The use of boron and boron loaded materials in the shielding in nuclear facilities to suppress thermal neutron fluxes is widely known. The inclusion of boron in the ITER non-structural elements in the form of borated-steel or boron carbide was considered in early vacuum vessel and shielding blanket designs to reduce the operational nuclear responses in the superconducting magnets. Recent investigations of the reactor and port shielding have focused on reducing the dose rates in the cryostat and biological shield at two weeks after shutdown to levels of ~100 mSv/hr in order to perform limited hands-on maintenance activities inside the cryostat. It is important, therefore to reduce the shutdown dose rates as much as possible from the point-of-view of safety and maintenance considerations.

In this paper, the results of calculations to investigate the use of borated concrete in the biological shield are summarised. Inclusion of a small fraction of boron additive (~0.1 g/cc) in the biological shield concrete decreases the low energy neutron component (particularly the thermal neutron flux) in the concrete walls. As a result, the corresponding nuclear energy release in the steel cryostat decreases by as much as ~1.5 times during reactor operation. A concomitant reduction in the residual photon source intensity occurs in the concrete biological shield and in the adjacent steel cryostat as well. Residual dose rates in the cryostat and biological shield are 3-4 times lower than for the case when non-borated concrete is used. This reduction is observed at times immediately after shutdown to several years later.

Calculations were performed to compare the effects of borating the concrete with the required additional thickness of the blanket, vacuum vessel, and port shielding. Comparable cryostat dose rate reduction can be achieved by increasing the bulk shielding using 7-9 cm of stainless-Steel and water in the blanket, vacuum vessel and port walls or by adding 15-18 cm of Stainless-Steel. These alternatives are significantly more expensive than borating the concrete and require major design changes.