AbstractTIBER-II is the United States contribution to the design of an international thermonuclear experimental reactor (ITER). The compactness of the reactor has placed a premium on the design of a high performance shield to protect the toroidal field (TF) magnets, particularly in the inboard (i/b) side where the shielding space is constrained to 48 cm. The use of tungsten in the i/b shield is mandatory to protect the inner legs of the TF coils against the 1.5 MW/m2 neutron wall loading impinging on the midplane of i/b side. A shield optimization study is performed to minimize the fast neutron fluence, which is the most crucial radiation effect in the magnet. In the optimization study, the performances of various candidate materials were examined. Beside W, the evaluated materials are TiH2, B4C, Pb, water, borated water, and LiNO3 salt in water. The optimal shield is composed of two layers: a thick W layer followed by an 8 cm thick H2O/LiNO3 layer. The peak fast neutron fluence amounts to 7.7 × 1018 n/cm2 and the radiation limits are all met with several magnet anneals needed during reactor life. The other critical area in the TIBER-II design occurs behind the divertor plates where the shield is thinned at some places to 48 cm. W in pebble form was proposed to shield the divertor zone and the less expensive PCA pebble bed is used in regions where the shielding space is less constrained. The proposed shield arrangement provides adequate protection for the TF coils and this is verified with a two-dimensional calculation where the poloidal variation of the radiation effects in the TF coils was generated.
Tungsten boride shields in a spherical tokamak fusion power plant