Assessment of personnel accessibility in the Particle Beam Fusion Accelerator facility PBFA-II

The dose during and after fusion shots around the PBFA-II facility and the line-of-sight (LOS) beam penetration has been calculated. The dose above the 6" thick concrete ceiling of the high bay was found to be excessive and additional shielding is required. On the other hand, the water and oil tanks provide significant radiation attenuation yielding a very low dose level in the screen room. No access during shots should be allowed in the building housing PBFA-II unless 6" thick concrete shield is used around the LOS. In the space between buildings, one should stay at least 2 m away from the LOS axis. In the building housing the neutron measurements laboratory (NML), access during shots should be limited to the area behind the 8" thick wall. A beam dump design with a cylindrical trap having an aspect ratio of 3 significantly reduces the reflected secondary neutrons. Access during shots is allowed anywhere at the back and side of the dump. The total activity in air, glass windows and concrete walls immediately following a DT shot is only 5 Ci and drops by two orders of magnitude in 10 minutes. Access to areas in front of the beam dump should be restricted for at least 15 minutes after shots