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Source efficiency and high-energy neutronics in accelerator-driven systems
KTH, School of Engineering Sciences (SCI), Physics.
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: urn:nbn:se:kth:diva-427ISBN: 91-7178-147-1 (print)OAI: oai:DiVA.org:kth-427DiVA: diva2:11549
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
List of papers
1. Investigation of neutron source effects in subcritical media and application to a model of the MUSE-4 experiments
Open this publication in new window or tab >>Investigation of neutron source effects in subcritical media and application to a model of the MUSE-4 experiments
2001 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Monte Carlo simulations have been performed to investigate the neutron sourceeffects in a sub-critical media successively coupled to a (d,d)-source, a (d,t)-source and aspallation source. The investigations have focused on the neutron energy spectra in thefuel and on the source relative efficiency j*. The calculations have been performed forthree sub-critical configurations, representative of the coming MUSE-4 experiments.The Monte Carlo codes MCNP and MCNPX have been used to compute j*. j*has been found to be low for the (d,d)-source (~1.35 compared to 1.0 for an averagefission neutron), while considerably higher for the (d,t)-source (~2.15) and the spallationsource (~2.35). The high value of j* for the spallation source has been shown to be dueto the fraction of high-energy neutrons (17 % of total source with En > 20 MeV) bornfrom spallation, which contribute for 50 % to the total number of fission neutronsproduced in the core. The variations of j* with neutron importance have also beenstudied for some spherical configurations with a (d,d)- and a (d,t)-source. For the class ofvariations considered here, j* was found to remain constant or increase only slightly inthe interval 0.70 < keff < 0.996.

Keyword
MUSE-4, Neutron Source, Spallation, MCNP, MCNPX
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6745 (URN)
Conference
InternationalMeeting on Mathematical Methods for Nuclear Applications, Mathematicsand Computation, September 9-13, 2001, Salt Lake City, Utah, USA
Note
QC 20101005Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2010-10-05Bibliographically approved
2. Definition and application of proton source efficiency in accelerator driven systems
Open this publication in new window or tab >>Definition and application of proton source efficiency in accelerator driven systems
2003 (English)In: Nuclear science and engineering, ISSN 0029-5639, Vol. 145, no 3, 390-399 p.Article in journal (Refereed) Published
Abstract [en]

In order to study the beam power amplification of an accelerator-driven system (ADS), a new parameter, the proton source efficiency psi* is introduced. psi* represents the average importance of the external proton source, relative to the average importance of the eigenmode production, and is closely related to the neutron source efficiency rho*, which is frequently used in the ADS field. rho* is commonly used in the physics of subcritical systems driven by any external source (spallation source, (d,d), (d, t), Cf-252 spontaneous fissions, etc.). On the contrary, psi* has been defined in this paper exclusively for ADS studies where the system is driven by a spallation source. The main advantage with using psi* instead of rho* for ADS is that the way of defining the external source is unique and that it is proportional to the core power divided by the proton beam power, independent of the neutron source distribution.

Numerical simulations have been performed with the Monte Carlo code MCNPX in order to study psi* as a function of different design parameters. It was found that, in order to maximize psi* and therefore minimize the proton current needs, a target radius as small as possible should be chosen. For target radii smaller than similar to30 cm, lead-bismuth is a better choice of coolant material than sodium, regarding the proton source efficiency, while for larger target radii the two materials are equally good. The optimal axial proton beam impact was found to be located similar to 20 cm above the core center. Varying the proton energy, psi*/E-p was found to have a maximum for proton energies between 1200 and 1400 MeV Increasing the americium content in the fuel decreases psi* considerably, in particular when the target radius is large.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6746 (URN)000186289600008 ()
Note
QC 20101005Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2012-01-31Bibliographically approved
3. Radiation shielding of high-energy neutrons in SAD
Open this publication in new window or tab >>Radiation shielding of high-energy neutrons in SAD
Show others...
2005 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 550, 313-328 p.Article in journal (Refereed) Published
Abstract [en]

The radiation fields and the effective dose at the Sub-critical Assembly in Dubna (SAD) have been studied with the Monte Carlo code MCNPX. The effective dose above the shielding, i.e. in the direction of the incident proton beam of 3.0 mu A, was found to be about 190 mu Sv h(-1). This value meets the dose limits according to Russian radiation protection regulations, provided that access to the rooms in this area is not allowed for working personnel during operation.By separating the radiation fields into a spallation- and a fission-induced part, it was shown that the neutrons with energy higher than 10MeV, originating exclusively from the proton-induced spallation reactions in the target, contribute for the entire part of the radiation fields and the effective dose at the top of the shielding. Consequently, the effective dose above the SAD reactor system is merely dependent on the proton beam properties and not on the reactivity of the core.

Keyword
SAD, effective dose, MCNPX, high-energy neutrons, sub-critical, ADS
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6747 (URN)10.1016/j.nima.2005.04.071 (DOI)000231964500030 ()2-s2.0-24344500868 (Scopus ID)
Note
QC 20101005Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2010-10-05Bibliographically approved
4. Proton source efficiency for heterogeneous distribution of actinides in the core of an accelerator-driven system
Open this publication in new window or tab >>Proton source efficiency for heterogeneous distribution of actinides in the core of an accelerator-driven system
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.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6748 (URN)000240969800005 ()2-s2.0-33750088997 (Scopus ID)
Note

Uppdaterad från submitted till published: 20101005. QC 20101005

Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2016-05-25Bibliographically approved
5. Analysis of reactivity determination methods in the subcritical experiment Yalina
Open this publication in new window or tab >>Analysis of reactivity determination methods in the subcritical experiment Yalina
Show others...
2005 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 554, no 1-3, 374-383 p.Article in journal (Refereed) Published
Abstract [en]

Different reactivity determination methods have been investigated, based on experiments performed at the subcritical assembly Yalina in Minsk, Belarus. The development of techniques for on-line monitoring of the reactivity level in a future accelerator-driven system (ADS) is of major importance for safe operation. Since an ADS is operating in a subcritical mode, the safety margin to criticality must be sufficiently large. The investigated methods are the Slope Fit Method, the Sjostrand Method and the Source Jerk Method. The results are compared with Monte Carlo simulations performed with different nuclear data libraries. The results of the Slope Fit Method are in good agreement with the Monte Carlo simulation results, whereas the Sjostrand Method appears to underestimate the criticality somewhat. The Source Jerk Method is subject to inadequate statistical accuracy.

Keyword
Yalina, reactivity determination, subcritical, MCNP, ADS, ACCELERATOR-DRIVEN SYSTEMS, KINETICS
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-12677 (URN)10.1016/j.nima.2005.07.058 (DOI)000233978500033 ()2-s2.0-27844541305 (Scopus ID)
Note
QC 20100621Available from: 2010-05-05 Created: 2010-05-05 Last updated: 2017-12-12Bibliographically approved
6. Source efficiency as function of fuel and coolant in accelerator-driven systems
Open this publication in new window or tab >>Source efficiency as function of fuel and coolant in accelerator-driven systems
2006 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 33, no 9, 829-832 p.Article in journal (Refereed) Published
Abstract [en]

We have studied the efficiency of spallation neutron sources for different combinations of coolant and fuel in 80 MWth, sub-critical, cores. It has been found that the proton source efficiency, psi*, is reduced by 10% when switching coolant from helium to lead-bismuth eutectic. Substituting MOX fuel with an americium based fuel, results in another 10% reduction of psi*. The relatively high source efficiencies found for prototype accelerator-driven systems, using standard MOX fuel and helium coolant, may thus be difficult to achieve in future systems dedicated to the transmutation of higher actinides. Our results are in agreement with previous investigations of the dependence of the source efficiency on the selection of coolant.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6750 (URN)10.1016/j.anucene.2006.03.007 (DOI)000239532900010 ()2-s2.0-33745584785 (Scopus ID)
Note
Tidigare titel: Source efficiency studies in gas- and leadbismuth- cooled sub-critical accelerator-driven cores. Uppdaterad från submitted till published: 20101005. QC 20101005Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2011-10-03Bibliographically approved

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Citation style
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Output format
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