| 1. |
- Juslin, N., et al.
(författare)
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Simulation of threshold displacement energies in FeCr
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 255:1, s. 75-77
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the role of chromium on threshold displacement energies in FeCr for the fusion reactor steel relevant concentration 10% Cr. We have used molecular dynamics simulations in order to determine whether the observed Cr-content dependence of macroscopic properties can be due to the defect production. We compare FeCr-alloys with pure iron and chromium, employing two different potential sets for the Fe-Cr system. We find that there are no significant differences between pure iron and FeCr with 10% Cr for the 100, 110 and 111 directions and the average threshold energy.
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| 2. |
- Sandberg, Nils, et al.
(författare)
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Carbon impurity dissolution and migration in bcc Fe-Cr : First-principles calculations
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:9
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Tidskriftsartikel (refereegranskat)abstract
- First-principles density-functional theory calculations for C solution enthalpies, H-sol, and diffusion activation enthalpies, H-diff, in body-centered-cubic Fe and Cr are presented. The results for C in Fe compare well with experiments, provided that the effect of magnetic disordering is accounted for. Likewise, in Cr, the calculated Hsol and Hdiff agree well with available experiments. In both materials, the deviation between calculated enthalpies and critically assessed experimental enthalpies are less than 0.05 eV. Further, first-principles calculations for the interaction energies between a solute (e.g., a Cr atom in bcc Fe) and an interstitial C atom are presented. The results are in conflict with those inferred from internal friction (IF) experiments in disordered Fe-Cr-C alloys. A simple model of C relaxation in disordered Fe-Cr is used to compare theoretical and experimental IF curves directly. The results suggest that a more extensive study of the energetic, thermodynamic, and kinetic aspects of C migration in Fe-Cr is needed.
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| 3. |
- Wallenius, Janne, 1968-, et al.
(författare)
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Muonic atom deexcitation via formation of metastable molecular states in light of experimental verification
- 2001
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Ingår i: Hyperfine Interactions. - 0304-3843 .- 1572-9540. ; 138:04-jan, s. 285-288
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Tidskriftsartikel (refereegranskat)abstract
- In a recent experiment performed at PSI, a peak in the time-of-flight distribution of pmu(1s) atoms could be identified with decay of ppmu* molecular ions situated below the 2s threshold, providing 900 eV of kinetic energy to the pmu atom. This finding may be interpreted in terms of the side path model which suggests that metastable muonic molecules may form with high probability in resonant collisions between muonic hydrogen in the 2s state and hydrogen molecules, e.g., pmu(2s)H-2-->[(ppmu*)(vJ)(pq) - pee(])v(K) --> [(ppmu*)(v'J')(p'q') - pe](+) + e(-). The Coulombic decay of the Auger stabilised ppmu* molecular ion then leads to the formation of highly energetic pmu(1s) atoms. In the present paper calculations of resonant formation rates in pure hydrogen are presented and compared to the quenching rate of pmu(2s) atoms measured at low hydrogen density.
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| 4. |
- Ackland, G. J., et al.
(författare)
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Interatomic forces for transition metals including magnetism
- 2010
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Ingår i: 139th Annual Meeting & Exhibition - Supplemental Proceedings, Vol 2. - 9780873397520 ; , s. 85-92
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Konferensbidrag (refereegranskat)abstract
- We present a formalism for extending the second moment tight-binding model[1], incorporating ferro- and anti-ferromagnetic interaction terms which are needed for the FeCr system. For antiferromagnetic and paramagnetic materials, an explicit additional variable representing the spin is required. In a mean-field approximation this spin can be eliminated. and the potential becomes explicitly temperature dependent. For ferromagnetic interactions, this degree of freedom can be eliminated, and the formalism reduces to the embedded atom method (EAM[2]), and we show the equivalence of existing EAM potentials to "magnetic" Potentials.
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| 5. |
- Berglöf, Carl, 1980-
(författare)
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On measurement and monitoring of reactivity in subcritical reactor systems
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Accelerator-driven systems have been proposed for incineration of transuranic elements from spent nuclear fuel. For safe operation of such facilities, a robust method for reactivity monitoring is required. Experience has shown that the performance of reactivity measurement methods in terms of accuracy and applicability is highly system dependent. Further investigations are needed to increase the knowledge data bank before applying the methods to an industrial facility and to achieve license to operate such a facility. In this thesis, two systems have been subject to investigation of various reactivity measurement methods. Conditions for successful utilization of the methods are presented, based on the experimental experience. In contrast to previous studies in this field, the reactivity has not only been determined, but also monitored based on the so called beam trip methodology which is applicable also to non-zero power systems. The results of this work constitute a part of the knowledge base for the definition of a validated online reactivity monitoring methodology for facilities currently being under development in Europe (XT-ADS and EFIT).
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| 6. |
- Bortot, Sara, et al.
(författare)
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BELLA : a multi-point dynamics code for safety-informed design of fast reactors
- 2015
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Ingår i: Annals of Nuclear Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0306-4549 .- 1873-2100. ; 85, s. 228-235
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the multi-point dynamics code BELLA and its benchmarking with respect to SAS4A/SASSYS-1 is described for a small fast reactor cooled with natural convection of lead (ELECTRA). It is shown that BELLA is capable of reproducing the magnitude of mass-flow, reactivity, power and temperature excursions during design extension conditions with an accuracy better than 10%. Hence, the BELLA code can be used for safety-informed design and stability analyses of fast reactor systems, permitting to isolate essential phenomena and trends of significance for their safety assessment. (C) 2015 Elsevier Ltd. All rights reserved.
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| 7. |
- Bortot, Sara, 1983-, et al.
(författare)
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BELLA : a multi-point dynamics code for simulation of fast reactors
-
Ingår i: Annals of Nuclear Energy. - 0306-4549 .- 1873-2100.
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the multi-point dynamics code BELLA and its benchmarking with respect to SAS4A/SASSYS- 1 is described for a small fast reactor cooled with natural convection of lead (ELECTRA). It is shown that BELLA is capable of reproducing the magnitude of mass-flow, reactivity, power and temperature excursions during design extension conditions with an accuracy better than 10%. Hence, the BELLA code can be used for safety-informed design and stability analyses of fast reactor systems, permitting to isolate essential phenomena and trends of significance for their safety assessment.
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| 8. |
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| 9. |
- Bubelis, E., et al.
(författare)
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System codes benchmarking on a low sodium void effect SFR heterogeneous core under ULOF conditions
- 2017
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Ingår i: Nuclear Engineering and Design. - : Elsevier. - 0029-5493 .- 1872-759X. ; 320, s. 325-345
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses system codes benchmarking activities on an ASTRID-like heterogeneous fast core under a representative design basis accident condition: the unprotected loss of flow accident (ULOF). The paper provides evidence that all the system codes used in this exercise are capable to simulate the transient behavior of heterogeneous SFR cores up to the initiation of sodium boiling. As a proof of this, a comparison of steady-state results and dynamic simulation results for a ULOF transient (simulated using system codes in combination with neutron point kinetics) are provided and discussed in this paper. The paper contains a brief description of the system codes (TRACE, CATHARE, SIM-SFR, SAS-SFR, ATHLET, SPECTRA, SAS4A) used by the participants (PSI, CEA, EDF, KIT, GRS, UPVLC, NRG, KTH), assumptions made during the simulations, as well as results obtained.
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| 10. |
- Claisse, Antoine, 1988-
(författare)
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Multiscale modeling of nitride fuels
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitride fuels have always been considered a good candidate for GENIV reactors, as well as space reactors, due to their high fissile density, highthermal conductivity and high melting point. In these concepts, not beingcompatible with water is not a significant problem. However, in recent years,nitride fuels started to raise an interest for application in thermal reactors,as accident tolerant or high performance fuels. However, oxide fuels havebenefited from decades of intensive research, and thousands of reactor-years.As such, a large effort has to be made on qualifying the fuel and developingtools to help assess their performances.In this thesis, the modeling side of this task is chosen. The effort istwo-fold: determining fundamental properties using atomistic models andputting together all the properties to predict the performances under irradi-ation using a fuel performance code. The first part is done combining manyframeworks. The density functional theory is the basis to compute the elec-tronic structure of the materials, to which a Hubbard correction is added tohandle the strong correlation effects. Negative side effects of the Hubbardcorrection are tackled using the so-called occupation matrix control method.This combined framework is first tested, and then used to find electronic andmechanic properties of the bulk material as well as the thermomechanicalbehavior of foreign atoms. Then, another method, the self-consistent meanfield (SCMF) one, is used to reach the dynamics properties of these foreignatoms. In the SCMF theory, the data that were obtained performing the abinitio simulations are treated to provide diffusion and kinetic flux couplingproperties.In the second step of the work, the fuel performance code TRANSURA-NUS is used to model complete fuel pins. An athermal fission gas releasemodel based on the open porosity is developed and tested on oxide fuels.A model for nitride fuels is introduced, and some correlations are bench-marked. Major issues remaining are pointed out and recommendations asto how to solve them are made.
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