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Proton source efficiency for heterogeneous distribution of actinides in the core of an accelerator-driven system
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.ORCID iD: 0000-0002-6082-8913
2006 (English)In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 154, no 2, 202-214 p.Article in journal (Refereed) Published
Abstract [en]

The distribution of actinides in the core of an accelerator-driven system loaded with plutonium, americium, and curium has been studied in order to optimize the proton source efficiency psi*. The optimization of psi* was performed by keeping some important characteristics of the system, e.g., the radial power profile and the reactivity of the core, constant. One of the basic assumptions of the study, that the magnitude of psi* is sensitive primarily to the composition of actinides in the inner part of the core, whereas only marginally to that in the outer part, has been confirmed. It has been shown that the odd-N nuclides (those nuclides with an even number of neutrons) in general and Am-241 and Cm-244 in particular have favorable properties with respect to improving psi* if they are placed in the innermost part of the core. The underlying reason for this phenomenon is that the energy spectrum of the source neutrons in the inner part of the core is harder than that of the average fission neutrons. Moreover, it has been shown that loading the inner part of the core with only curium increases psi* by similar to 7%. Plutonium, on the other hand, in particular high-quality plutonium consisting mainly of Pu-239 and Pu-241, was found to be a comparatively source inefficient element and is preferably located in the outer part of the core. The differences in psi* are due to combined effects from relative changes in the average fission and capture cross sections and in the average fission neutron yield.

Place, publisher, year, edition, pages
2006. Vol. 154, no 2, 202-214 p.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6748ISI: 000240969800005Scopus ID: 2-s2.0-33750088997OAI: oai:DiVA.org:kth-6748DiVA: diva2:11546
Note

Uppdaterad från submitted till published: 20101005. QC 20101005

Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Source efficiency and high-energy neutronics in accelerator-driven systems
Open this publication in new window or tab >>Source efficiency and high-energy neutronics in accelerator-driven systems
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Transmutation of plutonium and minor actinides in accelerator-driven systems (ADS) is being envisaged for the purpose of reducing the long-term radiotoxic inventory of spent nuclear reactor fuel. For this reason, the physics of sub-critical systems are being studied in several different experimental programs across the world. Three of these experiments have been studied within the scope of the present thesis; the MUSE experiments in France, the Yalina experiments in Belarus and the SAD experiments in Russia. The investigations of the MUSE experiments have focused on three different neutronic parameters; the neutron energy spectrum, the external neutron source efficiency and the dynamic neutron source response. It has been shown that the choice of external neutron source has negligible effect on the neutron energy spectrum in the core. Therefore, from this point of view, the MUSE experiments can be considered representative of an ADS. From the analyses of different reactivity determination methods in the Yalina experiments, it can be concluded that the slope fit method gives results in good agreement with the results obtained by the Monte Carlo method MCNP. Moreover, it was found that the Sjöstrand method underestimates keff slightly, in comparison with MCNP and the other investigated methods. In the radiation shielding studies of the SAD experiments, it was shown that the entire part of the effective dose detected at the top of the biological shielding originates from the proton-induced spallation reactions in the target. Thus, it can be concluded that the effective dose is directly proportional to the proton beam power, but independent of the reactivity of the sub-critical core. In order to study the energy gain of an ADS, i.e., the core power divided by the proton beam power, the proton source efficiency, ψ*, has been studied for various ADS models. ψ* is defined in analogy with the neutron source efficiency, φ*, but relates the core power directly to the source protons instead of to the source neutrons. φ* is commonly used in the physics of sub-critical systems, driven by any external neutron source (spallation source, (D,D), (D,T), 252Cf spontaneous fission etc.). On the contrary, ψ* has been defined only for ADS studies, where the system is driven by a proton-induced spallation source. The main advantages of using ψ* instead of φ* are that the way of defining the external source is unique and that ψ* is proportional to the energy gain. An important part of this thesis has been devoted to studies of ψ* as a function of different system parameters, thereby providing a basis for an ADS design with optimal properties for obtaining a high core power over beam power ratio. For instance, ψ* was found to decrease considerably with increasing spallation target radius.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. xiv, 136 p.
Series
Trita-FYS, ISSN 0280-316X ; 2005:46
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-427 (URN)91-7178-147-1 (ISBN)
Public defence
2005-09-30, Sal FA32, AlvaNova, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20101005Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2010-10-05Bibliographically approved

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