Monte Carlo analysis of helium production in the ITER shielding blanket module

In order to examine the shielding performances of the inboard blanket modul e in the International Thermonuclear Experimental Reactor (ITER), shielding calculations have been carried out using a three-dimensional Monte Carlo m ethod. The impact of radiation streaming through the front access holes and gaps between adjacent blanket modules on the helium gas production in the branch pipe weld locations and back plate have been estimated. The three-di mensional model represents an 18 degrees sector of the overall torus region and includes the vacuum vessel. inboard blanket and back plate, plasma reg ion, and outboard reflecting medium. And it includes the 1 m high inboard m id-plane module and the 20 mm wide gaps between adjacent modules. From the calculated results for the reference design, it has been found that the hel ium production at the plug of the branch pipe is four to five times higher than the design goal of 1 appm for a neutron fluence of 0.9 MW a m(-2) at t he inboard mid-plane first wall. Also, it has been found that the helium pr oduction at the back plate behind the horizontal gap is about three times h igher than the design goal. In the reference design, the stainless steel (S S):H2O composition in the blanket module is 80:20%. Shielding calculations also have been carried out for the SS:H2O composition of 70:30, 60.40, 50:5 0 and 40.60%. From the evaluated results for their design, it has been foun d that the dependence of helium production on the SS:H2O composition in the blanket module is small at the branch pipe. Altering the steel-water ratio to reduce the amount of steel and increasing the thickness by > 170 mm wil l reduce helium production to satisfy the design goal and not have a signif icant impact on weight limitations imposed by remote maintenance handling l imitations. Also based on the calculated results, about 200 mm thick shield s such as a key structure in the vertical gap an suggested to be installed in the horizontal gap as well to reduce the helium production at the back p late and to satisfy the design goal. (C) 1999 Elsevier Science S.A. All rig hts reserved.