Calculations of Operational and Residual Doses for the SNS Linac

Dose profiles throughout the front-end building and the accelerator tunnel were calculated for the SNS linac system both for normal operation and after shut down of the facility based on normal operational beam losses. The calculated dose levels at a cylindrical envelope with 60 cm radius, range from 0.08 to 10 rem/hr for the drift tube linac, from 50-80 rem/hr for the coupled cavity linac, from 1 to 20 rem/hr for the superconducting linac, and from 70-200 rem/hr for the spare section extending after the linac. In the front-end building that houses the first 10 meters of the drift tube linac, dose levels of up to 500 mrem/hr were calculated. This dose rate will need to be reduced by adequate shielding, for example, an ordinary concrete shield of up to 120 cm thickness. The shield thickness can be reduced by 25% using borated concrete or a 20 cm layer of borated polyethylene followed by ordinary concrete. The calculated residual dose levels in the accelerator tunnel are a factor of 2000- 3000 lower compared to the operational doses assuming a 30-year operation period and a 1 hour decay period. (author)