[en] During the operation cycle of the PWR plants, oxides deposits (sludge) generated in the secondary circuit by erosion corrosion, chemical additives, etc. Which are deposited on the tube plate of GVs, limiting their efficiency and lifespan. To reduce them, Iberdrola Engineering and Construction, together with SRA SAVAC cleaned by high-pressure water means and tele visual inspection between tubes of the GVs. After Sludge Lancing cleanings performed by 250 bar from the center line, an area of solidified sludge remaining on the tubular plate was identified. Late 2010, Iberdrola Engineering and Construction, together with SRA SAVAC developed the Inner Bundle Lancing (IBL) system, which is based on a jet of water of high pressure>500 bar directly impacting areas of hard sludge within the tube bundle to detach and break the deposits into small pieces that can be extracted from GV through a closed circuit suction. (Author)

[en] During the cycle of operation of the PWR plants, oxides (sludge) tanks are generated in the secondary circuit by corrosion, chemical additives, etc which are deposited onto the tubular steam generators (GVs), limiting its efficiency and service life.

[en] Millstone Hill radar spectra exhibit pronounced spectral asymmetries in the presence of field-aligned currents in the topside ionosphere. The enhanced, often intense, returns associated with the current-driven growth of the ion acoustic mode exhibit the characteristics of hard-target backscatter suggesting that many ''satellite echoes'' observed by UHF radars at high latitudes might be caused by this mechanism. A large current density (>100 μamp/m²) is calculated for the conditions observed, consistent with that seen in intense earthward-directed current filaments. Our observations indicate that the ion acoustic mode grows toward instability with increasing altitude. Backscatter observed from the unstable region at higher altitudes is characteristically at the ion plasma frequency consistent with the unstable growth of the acoustic mode for large ratios of electron to ion temperature. copyright American Geophysical Union 1988

[en] This paper presents the results of a numerical investigation of transient redox conditions in argillaceous material in the context of HLW deep geological disposal. The redox state is a crucial parameter not only for the lifetime of the canisters but also for the migration of radionuclides after canister failure. Since reducing redox conditions prevail in deep underground porous media, the digging of excavations to build the repository will induce an oxidising perturbation in the vicinity of the galleries and tunnels. After emplacement of waste packages and closure of galleries, other processes will control the evolution of the redox conditions such as the corrosion of steel canisters and structures, or the radiolysis of water close to the waste packages. Since reducing conditions are considered favourable for the confining function of the repository, the purpose of this study is to quantify the persistence in time and space of the initial oxidising atmospheric perturbation. (authors)

[en] Full text of publication follows: The interactions between glass and clay are investigated using a modified version of the reaction transport code Crunch [1], especially looking at pH changes and possible cementation at the interface with the clayey materials (here the argillite of Bure). These perturbations may indeed affect the lifetime of glass matrix in deep repositories since high pH enhances the rate of glass alteration while porosity could prevent it. The glass material used in the calculations is a simplified glass containing silica, boron, and sodium. The calculations were performed at 50 deg. C with constant parameters for the glass alteration (irreversible rate constant and surface area). The results show that the glass alteration is imposing a high pH value in the vicinity of the interface: up to a value of 9.2, compared to 7.3 which is the initial pH value in the argillite. Experimentally, the rate of glass alteration is much higher in such pH conditions (the rate is ca. 5 times higher for R7T7-type glass at pH 9 compared to the value at pH 7). This pH perturbation migrates through the clayey domain following mobile elements such as boron and sodium, despite the existence of strong pH buffers in the argillite (carbonates and ion exchange). The argillite does not seem to be much destabilized except for some dissolution of kaolinite and K-feldspar and some adjustments of carbonate minerals (calcite, dolomite, and siderite). The cementation of porosity at the interface between glass and clay is predicted by the model due to the massive precipitation of silica minerals (essentially amorphous silica, but also chalcedony) while kaolinite is strongly destabilized at this location. As porosity drops to zero, the migration of the alteration products of glass is reduced leading to their accumulation in solution at the interface. At this point, the pH starts to decrease in the whole domain and the alteration of the glass could be significantly reduced. This porosity clogging effect has yet to be confirmed by experiments since existing data tend to show a pervasive precipitation of silica in the domain instead of a localized precipitation at the interface. This model was developed as a template for future developments on the Alliances platform and will be used to help testing and qualifying such developments. [1] CRUNCH: Software for modeling multicomponent, multidimensional reactive transport. User's Guide, UCRL-MA-143182. Livermore, California. Steefel, C.I. (2001). (authors)

[en] During geomagnetically active periods, the 440-MHz steerable Millstone Hill incoherent scatter radar system often receives powerful coherent radar echoes when observing the lower ionosphere in regions roughly to the north of the antenna, and for distances ranging between 700 and 1,000 km. With the exception of a few anomalous events, the echoes clearly originate from the E region, and the aspect angle of the irregularities responsible for the coherent echoes is within one half degree of perpendicularity to the magnetic field. The strength of these coherent E region echoes increases with the inferred electric field strength. In contrast with similar experiments reported earlier with the Homer system, the Doppler shift of the coherent spectrum that the authors observe seems to correspond to the line of sight component of the plasma drift unless this component exceeds the ion acoustic speed. In the latter case, the Doppler shift then appears to be limited to the ion acoustic speed as it does with other coherent radar systems. The mean height of the scattering layer varies between 105 and 115 km for any single event, while there is some evidence to suggest that the vertical width of the scattering volume may be as small as 4 to 5 km at times. They saw evidence for an occasional layering of the E region scattering into two distinct regions. As a result of the present study, they plan to exploit the unique sensitivity of the Millstone Hill radar to make direct simultaneous comparisons between mean F region plasma drifts and the Doppler shift of E region irregularities

[en] Long term integrated in situ experiments are performed in the HADES underground research facility (Mol, Belgium) in order to study the coupled reactivity between the different components of an underground repository for vitrified high level radioactive waste (HLW): glass, compacted clay, and stainless steel containers, at 90 degrees C and under gamma irradiation. Studies pertaining to the behaviour of silicon, a major element released during glass alteration, are presented here. Data collected from the integrated experiment, from simplified tests, and from modelling are put together, giving complementary information. The integrated experiment is used to investigate overall reactivity, whereas diffusion experiments coupled with modelling focused on the precipitation of silica in clay media. In the integrated in situ experiment, a bentonite clay (FoCa7) mixed with 5 wt.% of powdered glass frit was put in contact with U/Th-doped SON68 reference glass specimens for 1.2 years. One of the samples was thoroughly analysed by ESEM, SEM-EDS, TEM, XRD, and FTIR. The observations showed that after combined heating and gamma irradiation, the glass/clay interface is still fully reactive. At this interface, the most important process occurring is silica precipitation either as spherical flaky nodules, or in the form of coatings on the clay surface, as chalcedony and amorphous silica. In parallel, numerical modelling was used to investigate the interactions between silica and clay material in a simplified experiment using diffusion cells. A fit between calculation results and silica migration measurements in diffusion cells was performed, including sensitivity tests with regard to the diffusion coefficients and the precipitation rate of amorphous silica. A satisfactory agreement is reached with the experimental results, using a set of reasonable fitting parameters for the FoCa7 clay material. Surface area values for silica precipitation are found to be very high, i.e. 2% of the total surface area of the clayey material indicating that silica precipitation occurs on surfaces other than those of pure silica minerals. (authors)

[en] The removal of long-lived radionuclides, which belong to the so-called minor actinides elements, neptunium, americium and curium, from the high level nuclear wastes separated during the reprocessing of the irradiated nuclear fuels in order to transmute them into short-lived nuclides, can substantially decrease the potential hazards associated with the management of these nuclear wastes. In order to separate minor actinides from high-level liquid wastes (HLLW), a liquid-liquid extraction process was considered, based on the use of diamide molecules, which display the property of being totally burnable, thus they do not generate secondary solid wastes. The main extracting properties of dimethyldibutyltetradecylmalonamide (DMDBTDMA), the diamide selected for the development of the DIAMEX process, are briefly described in this paper. Hot tests of the DIAMEX process (using DMDBTDMA) related to the treatment of an mixed oxide fuels (MOX) type HLLW, were successfully performed. The minor actinide decontamination factors of the HLLW obtained were encouraging. The main results of these tests are presented and discussed in this paper. (authors). 9 refs., 2 figs., 7 tabs

[en] The presence of iodine in UO₂ has a great impact on nuclear fuel behaviour, both during-in reactor operation or under long-term repository conditions. Here the volume diffusion coefficient of iodine is studied using a methodology which involves ion implantation, annealing under different oxygen potentials and SIMS (Secondary Ion Mass Spectroscopy) for the concentration profile characterization of samples. The changes in the initial concentration profile induced by annealing are interpreted using Fick's second law to determine the diffusion coefficient. The first part of this paper is devoted to the description of the applied methodology. The iodine diffusion coefficients in the bulk are shown to depend upon the annealing temperature and oxygen potential. In smaller grained polycrystalline samples, the SIMS signal is averaged out over several grains and therefore, the analysis of the depth profile changes in samples due to annealing may be efficiently compared to depth profiles in as-implanted samples. By contrast, in Cr-doped UO₂ samples in which the grain size is larger than the zone analysed by SIMS, a particular methodology has to be developed. To this end, large grained material was examined using EBSD (Electron Back Scattering Diffraction) in order to determine the relative crystalline orientations of the grains. Following iodine implantations, various grains with different orientations were studied using SIMS. An attempt is presented at correlating the different sputtering rates with the various grain orientations. (authors)

[en] The long term behaviour of materials such as glass, steel and clay has been investigated in the context of deep geological disposal of radioactive wastes. The interactions between vitrified wastes, canister corrosion products (CPs) and clay are studied using a modified version of the reaction-transport code Crunch, especially looking at pH changes and possible cementation at the interface with the clayey materials. These perturbations may indeed affect the lifetime of glass matrix in deep repositories, e.g., high pH enhances the rate of glass alteration. This work focuses on the argillite of Bure. The calculations were performed at 323 K with a glass alteration rate switching from a high initial rate to a residual rate according to the sorption capacity of CPs. The time at which this sorption capacity is saturated is crucial to the system in terms of wastes package lifetime. The results show that the glass alteration imposes a high pH value at the interface with CPs and clay: up to a value of 9.2, compared to 7.3 which is the initial pH value in the argillite. Experimental data show that the rate of glass alteration is much higher in such pH conditions. For a R7T7-type glass, the rate is about five times higher at pH 9 than at pH 7. This pH perturbation migrates through the clayey domain as a result of the migration of mobile elements such as boron and sodium, and despite the existence of strong pH buffers in the argillite. The cementation of porosity at the interface between glass and clay is predicted by the model due to the massive precipitation of iron corrosion products and glass alteration products. At this point of the evolution of the system, the pH starts to decrease and the alteration rate of the glass could be significantly reduced. This porosity clogging effect is difficult to confirm by experiments especially since existing data on short term experiments tend to show a pervasive precipitation of silica in the domain instead of a localized precipitation at the interface