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Detection of coolant bubbles in lead-cooled fast reactors
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. (Nuclear Fuel and Nuclear Data)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Previous work [1] has shown that using fission chambers coated with 242Pu and 235U, respectively, can provide the means of detecting changes in the neutron flux that are connected to coolant density changes in a small lead cooled fast reactor. Such density changes may be due to leakages of gas into the coolant, which, over time, may coalesce to large bubbles implying a high risk of causing severe damages of the core. By using the ratio of the information provided by the two types of detectors a quantity is obtained that is sensitive to these density changes and, to the first order approximation, independent of the power level of the reactor.

 

In this work we continue the investigation of this proposed methodology by applying it to the Advanced LFR European Demonstrator (ALFRED) and using realistic modelling of the neutron detectors. The results show that the methodology may be used to detect density changes indicating the initial stages of a coalescence process that may result in a large bubble. Also, it is shown that under certain circumstances, large bubbles passing through the core could be detected with this methodology.

National Category
Energy Systems
Identifiers
URN: urn:nbn:se:uu:diva-232237OAI: oai:DiVA.org:uu-232237DiVA: diva2:747156
Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2014-10-22
In thesis
1. Development of a Methodology for Detecting Coolant Void in Lead-cooled Fast Reactors by Means of Neutron Measurements
Open this publication in new window or tab >>Development of a Methodology for Detecting Coolant Void in Lead-cooled Fast Reactors by Means of Neutron Measurements
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In a lead-cooled fast reactor (LFR), small bubbles (in the order of one mm or less) may enter the coolant from a leaking steam generator. If such a leakage is undetected the small bubbles may eventually coalesce into a larger bubble in local stagnation zones under the active core. If such a bubble or void releases and passes through the core, it could drive the reactor into prompt criticality. It is therefore desirable to be able to detect the initial stages of such void formation.

In this thesis, a methodology to detect such leaks is presented together with a study on void-induced reactivity effects in various LFR's. The methodology developed is based on information from two fission chambers positioned radially outside the core. The fissile content of the fission chambers consist either of 235U or 242Pu making them sensitive to different parts of the neutron spectrum. It is shown that the information from the fission chambers can be used to obtain an early indication of the presence of a small leak within typically a month. Furthermore, it is shown that for all but the smallest LFR’s, prompt criticality due to voids passing the core cannot be excluded.

One conclusion is that the methodology may form an attractive complement to the general monitoring system of future LFR’s but, as is noted, it has potential for further developments.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 54 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1180
Keyword
LFR, fission chamber, nuclear, reactor, leak, criticality
National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-232252 (URN)978-91-554-9037-9 (ISBN)
Public defence
2014-10-31, room 2001, Lägerhyddsvägen 1, Ångströmslaboratoriet, Uppsala, 08:15 (English)
Opponent
Supervisors
Available from: 2014-10-08 Created: 2014-09-16 Last updated: 2015-01-23Bibliographically approved

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Wolniewicz, Peter

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