32 research outputs found
Properties of low-lying states in some high-nuclearity Mn, Fe and V clusters: Exact studies of Heisenberg models
Using an efficient numerical scheme that exploits spatial symmetries and spin
parity, we have obtained the exact low-lying eigenstates of exchange
Hamiltonians for the high nuclearity spin clusters, Mn_{12}, Fe_8 and V_{15}.
The largest calculation involves the Mn_{12} cluster which spans a Fock space
of a hundred million. Our results show that the earlier estimates of the
exchange constants need to be revised for the Mn_{12} cluster to explain the
level ordering of low-lying eigenstates. In the case of the Fe_8 cluster,
correct level ordering can be obtained which is consistent with the exchange
constants for the already known clusters with butterfly structure. In the
V_{15} cluster, we obtain an effective Hamiltonian that reproduces exactly, the
eight low-lying eigenvalues of the full Hamiltonian.Comment: Revtex, 12 pages, 16 eps figures; this is the final published versio
Statistical Claim Checking: StatCheck in Action (demonstration)
International audienc
Main outcomes of the Phebus FPT1 uncertainty and sensitivity analysis in the EU-MUSA project
The Management and Uncertainties of Severe Accidents (MUSA) project was funded in HORIZON 2020 and is
coordinated by CIEMAT (Spain). The project aims at consolidating a harmonized approach for the analysis of
uncertainties and sensitivities associated with Severe Accidents (SAs) analysis, focusing on source term figures of
merit. The Application of Uncertainty Quantification (UQ) Methods against Integral Experiments (AUQMIE –
Work Package 4 (WP4)), led by ENEA (Italy), was devoted to apply and test UQ methodologies adopting the
internationally recognized PHEBUS FPT1 test. FPT1 was chosen to test UQ methodologies because, even though
it is a simplified SA scenario, it was representative of the in-vessel phase of a severe accident initiated by a break
in the cold leg of a PWR primary circuit.
WP4 served as a platform to identify and discuss the issues encountered in the application of UQ methodol ogies to SA analyses (e.g. discuss the UQ methodology, perform the coupling between the SA codes and the UQ
tools, define the results post-processing methods, etc.). The purpose of this paper is to describe the MUSA
PHEBUS FPT1 uncertainty application exercise with the related specifications and the methodologies used by the
partners to perform the UQ exercise. The main outcomes and lessons learned of the analysis are: scripting was in
general needed for the SA code and uncertainty tool coupling and to have more flexibility; particular attention should be devoted to the proper choice of the input uncertain parameters; outlier values of figures of merit
should be carefully analyzed; the computational time is a key element to perform UQ in SA; the large number of
uncertain input parameters may complicate the interpretation of correlation or sensitivity analysis; there is the
need for a statistically solid handling of failed calculations
First outcomes from the PHEBUS FPT1 uncertainty application done in the EU MUSA project
The Management and Uncertainties of Severe Accidents (MUSA) project, founded in HORIZON 2020 and coordinated by CIEMAT (Spain), aims to consolidate a harmonized approach for the analysis of uncertainties and sensitivities associated with Severe Accidents (SAs) by focusing on Source Term (ST) Figure of Merits (FOM). In this framework, among the 7 MUSA WPs the Application of Uncertainty Quantification (UQ) Methods against Integral Experiments (AUQMIE – Work Package 4 (WP4)), led by ENEA (Italy), looked at applying and testing UQ methodologies, against the internationally recognized PHEBUS FPT1 test. Considering that FPT1 is a simplified but representative SA scenario, the main target of the WP4 is to train project partners to perform UQ for SA analyses. WP4 is also a collaborative platform for highlighting and discussing results and issues arising from the application of UQ methodologies, already used for design basis accidents, and in MUSA for SA analyses. As a consequence, WP4 application creates the technical background useful for the full plant and spent fuel pool applications planned along the MUSA project, and it also gives a first contribution for MUSA best practices and lessons learned. 16 partners from different world regions are involved in the WP4 activities. The purpose of this paper is to describe the MUSA PHEBUS FPT1 uncertainty application exercise, the methodologies used by the partners to perform the UQ exercise, and the first insights coming out from the calculation phase
Toward UO2 micro/macro machining: a laser processing approach
Conference: Animma 2021, Prague (CZ); June 21-25International audienceLinked to experimental data acquisition and to development of improved models, a better detailed description of the behaviour of the nuclear ceramics as regard to the fission gases release during thermal transient representative of nuclear accidents such as RIA (Reactivity Initiated Accident) and or LOCA (LOss of Coolant Accident) requires access to local information within the fuel pellet, and no longer averaged over the whole of the pellet. One of the major challenge in this context is the sample size, which depends on the main objective of the study, typically from the order of a few hundred microns to millimeters. Few techniques allow this dynamic while being compatible with irradiated fuel constraints. Laser micromachining is a high precision non-contact material removal process that would be adapted to this dynamic. We present experimental and numerical studies, carried out in order to evaluate the possibility to apply this process for the preparation of irradiated UO samples of various dimensions. First, preliminary experimental and numerical works conduced on graphite, as model material, which have comparable properties (in particular their behaviours under laser irradiation and their melting point) in order to validate the feasibility, will be detailed. Afterwards, based on these results, we present our first results on UO . The objective is to transfer the technique to non-irradiated UO and then to the irradiated material
High power CW laser heating of graphite at high temperature and applications in material studies and laser processing’
International audienc
Investigation of nuclear fuels behaviour under thermal stresses: new insights gained thanks to laser-based experiments
International audienc