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Accelerator-driven systems: safety and kinetics
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The accelerator-driven system (ADS) is recognized as a promising system for the purpose of nuclear waste transmutation and minimization of spent fuel radiotoxicity. The primary cause for this derives from its accelerator-driven, sub-critical operating state, which introduces beneficial safety-related features allowing for application of cores employing fuel systems containing pure transuranics or minor actinides, thereby offering increased incineration rate of waste products and minimal deployment of advanced (and expensive) partitioning and transmutation technologies. The main theme of the thesis is safety and kinetics performance of accelerator-driven nuclear reactors. The studies are confined to the examination of ADS design proposals employing fast neutron spectrum, uranium-free lattice fuels, and liquid-metal cooling, with emphasis on lead-bismuth coolant. The thesis consists of computational studies under normal operation and hypothetical accidents, and of evaluation and identification of safety design features.

By itself, subcritical operation provides a distinct safety advantage over critical reactor operation, distinguished by high operational stability and additional margins for positive reactivity insertion. For a uranium-free minor actinide based fuel important safety parameters deteriorate. Specific analyses suggest that operation of such cores in a critical state would be very difficult. The studies of unprotected transients indicate that lead-bismuth cooled accelerator-driven reactors can be effective in addressing the low effective delayed neutron fraction and the high coolant void reactivity that comes with the minor actinide fuel, but some supportive prompt negative feedback mechanism might be considered necessary to compensate for a weak Doppler effect in case of a prompt critical transient. Although lead-bismuth features a high boiling point, the work underlines the importance of maintaining a low coolant void reactivity value. The transient design studies identified a molybdenum-based Ceramic-Metal (CerMet) fuel with favourable inherent safety features. A higher lattice pitch is suggested to avoid mechanical failure during unprotected loss-of-flow. Detailed coupled neutron kinetics and thermal hydraulic analyses demonstrated that the point kinetics approximation is capable of providing highly accurate transient calculations of subcritical systems. The results suggest better precision at lower keff levels, which is an effect of the reduced sensitivity to system reactivity perturbations in a subcritical state resulting in small spatial distortions. In the course of a beam reliability study, the accelerator was identified as responsible for frequent beam interruptions. It is clear that extensive improvement in the mean-time between beam failures is required.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , p. 73
Series
Trita-FYS, ISSN 0280-316X ; 2005:13
Keywords [en]
Nuclear physics
Keywords [sv]
Kärnfysik
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-146ISBN: 91-7283-988-0 (print)OAI: oai:DiVA.org:kth-146DiVA, id: diva2:7342
Public defence
2005-03-18, Sal FA32, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101011Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2010-10-11Bibliographically approved
List of papers
1. Inherent Safety of Fuels for Accelerator-driven Systems
Open this publication in new window or tab >>Inherent Safety of Fuels for Accelerator-driven Systems
2005 (English)In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 151, no 3, p. 314-333Article in journal (Refereed) Published
Abstract [en]

Transient safety characteristics of accelerator-driven systems using advanced minor actinide fuels have been investigated. Results for a molybdenum-based Ceramic-Metal (CerMet) fuel, a magnesia-based Ceramic-Ceramic fuel, and a zirconium-nitride-based fuel are reported. The focus is on the inherent safety aspects of core design. Accident analyses are carried out for the response to unprotected loss-of-flow and accelerator beam-overpower transients and coolant voiding scenarios. An attempt is made to establish basic design limits for the fuel and cladding. Maximum temperatures during transients are determined and compared with design limits. Reactivity effects associated with coolant void, fuel and structural expansion, and cladding relocation are investigated. Design studies encompass variations in lattice pitch and pin diameter. Critical mass studies are performed. The studies indicate favorable inherent safety features of the CerMet fuel. Major consideration is given to the potential threat of coolant voiding in accelerator-driven design proposals. Results for a transient test case study of a postulated steam generator tube rupture event leading to extensive coolant voiding are presented. The study underlines the importance of having a low coolant void reactivity value in a lead-bismuth system despite the high boiling temperature of the coolant. It was found that the power rise following a voiding transient increases dramatically near the critical state. The studies suggest that a reactivity margin of a few dollars in the voided state is sufficient to permit significant reactivity insertions.

Keywords
accelerator-driven systems, accidents, minor actinide fuel
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4980 (URN)000231203900010 ()2-s2.0-23844448469 (Scopus ID)
Note
QC 20101008. Uppdaterad från accepted till published (20101008).Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
2. Neutronics of minor-actinide burning accelerator-driven systems with ceramic fuel
Open this publication in new window or tab >>Neutronics of minor-actinide burning accelerator-driven systems with ceramic fuel
2005 (English)In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 152, no 3, p. 367-381Article in journal (Refereed) Published
Abstract [en]

We have investigated neutronic properties of lead-bismuth-cooled accelerator-driven systems with different minor-actinide-based ceramic fuels (two composite oxides and one solid-solution nitride). Adopting a transuranic composition with 40% plutonium in the initial load, transmutation rates of higher actinides (americium and curium) equal to 265 to 285 kg/GW(thermal) -yr are obtained. The smallest reactivity swing is provided by the magnesium oxide-based cercer fuel. The cercer cores, however, exhibit large coolant void worths, which is of concern in the case of gas bubble introduction into the core. Nitride and cermet cores are more stable with respect to void formation. The poorer neutron economy of the molybdenum-based cermet makes it difficult, however, to accommodate an inert matrix volume fraction exceeding 50%, a lower limit for fabricability. Higher plutonium fraction is thus required for the cermet, which would lead to lower actinide burning rates. The nitride core yields high actinide burning rates, low void worths, and acceptable reactivity losses.

Keywords
accelerator-driven system, minor-actinide burner, ceramic fuel
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4981 (URN)000233378500010 ()2-s2.0-28044451522 (Scopus ID)
Note
QC 20101008. Uppdaterad från accepted till published (20101008).Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
3. On the Performance of Point Kinetics for the Analysis Accelerator-driven Systems
Open this publication in new window or tab >>On the Performance of Point Kinetics for the Analysis Accelerator-driven Systems
2005 (English)In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 149, no 3, p. 298-311Article in journal (Refereed) Published
Abstract [en]

The ability of point kinetics to describe dynamic processes in accelerator-driven systems (ADSs) is investigated. Full three-dimensional energy-space-time-dependent calculations, coupled with thermal and hydraulic feedback effects, are performed and used as a standard of comparison. Various transient accident sequences are studied. Calculations are performed in the range of k(eff) = 0.9594 to 0.9987 to provide insight into the dependence of the performance on the subcritical level. Numerical experiments are carried out on a minor-actinide-loaded and lead-bismuth-cooled ADS. It is shown that the point kinetics approximation is capable of providing highly accurate calculations in such systems. The results suggest better precision at lower k(eff) levels. It is found that subcritical operation provides features that are favorable from a point kinetics view of application. For example, reduced sensitivity to system reactivity perturbations effectively mitigates any spatial distortions. If a subcritical reactor is subject to a change in the strength of the external source, or a change in reactivity within the subcritical range, the neutron population will adjust to a new stationary level. Therefore, within the normal range of operation, the power predicted by the point kinetics method and the associated error in comparison with the exact solution tends to approach an essentially bounded value. It was found that the point kinetics model is likely to underestimate the power rise following a positive reactivity insertion in an ADS, which is similar to the behavior in critical systems. However, the effect is characteristically lowered in subcritical versus critical or near-critical reactor operation.

Keywords
Actinides, Approximation theory, Bismuth, Boundary value problems, Error analysis, Hydraulics, Lead, Mathematical models, Nuclear reactors, Perturbation techniques, Reaction kinetics, Thermal effects, Accelerator-driven systems (ADS), Point kinetics, Spatial distortions, Subcritical reactor
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4982 (URN)000227311600006 ()2-s2.0-14544271669 (Scopus ID)
Note

QC 20101008

Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
4. Safety Analysis of Na and Pb-Bi Coolants in Response to Beam Instabilities
Open this publication in new window or tab >>Safety Analysis of Na and Pb-Bi Coolants in Response to Beam Instabilities
Show others...
2003 (English)In: UTILISATION AND RELIABILITY OF HIGH POWER PROTON ACCELERATORS, WORKSHOP PROCEEDINGS, 2003, p. 227-236Conference paper, Published paper (Refereed)
Abstract [en]

A comparative safety study has been performed on sodium vs. lead/bismuth as coolant for accelerator-driven systems. Transient studies are performed for a beam overpower event. We examine a fuel type of recent interest in the research on minor actinide burners, i.e. uranium-free oxide fuel. A strong positive void coefficient is calculated for both sodium and lead/bismuth. This is attributed to the high fraction of americium in the fuel. It is shown that the lead/bismuth-cooled reactor features twice the grace time with respect to fuel or cladding damage compared to the sodium-cooled reactor of comparable core size and power rating. This accounts to the difference in void reactivity contribution and to the low boiling point of sodium. For improved safety features the general objective is to reduce the coolant void reactivity effect. An important safety issue is the high void worth that could possibly drive the system to prompt criticality.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4983 (URN)000184283600019 ()92-64-10211-6 (ISBN)
Conference
3rd Workshop on Utilisation and Reliability of High Power Proton Accelerators
Note
QC 20101011 NR 20140805Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2012-01-31Bibliographically approved
5. Inherent Shutdown Capabilities in Accelerator-driven Systems
Open this publication in new window or tab >>Inherent Shutdown Capabilities in Accelerator-driven Systems
2002 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 29, no 14, p. 1689-1706Article in journal (Refereed) Published
Abstract [en]

The applicability for inherent shutdown mechanisms in accelerator-driven systems (ADS) has been investigated. We study the role of reactivity feedbacks. The benefits, in terms of dynamics performance, for enhancing the Doppler effect are examined. Given the performance characteristics of source-driven systems, it is necessary to manage the neutron source in order to achieve inherent shutdown. The shutdown system must be capable of halting the external source before excessive temperatures are obtained. We evaluate methods, based on the analysis of unprotected accidents, to accomplish such means. Pre-concepted designs for self-actuated shutdown of the external source suggested. We investigate time responses and evaluate methods to improve the performance of the safety system. It is shown that maximum beam output must be limited by fundamental means in order to protect against accident initiators that appear to be achievable in source driven systems. Utilizing an appropriate burnup control strategy plays a key role in that effort.

Keywords
Doppler effect, Natural convection, Neutron sources, Particle accelerators, Security systems, Thermal expansion, Accelerator driven systems (ADS)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4984 (URN)10.1016/S0306-4549(01)00129-3 (DOI)000175981500005 ()
Note
QC 20101011Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
6. Reliability Assessment of the LANSCE Accelerator System
Open this publication in new window or tab >>Reliability Assessment of the LANSCE Accelerator System
1999 (English)In: Proceedings of the Workshop on Utilisation and Reliability of High Power Proton Accelerators: 13-15 October 1998, Mito, Japan, 1999, p. 183-Conference paper, Published paper (Other academic)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4985 (URN)92-64-17068-5 (ISBN)
Note
QC 20101011Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2010-10-11Bibliographically approved

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