Shielding proposal to reduce cross-talk from ITER lower port to equatorial port

Abstract

Radiation cross-talk from Torus Cryopump LP to EP was found to be a phenomenon driving Shutdown Dose Rates at EP Port Interspace after 12 days of cooling time, as relevant as neutron permeation through EP itself. In this work three different shields are proposed to mitigate the radiation cross-talk: two neutron shields placed inside LP, and a temporary gamma shield placed at EP PI during maintenance activities. Contributions from different reactor regions to Shutdown Dose Rates are computed, for the unshielded design, as long as the different shielded cases. The Rigorous-Two-Steps (R2S) method was used. The neutron shields inside TCP-LP are found to reduce SDR at EP PI 43μSv/h and 99μSv/h, while the gamma shield inside EP PI offers a reduction of 157μSv/h in its heaviest configuration. Among these relevant reductions, the gamma shield inside the EP PI offers the best shielding option, as it reduces gamma cross-talk from TCP-LP and also protects EP PI from Port Duct and EP bellows activation, while it does not interfere with TCP performance.