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On the Performance of Point Kinetics for the Analysis Accelerator-driven Systems
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
Argonne National Laboratory, Nuclear Engineering Division.
Argonne National Laboratory, Nuclear Engineering Division.
2005 (English)In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 149, no 3, 298-311 p.Article 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.

Place, publisher, year, edition, pages
2005. Vol. 149, no 3, 298-311 p.
Keyword [en]
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: urn:nbn:se:kth:diva-4982ISI: 000227311600006Scopus ID: 2-s2.0-14544271669OAI: oai:DiVA.org:kth-4982DiVA: diva2:7338
Note

QC 20101008

Available from: 2005-03-07 Created: 2005-03-07 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Accelerator-driven systems: safety and kinetics
Open this publication in new window or tab >>Accelerator-driven systems: safety and kinetics
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. 73 p.
Series
Trita-FYS, ISSN 0280-316X ; 2005:13
Keyword
Nuclear physics, Kärnfysik
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-146 (URN)91-7283-988-0 (ISBN)
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

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