose rate at 1 m from the assembly is 25 $\mu$ Sv/h. (a) Calculate the dose rate at 1.5 m using the inverse square law. (b) Calculate the worker’s annual dose. (c) Comment on whether this is acceptable and suggest one ALARP measure.

(a) $\dot{D}$ (1.5 m) = 25 $\times$ (1/1.5) $^2$ = 25 $\times$ 0.444 = 11.1 $\mu$ Sv/h

(b) Annual time = 3 $\times$ 230 = 690 hours. Annual dose = 11.1 $\times$ 690 = 7,660 $\mu$ Sv = 7.66 mSv.

(c) This is below the 20 mSv/yr occupational dose limit, so it is within legal limits. However, ALARP requires doses to be reduced so far as reasonably practicable. Measures could include: increasing distance (rearranging the workspace), reducing time near assemblies (rotating workers), or adding local shielding.

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