Amounts Of Kr Research Articles

Effect of hydrogen gas and leaching solution on the fast release of fission products from two PWR fuels

To study the dissolution of UOX spent nuclear fuel in a deep geological environment and the fast release of a selection of relevant radionuclides for long-term safety of this high level waste, leaching experiments were performed with spent nuclear fuel samples originating from the pressurized water reactors (PWRs) Tihange 1 and Gösgen with a similar burnup (50 – 55 MWd.kgHM−1) but different irradiation histories. Six experiments were conducted to investigate the effect of two critical parameters: (1) the highly alkaline environment caused by the presence of cementitious materials in the “Supercontainer design”, which is currently the reference design for the long-term management of the high-level nuclear waste forms in Belgium, and (2) the reducing conditions imposed by the presence of hydrogen from the corrosion of iron-based materials present in the engineered barriers. The experiments were performed using autoclaves under pressure from 1 to 40 bar with a pure Ar atmosphere or a mixture of H2/Ar. Divided into two consecutive phases, the total experimental duration was about 1400 days. The Phase I provided mainly information about the fast release of the fission products while the perspective of the Phase II was to study the long-term evolution of the spent fuel matrix. During the leaching experiment, concentrations of a selection of radionuclides (238U, 129I, 137Cs, 90Sr and 99Tc) were monitored in solution and the amounts of Kr and Xe were measured in the gas phase. Based on results of the experiments conducted for up to 40 months (i.e. during Phase I of the experimental program), we observe that there is a continuous release of 137Cs, 90Sr and of the fission gases and a clear impact of the irradiation history on the release of certain fission products.

Pulsed-periodic UV emitter tunable near the main absorption maximum of a DNA molecule

The spectral characteristics of a pulsed-periodic lamp with three dielectric barriers are presented for the range 220–250 nm. As the active media of the lamp, krypton (Kr)-sulfur hexafluoride (SF6) and krypton-carbon tetrachloride (CCl4) mixtures are tested. The use of Kr-SF6 and Kr-CCl4 binary mixtures in two noncommunicating volumes is shown to be more effective than the use of a Kr-SF6-CCl4 ternary mixture with the same amount of Kr, SF6, and CCl4 constituents. The emission spectrum of the lamp near the maxima of the KrF(X-B) 248-nm and KrCl(X-B) 222-nm bands can be controlled by varying the partial pressures of halogen carriers and krypton.

Fission-Product Release during Transient Heating of Irradiated CANDU Fuel

A direct-electric-heating (DEH) apparatus was developed to heat Zircaloy-sheathed irradiated fuel samples. The apparatus was used in the temperature gradient 1 (TG1) experiment to measure fission product releases from Zircaloy-sheathed irradiated Canada deuterium uranium (CANDU) UO2 fuel samples during fast temperature ramps in the presence of a radial temperature gradient in the fuel. The ohmic heating of the UO2, combined with surface heat removal by the surrounding helium coolant flow, produced a radial temperature profile that approximates the profile for fission- or decay-heated fuel.The 11 tests conducted in the TG1 experiment simulated various transient heating rates and high-temperature annealing conditions. The results indicate that the DEH technique can produce large radial temperature gradients and rapid heating rates. Ceramographic examinations showed columnar grain growth and evidence of UO2 melting. Chemical interactions between the tungsten electrodes and the UO2 were also observed. Releases of krypton, and release and redistribution of cesium were measured. Fission product release and redistribution results from some of the tests are also reported.The Kr measurements indicated that the amount of Kr released was highly dependent upon the peak dwell power: The higher the dwell power, the higher the cumulative release. The redistribution of cesium was mapped using emission gamma radiography of the fuel specimen after the test. Cesium was released from the center of the fuel sample where temperatures were the highest. A well-defined area was confirmed near the center where the Cs activity was depleted. The measured Kr releases were in good agreement with the Cs migration and release.

The slowing down of atoms with kinetic energies ofW?5 eV in Noble Gases: Evidence for inelastic interactions

Profiles of the 264.6 keVγ-line of75As emitted after the electron capture decay of75Se have been measured using nuclear resonance fluorescence in combination withγγ-coincidences as a high resolution, variable-energyγ spectrometer. The sources consisted of gaseous75SeH2 with different amounts of Kr or Xe. From the line profiles information has been obtained about the velocity distribution of the radioactive75As ions after electron capture decay and about the slowing down of the75As ions in the moderator gas. The75As ions obtain kinetic energies of up toW∼5 eV by neutrino recoil and Coulomb fragmentation of the75SeH2 molecules, corresponding to velocities of the order of 105 cm s−1. The slowing down of the75As ions has been interpreted in terms of the model of colliding elastic spheres, taking into account the thermalization in an exact way. No satisfactory agreement has been obtained between measured and calculated line profiles. This result indicates that inelastic processes are of great importance in the interaction of75As ions or atoms with the noble gas moderator atoms.

Sputtering and depth-distribution phenomena in KCl, Al2O3, and TiO2

If a solid is bombarded with an inert gas, the thickness removed by sputtering is proportional to (S) (μA min/cm2), where S is the sputtering coefficient. We have used this effect first to evaluate S for Kr–Al2O3, O2–Al2O3, Kr–TiO2, and O2–TiO2 in the region 2–10 keV. With Al2O3, pieces of free anodic oxide were bombarded until perforated, while with TiO2 the changes in the interference colors of anodized Ti were noted. Knowing the values of S, we have then obtained depth distributions for 10-keV Kr in KCl, Al2O3, and TiO2 at doses of 1–50 μA min/cm2, the amount of Kr remaining in the targets being determined by radioactivity measurements. Rm, the median range, was 105 Å with KCl, and thus within a factor-of-2 agreement of other range data for crystalline materials; with Al2O3 and TiO2, however, Rm was only 11–18 Å, and thus a factor of 4–6 lower than expected on the basis of low-dose data for anodic oxides. In the case of Al2O3, the low values of Rm were explicitly shown to be due in part to a dose effect, such that Rm is at least a factor of 2.3 lower for doses over 1 μA min/cm2, and similar behavior can probably be assumed also for TiO2. In addition, however, gas sputtering or surface roughening may possibly play a role with Al2O3 and TiO2.