Neutron Leakage Through Fusion Chamber Ports: A Comparison of Lithium and Lead-Lithium Blankets

Monte Carlo neutronics calculations have been carried out to compare the effects of chamber ports on the neutron leakage and blanket performance for lithium and lead-lithium blankets. A spherical chamber with diametrically opposed, conical penetrations through the blanket and a 14.1-MeV point source at its center is the basis for the comparison. The total neutron leakage through ports in a lithium blanket is about two times greater than one would estimate based on the solid angle fraction subtended by the holes. For a blanket comprised primarily of the lead-lithium eutectic, Pb₈₃Li₁₇, the leakage per deuterium-tritium neutron is about six times the subtended solid angle fraction. As a result of the enhanced neutron leakage, the tritium-breeding ratio and neutron energy deposited in the blanket decrease more rapidly than the loss of blanket coverage. For example, for a chamber in which the ports subtend 5% of the total solid angle, the tritium-breeding ratios are ∼s and ∼20% less than the results without ports for the lithium and Pb₈₃Li₁₇ blankets, respectively. The neutron energy deposited in the blanket decreases ∼7% for lithium and ∼14% for Pb₈₃Li₁₇ for the same 5% loss in blanket coverage.