One form of damage on SN plate is cracking lt is necessary to know temperature and stress distribution within SN plate in order to eliminate such cracking，We first confimed that the simulated results of temperature distribution by FEM （finite element method） in the heating experiment accords with the actually measured temperature distribution results．
Next，we analyzed thermal stress （distribution） analysis by FEM under operating conditions．As a result，the analysis shows that the numerical estimation for crack formation coincides well with the real crack profiles．The location of the cracking depended on the confinement condition of the SN plate．We demonstrated that four－sided confinement was the most for the elimination of cracking．
