Environment source terms for ex-vessel FW/SB LOCA accident sequences in ITER EDA

Abstract

The paper presents the environmental source term EST evaluation results for some ITER accident sequences, with reference to the activated materials contribution. The assessment is based on the end-of-1994 ITER baseline design and it refers to ex-vessel LOCAs in the first wall FW and shielding blanket SE heat transport system I-ITS. The main ITER characteristics are: fusion power 1.5 GW, average neutron power load on the outboard first wall 1 MW/m/sup 2/, fluence 3 MW-y/m/sup 2/, average pulse length 1000 s, dwell time 1200 s. The structural material for FW and SE is AISI 3161, (Mn 1.8 wt.%, Co 0.17 wt.%) stainless steel. Four independent loops for FW and SE heat transport system are considered. The European multi-code approach is briefly described jointly with the computer tools used for the assessment, A 1-D Sn neutron transport analysis in the cylindrical geometry has been considered for radioactive inventory RI evaluation by ANITA-2 activation codes. The mobilization of radioactive materials has been estimated with reference to the accident sequence phenomenology (e.g. the corrosion in HTS by using the PACTOLE code and the cooling blow down). The containment response to the accident sequences has been assessed (using the CONSEN code) to obtain the post accident thermal-hydraulic conditions inside the containment that are needed to estimate its retention factor. Finally, the NAUA code is considered to obtain the environmental source terms EST. A sensitivity analysis has been performed to verify the impact of the water chemistry on the environmental release composition and mass.