[en] The geochemical characteristics of the host rocks play a major role with regard to the mobility of radionuclides contained in wastes disposal in geological formations. Redox conditions in particular may control the potential migration of radionuclides within the geosphere. Geological and geochemical investigations were conducted in a quarry in the Tiber Valley, near Orte, with the aim of understanding the geochemical variations as well as their evolutive trend of local clay at the oxido-reduction front. The upper part of the local plio-pleistocenic series is made up of clay banks interbedded with sandy levels. Clay is dominant in the lower part of the series; sand constitutes on the contrary the final cover of the sequence. The different colors shown by the two different lithological components, grey for clay and yellow for sand, probably reflects a different geochemical condition, reduction for the grey, oxidation for the yellow one. Both clay and sand components were presumably originally characterized by reducing conditions; they were therefore grey colored. The preferential permeation of meteoric water within the permeable sands is at the origin of the oxidation of this component, once the whole series had been uplifted in the continental environment yellow color is a record of this event. The original geochemical content of U, Th and V of the clayey levels appear to be unaffected by the strong oxidizing environment of surficial water. This fact testifies the substantial impermeability of clay as well its capacity of maintaining the original reducing characters which should prevent the transuranic radionuclides of waste to be mobilized. Bacteria have been demonstrated to be at a latent state of life within clay. They may contribute in maintaining the original reducing character of clay

[en] Research is carried out on the more representative italian argilaceous basins. The work includes systematic sampling and mineralogic analyses of pliocene clay formations, in the area identified variations of mineralogic and structural characteristics are studied. Results obtained show a regional distribution for mineralogic associations, mineralogic distribution comes from deposition mechanisms and lithologic nature of parent rock producing clay formations. Forecasting of mineralogic composition of deep clay formation from surface observations is possible and more expensive detailed studies can be realized on a reduced number of geologic formations suitable for radioactive waste storage

[en] Permeability is a major problem with regard to the isolation capacity of clay deposits. Faults and fractures are usually considered as potential pathways for migration of radionuclides from deep deposits towards the biosphere. Several investigations have been conducted in Italy to examine the induced permeability of clay caused by tectonic events. Research has been conducted on: civilian tunnels crossing deep clay formations in all parts of Italy; hydrothermal and geothermal belts of central Italy directly or indirectly connected with clay basins; faults and fractures, affecting clay deposits, that are observable in field investigations; and the relation between surface manifestations of tracers of very deep origin, such as helium, and the geometry of the clay deposits. All the research indicates that clay behaves as an almost completely impermeable mass. Penetration of water occurs in particular situations, such as in marginal parts of the series where clay deposits grow thinner and where tectonic disturbances are frequently more important. Permeability caused by the opening of latent fractures in surficial conditions has proved to extend only to a depth of the order of 10 m. (author)

[en] Clay basins of EC territory fall into two main types: 1) basins developed in northern Europe around peneplanated rather stable basement (Mol, Harwell) displaying a very extended, regular series of homogeneous sand and clay layers; 2) basins of the mediterranean area (Italy), corresponding to an active orogenic belt, and containing sand-clay series of a thickness and homogeneity variable. Clays generally inherit the geochemical characters of the depositional and early diagenetic phase. They in fact maintain negative values of Eh, which cause trace elements cations, including radionuclides, to be fixed into stable forms. The penetrating oxigenated water may determine the Eh to turn to positive values. As demonstrated from natural evidence in Italy this perturbation may only affect a very thin thickness of clay at the surface and in short superficial fractures. Risk analysis conducted on Boom clay (Belgium) shows that tectonic evolution of the site and development of a new glacial phase may rule the stability of the waste deposit

[en] Excitation functions for the ²⁸Si(p,γ)²⁹P capture reaction have been measured in the proton energy range Esub(p)=1.3-2.3 MeV. The analysis of the data reveals the presence of the direct capture process to the ground state and first excited state of ²⁹P. The strengths of the resonances at Esub(p)=1.65, 2.09 and 2.88 MeV and the spectroscopic factors of the ground state and first excited state in ²⁹P are deduced. (auth.)

[en] The excitation function of the ⁵⁸Fe(p,γ) ⁵⁹Co reaction was measured in the analogue region Esub(n)=(2150/2270)keV. Gamma-ray spectra were measured at four resonances; excitation energies and branchings of the resonance levels and several bound states were extracted. A decay scheme involving 36 excited states is proposed for ⁵⁹Co. A Q value of (7363.2R+-+-R1.4)kev was obtained for the reaction ⁵⁸Fe(p,γ) ⁵⁹Co. Total and partial radiation widths and inelastic widths were measured for eight components of the fragmented analogue of the ⁵⁹Fe ground state. The strength of the analogue to antianalogue transition was found to be 0.07 W.n. Correlations between different channels were investigated

[en] It is well known that nuclear viscosity plays a fundamental role in the fission process. Although much experimental and theoretical work has been devoted to this subject, many questions still remain open. They mainly refer to a precise determination of the fission time scale as well as to the nature of the dissipation. At issue is whether nuclear dissipation proceeds primarily by means of individual two-body collisions (two-body friction), as in the case of ordinary fluid, or by means of nucleons colliding with a moving potential wall (one-body friction). The modified statistical model as well as dynamical models based on the Lagrange, Fokker Planck and Langevin equations have been used in order to gain insight on these aspects of fission dynamics. The lack of constraints to the models appears to be, in several cases, the main source of controversies. In this framework, we are carrying on a research program with 8πLP apparatus at LNL, aimed at studying the fission dynamics in systems of intermediate fissility. These systems, compared to the heavier ones, have larger prescission charged particle multiplicities as well as comparable fission and evaporation residue (ER) cross sections. Therefore, the measurements of the relevant quantities in both channels allow to put severe constraints on the models, providing more reliable estimates of fission delay and of viscosity parameter. We report on the system ³²S + ¹⁰⁰Mo at E_lab=200 MeV which produces the composite system ¹³²Ce at E_x=122 MeV. The analysis of the pre-scission charged particles was already described in a previous report. We have proceeded in the analysis of this system extracting the charged particle multiplicities in the ER channel as well as the ER and fission cross sections. The whole set of extracted quantities has been compared with the predictions of a dynamical model based on the Langevin equation

[en] A borehole has been drilled in the clay formation underlying the Trisaia Nuclear Research Center (CNEN) in Southern Italy. The local stratigraphic series includes 850 m of marly clay of Pliocene-Calabrian age. The drilling operation has been interrupted at about -400 m, due to the occurrence of methane gas. The presence of gas, the reducing conditions of the clay and the lack of water in fracture zones testify the extremely low permeability of this clay formation. Reducing conditions may prevent the migration of many radionuclides. The occurrence of some sandy levels and lenses is due to the coastal character of the paleosedimentary environment. Previsions on the homogeneity of clay bodies may be indirectly inferred by examination of feeder paleobasins

No abstract available

[en] This work concerns the results of the studies conducted at many sites in Italy aimed at collecting information on natural evidences of the isolation capacity of clay. Field observations allow to get the opportunity to know directly or infer the evolutive geological processes which are of concern for the waste disposal problems. As a major advantage such observations concern natural phenomena acting at the same, or at a greater, time-space scale involved in the geological disposal of wastes. The explored situations regard the secondary permeability of clay, detected by means of natural tracers (Hg, He, hydrothermal and geothermal fluids, ....) at the ground surface or directly studied in deep civilian tunnels. Another treated topic is the meaning of the oxido-reduction front as a control factor of the physico-chemical environment of clay as well as of the radionuclides migration. The mechanical and thermal effects which accompany the intrusion of a subvolcanic body within clay represent an extreme worst case for a comparison of the effects on clay due to heat developed by radionuclide decay. Finally the case of a fossil forest maintained almost inaltered by the clay cover for over 1,500,000 years is described. All the results of the geological researches point univocally to an almost total and long lasting isolation capacity of clay formations