Irradiated Uranium Research Articles

Short-lived isotopes of lanthanum, cerium and praseodymium in neutron irradiated uranium

The separation of fission product La, Ce and Pr was performed within 90–180 sec by electromigration. As a supporting electrolyte, the solution of nitrilotriacetic acid ([NTA] = 3·7 × 10 −3M, pH = 2·0, μ ∼ 0·05) was used. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated uranyl nitrate solution. The γ-ray spectrum of each element was measured by a Ge(Li) detector connected with 512 channel pulse-height analyzer. In lanthanum fraction, at early times two prominent photopeaks at 395 keV ( T 1 2 = 40 ± 2 sec ) and 541 keV ( T 1 2 = 43 ± 3 sec ) were observed. From their decay rates, we presumed that they could be attributed to 144La ( T 1 2 = 41 sec ) whose γ-ray energies have not yet been reported. The two other photopeaks at 619 and 642 keV were assigned to the 14 min 143La and 92 min 142La. In Ce fraction, the photopeaks assigned to the 3 min 145Ce and to the 14 min 146Ce were observed, while no photopeaks could definetely be assigned to the 65 sec 147Ce. Some unreported γ-rays of 145Ce were found to be 233, 300, 429 and 915 keV. In Pr fraction, the 2·0 min 148Pr (γ-ray energy = 300 keV) and 12 min 147Pr (the photopeaks at 123 and 313 keV) were identified.

Recovery of Electrical Resistivity in Neutron Irradiated Uranium Monocarbides

Recovery of Electrical Resistivity in Neutron Irradiated Uranium Monocarbides

Heterogeneous nucleation of fission gas bubbles and gas migration in uranium dioxide

Abstract The number and size of fission gas bubbles precipitated in irradiated uranium dioxide are calculated from a theory based on a balance between nucleation of bubbles at vacancy clusters produced by fission fragments and the agglomeration of bubbles by random motion. The distribution of bubble sizes is determined by gas atom capture, bubble agglomeration and irradiation re-solution. Irradiation re-solution exceeds gas atom capture for large bubbles and causes the larger bubbles formed by agglomeration to shrink. The effect of the precipitated gas bubbles on gas migration is considered, and it is shovrm that the bubble diffusion coefficient is likely to be larger than the trap-release diffusion coefficient. The predictions are compared with other theories of bubble nucleation, and with experimental observation.

A Comparison of Radiochemical Methods for Cesium-137 Determination

The results are presented of a comparative study seeking an accurate and precise radiochemical method for 137Cs determination in burnup measurements. The methods taken up are chloroplatinate-precipitation (Method I), tetraphenylborate-precipitation (Method II), tetraphenylborate-extraction (Method III), potassium hexacyanocobalt(II) ferrate(II)-substitution (Method IV) and ion-exchange (Method V). A common sample, an aqueous solution obtained from dissolving irradiated uranium fuel and containing approximately 5μCi of 137Cs, was analyzed by seven analysts using the five methods. A statistical analysis of the results obtained (105 values in all) show that the expected precision, at the 0.05 probability level, of a single determination in non-rehearsed trials of each method are: Method I, ±3.0%; Method II, ±5.6%; Method III, ±5.3% Method IV, ±10.9%; Method V, ±4.2%. The accuracy follows the same pattern except Method III and Method IV. The advantages and disadvantages of the five methods are discussed from the standpoint of utilization in burnup measurements.

A Comparison of Radiochemical Methods for Cesium-137 Determination

The results are presented of a comparative study seeking an accurate and precise radiochemical method for 137Cs determination in burnup measurements. The methods taken up are chloroplatinate-precipitation (Method I), tetraphenylborate-precipitation (Method II), tetraphenylborate-extraction (Method III), potassium hexacyanocobalt(II) ferrate(II)-substitution (Method IV) and ion-exchange (Method V). A common sample, an aqueous solution obtained from dissolving irradiated uranium fuel and containing approximately 5μCi of 137Cs, was analyzed by seven analysts using the five methods. A statistical analysis of the results obtained (105 values in all) show that the expected precision, at the 0.05 probability level, of a single determination in non-rehearsed trials of each method are: Method I, ±3.0%; Method II, ±5.6%; Method III, ±5.3% Method IV, ±10.9%; Method V, ±4.2%. The accuracy follows the same pattern except Method III and Method IV. The advantages and disadvantages of the five methods are discussed from the standpoint of utilization in burnup measurements.

Recovery of Electrical Resistivity in Neutron Irradiated Uranium Monocarbides

Recovery of Electrical Resistivity in Neutron Irradiated Uranium Monocarbides

Formation of organic iodides on dissolution of irradiated uranium metal in nitric acid

Formation of organic iodides on dissolution of irradiated uranium metal in nitric acid

The chemical effects of composition changes in irradiated oxide fuel materials

When uranium or plutonium undergoes fission, the mean valency of the resulting fission product mixture may differ from that of the starting material. This paper describes the use of a computer programme to derive the composition of irradiated fuel, and how a combination of thermodynamic assessment and direct experiment is used to predict and confirm some of the consequences of the valency change in irradiated oxide fuels. The experiments consist of an X-ray study of the lattice dilation of uranium dioxide, a direct measurement of the oxygen/metal ratio in plutonium and mixed uranium-plutonium oxides, and electron probe microanalysis of inclusions formed in plutonium oxides. These demonstrate that the lanthanide fission products enter the oxide lattice so that irradiated uranium oxide does not become more oxidising with burn-up, but that plutonium oxide becomes significantly oxygen-rich during fission owing to the shift in the fission yield spectrum.

A Method of Nondestructive Measurement of the Absolute Cumulative Barium-140 Yield of Uranium Irradiated in Thermal and Fast Neutron Spectra

The 140Ba cumulative yield of irradiated uranium has been determined absolutely by a nondestructive method. Thin uranium foils are irradiated in the fast thermal zero-power reactor STARK. To avoid radiochemical separation, the 1596.5-keV gamma activity of 140La, the daughter nucleus of 140Ba, is measured with a high resolution (2.6 keV fwhm) Ge (Li) detector. From this 140La activity the absolute 140Ba yield is evaluated from the corresponding absolute fission rate and. the detector efficiency known for the 1596.5-keV photopeak. The uranium fission rate in the foil is normalized to the absolute fission rate measured with a calibrated parallel-plate chamber. Calibration of the gamma spectrometer is performed with activated thin La2O3 foils whose absolute activities are determined by 2π beta counting.The 140Ba cumulative yield data obtained are 6.29 ± 0.14% for 235 U thermal neutron fission and 6.10 ± 0.15(%) and 6.34 ± 0.41(%) for fast neutron fission of 235U and 238U, respectively. They are in good agreement (within ±1%) with the values reported to date.

Nuclear Reactions initiated by Recoil Nuclei

It is difficult to comment on the calculations for the direct production of heavy recoils by elastic scattering as no experimental data are available over the relevant angular region. The calculations for the production of fast heavy fragments, however, would seem to be in contradiction with experiment. For example the recent results of Maly1 show that fragments of energy > 100 MeV and A>25 are emitted with production cross-sections of > 1 µ in the irradiation of heavy targets with 1,300 MeV electrons. Similarly the work of Poskanzer et al.2 shows that in the irradiation of uranium by 5.5 GeV protons, fragments as heavy as argon may be emitted with energies of 200 MeV and cross-sections of 0.1 µbarn MeV−1 sr−1. These results also show that the production cross-section is constant or slowly increasing for fragments between carbon and argon implying very similar production cross-section for fragments of larger Z and A. Thus there seems to be a direct conflict between the predictions of the paper by Kabir and Trefil and the available experimental data. This would imply that more complicated interactions than those considered in that paper can occur.

Some observations on the effect of internal surfaces on the ignition behaviour of irradiated uranium in carbon dioxide

Some observations on the effect of internal surfaces on the ignition behaviour of irradiated uranium in carbon dioxide

An electron microscope examination of matrix fission-gas bubbles in irradiated uranium dioxide

Uranium dioxide irradiated over a wide temperature range to a dose of greater than ~ 3.2 × 10 16 fissions/ mm 3 is always found to contain a high concentration of intragranular fission-gas bubbles which contain a constant amount of gas approximately independent of both irradiation temperature and burn-up. These bubbles, which are assumed to be nucleated heterogeneously upon the sites of the energetic fission fragments, have a lifetime which lies in the range of 4–40 h with thermal neutron fluxes of ~ 5 × 10 11 n/ mm 2 · sec. The collection of fission-gas at grain boundaries is controlled by resolution and atomic diffusion of gas atoms through the uranium dioxide lattice rather than by the migration of bubbles up the temperature gradient. The diffusion coefficient of the fission-gas atoms in irradiated uranium dioxide has been shown to be considerably enhanced at temperatures below ~ 1300 °C.

Systematic radiochemical analysis of fission products

A scheme for the sequential separation of fission products has been developed on the basis of ion-exchange techniques. It consists of a main cation-exchange process for group separation and subsidiary processes of cation or anion exchange for further separations or purifications of the individual fission products. By the present method, Zn, Rb, Sr, Y, (Zr), Mo, Pd, Cd, Te, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu and Tb can be separated simultaneously from an irradiated uranium sample. Of these, alkali, alkaline earth and rare earth metal ions are separated quantitatively. A polarographic method was applied to determine the recoveries of Zn, Mo, Pd, Cd and Te, which were not separated quantitatively.

Chlorination-Volatilization Processing of Irradiated Uranium Dioxide, (II)

A study was made on the decontamination of F.P. from irradiatcd UO2 fuel by means of a sorption-desorption process using BaC12 bed. A very high degree of decontamination was obtained. Irradiated UO2 pellets were pulverized through a repeated oxidation-reduction process, and then chlorinated with CCl4 vapor at 580°C. The gas containing the vapor of the chlorides formed thereupon was passed through the BaCl2 bed whose temperature varied along its length from 500° to 100°C. The vapor of the chlorides was sorbed on the bed. From this bed, zirconium and niobiutn chlorides were selectively desorbed by maintaining the bed at batween 460° and 480°C in a mixed gas stream of Ar and CCl4 vapor. The uranium chlorides, remaining on the bed, were then desorbed by maintaining the bed at 500°C in a mixed gas stream of Ar, Cl2 and CCl4 vapor. Cesium chloride accomparlied the uranium chlorides in this process. Cerium and ruthenium chlorides remained undesorbed on the bed after both desorption processes. The vapor of uranium chlorides desorbed was trapped to recover the U. The γ-decontamination factor of the U recovered after 1, 2 and 3 cycles of the sorption-dcsorption process was of the order of 102, 103 and 104, respectively.

85Kr release during the oxidation and self-heating of irradiated uranium in air

The behaviour of the fission gas 85Kr has been studied during the oxidation of irradiated uranium in air. Over the temperature range 220–320 °C there is a direct proportionality between the extent of isothermal oxidation and the amount of 85Kr released. Above 300 °C the irradiated metal can self heat and although well defined ignitions do not occur a thermal cycling reaction is observed, which with unirradiated uranium is initiated at a temperature at least 200 °C higher. During thermal cycling the 85Kr release curve follows with considerable sensitivity the irradiated metal temperature curve. The degree of self heating is insufficient for fission gas bubble growth to play a significant role during the oxidation and it is concluded that the solid fission product concentration in the oxide and oxide stoichiometry are important parameters in the initiation and continuation of the temperature cycling reactions.

Chlorination-Volatilization Processing of Irradiated Uranium Dioxide, (I)

A study was made on the decontamination of F.P. from irradiatcd UO2 fuel by means of a sorption-desorption process using BaC12 bed. A very high degree of decontamination was obtained. Irradiated UO2 pellets were pulverized through a repeated oxidation-reduction process, and then chlorinated with CCl4 vapor at 580°C. The gas containing the vapor of the chlorides formed thereupon was passed through the BaCl2 bed whose temperature varied along its length from 500° to 100°C. The vapor of the chlorides was sorbed on the bed. From this bed, zirconium and niobiutn chlorides were selectively desorbed by maintaining the bed at batween 460° and 480°C in a mixed gas stream of Ar and CCl4 vapor. The uranium chlorides, remaining on the bed, were then desorbed by maintaining the bed at 500°C in a mixed gas stream of Ar, Cl2 and CCl4 vapor. Cesium chloride accomparlied the uranium chlorides in this process. Cerium and ruthenium chlorides remained undesorbed on the bed after both desorption processes. The vapor of uraniu...

New etchants for irradiated uranium alloys

New etchants for irradiated uranium alloys

Some yields and isomeric yield ratios of indium isotopes produced by high-energy fission

Cross-sections of some indium isotopes have been determined from fission of uranium with 570 MeV and 18·2 GeV protons. Charge dispersion curves have been determined for A = 117 at the two energies. The first has N Z p = 1·414 and a full width at half-maximum of 2·93 Z units; the second is double-humped with a neutron-rich part equal in form and position to the curve at 570 MeV. The excitation function for 111In is constructed and peaks above 10 GeV. A thick-target recoil study of 111In at 570 MeV, 7·1 GeV, and 18·2 GeV shows a decrease in kinetic energy by a factor of 2, and also a considerable decrease in the cascade deposition energy in this energy range. The independent high-spin to low-spin isomeric yield ratios of the 117In isomers have been determined by irradiation of uranium and bismuth with protons of energies ranging from 159 MeV-18·2 GeV. These ratios seem to be constant (23±5) above 250 MeV proton energy, independent of target.

The release of krypton 85 during the oxidation and ignition of irradiated uranium in carbon dioxide

The oxidation of irradiated uranium in carbon dioxide has been studied by continuously monitoring the behaviour of the fission gas 85Kr. In carbon dioxide between 500 °C and 700 °C the 85Kr release is directly proportional to the degree of oxidation and the extent of oxide damage although additional losses of the active gas occur when specimens are thermally cycled through the α-β phase transition. By defining the ignition temperature as that gas temperature which produces a sudden rapid and continued release of 85Kr from the specimen, it is shown that an Arrhenius type dependency exists between the ignition temperature and the macroscopic specific area. Using this relationship, which applies to samples having microscopic specific areas of ⩽ 150 cm 2/g, the calculated activation energy (32 kcal/mole) suggests that up to ignition temperatures of at least 730 °C the oxidation is controlled by O 2− ion diffusion across a layer of non-stoichiometric UO 2 next to the metal.

Vaporization of fission products from irradiated uranium—II: Some observations on the chemical behavior of fission products iodine and cesium

The results of an experimental investigation of the chemical nature of fission products iodine and cesium vaporized from irradiated uranium specimens into helium and air are reported. The thermochromatographic technique, which has been described in detail in the first paper of the present series, was employed in the study. It was observed that iodine released from uranium heated to 1250°C in helium was not in chemical combination with either cesium or any other fission product, but rather was vaporized as a uranium-iodine compound. Partial dissociation of this compound into atomic iodine occurred when the uranium was heated to temperatures above 1900°C. In an oxidizing atmosphere, only elemental iodine was vaporized.