UNCLASSIFIED UNCLASSIFIED ANL-5206 Subject Category: CHEMISTRY UNITED STATES ATOMIC ENERGY COMMISSION RADIATION CHEMISTRY OF NORMAL AND HEAVY WATER SOLUTIONS. I. RADIATION- INDUCED OXIDATION OF FERROUS SULFATE By William R. McDonell 19 lii^^ January 12, 1954 Argonne National Laboratory Lemont, Illinois Technical Information Service, Oak Ridge, Tennessee Date Declassified: December 2, 1955' This report was prepared asa scientific account of Govern- ment-sponsored work. Neither the United States, nor the Com- mission, nor any person acting on behalf of the Commission makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the in- formation contained in this report, or that the use of any infor- mation, apparatus, method, or process disclosed in this report may not infringe privately owned rights. The Commission assumes no liability with respect to the use of, or from damages resulting from the use of, any information, apparatus, method, or process disclosed in this report. Tliis report has been reproduced directly from the best available copy. Issuance of this document does not constitute authority for declassification of classified material of the same or similar content and title by the same authors. Printed in USA, Price 15 cents. Available from the Office of Technics^. Services, Department of Commerce, Weish- ington 25, D. C. GPO 9880t8 ANL-5206 ARGONNE NATIONAL LABORATORY P. O. Box 299 Lemont, Illinois RADIATION CHEMISTRY OF NORMAL AND HEAVY WATER SOLUTIONS I. RADIATION-INDUCED OXIDATION OF FERROUS SULFATE by William R. McDonell* CHEMISTRY DIVISION *E. I. duPont de Nemours Loaned Employee January 12, 1954 Operated by The University of Chicago under Contract V;-3 1 -109-eng-38 Digitized by tine Internet Archive in 2010 with funding from University of Florida, George A. Smathers Libraries with support from Lyrasis and the Sloan Foundation http://www.archive.org/details/radiationchemist1954mcdo RADIATIO N CHEMISTRY OF NORMAL AND HEAVY WATER SOLUTIONS I. RADLA.TION-INDUCED OXIDATION OF FERROUS SULFATE by William R. McDonell ABSTRACT The Co gamma-ray-induced oxidation of ferrous sulfate in 0.8 N sulfuric acid-heavy water solutions proceeds with a specific yield, Gpe+ + + , of 1 7.5 , compared to 15.6 for normal water solutions. Pile irradiation yields show a similar but smaller enhancement of ferric ion yields in heavy water solu- tions, the difference probably due to greater flux of capture gamma radiation in the normal water, than in heavy water solutions. EXPERIMENTAL PROCEDURE Solutions of 0.001 N ferrous sulfate and 0.8 N sulfuric acid were pre- pared in normal and heavy water using recrystallized FeS04 • H^O and reagent grade sulfuric acid. The normal water used was purified by a standard triple -distillation procedure described previously. lU The heavy water was purified in a similar fashion; Successive distillations from two alkaline potassium permanganate solutions were made, and the vapor distillate from the second distillation was swept in a stream of oxygen through a quartz fur- nace tube heated to 800°C and condensed into a slightly acid dichromate solu- tion. The water was redistilled from this solution, again heated to 800°C in an oxygen stream, and condensed into a quartz receptacle. Using exhaustive irradiation with Co gamma rays as a test for purity, negligible amounts of gaseous products were yielded by both normal and heavy water, indicating a high degree of purity with respect to organic contaminants. The heavy water, with an isotopic analysis of 99.6% D^O, was diluted by the dissolved reagents to a calculated purity of about 99%. The solutions, air saturated, ^^' were drawn into 12 ml, 2-cm diameter irradiation cells, which were made of Pyrex for the Co source irradiations and of quartz for the pile irradiations. For the pile irradiations, the cells were placed in standard 15-in. aluminum cans, two to a can, one with normal and the other with heavy water as solvent. These cells were situated one above the other in such a fashion that, when irradiated, they occupied mean vertical positions about 6 in. apart; they were thus susceptible to any flux variation which might be encountered over this distance in the vertical thimble. The relative positions, above and below, of the normal and heavy water samples were alternated, however, to detect such a variation. Irradiations of one, two, and three minutes duration were carried out with the 400-curie Co source at 3 cm distance; irradiations of 0.5, 1.0, 1.5, and 2.0 minutes duration were carried out in the Argonne heavy- water reactor, CP-3 ' . The pile irradiations were made in vertical thimble #2 (VT-2). Each can was dropped into the thimble with the pile at full power the irradiation timed by stopwatch, and the can rapidly withdrawn. The timing precision was estimated at i 5 seconds. The analysis of the solutions for ferric ion was made in standard fashion(3J by ultraviolet absorption at wavelength 3020A on a Becknnan Model DU quartz spectrophotometer. The concentration of ferric ion in juN is given by 449dD where D^ is the optical density of the solution and d. is the dilution employed. RESULTS AND DISCUSSION Ferrous sulfate was oxidized by Co^" gamma radiation at a rate 12% greater in heavy water than in light water (Figure 1), indicating a Gpg+++ of 17.5, as compared with Hochanadel and Ghormley's value of 15.6 for light water.\^/ Since the linear absorption efficiency for gamma radiation in the one Mev range is essentially the same in heavy water as in light water,* the en- hancement of the rate of oxidation in the heavy water may be ascribed to a difference in its radiation chemical behavior. Radiation-induced oxidation of ferrous ion comes about as a consequence of the production of free radicals and molecular decomposition products by the reactions (l) and (2), respectively. H2O - H + OH (1) H2O -. 1/2 H2 + 1/2 H2O2 (2) The mechanism(2) requires that in aerated solutions, the yield of ferric ion from (1) be four times that resulting from (2). *The electron (unit volume) density of light and heavy water can be seen to be approximately equal by a comparison of their respective molecular weights and volume densities (p). Ratio electrons (per unit volume) = ratio of moles (per unit volume) = [{ Po^o)/{MUzO)Vl.i PD^oVi^HzO)^ = 1 where pj^ q = 1.1, Mq^q = 20, Mj^^o = 18. 400 350 - 300 250 - 200 - 150 - 100 - 60 120 180 TIME IRRADIATED (sec.) FIGURE 1. 240 Co^° GAMMA RAY INDUCED OXIDATION OF FERROUS SULFATE IN LIGHT AND HEAVY WATER-0.8N SULFURIC ACID SOLUTIONS. DOSAGE RATE 3.3 x I0^° ev/liter min. Hartw) has determined the fraction of water molecules decomposing by means of reaction (1) under Co^" and pile gamma radiation as 79% in normal water solutions, while 85% of heavy water molecules decompose to radicals under Co irradiation. V°) Thus the ferrous ion yield per molecule of water decomposed is 5%) higher for heavy water than for normal water, and a 7% enhancement in the effective total yield of water molecules decom- posed occurs in the heavy water solutions. The absolute yields of water molecules decomposed per 100 ev calculated from the stoichiometry of the reaction are 4.6 for the normal water solutions and 4.9 for the heavy water solutions. In Figure 2 are shown the rate of oxidation curves for irradiation in VT-2 of reactor CP-3' . It is obvious from the data that the difference in vertical position of the cells in the column during irradiation, alternately top and bottom of the can, results in a variation in gamma flux. The normal and heavy water oxidations are comparable only under the same flux con- ditions, and thus the data must be considered in two parts. Curves A and B represent the rates of oxidation in heavy and normal water respectively, the samples irradiated being at the top of the irradiation can; these are 327 and 299 ^N Fe /min respectively. Curves C and D are analogous rate curves for the samples at the bottom of the can, 291 and 289 Fe"''"'"/liter min. The cans were irradiated at the bottom of the vertical thimble. Such an arrange- ment places the cells in the bottom of the can out of the region of maximum flux, presumably some 6 to 18 in. up on the thimble. Thus, the higher rate of oxidation in cells at the top of the can is in accord with what is expected from the flux variations along the vertical thimble. The variation in ratio of rates of oxidation in heavy and normal water is decreased in the lower irradiation position relative to that of the upper position. The upper position shows a ratio of rates of 1.09 while in the lower position the ratio is about 1.01. These represent, as well, a decrease from the ratio 1.12 observed for Co gamma irradiation. The general decrease in the ratio of the rates of oxidation by the pile radiation may be attributed to neutron effects. The relatively greater capture cross section of hydrogen over deuterium tends to enhance the gamma flux in the light water over that in the heavy water. In addition, the greater moder- ating efficiency of normal water over heavy water results in a higher rate of fast neutron energy dissipation and may give rise to an enhancement of the chemical effect produced by knock-on protons. It can be assumed that the upper cans irradiated toward the center of the pile were in a region of higher neutron flux and lower moderation (i.e., higher mean energy) than the lower cans. Thus a greater probability for production of an extra gamma flux component by capture of thermal neutrons in the normal water would exist in the lower cans, in the region of the higher moderation. This would tend to decrease the difference in ferric ion yields in normal and heavy water solutions in the lower cans, as was observed. 700 600 - 500 - + 400 + « ^ 300 - 200 100 O H2O solutions • D2O solutions ^l Top of irradiation cons Bottom of irradiation cans 0.5 1.0 1.5 TIME IRRADIATED (min.) 2.0 FIGURE 2. OXIDATION OF FERROUS SULFATE IN NORMAL AND HEAVY WATER-0.8N SULFURIC ACID SOLUTION BY ARGONNE HEAVY WATER REACTOR RADIATIONS. PILE POWER 275 kw. ACKNOWLEDGEMENTS I am indebted to Dr. E. J. Hart for enlightening discussions of this research, to Miss Patricia Walsh for technical assistance, and to Dr, W. H. McCorkle and the operating crev of the Argonne reactors for carrying out the pile irradiations. REFERENCES 1. E. J. Hart, J. Am. Chem. Soc. 73. 68 (1951). 2. E. J. Hart, J. Am, Chem. Soc. 73, 1891 (1951), 3. E. J. Hart, J. Am. Chem, Soc. 74, 4174 (1952). 4. C. J, Hochanadel and J. A. Ghormley, J. Chem. Phys. 21, 880 (1953), 5. E. J. Hart, J. Phys. Chem. 56, 594 (1952). 6. E. J. Hart, private communication. UNIVERSITY OF FLORIDA 3 1262 08586 8379