Fission Elements Research Articles

Removal of ruthenium from PUREX process. (II). Fundamental research of electrolytic oxidation of ruthenium.

A new method was developed for the removal of ruthenium from nitric acid solutions. Ruthenium in 3 M nitric acid solution is oxidized electrolytically to ruthenium tetraoxide, and the tetraoxide is extracted into n-paraffin. The ruthenium tetraoxide extracted in paraffin is readily reduced to ruthenium dioxide by the solvent as black suspension, and it can be easily filtered off through an ordinary cellulose fiber filter. By this method, ruthenium, one of the most troublesome fission elements in PUREX Process, can be removed.

X-Ray Photoelectron Spectroscopy and Electron Probe X-Ray Microanalysis Investigation and Chemical Speciation of Aerosol Samples Formed in Light Water Reactor Core-Melting Experiments

Aerosol samples consisting of fission products and elements of light water reactor structural materials were collected during laboratory-scale simulation of the heat-up phase of a core melt accident. The aerosol particles were formed in a steam atmosphere at temperatures of the melting charge between 1200 and 1900/sup 0/C. The investigation of the samples by use of x-ray photoelectron spectroscopy (XPS) permitted the chemical speciation of the detected aerosol constituents silver, cadmium, indium, tellurium, iodine, and cesium. A comparison of the elemental analysis results obtained from XPS with those achieved from electron probe x-ray microanalysis revealed that aerosol particle surface and aerosol particle bulk are principally composed of the same elements. The compositions determined in dependence of the release temperature reflect the differing volatilities of the detected elements. Quantitative differences between the composition of surface and bulk have been observed only for those aerosol samples that were collected at higher melting charge temperatures. These samples show an enrichment of more volatile species at the particles' surfaces. In order to obtain direct information on chemical species below the surface, selected samples were argon ion bombarded. Changes in composition and chemistry were monitored by XPS, and the results were interpreted under consideration ofmore » possible influences of the sputter process on the surface composition.« less

Änderung der mechanischen Eigenschaften von Zircaloy-2 nach Langzeitglühung in Gegenwart von simulierten Spaltprodukten

The effect of various simulated fission products on the tensile properties of Zircaloy-2 on long-term exposure has been investigated. The fission elements and compounds, Cs, CsI, I, Br, Te, Se, Mo, Pd, Cd, and Nd 2O 3, were tested for activity in the embrittlement of Zircaloy-2. Room temperature tensile tests were carried out on flat specimens annealed in argon and in the individual fission product environments to 7.2 Ms (2000 h) at 623, 773, and 973 K. Except for Nd 2O 3, exposure at 623 or 773 K did not significantly affect either strength or elongation values of Zircaloy-2, though a gradual degradation of the mechanical properties was observed with annealing time. All specimens showed high reduction of area and ductile fracture morphology. The effect of Nd 2O 3 is to severely embrittle the specimens on annealing at 773 K, irrespecttive of exposure time. At 623 K, annealing times in excess of 3.6 Ms (1000 h) were needed to cause significant embrittlement of the specimens. Exposure to these environments at 973 K, on the other hand, results in a general reduction of the tensile properties at room temperature, the exceptions being Cs and CsI environments. In fact, I, Br, Cd, Mo, and Nd 2O 3 cause non-ductile fracture with little or no reduction of area. These results are discussed for their implications to fuel/ cladding interactions.

An experiment to synthesize and identify volatile superheavy elements

The paper describes an experimental method to synthesize and identify volatile superheavy elements at the heavy-ion accelerator UNILAC. It has been predicted for some of the superheavy elements that they should be highly volatile. Thus the observation of a volatile spontaneous fission activity under conditions under which the known spontaneous fission elements are not volatile should be definite proof that a superheavy element has been produced. The system combines the gas recoil transport method to be run with a pure aerosol-free gas with a collection chamber formed as a cooled trap in which volatile elements are condensed and thus separated from the carrier gas. The volatile elements are condensed on nuclear track detectors to observe spontaneous fission events. The method has been used in bombardments of a Ta/Er target with 136Xe ions.

Characterization of aerosols containing fissionable elements using solid-state track recorders

An aerosol of U 3O 8 highly enriched in 235U was generated with a nebulizer from a suspension of U 3O 8 powder in distilled water. The aerosol was collected on a membrane filter. Polycarbonate plastic, placed in good contact with the filter, was used to record fission tracks when the package was exposed to known fluences of slow neutrons. Fission-track stars associated with individual particles of U 3O 8 were observed in the plastic. The fission-track distributions were converted to a particle-size distribution for the aerosol. For a log normal distribution the geometric mean and standard deviation can be determined with better than 5% accuracy. This method can be applied to plutonium and other transuranic aerosols.

Cumulative yields of rare earth elements in the thermal neutron-induced fission of 249Cf

Cumulative yields of rare earth elements in the thermal neutron-induced fission of 249Cf

Light Charged Particles and Fission Elements from Californium-252 Fission

Light charged particles (LCP) and fission elements formed in ternary fission of /sup 252/Cf have been investigated. The energy spectra of light particles, alphas, and protons were studied using a ..delta.. E X (E + ..delta.. E) particle-identifying telescope apparatus. A coincidence circuit was used in such a way that the K x rays from the ternary fission fragments were electronically gated by a designated LCP and then stored in a multichannel analyzer. The K x rays were analyzed using a high-resolution lithium-drifted silicon spectrometer, permitting accurate identification of the elements in the charge distribution of fission fragments. Experimental results indicate the influence of the odd-even effect and also of shape deformation of alpha-accompanied ternary fission.

Two specialized delayed-neutron detector designs for assays of fissionable elements in water and sediment samples

Two specialized neutron-sensitive detectors are described which are employed for rapid assays of fissionable elements by sensing for delayed neutrons emitted by samples after they have been irradiated in a nuclear reactor. The more sensitive of the two detectors, designed to assay for uranium in water samples, is 40% efficient; the other, designed for sediment sample assays, is 27% efficient. These detectors are also designed to operate under water as an inexpensive shielding against neutron leakage from the reactor and neutrons from cosmic rays.

Odd-even systematics in neutron fission yields ofU233andU235

An analysis of the distribution of independent yields in neutron induced fission of $^{233}\mathrm{U}$ and $^{235}\mathrm{U}$ revealed a constant enhancement of products with an even number of protons, relative to those with an odd number. This odd-even effect in the proton pairing, related to calculated normal yields of elements in fission, constitutes a sawtooth structure with an amplitude of (22\ifmmode\pm\else\textpm\fi{}7)% for both $^{233}\mathrm{U}$ and $^{235}\mathrm{U}$ thermal neutron induced fission. The residual neutron pairing effect evident after the emission of prompt neutrons, while it is insignificant (3%) in the light mass peaks, is partly preserved in the heavy mass peaks of both $^{235}\mathrm{U}$ and $^{233}\mathrm{U}$ thermal neutron fission products. Its average magnitude is about (8\ifmmode\pm\else\textpm\fi{}5)% relative to the normal distribution of isotonic yields. In the fission of $^{235}\mathrm{U}$ with fission spectrum neutrons, the proton pairing effect drops to (8\ifmmode\pm\else\textpm\fi{}4)%. The odd-even effect is discussed in view of the various mass splits, the excitation energy and potential energy surfaces in the descent from the saddle to the scission configuration.

Investigation of the possibility for the application of the Keepin method in order to distinguish fissionable elements in mixtures, utilizing a beam of gamma-quanta

Investigation of the possibility for the application of the Keepin method in order to distinguish fissionable elements in mixtures, utilizing a beam of gamma-quanta

Über das Vorkommen von überschweren Nukliden in der Natur

The possibility of the occurrence of superheavy elements in nature is pointed out. The corresponding abundances were obtained by extrapolating the already known abundance values of the elements and their isotopes. According to their expected half-lives, and the spontaneous fission elements 108, 109 and 110 might occur in nature with abundances between 10−14 and 10−15%, probably in Ru−Rh−Pd and Os−Ir−Pt ores. These elements will be detectable directly by means of activity measurements or indirectly via their fission and decay products.

Radioactivity of the waters of the world oceans and behavior of some fission elements in the oceans

Radioactivity of the waters of the world oceans and behavior of some fission elements in the oceans

Gamma Rays in Coincidence withKX Rays from the La, Ce, and Pr Fission Fragments ofCf252

An experiment has been carried out to study the $\ensuremath{\gamma}$ rays from the fission fragments of ${\mathrm{Cf}}^{252}$. The $Z$ values of the fragments studied were determined by detecting their $K{\ensuremath{\alpha}}_{1}$ x rays with a Si(Li) x-ray speectrometer. A single-channel analyzer was used to accept only pulses corresponding to the $K{\ensuremath{\alpha}}_{1}$ x rays of the element under study. The $\ensuremath{\gamma}$ rays were detected with a Ge(Li) detector, and a time coincidence system was used to accept only the $\ensuremath{\gamma}$-ray pulses that occurred within 0.175 \ensuremath{\mu}sec of the preselected x ray. Energy transitions in three fission elements, $\mathrm{La}(Z=57)$, $\mathrm{Ce}(Z=58)$, and $\mathrm{Pr}(Z=59)$, were observed in an energy range 125-300 keV. Eleven $\ensuremath{\gamma}$ transitions were seen in La, fourteen in Ce, and four in Pr, although some of the weaker $\ensuremath{\gamma}$ rays attributed to La and Pr may belong to $\mathrm{Ba}(Z=56)$ and $\mathrm{Nd}(Z=60)$, respectively.

Vertical distribution of fission elements in some soils of the USSR

Vertical distribution of fission elements in some soils of the USSR

Radioactivation Analysis of Manganese by Counting Deuterium Photoneutrons

Summary A method is described for the assay of 2.58 hour 56Mn in different radioactive samples by counting photoneutrons. The high energy portion of the gamma radiation of seMn, produced upon neutron activation of samples containing manganese, causes emission of photoneutrons from a D2O reservoir incorporated in a 4π neutron counting assembly. To cause photoneutron emission from D2O the gamma ray energy must exceed 2.23 MeV and thus the method discriminates efficiently against all gamma rays of lower energies. The photoneutron activity is proportional to the 56Mn content of the sample, and submilligram quantities of manganese have been analysed with a precision of ~ 1%. Sensitivities of ~ 1 /μg and better are indicated. The only serious sources of interference are sodium and fissionable elements, when present in large proportions. The method is rapid and can be used to analyse manganese in complex matrices, without any chemical processing. The neutron counting apparatus required is relatively cheap, simple and versatile.

The absorption and distribution of SR-85 by field grownGlycine max

Abstract Introduction Contamination of crops and cropland by fission products as a result of fallout from nuclear explosions and waste from nuclear reactors is a matter of concern. It has been shown (4, 5) that the fission elements yttrium, cerium, zirconium, columbium, tellurium and strontium are absorbed from the soil and translocated in plants only to a limited extent. Of these elements, strontium is absorbed and translocated to the greatest extent. The other elements are apparently more strongly bound to the soil colloid.

Photofission of Bi, W and Ag from 300 to 1000 MeV

The fission of Bi, W and Ag induced by (300÷1000) MeV photons has been studied. Nuclear emulsions, loaded with known amounts of suitable salts of the fissionable elements were used. The cross-section per photon and the fissility were obtained.

Multicycle Reprocessing and Refabrication Experiments on Sintered UO2-Fissia Pellets

A multicycle reprocessing and refabrication scheme was simulated (using UO/sub 2/ spiked'' with fissia) to evaluate the feasibility of refabricating high-burnup UO/sub 2/ to a cumulative level of 10/sup 5/ Mwd/MTU. Various powder characteristics were studied, using oxidation-reduction methods as the reprocessing scheme. Processing conditions were established for the multicycle tests. Fissia, typical fission products (mostly oxides), were added to the reprocessed powder prior to compacting operations. There should be no difficulty in refabricating pellets from high-burnup material; conversely, the sinterability of UO/sub 2/ containing comparatively iarge concentrations of fissia is even enhanced. Well-formed pellets of density near 98% of theoretical were made for simulated burnups of 60,000, 80,000, and 100,000 Mwd/MTU. Cesium was the only fission element removed during processing.

Analytical Applications of Delayed Neutron Emission in Fissionable Elements.

Analytical Applications of Delayed Neutron Emission in Fissionable Elements.

Fractionation of Fission Elements by Electrodialysis

An electrodialysis process, employing ion exchange membranes, is developed for separating and recovering Cs--Ba/sup 137/, Zr--Nb/sup 95/, Ce-- Pr/ sup 144/, Sr--Y/sup 90/ , and Pm/sup 147/ from fission product waste solutions. Both a three and a seven cell electrodialysis unit are used for the separation process. Separation is not as complete with the seven cell unit as with the three cell unit, however, better separation can be expected by increasing the current density. The studies were performed on nitric, oxalic, and hydrofluoric acids in the three cell unit and nitric acid and ammonium acid fluoride in the seven cell unit. (N.W.R.)