The minor element in alloy greatly aggravate the segregation of main elements and formation of harmful phase, resulting the deterioration of mechanical properties. Low segregation technology of cast superalloy was pioneered by Prof. Shi Changxu and co-workers in the early eighties. The technology is to control the content of minor element, such as P, Si, B and Zr, to lower the solidification segregation in the super-alloy. The working temperature and mechanical properties of superalloy can be increased greatly by using the low segregation technology. A series of alloys, such as M17 and GH738 with low segregation and excellent properties, had been developed. This study extends low segregation technology to 30Cr2Ni4MoV steel of large shaft for thermal power equipment, 690 alloy for steam generator tube in nuclear power plant, and uranium alloy for nuclear fuel. The solidification and segregation behaviour in the 30Cr2Ni4MoV steel was investigated, it is found that the minor elements of O and Al are essential for the formation of serious solidification segregation in the steel. Moreover, the solidification behavior of 690 alloy has been studied. S and N increases solidification interval, and the effect of S is greater than that of N. The solidification segregation of 690 alloy can be alleviated by controlling the contents of the S and N. Finally, the solidification temperature interval of high carbon uranium is calculated. With the car bon content increasing from 0.01% to 0.03%, the solidification interval is from 40 ℃ to 75 ℃. Thus, for the radioactive uranium alloys, minor elements show segregation to some extent in the residual liquids of final solidification zone. The minor elements in U-6Nb alloy are C, N and O. For uranium with high carbon content, the minor elements are C and O.