Thermal fatigue damage of the divertor plate

Thermal fatigue of the divertor plate is one of the key issues which govern s the lifetime of the divertor plate. A thermal cycling experiment of diver tor mock-ups was carried out to investigate the thermal fatigue behavior of the divertor structure in a high heat flux test facility at Japan Atomic E nergy Research Institute (JAERI). A cyclic heat flux of 5 MW/m(2) was loade d onto the mock-ups to simulate the steady state thermal condition of ITER divertor plate. A pulse duration of 30 s was selected so that the mock-ups reach thermal steady state. The mock-ups showed water leakage due to therma l fatigue cracking of the cooling tube after 400 cycles. The fatigue crack was observed at the top of the cooling tube. According to a numerical analy sis, the maximum strain amplitude was over 5% at the top of the cooling tub e. The cracking of the cooling tube was caused by the large strain concentr ation due to structural discontinuity of the copper heat sink. It was found that the heat sink block should be separated into smaller blocks to reduce the strain concentration at the cooling tube. (C) 2000 Elsevier Science B. V. All rights reserved.