Raw materials for low-activation concrete neutron shields

Concrete surrounding a nuclear accumulates radioisotopes induced by neutron reactions during operation, and this concrete still remains to an enormous degree as radioactive waste after decommissioning. The disposal of such activated concrete is very costly and requires strict supervision. Hence, there has been a strong desire to develop a concrete that retains little residual radioactivity, that is, ''low-activation'' concrete. In the present study, we have identified several raw materials for such concrete - low-activation limestone, quartzite, colemanite, alumina-ceramics, while Portland cement and high-alumina cement - by performing a screening test for neutron irradiation. The results show that low-activation concrete compounded from such low-activation raw materials should serve for neutron shielding. Another noteworthy finding is that limestone occurring near schalstein deposits, and especially when sandwiched between two beds of schalstein, is an excellent low-activation raw material. (author)