Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm-149 and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: -4 10^{-17}year^{-1} < d alpha/dt/alpha < 3 10^{-17} year^{-1} A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress.Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos correcte

Preparation of calix[4]arene crown ethers for selective extraction of cesium and actinides from aqueous wastes

C.A. 122: 23973

I calixareni nel trattamento dei rifiuti radioattivi

Riassunto Molecole a forma di calice (calixareni) sono state utilizzate come macrocicli di partenza per la realizzazione di nuovi ionofori altamente efficienti e selettivi nella rimozione di cationi radioattivi dai rifiuti liquidi provenienti da centrali nucleari. Calix[4]areni contenenti funzioni chelanti bidentate (CMPO) estraggono tutti gli attinidi, mentre i calix[4]crowns sono in grado di complessare il 137Cs con una selettività eccezionale. I risultati ottenuti hanno portato, in alcuni casi, allo sviluppo di processi industriali di separazione. Abstract Calix shaped macrocycles, and therefore named calixarenes, were used as building blocks for the synthesis of new ionophores highly efficient and selective in the extraction of radioactive cations from waste resulting from the reprocessing of exhausted nuclear fuel. Calix[4]arenes with bidentate chelating units such as CMPO extract all actinides, while calix[4]crowns are able to complex 137Cs with an outstanding selectivity. In some cases, the results obtained allowed to develop an industrial separation process