Development of coating technique on inner surface of fuel cladding tubes (B)

not registered; not registered; not registered

Alleviation of Fuel Clad Chemical Interaction (FCCI) is urgently needed for the prolongation of fuel life. Appropriate coating material as well as coating technique, which are both practical and economical, should be developed for this purpose. In this work, the method of chemical vapor deposition (CVD) and lining were applied on 316 stainless steel 12%Cr steel. By using these techniques, such elements as Cr, V, Nb, Ti and Zr were coated or lined either individualluy or in combination. The results obtained are summarized as follows. (1)The coating of Cr and V through CVD method is not suitable for final product of 316 stainless steel, because processing temperature is required over 1000C. (2)Application of the above coating to in-processed product also seems difficult, since the carbide film formed on the outermost surface shows poor ductility and gets cracked and peeled off during hot and cold rolling operation. (3)The method of using the V and Cr coating as insert material between Ti or Zr and stainless steel or 12%Cr steel does not seem applicable, since cracking of the carbide layer takes place and the eutectic reaction occurs between Zr or Ti and steel, because of rather rich concentration of iron in the surface region (60-70% Fe-30-40%Cr or V). (4)The lining of Nb sheet on the steels seems applicable. Using of Nb sheet as insert material between Ti and stainless steel is also applicable and, in this case, the eutectic reaction is completely prevented. (5)The problem of Nb clad technique is that Nb carbide layer forms at the interface of steel and Nb during hot rolling and heat treatment and this layer shows poor ductility which leads to microcracks during hot and cold rolling. (6)The prevention of carbide formation can be possible by using Ni as insert material between Nb and steel.