A cascade theory of isotope fractionation in partly reversible reactions involving triplet radical pairs is developed. Each step of the cascade process is accompanied by nuclear spin selective renaissance of the molecule after its dissociation and results in accumulation of magnetic isotopes in the regenerated molecule. The factors stimulating nuclear spin selectivity in the cascase process are considered. The size of the microreactor and microwave pumping of the radical pairs are shown to be of paramount importance to Provide a highly efficient chemically induced magnetic isotope fractionation.