Search Results (4)

Following the 1987 referendums, the Italian government stopped its nuclear energy production. Radioactive waste produced by existing nuclear facilities and the very-low- and low-level radioactive waste due to other activities (e.g., healthcare) require the construction of a National Repository. To this end, the National Map of Suitable Areas (CNAI), through which the optimal site to host the National Repository would be identified, was published on 23 December 2023. Over the years, the possible location of the National Repository has been repeatedly contested by the citizens of the territories concerned. However, the need to identify a site and build the National Repository is unavoidable. This study proposes an approach based on multi-criteria analysis. The approach represents an alternative model useful for enriching the public debate with additional information and criteria and is also consistent with the local needs of the communities involved. The proposed approach compares the sites proposed in the CNAI by analyzing their main short- and long-term risks, namely their seismic, transport-related and socio-economic risks. The obtained results show a possible different priority order of the CNAI sites. They highlight the possibility of identifying the optimal site mainly via using site safety criteria assessed throughout the entire service life of the infrastructures to be built and also consider the possible short-term economic advantages deriving from the construction of the National Repository. Full article

In the development of deep geological repositories (DGRs), performance assessment modeling is used to evaluate the integrity and performance of the engineered and geological barriers for thousands or millions of years of evolution of the disposal system. To evaluate the suitability of a site for a DGR, geoscientific data from dedicated site investigation programs are integrated into site-specific assessments. This paper presents the development and implementation of a modeling workflow aimed at comparing three potential siting areas for a DGR in Switzerland from the viewpoint of long-term safety and technical feasibility. The workflow follows the guidelines of the national regulator addressing safety relevant criteria such as the barrier efficiency of the host rock and its mechanical and chemical integrity in response to repository-induced influences and the long-term stability of the repository site over geological scales. In the regulatory requirements, the role of parametric, conceptual, and scenario uncertainty has been identified as an issue of special importance in the site selection process. The assessment approach comprises a portfolio of numerical models for the simulation of solute, gas and heat transport in the repository nearfield. The modeling was performed with deterministic as well as probabilistic variants integrated in an indicator-based approach that allows the consistent comparison of the candidate sites using quantitative dimensionless performance indices. The model-based assessment of the sites allows a traceable, transparent, and verifiable implementation of the site selection process. Full article

Presently, a criticality safety evaluation methodology for the final geological disposal of Swiss spent nuclear fuel is under development at the Paul Scherrer Institute in collaboration with the Swiss National Technical Competence Centre in the field of deep geological disposal of radioactive waste. This method in essence pursues a best estimate plus uncertainty approach and includes burnup credit. Burnup credit is applied by means of a computational scheme called BUCSS-R (Burnup Credit System for the Swiss Reactors–Repository case) which is complemented by the quantification of uncertainties from various sources. BUCSS-R consists in depletion, decay and criticality calculations with CASMO5, SERPENT2 and MCNP6, respectively, determining the keff eigenvalues of the disposal canister loaded with the Swiss spent nuclear fuel assemblies. However, the depletion calculation in the first and the criticality calculation in the third step, in particular, are subject to uncertainties in the nuclear data input. In previous studies, the effects of these nuclear data-related uncertainties on obtained keff values, stemming from each of the two steps, have been quantified independently. Both contributions to the overall uncertainty in the calculated keff values have, therefore, been considered as fully correlated leading to an overly conservative estimation of total uncertainties. This study presents a consistent approach eliminating the need to assume and take into account unrealistically strong correlations in the keff results. The nuclear data uncertainty quantification for both depletion and criticality calculation is now performed at once using one and the same set of perturbation factors for uncertainty propagation through the corresponding calculation steps of the evaluation method. The present results reveal the overestimation of nuclear data-related uncertainties by the previous approach, in particular for spent nuclear fuel with a high burn-up, and underline the importance of consistent nuclear data uncertainty quantification methods. However, only canister loadings with UO₂ fuel assemblies are considered, not offering insights into potentially different trends in nuclear data-related uncertainties for mixed oxide fuel assemblies. Full article

The deep borehole disposal (DBD) concept for certain types of radioactive wastes has been discussed for many decades, but has enjoyed limited R&D interest compared to ‘conventional’ geological disposal in an excavated repository at a few hundreds of metres depth. This article explores the circumstances under which a national waste management programme might wish to consider DBD. Starting with an assumption that further R&D will answer technical issues of DBD feasibility, it examines the types of waste that might be routed to borehole disposal and the strategic drivers that might make DBD attractive. The article concludes by identifying the types of national programme that might wish to pursue DBD further and the pre-requisites for them to give it serious consideration. Full article