High temperature, high radiation strain sensors and thermal compensators for ITER vacuum vessel

This study describes the development and qualification of strain sensors and thermal compensator for monitoring of ITER vacuum vessel. The operating conditions require 20000h at 200 degrees C and gamma radiation doses up-to 10MGy under high vacuum. A sensor concept was designed based on two spot weldable sensing elements: one weldable strain sensor and one weldable temperature compensator. The developed elements were subjected to qualification tests including optical, thermal cycling, thermal aging, mechanical and radiation. The results validated the solution and proved that the elements comply with requested vacuum vessel environment, withstanding 10MGy radiation, +/- 1000 mu m/m for 10E+5 cycles at 100 degrees C, 500 cycles from 100 degrees C to 200 degrees C, 100 degrees C for 120000h, 200 degrees C for 20000h and being fully operational after 80h at 250 degrees C.