128. 



was mined out, producing an equivalent space estimated to be 1547 

 acre- feet. During the last twenty years (1934-53) the reported pro- 

 duction of rock salt is 61,639,696 tons, equivalent to 21,250 acre- 

 feet. Assuming that the average thickness of salt mined was 10', the 

 area mined out would be 2125 acres. These figures give a general 

 idea of the large amount of underground space that has resulted from 

 the mining of the salt. 



5.8 In the potash mines of New Mexico, a large volume of underground 

 space is produced by the removal of the sylvanite ore . The total amount 

 of ore mined in 1952 was approximately 7,850,000 short tons. Assum- 

 ing 15 cubic feet of ore to the ton, the volume would be about 2700 acre- 

 feet per year. If the average thickness mined is 8', the total number of 

 acres mined out annually would be about 335 acres. Pillars are left to 

 support the roof during the mining operations but these are usually 

 pulled after mining operations cease to recover the additional ore. Be- 

 cause of the plasticity of the sylvanite it is doubtful if the mined out 

 space would be suitable for long-time storage of atomic waste. The 

 subjacent salt would provide a more suitable potential storage space be- 

 cause of the greater resistance of the halite to pressure. 



6. PRODUCTION OF RADIOACTIVE WASTE 



6.1 Fission-product waste is produced -when a nuclear fuel, such as 



2^5 233 239 f2fH 



U , U , or Pu , is fissioned in a nuclear reactor/ u ' In nuclear 



•p o c 



reactors, the fission of one gram of U produces about 1 gram of fis- 



sion products. The fission products are, in part, gaseous and, in part, 

 in liquid or solid form, depending upon the fuel used. 



6.2 Fuel systems used or considered for power reactors may be grouped 

 as follows: 



6.2.1 Liquid-fuel systems, in which the fuel is dissolved in water or 

 heavy water; 



6.2.2 Solid-fuel systems, using metals such as uranium and plutonium, 

 in which these metals are contained in corrosion- and temperature- 

 resistant cans; 



6.2.3 Liquid-metal systems, using sodium, bismuth, etc. as a solvent; 



6.2.4 Fused- salt systems, in which the nuclear fuel is mixed, for ex- 

 ample, with a fluoride or hydroxide of sodium, lithium, etc. 



