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Advanced fuels for thermal spectrum reactors
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The advanced fuels investigated in this thesis comprise fuels non− conventional in their design/form (TRISO), their composition (high content of plutonium and minor actinides) or their use in a reactor type, in which they have not been used before (e.g. nitride fuel in BWR). These fuels come with a promise of improved characteristics such as safe, high temperature operation, spent fuel transmutation or fuel cycle extension, for which reasons their potentialis worth assessment and investigation. Their possible use also brings about various challenges, out of which some were addressed in this thesis. TRISO particle fuels with their superior retention abilities enable safe, high−temperature operation. Their combination with molten salt in the Advanced High Temperature Reactor (AHTR) concept moreover promises high operating temperature at low pressure, but it requires a careful selection of the cooling salt and the TRISO dimensions to achieve adequate safety characteristic, incl. a negative feedback to voiding. We show that an AHTR cooled with FLiBe may safely operate with both Pu oxide and enriched U oxide fuels. Pu and Minor Actinides (MA) bearing fuels may be used in BWR for transmutation through multirecycling; however, the allowable amounts of Pu and MA are limited due to the degraded feedback to voiding or low reactivity.We showed that the main positive contribution to the void effect in the fuelswith Pu and MA content of around 11 to 15% consist of the decreased thermalcapture probability in Pu-240, Pu-239 and Am-241 and increased fast and resonance fission probability of U-238, Pu239 and Pu-240. The total void worthmoreover increases during multirecycling, limiting the allowable amount ofMA to 2.45% in uranium−based fuels. An alternative, thorium−based fuel allows for 3.45% MA without entering the positive voiding regime at any point of the multirecycling. The increased alpha−heating associated with the use of transmutation fuels, is at level 24−31 W/kgFUEL in the uranium based fuels and 32−37 W/kgFUEL in the thorium−based configurations. The maximum value of the neutron emission, reached in the last cycle, is 1.7·106 n/s/g and 2·106 n/s/g for uranium and for thorium−based fuels, respectively. Replacing the standard UO2 fuel with higher−uranium density UN orUNZrO2 fuels in BWR shows potential for an increase of the in-core fuelresidence time by about 1.4 year. This implies 1.4% higher availability of the plant. With the nitride fuels, the total void worth increases and the efficiency of the control rods and burnable poison deteriorates, but no major neutronics issue has been identified. The use of nitride fuels in the BWR environment is conditioned by their stability in hot steam. Possible methods for stabilizing nitride fuels in water and steam at 300◦ C were suggested in a recent patentapplication.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xii, 55, p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:73
Keyword [en]
BWR, transmutation, thorium, Pu, MA, Am, Cm, AHTR, thermal, reactor, neutron
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-103085OAI: oai:DiVA.org:kth-103085DiVA: diva2:558528
Public defence
2012-10-12, FA32, AlbaNova University Center, Roslagstullsbacke 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121004

Available from: 2012-10-04 Created: 2012-10-03 Last updated: 2012-10-04Bibliographically approved
List of papers
1. Analysis of the reactivity coefficients of the advanced high-temperature reactor for plutonium and uranium fuels
Open this publication in new window or tab >>Analysis of the reactivity coefficients of the advanced high-temperature reactor for plutonium and uranium fuels
2008 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 35, no 5, 904-916 p.Article in journal (Refereed) Published
Abstract [en]

The conceptual design of the advanced high-temperature reactor (AHTR) has recently been proposed by the Oak Ridge National Laboratory, with the intention to provide and alternative energy source for very high temperature applications. In the present study, we focused on the analyses of the reactivity coefficients of the AHTR core fueled with two types of fuel: enriched uranium and plutonium from the reprocessing of light water reactors irradiated fuel. More precisely, we investigated the influence of the outer graphite reflectors on the multiplication factor of the core, the fuel and moderator temperature reactivity coefficients and the void reactivity coefficient for five different molten salts: NaF, BeF2, LiF, ZrF4 and Li2BeF4 eutectic. In order to better illustrate the behavior of the previous parameters for different core configurations, we evaluated the moderating ratio of the molten salts and the absorption rate of the key fuel nuclides, which, of course, are driven by the neutron spectrum. The results show that the fuel and moderator temperature reactivity coefficients are always negative, whereas the void reactivity coefficient can be set negative provided that the fuel to moderator ratio is optimized (the core is undermoderated) and the moderating ratio of the coolant is large.

Keyword
Light water reactors, Moderators, Nuclear fuel accounting, Nuclear fuel reprocessing, Plutonium compounds, Reactivity (nuclear), Uranium compounds, Advanced high temperature reactors, Graphite reflectors, Reactivity coefficients, Uranium fuels
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-34302 (URN)10.1016/j.anucene.2007.09.003 (DOI)000255791500015 ()2-s2.0-41749111385 (Scopus ID)
Note
QC 20110601Available from: 2011-06-01 Created: 2011-06-01 Last updated: 2017-12-11Bibliographically approved
2. Void reactivity feedback in BWRs with MA bearing MOX fuels
Open this publication in new window or tab >>Void reactivity feedback in BWRs with MA bearing MOX fuels
2011 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 38, no 9, 1968-1977 p.Article in journal (Refereed) Published
Abstract [en]

In this study, we analyzed a response of a boiling water reactor (BWR) core with homogeneous U-Pu-MA fuel to a change of an in-core void percentage. We employed a 3D, full core BWR model for the stochastic code MCNPX together with the continuous energy cross-section library ENDF B-VII.0. The results show that the main positive contribution to the void effect in the fuels with Pu-MA content around 11-15% consist of the decreased thermal capture in Pu-240, Pu-239 and Am-241 and increased fast and resonance fission of U-238, Pu-239 and Pu-240. We also present a core configuration with as much as 3.45% MA of heavy metal content that still provides a negative total void worth and also a global negative void coefficient in the vicinity the operational void profile. The corresponding Pu/MA fraction indicates that a BWR may be used for MA burning without entering into a positive void feedback regime. Eventually, we show why a 3D model is necessary for a correct assessment of the void behavior.

Keyword
Void reactivity coefficient, Total void worth, Boiling water reactor, BWR, Minor actinides recycling, Transmutation
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-37538 (URN)10.1016/j.anucene.2011.04.023 (DOI)000293307200019 ()2-s2.0-79960271332 (Scopus ID)
Note
QC 20110816Available from: 2011-08-16 Created: 2011-08-15 Last updated: 2017-12-08Bibliographically approved
3. Fuel residence time in BWRs with nitride fuels
Open this publication in new window or tab >>Fuel residence time in BWRs with nitride fuels
2012 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 47, 182-191 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a neutronics study of a BWR core with uranium nitride fuels. Replacing the standard UO2 fuel with UN or UN-ZrO2 allows for a higher uranium content, which leads to an increase of the in-core fuel residence time. With the nitride fuels, the total void worth increases and the efficiency of the control rods and burnable poison deteriorates. Taking into account the higher amount of burnable poison needed at the beginning of life, the in-core fuel residence time increases by about 1.4 year comparing to UO2 fuel with the same enrichment. This implies 1.4% higher availability of the plant and it is therefore of economic interest to the nuclear power plant operators. A similar increase of the fuel in-core lifetime in a UO2 core could be reached by an increase of the average enrichment of the oxide fuel by roughly 1%.

Keyword
BWR, Uranium nitride, Enrichment, Fuel cycle, Neutronics
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-100775 (URN)10.1016/j.anucene.2012.03.033 (DOI)000306448800026 ()2-s2.0-84861828049 (Scopus ID)
Note
QC 20120817Available from: 2012-08-17 Created: 2012-08-17 Last updated: 2017-12-07Bibliographically approved
4. Multirecycling of Pu, Am and Cm in BWR
Open this publication in new window or tab >>Multirecycling of Pu, Am and Cm in BWR
2013 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 58, 255-267 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated neutronics aspects of multirecycling of Pu, Am and Cm in BWRs, employing three uranium and three thorium-supported transmutation fuels. Our results show, that thorium-based cores allow for higher shares of MA in the fuel and thereby higher MA incineration without encountering a positive total void worth at any point of the multirecycling. In the uranium-based configuration the total void worth sets the limit on the MA share around 2.45%. The thorium-based fuels also exhibit a stronger Doppler feedback and somewhat degraded reactivity as compared to uranium-fuels. The alpha-heating in the fuel reaches equilibrium after six cycles, maintaining values of 24-31 W/kg(FUEL) in the uranium-based configurations and 32-37 W/kg(FUEL) in the thorium-based configurations. The neutron emission keeps rising through the multirecycling, the maximum value reached in the XV cycle ranges from 1.4 x 10(6) to 1.7 x 10(6) n/s/g for uranium fuels and 2 x 10(6) n/s/g for the thorium-based fuels.

Place, publisher, year, edition, pages
Pergamon Press, 2013
Keyword
Transmutation, Am, Cm, TRU, BWR
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-103091 (URN)10.1016/j.anucene.2013.03.024 (DOI)000320481600033 ()2-s2.0-84876270150 (Scopus ID)
Note

QC 20130729. Updated from submitted to published.

Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved

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