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On measurement and monitoring of reactivity in subcritical reactor systems
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Accelerator-driven systems have been proposed for incineration of transuranic elements from spent nuclear fuel. For safe operation of such facilities, a robust method for reactivity monitoring is required. Experience has shown that the performance of reactivity measurement methods in terms of accuracy and applicability is highly system dependent. Further investigations are needed to increase the knowledge data bank before applying the methods to an industrial facility and to achieve license to operate such a facility. In this thesis, two systems have been subject to investigation of various reactivity measurement methods. Conditions for successful utilization of the methods are presented, based on the experimental experience. In contrast to previous studies in this field, the reactivity has not only been determined, but also monitored based on the so called beam trip methodology which is applicable also to non-zero power systems. The results of this work constitute a part of the knowledge base for the definition of a validated online reactivity monitoring methodology for facilities currently being under development in Europe (XT-ADS and EFIT).

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 72 p.
Series
Trita-FYS, ISSN 0280-316X ; 2010:18
Keyword [en]
reactor, ADS, accelerator-driven systems, subcriticality determination, noise techniques, pulsed neutron source, reactivity monitoring
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-12483ISBN: 978-91-7415-623-2 (print)OAI: oai:DiVA.org:kth-12483DiVA: diva2:315354
Public defence
2010-05-12, FA32, Albanova University Center, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20100621Available from: 2010-05-06 Created: 2010-04-29 Last updated: 2011-06-09Bibliographically approved
List of papers
1. 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
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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
2. Pulsed neutron source measurements in the subcritical ADS experiment YALINA-Booster
Open this publication in new window or tab >>Pulsed neutron source measurements in the subcritical ADS experiment YALINA-Booster
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2008 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 35, no 12, 2357-2364 p.Article in journal (Refereed) Published
Abstract [en]

A subcritical zero-power source-driven coupled core, the YALINA-Booster. has been constructed for experimental investigations of neutron kinetics of source-driven systems. In this study, the reactivity of two subcritical configurations has been determined by the area ratio method. The prompt neutron decay constants have been evaluated through slope fitting of the prompt neutron decay as well as through the pulsed Rossi-alpha method. It is shown that the slope fitting method and the pulsed Rossi-alpha method give stable results whereas the area ratio method results show spatial dependence. The reasons for the spatial spread are addressed.

Keyword
REACTIVITY DETERMINATION
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-12370 (URN)10.1016/j.anucene.2008.07.011 (DOI)000261729300023 ()2-s2.0-55949092840 (Scopus ID)
Note
QC 20101115Available from: 2010-04-12 Created: 2010-04-12 Last updated: 2017-12-12Bibliographically approved
3. Spatial and Source Multiplication Effects on the Area Ratio Reactivity Determination Method in a Strongly Heterogeneous Subcritical System
Open this publication in new window or tab >>Spatial and Source Multiplication Effects on the Area Ratio Reactivity Determination Method in a Strongly Heterogeneous Subcritical System
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2010 (English)In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 166, no 2, 134-144 p.Article in journal (Refereed) Published
Abstract [en]

The area ratio method of Sjostrand is generally considered one of the most reliable reactivity determination methods and thus is a major candidate for off-line calibration purposes in future accelerator-driven systems for high-level waste incineration. In this work, the Sjostrand area ratio method has been evaluated experimentally under thorough conditions in the strongly heterogeneous subcritical facility YALINA-Booster. Both strengths and weaknesses of the method have been identified. Most surprisingly, it has been found that the area ratio reactivity estimates may differ a factor of 2 depending on detector position. It is also shown that this strong spatial dependence can be explained based on a simple two-region point-kinetics model and corrected by means of correction factors obtained through Monte Carlo simulations. A new Monte Carlo correction method is proposed that includes, at the same time, the spatial disturbance and the effective delayed neutron fraction. In that way, the value of the effective multiplication factor is obtained from the measured dollar reactivity without the need of calculating the effective delayed neutron fraction explicitly, and thereby, the delayed neutron transport is performed only once. Further, it has been found that the Sjostrand area ratio method is not sensitive to perturbations of the source multiplication factor.

Keyword
Accelerator driven system, Area ratios, Correction factors, Correction method, Delayed neutrons, Detector positions, Effective delayed neutron fraction, Effective multiplication factor, MONTE CARLO, Monte Carlo Simulation, Point-kinetics models, Reactivity determination, Source multiplication, Spatial dependence, Subcritical systems, Computer simulation, Neutrons, Reactivity (nuclear), Waste incineration
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-13581 (URN)000282239100004 ()2-s2.0-77958063824 (Scopus ID)
Note
QC 20100621. Uppdaterad från accepted till published (20101203).Available from: 2010-06-21 Created: 2010-06-21 Last updated: 2017-12-12Bibliographically approved
4. Auto-correlation and variance-to-mean measurements in a subcritical core obeying multiple alpha-modes
Open this publication in new window or tab >>Auto-correlation and variance-to-mean measurements in a subcritical core obeying multiple alpha-modes
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2011 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 38, no 2-3, 194-202 p.Article in journal (Refereed) Published
Abstract [en]

Neutron noise measurements based on the Rossi-alpha and Feynman-alpha methodologies have been performed in a heterogeneous subcritical system. It is shown that the traditional single alpha-mode formulations of the Rossi-alpha and Feynman-alpha methods are not applicable due to the presence of higher alpha-modes. Formalisms taking into account multiple alpha-modes are applied resulting in satisfactory results. Three alpha-modes could be identified using the Rossi-alpha method, whereas only two could be obtained using the Feynman-alpha method. In the Feynman-alpha case, the possibility to obtain the fastest decaying alpha-mode was diminished due to detector dead time effects. It was found that the slowest decaying alpha-mode does not exactly correspond to the prompt decay found in pulsed neutron source measurements, which confirms the results of previous studies. Strengths and weaknesses of the multiple alpha-mode Rossi-alpha and Feynman-alpha methods observed in this study are pointed out.

Keyword
Neutron noise experiment, Auto-correlation, Rossi-alpha, Variance-to-mean, Feynman-alpha, Reactivity determination
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-13583 (URN)10.1016/j.anucene.2010.11.009 (DOI)000287571100004 ()2-s2.0-78751615182 (Scopus ID)
Note
QC 20100621 Uppdaterad från submitted till published (20110315).Available from: 2010-06-21 Created: 2010-06-21 Last updated: 2017-12-12Bibliographically approved
5. Feynman-alpha and Rossi-alpha formulas with spatial and modal effects
Open this publication in new window or tab >>Feynman-alpha and Rossi-alpha formulas with spatial and modal effects
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2011 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 38, no 2-3, 590-600 p.Article in journal (Refereed) Published
Abstract [en]

Feynman-alpha and Rossi-alpha formulas including multiple alpha-modes are derived for stochastic and continuous neutron sources. The presented formalism is further developed to achieve spatial correction factors for the single alpha-mode point kinetics representations of the Feynman-alpha and Rossi-alpha formulas. As a natural extension of the multiple alpha-mode formalism, delayed neutrons are included in the Feynman-alpha formula. The obtained formulas are validated experimentally in a strongly heterogeneous system obeying multiple alpha-modes, resulting in good agreement with the presented theoretical framework.

Keyword
Feynman-alpha, Rossi-alpha, Stochastic transport theory, Reactivity determination
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-13586 (URN)10.1016/j.anucene.2010.09.027 (DOI)000287571100047 ()2-s2.0-78751608739 (Scopus ID)
Note
QC 20100621 Uppdaterad från submitted till published (20110315).Available from: 2010-06-21 Created: 2010-06-21 Last updated: 2017-12-12Bibliographically approved
6. Validation of ADS reactivity monitoring techniques in a strongly heterogeneous subcritical system
Open this publication in new window or tab >>Validation of ADS reactivity monitoring techniques in a strongly heterogeneous subcritical system
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(English)Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:kth:diva-13587 (URN)
Note
QC20100621Available from: 2010-06-21 Created: 2010-06-21 Last updated: 2010-06-21Bibliographically approved
7. Reactivity deter-mination of the Yalina-Booster subcritical assembly using the prompt decay constant method
Open this publication in new window or tab >>Reactivity deter-mination of the Yalina-Booster subcritical assembly using the prompt decay constant method
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(English)Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:kth:diva-13588 (URN)
Note
QC20100621Available from: 2010-06-21 Created: 2010-06-21 Last updated: 2010-06-21Bibliographically approved

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