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Development of a Neutron Flux Monitoring System for Sodium-cooled Fast Reactors
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. (Fission Diagnostics and Safeguards)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Safety and reliability are one of the key objectives for future Generation IV nuclear energy systems. The neutron flux monitoring system forms an integral part of the safety design of a nuclear reactor and must be able to detect any irregularities during all states of reactor operation. The work in this thesis mainly concerns the detection of in-core perturbations arising from unwanted movements of control rods with in-vessel neutron detectors in a sodium-cooled fast reactor. Feasibility study of self-powered neutron detectors (SPNDs) with platinum emitters as in-core power profile monitors for SFRs at full power is performed. The study shows that an SPND with a platinum emitter generates a prompt current signal induced by neutrons and gammas of the order of 600 nA/m, which is large enough to be measurable. Therefore, it is possible for the SPND to follow local power fluctuations at full power operation. Ex-core and in-core detector locations are investigated with two types of detectors, fission chambers and self-powered neutron detectors (SPNDs) respectively, to study the possibility of detection of the spatial changes in the power profile during two different transient conditions, i.e. inadvertent withdrawal of control rods (IRW) and one stuck rod during reactor shutdown (OSR). It is shown that it is possible to detect the two simulated transients with this set of ex-core and in-core detectors before any melting of the fuel takes place. The detector signal can tolerate a noise level up to 5% during an IRW and up to 1% during an OSR.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1508
Keyword [en]
Protection systems, safety, accidents, sodium-cooled fast reactor, instrumentation, fission chamber, self powered neutron detector
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-319945ISBN: 978-91-554-9897-9 (print)OAI: oai:DiVA.org:uu-319945DiVA: diva2:1088118
Public defence
2017-06-01, Polhemsalen, Ångströmlaboratoriet, Lågerhyddsvägen 1, Uppsala, 09:15 (English)
Supervisors
Available from: 2017-05-10 Created: 2017-04-11 Last updated: 2017-05-23
List of papers
1. Neutron flux monitoring with in-vessel fission chambers to detect an inadvertent control rod withdrawal in a sodium-cooled fast reactor
Open this publication in new window or tab >>Neutron flux monitoring with in-vessel fission chambers to detect an inadvertent control rod withdrawal in a sodium-cooled fast reactor
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2016 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 94, 487-493 p.Article in journal (Refereed) Published
Abstract [en]

The neutron flux monitoring system forms an integral part of the safety design of a Generation IV sodium-cooled fast reactor. During the initial design phase of the neutron flux monitoring system, one needs to explore various detector locations and configurations. Diverse possibilities of the detector system installation should be studied for different locations in the reactor vessel in order to detect any perturbations in the core. In this paper, we investigate the possibility of placing fission chambers beyond the lateral neutron shield, ex-core but in-vessel and study the detectability of an inadvertent control rod withdrawal with these fission chambers. A generic core design of a Generation IV 1500 MWth French sodium-cooled fast reactor is used for the study, and calculations are performed with the Monte Carlo code SERPENT2. We propose certain design changes that are needed to be incorporated, w.r.t. the facilitation of neutron transport to this ex-core location.

We are able to show that there is a detectable signature in the fission chambers following an inadvertent control rod withdrawal in the core. The equally-spaced azimuthal detectors are able to follow changes in the neutron flux distribution in the core. This study helps us to analyze multiple detector locations and give the general trends for monitoring indications to detect any perturbations in the core.

Keyword
Protection systems; Safety; Accidents; Instrumentation; Sodium cooled fast reactors; Fission chambers
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-297046 (URN)10.1016/j.anucene.2016.04.019 (DOI)000377231600054 ()
Funder
Swedish Research Council, B0774801
Available from: 2016-06-21 Created: 2016-06-21 Last updated: 2017-04-11Bibliographically approved
2. CALCULATION METHODOLOGY ASSESSMENT TO DETECT LOCALISED PERTURBATION IN SODIUM-COOLED FAST REACTOR WITH EX-CORE INSTRUMENTATION
Open this publication in new window or tab >>CALCULATION METHODOLOGY ASSESSMENT TO DETECT LOCALISED PERTURBATION IN SODIUM-COOLED FAST REACTOR WITH EX-CORE INSTRUMENTATION
2016 (English)In: CALCULATION METHODOLOGY ASSESSMENT TO DETECTLOCALISED PERTURBATION IN SODIUM-COOLED FAST REACTORWITH EX-CORE INSTRUMENTATION, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Safety and reliability are essential requirements for development and operation of SodiumcooledFast Reactors. Development of a neutron flux monitoring system (NFMS) for the FrenchSFR is one of the key R&D areas identified. Diverse possibilities of detector system installationshould be studied for different locations in the reactor vessel in order to detect any perturbations inthe core. In this paper, we aim to explore two calculation routes available for neutron flux monitoring,assess them for their efficiency to detect fission rate variation at Above-core structure (ACS)location and discuss the associated pros and cons. The two calculational approaches we refer hereare criticality mode and external source mode. We discuss the feasibility of choosing this locationfor detecting in-core perturbations and evaluate the methodology needed to achieve it. The paperfocuses on the difficulties associated with neutron detection when the detectors are located at far-offdistances from the source. We found that for a difficult case such as ours where the detectors arelocated far-away from the source, criticality mode doesn’t work. Variance reduction techniques,employed in the external source mode are indispensable to drive neutrons to areas of interest.

Keyword
Sodium Cooled Fast reactors, Fission chambers, Instrumentation, Variance reduction
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-297045 (URN)
Conference
PHYSOR 2016
Funder
Swedish Research Council, B0774801
Available from: 2016-06-21 Created: 2016-06-21 Last updated: 2017-05-09
3. Progress in the development of the neutron fluxmonitoring system of the French GEN-IV SFR:simulations and experimental validations
Open this publication in new window or tab >>Progress in the development of the neutron fluxmonitoring system of the French GEN-IV SFR:simulations and experimental validations
2015 (English)Conference paper, Published paper (Other academic)
Abstract [en]

The neutron flux monitoring system of the FrenchGEN-IV sodium-cooled fast reactor will rely on hightemperaturefission chambers installed in the reactor vessel andcapable of operating over a wide-range neutron flux. Thedefinition of such a system is presented and the technologicalsolutions are justified with the use of simulation andexperimental results.

National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-269891 (URN)
Conference
4th International Conference on Advances in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), Lisbon, Portugal, April 20-24, 2015
Funder
Swedish Research Council, 349-2011-7748
Available from: 2015-12-18 Created: 2015-12-18 Last updated: 2017-05-09
4. Self Powered Neutron Detectors as in-core detectors for Sodium-cooled Fast Reactors
Open this publication in new window or tab >>Self Powered Neutron Detectors as in-core detectors for Sodium-cooled Fast Reactors
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2017 (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. 860, 6-12 p.Article in journal (Refereed) Published
Abstract [en]

Neutron flux monitoring system forms an integral part of the design of a Generation IV sodium cooled fast reactor. Diverse possibilities of detector system installation must be studied for various locations in the reactor vessel in order to detect any perturbations in the core. Results from a previous paper indicated that it is possible to detect changes in neutron source distribution initiated by an inadvertent withdrawal of outer control rod with in-vessel fission chambers located azimuthally around the core. It is, however, not possible to follow inner control rod withdrawal and precisely know the location of the perturbation in the core. Hence the use of complimentary in-core detectors coupled with the peripheral fission chambers is proposed to enable robust core monitoring across the radial direction.

In this paper, we assess the feasibility of using self-powered neutron detectors (SPNDs) as in-core detectors in fast reactors for detecting local changes in the power distribution when the reactor is operated at nominal power. We study the neutron and gamma contributions to the total output current of the detector modelled with Platinum as the emitter material. It is shown that this SPND placed in an SFR-like environment would give a sufficiently measurable prompt neutron induced current of the order of 600 nA/m. The corresponding induced current in the connecting cable is two orders of magnitude lower and can be neglected. This means that the SPND can follow in-core power fluctuations. This validates the operability of an SPND in an SFR-like environment.

Keyword
Sodium cooled fast reactors, Self powered neutron detector, Instrumentation, Core monitoring, In-core detection
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-314035 (URN)10.1016/j.nima.2017.04.011 (DOI)000402464900002 ()
Funder
Swedish Research Council, B0774801
Available from: 2017-01-26 Created: 2017-01-26 Last updated: 2017-09-15Bibliographically approved
5. Neutron flux monitoring during slow transient conditions in a Sodium-cooled fast reactor.
Open this publication in new window or tab >>Neutron flux monitoring during slow transient conditions in a Sodium-cooled fast reactor.
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-319943 (URN)
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-05-09

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