ABSTRACT
The ultrapure graphite used as a moderator in nuclear industry is made from graphitised carbon by eliminating its impurities. The two processes in use (singly or jo intly) are thermal purification , and purification by halogenated derivatives (Odening and Bowman, 1 958 ) . Thus, heating at 3000°C for 1 5-50 hours b rings the boron content of some American nuclear graphites to less than 0 . 8 ppm and the ash content down to 700 ppm. In France, the Carbone-Lorraine process yields equivalent results by heating at about 2600°C under C12 . By incorporating metallic fluorides (2 . 5 wt%) into the coke used in the Acheson process prior to heating, the boron content falls to 0 .4-0 . 8 ppm and the ashes to 1 00 ppm (Des Rochettes, 1 9 6 1 ) .
