The amounts of the individual fission products and tritium produced by a detonation of a given yield depend of course, on the type of device used. It has been assumed in investigations that most of the energy would be derived from fusion.

At 8 or 10 months after a 20 kt shot, the tritium activity would be much higher than the total fission product activities. In addition, radionuclides formed by neutron activation of the ore surrounding the explosive would be present. The amounts of these radionuclides formed is dependent on the chemical composition of the copper ore and certain conditions of the experiment. Irradiation of Safford copper ore in the Oak Ridge Research Reactor indicated that Sc46, Co60, Mn, Fe59, Zn65, and Se75 would probably be the most important of the long-lived induced radionuclides. Possible contamination of the copper with radioactive copper is not of concern since all of the radioactive copper isotopes have very short halflives and any formed decay almost completely prior to the start of leaching.

II. Radionuclides Dissolved

It is known from experience that most of the fission products and induced radionuclides are trapped fairly efficiently in the fused melt that accumulates at the bottom of the chimney and that this fused material is not very leachable. However, appreciable amounts of certain fission products, for example Sr and Cs137, which have gaseous precursors, and ruthenium, which forms volatile compounds, move up into the chimney and are deposited on the rubble. That portion of each radioisotope deposited on the rubble would be expected to be much more leachable than the portion trapped in the melt. Batch leaching tests in which radioactive debris from one of the Nevada Test Site shots was leached with sulfuric acid confirmed this expected behavior.

The ion exchange properties of the copper ore are highly important in regulating the quantities of certain radionuclides that dissolve from the ore. Safford ore adsorbed Cs137 and Zr-Nb5 very strong

ly from leach liquors. Strontium was adsorbed much less, although still significantly. In an in-situ leaching operation, the chimney of broken ore would function as an ion-exchange column several hundred feet high. Radionuclides dissolved from the ore in the early phases of the leaching cycle would tend to be adsorbed on the ore as the leach solution was recycled through the ore column. This would limit the build-up in concentrations of certain radionuclides in the leach liquor to levels far below those that would be predicted on the basis of simple batch leaching tests. A cyclic column leaching test in which soluble radioisotopes were added to the system confirmed this expected behavior. Those isotopes that are adsorbed strongly were not found in significant amounts in the effluent.

Radionuclides formed by neutron activation of the copper ore should not be of importance in processing nuclear-broken ore. In a column leaching test, only small fractions of the major long-lived radionuclides formed by irradiation of copper ores in a nuclear reactor were dissolved. In a nuclear detonation, the activation products should be entrained in the melt rock and, therefore, would be much less soluble than was observed in the test with reactor-irradiated ore.

III. Contamination of the Cement Copper

In conventional copper leaching practice, the pregnant leach solutions are stripped of their dissolved copper by precipitation of the copper on metallic iron. This precipitate is known as "cement copper". Cementation tests showed that, of the important fission products, only Ru106 and Zr-Nb cement with the copper to a significant extent. Certain potential activation products, such as silver and mercury, cement quantitatively with the copper. However, after considering the quantities of each of the various radionuclides that would be expected to be present in the leach liquor, it was concluded that Ru10% is the only radioisotope that appears important with respect to contamination of the cement copper. This assumes that the cement copper would be adequately washed to re

move occluded leach liquor containing soluble radioisotopes.

Attempts to remove ruthenium from the leach liquor with various absorbents prior to cementation have not been very effective. Most of the ruthenium can be removed from the recycle liquor by partial neutralization with lime but essentially continuous lime treatment would be required for this control method to be very effective. This, however, would destroy the liquor's usefulness as a leaching solvent and would require reacidification in each cycle which would be too expensive. IV. Effect of Smelting and Electrolysis on Radioactive Contaminants

As pointed out above, the cement copper concentrate is expected to be contaminated with Ru106. The cement copper usually is smelted to produce impure copper metal in the form of a consumable anode which is then converted to electrolytic copper in an electrolyic cell. Small-scale laboratory tests simulating the smelting and electrolysis operations indicate that essentially all of the ruthenium impurity follows the copper through the smelting process. However, an efficient separation occurs during electrolysis with the electrolytic copper being esssentially free of ruthenium. The ruthenium accumulates in the cell electrolyte with some of it dropping out in the "anode mud" that accumulates at the bottom of the cell. About 1% of the total ruthenium in the anode was found in the electrolytic copper. Some provision in the process would have to be made to prevent excessive build-up of Ru106 in the cell electrolyte and to handle the anode mud, should its radioactive content become too high.

V. Solvent Extraction of Copper from Leach Liquors Recovery of copper from the leach liquor by solvent extraction is a potential alternative to the cementation method. The extracted copper can be stripped from the solvent with 2 M H.SO, and this solution can be fed directly to electrolysis. Preliminary tests indicated good separation of copper from ruthenium as well as all other important fission products, except possibly Zr-Nb. Solvent extraction could be an attractive alternative to cementation provided the projected economics of this recovery process are competitive for a commercial size operation.

VI. Potential Radiation Hazards to Leach Plant Operating Personnel

Based on an estimate of the concentrations of each of the radionuclides that might be present in the

circulating leach liquor it was concluded that with the exception of tritium, the concentrations would be very low, certainly far below the level that would require shielding of the process equipment to prevent radiation exposure. In making the estimate, it was assumed that the radioisotopes would be uniformly dispersed in the total volume of leach liquor and that leaching would begin no sooner than 8 months following the shot. No allowance was made in the estimate for the possibility of "cleaning up" the chimney by flushing with air or water prior to commencing leaching. A substantial reduction in the tritium available for circulation in the leach fluid might be achieved by initially flushing the chimney with water or air and disposing of this product prior to introducing the leach solution*

The principal hazard from tritium would be from inhalation of tritiated water vapor. Therefore, it would be of greatest concern in underground operations such as in an open liquor collection tunnel and pump sumps for pumping to the surface.

VII. Summary and Conclusion

In summary, at this stage of the studies it is tentatively concluded that potential problems associated with the introduction of radioactivity into the leach system do not constitute an important obstacle to use of nuclear explosives in copper ore processing. Radio-contamination of the cement copper with ruthenium will occur. However, ruthenium in cement copper is largely eliminated in the electrolytic refining process. It appears therefore, that radio-contamination of the final copper product would be very low and should not be hazardous to the customer. With respect to hazards to plant personnel due to radioactivity, tritium is identified as the radioisotope of most concern. It does not appear to be a significant concern except possibly in underground operations. The expected concentrations of radionuclides in the circulating leach liquor are sufficiently low so that shielding of process equipment would not be required. However, the process facility should be designed to minimize spillage of leach solutions and to minimize contact of the operating personnel with the ruthenium-contaminated cement copper.

Any disposal of radioactive waste would be in compliance with established AEC and Arizona State regulations. I