Integral processing method for neutron irradiated material and welding method using the method

A helium concentration in a material is continuously kept to less than a concentration at which material failures are caused, by performing processings of heating the material to which neutrons are irradiated to release gaseous atoms in the material as solute atoms to the outside thereby reducing a helium concentration in the material to less than the concentration at which material failures caused. The procedures are intermittently performed within a time when the concentration is less than the concentration at which material failures are caused during the test period under a neutron irradiation circumstance. In addition, this method of integrally processing neutron-irradiated materials is applied as a pretreatment for welding. Namely, the concentration of helium in the material is continuously kept to less than the concentration at which failures of the material are caused by intermittently repeating the procedures of reducing the helium concentration in the material to lower than that before heating. Since helium concentration in the materials irradiated by neutrons is always kept low, undesired effects of helium to the welding can be suppressed, and integral welding can be performed even if welding is performed just after the welding of materials is required. (N.H.)