PURPOSE: To improve sepn. efficiency by passing an eluant in an ion exchange resin adsorbed with radioactive nuclides and adsorbing the non-radioactive nuclides of isotope on the ion exchange resin, then further passing the eluant when the quantity of the radioactive nuclides decreases.

CONSTITUTION: The used ion exchange resin (SR) is adsorbed with 1.6×10-6g/ml-R Ni-63 and 3×10-3g/ml-R Ni. This SR is passed therethrough with 2N-H2SO4 at 20 times the amt of the SR to adsorb the Ni-63 up to 3×10-3g/ml-R thereon. The 2N-H2SO4 is then passed therethrough at 20 times. The entire part of the Ni attains 1.5×10-5g/ml-R of 1/200 and the Ni-63 which exhibits the same chemical behavior attains 1/200 as well. The Ni-63, therefore, attains 4×10-11g/ml-R (1/40000 of the initial time). The degree of separating the radioactive nuclides from the radioactive ion exchange resin is improved in this way and the treatment for the subsequent storage and disposal is easy.