Chemical research at the Atomic Energy Research Establishment, Harwell By R. Spence Chief Chemist (Lecture delivered 9 May 1957—Received 29 June 1957) [Plate 1] I should like to say something about chemical researches at the Atomic Energy Research Establishment, but, as often happens, this simple desire leads to com plications : there are so many researches, often not very closely related, bearing on a wide variety of technical programmes, that to mention them all would oblige me to recite a mere catalogue of items.
2 R. Spence which have been made in the Chemistry Division. A very large number of scientific papers and reports have been published during the ten years of its existence and my selection is bound to be somewhat arbitrary. By and large, I have chosen those researches which constitute substantial advances in themselves and which do not require a description of a wider field to permit them to be reasonably evaluated. The fact that I shall say little or nothing about our work on the chemistry of plutonium and the higher actinides, or about the radiochemical determination of fission yields, for example, does not mean that little or nothing has been done. Our contribution in these fields has been greater than that of any other European laboratory but is still, nevertheless, supplementary to a more substantial American contribution.
Chemical research at Harwell 3 As a result of all this work, we now have the rather surprising situation that considerably more is known about the chemistry of polonium than about that of radium, which was discovered shortly afterwards by Mme Curie and which has been available in gram quantities for over 50 years.
4 R. Spence ordering of the interstitial oxygens. Kinetic studies of the uptake of oxygen by U02 at temperatures above 130° C showed that the rate can be represented by a diffusion expression, and it was concluded that there is a continuous variation of composition within each grain (Anderson, Roberts & Harper 1955). The contraction in the cell dimensions which takes place between U02 and U02.4 is to be connected with the substitution of the smaller ion U5+ for U4+. It has been shown by Roberts that instantaneous chemisorption of oxygen occurs at — 183° C on the surface of uranium dioxide which has been prepared by reduction with carbon monoxide or hydrogen at 500 to 700° C. Adsorption begins with a high initial heat of adsorption which then falls off with increase of surface coverage as shown in figure 3 (McConnell & Roberts 1956).
Chemical research at Harwell 5 When uranium dioxide is mixed with thoria, the thoria appears to act simply as an inert diluent; in the case of uranium dioxide + yttria mixtures, however, rapid oxygen uptake occurs which is associated with the presence of anion vacancies in the yttria lattice. Uptake ceases when all the vacancies are filled (Anderson, Ferguson & Roberts 1955).
Chemical research at Harwell 7 nitrate molecule, in the case of ether, for example, but the actual species present may range from a dihydrate to at least a hexahydrate. Tributyl phosphate ( TBP), which is a stronger complexing solvent, forms the unhydrated complex U02(N03)2.2 TBP, water being displaced from its complex with TBP, with the result that the water content of the organic phase decreases with increase of uranium concentration (Healy & McKay 1956).
8 R. Spence the more important of these systems in considerable detail using electrons from a 2 MV van de Graaff machine and y-rays from a 1000 c cobalt source but as the results are of special rather than general interest, I will leave the subject of solvent extraction and pass on to some of the radiation studies which have been carried out in the pile. Radiation reactions can be brought about in the pile either by the /?- and y-radiation and the neutrons resulting from the fission process or by the direct action of the fission fragments themselves. Most experiments are arranged so that one or the other of these two types predominates. Naturally, one of our first interests has been in the radiation reactions which occur in nuclear reactors themselves. The Windscale production reactors are air-cooled and the Calder Hall reactors are cooled by carbon dioxide. The rates of the radiation-induced reactions between oxygen and graphite and between carbon dioxide and graphite were gas/liquid volume ratio Figure 5. Dependence of yield of nitric acid and ammonia on gas/liquid volume ratio at constant thermal neutron dose of 2*92 x 1018 neutrons/cm2. O, air-water system, NO<T ; + , nitrogen-water system, NO^“; #, nitrogen-water system, NH4.