Monte Carlo radiation shielding and activation analyses for the Diagnostic Equatorial Port Plug in ITER

Highlights: ► Systematic neutronics analyses were conducted to assess the ITER Equatorial Port Plug radiation shielding performance. ► Shielding optimization was achieved by parametric analyses of several design variants using the MCNP5, FISPACT-2007, and R2Smesh codes. ► Dominant effect of radiation streaming along the port plug gaps was recognized. ► Combination of the gap labyrinths and streaming stoppers or rails reduces shutdown doses by 2 orders of magnitude. ► Using the proposed shielding, the shutdown dose in the ITER port interspace is less than the personnel access limit of 100 μSv/h. - Abstract: This paper addresses neutronics aspects of the design development of the Diagnostic Generic Equatorial Port Plug (EPP) in ITER. To secure the personnel access at the EPP back-end interspace, parametric neutronics analyses of the EPP radiation environment have been performed and practical shielding solutions have been found. Radiation transport was performed with the Monte Carlo MCNP5 code. Activation calculations were conducted with the FISPACT-2007 inventory code. The R2Smesh approach was applied to couple transport and activation calculations. Newly created EPP local MCNP5 model was devised by extracting the EPP and adjacent blanket modules from the ITER Alite-4.1 model with proper modification of the EPP geometry in accordance with recent 3D CAD CATIA model. The EPP local model reproduces the EPP neutronically important features and allows investigation of the EPP neutronics effects in isolation from all other ITER components. Thorough EPP parametric analyses revealed dominant effect of gaps around EPP and several EPP design improvements were implemented as the outcomes of the analyses. Gap labyrinths and streaming stoppers inserted into the gaps were shown are capable to reduce the shutdown dose rate which is below the 100 μSv/h limit of personnel access and by 2 orders of magnitude less than the value in the model with straight gaps.