Studies on development of highly corrosion resistant stainless steel for the equipments of spent fuel reprocessing and fabrication technology of an integral barrel with nozzles in a dissolver were carried out, and the following results were obtained.
(1) Cr is an essentially beneficial element for corrosion resistance of 25Cr-20Ni steel in hot oxidizing nitric acid even when it is in transpassivity. Whereas the detrimental effect of C and P for the corrosion resistance can be made negligibly small with Nb addition above 20 at the ratio of Nb/C in mass %.
Optimization of alloy design and improvement in the steel production method made it possible to develop an extremely corrosion resistant 25Cr-20Ni-Nb steel (Japanese 310 Nb steel).
(2) Good corrosion resistance of this alloy was evidenced in the operation tests of the mock up equipments simulating the dissolver and acid recovery evaporator. It has recently been satisfactorily put into use for commercial reprocessing equipments, i.e. the dissolver and acid recovery evaporator for Tokai Works, Power Reactor and Nuclear Fuel Development Corp.
(3) Development of new technology for fabricating an integral barrel with nozzles by the hot forming process succeeded in improving remarkably the localized corrosion resistance, particularly to tunneling corrosion.
