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Method For Analyzing Fission Gas Release In Fuel Rods Based On Gamma-Ray Measurements Of Short-Lived Fission Products
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.
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2013 (English)In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 184, no 1, 96-106 p.Article in journal (Refereed) Published
Abstract [en]

Fission gases are produced as a result of fission reactions in nuclear fuel. Most of these gases remain trapped within the fuel pellets, but some may be released to the fuel rod internal gas volume under certain conditions. This phenomenon of fission gas release is important for fuel performance since the released gases can degrade the thennal properties of the fuel rod. fill gas and contribute to increasing fuel rod internal pressure. Various destructive and nondestructive methods are available for determining the amount of fission gas release; however, the current methods are primarily useful for determining the integrated fission gas release fraction, i.e., the amount of fission gas produced in the fuel that has been released to the free rod volume over the entire lifetime of a nuclear fuel rod. In this work, a method is proposed for determining the fission gas release that occurs during short irradia-tion sequences. The proposed method is based on spectroscopic measurements of gamma rays emitted in the decay of short-lived fission gas isotopes. Determining such sequence-specific fission gas release can be of interest when evaluating the fuel behavior for selected times during irradiation, such as during power ramps. The data obtained in this type of measurement may also be useful for investigating the mechanisms behind fission gas release for fuel at high burnup. The method is demonstrated based on the analysis of experimental gamma-ray spectra previously collected using equipment not dedicated for this purpose; however, the analysis indicates the feasibility of the method. Further evaluation of the method is planned, using dedicated equipment at the Halden Boiling Water Reactor.

Place, publisher, year, edition, pages
2013. Vol. 184, no 1, 96-106 p.
Keyword [en]
fission gas release, gamma spectroscopy, nuclear fuel
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-187790ISI: 000325236100007OAI: oai:DiVA.org:uu-187790DiVA: diva2:575619
Available from: 2012-12-10 Created: 2012-12-10 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Nondestructive Fission Gas Measurements by Means of Gamma Spectroscopy and Gamma Tomography
Open this publication in new window or tab >>Nondestructive Fission Gas Measurements by Means of Gamma Spectroscopy and Gamma Tomography
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There is a continuous need in the nuclear industry to characterize irradiated nuclear fuel rods and assemblies, both for fuel performance and for safeguards purposes, and consequently there are various destructive and nondestructive measurement techniques available to meet this need. Gamma spectroscopy is one such nondestructive technique, which has been extensively used for a variety of fuel characterization applications. Furthermore, gamma tomography – a combination of gamma spectroscopic measurements and tomographic reconstruction – has in recent years been demonstrated as an efficient technique for characterization of irradiated nuclear fuel assemblies on a rod-by-rod basis without the need to dismantle the fuel. This thesis comprises four scientific papers in which novel applications of these two techniques have been developed and evaluated.

The major part of this work has been performed at the Halden Boiling Water Reactor (HBWR), where a gamma tomography measurement system is currently under construction, as presented in this thesis. The methods and evaluations presented in this work are based on the conditions at the HBWR.

Based on gamma spectroscopy, a novel nondestructive method for determining fission gas release which occurs over short irradiation sequences has been developed, comprising the measurement and analysis of short lived isotopes in individual fuel rods. The method has been demonstrated based on gamma-ray spectra recorded from an experimental fuel rod irradiated in the HBWR.

Based on gamma tomography, a novel method for identifying failed fuel rods within a nuclear fuel assembly has also been developed. The method comprises the measurement of gamma rays emitted in the decay of selected fission gas isotopes in the gas plenum region of a fuel assembly, tomographic image reconstruction of the internal source distribution and subsequent analysis of the resulting image in order to determine if any of the fuel rods in the assembly has unexpectedly low activity, indicating that it is a leaking fuel rod. Simulation studies performed for HBWR fuel show highly promising results for gamma rays emitted in the decay of two selected fission gas isotopes.

The methods will be further investigated at the HBWR, by performing dedicated gamma spectroscopy measurements and by using the tomographic measurement system currently under construction.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2012. 14 p.
National Category
Physical Sciences
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-185551 (URN)
Presentation
2012-11-15, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2008-5888
Note

Papers III and IV have been submitted for publication and while under review by the publishers they are not available here.

Available from: 2012-11-28 Created: 2012-11-26 Last updated: 2013-03-22Bibliographically approved
2. Gamma Spectroscopy and Gamma Emission Tomography for Fuel Performance Characterization of Irradiated Nuclear Fuel Assemblies
Open this publication in new window or tab >>Gamma Spectroscopy and Gamma Emission Tomography for Fuel Performance Characterization of Irradiated Nuclear Fuel Assemblies
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gamma spectroscopy and gamma emission tomography are two non-destructive measurement techniques for assessing the performance of nuclear fuel which have been investigated in this thesis for existing and novel applications through theoretical studies and experimental demonstrations. For assessment of individual fuel rods using gamma spectroscopy, fuel assemblies are dismantled so that the fuel rods may be measured separately, which is time-consuming and may cause damage to the fuel. Gamma tomography is more seldom used, but its application on complete fuel assemblies would enable the assessment of individual fuel rods without the need to disassemble the fuel. Both techniques are based on recording gamma rays, emitted at characteristic energies from decaying radioactive products in the fuel.

The feasibility of measuring short-lived fission gasses in the gas plenum of fuel rods with short cooling time was experimentally investigated. Based on the feasibility demonstration, a method was proposed and experimentally demonstrated for determining the fission gas release fraction of 133Xe in fuel rods with short cooling time. Additionally, a method for investigating the origin of released fission gasses based on the measured ratio of 133Xe/85Kr in the fuel rod gas plenum was demonstrated. These methods may be employed at research reactors, where fuel with short cooling time is available for measurement.

A gamma emission tomography instrument has been designed, constructed and experimentally demonstrated on a Halden Reactor fuel assembly. Simulation studies showed that the instrument and the tomographic reconstruction methods employed may be useful for: identifying a leaking fuel rod in an assembly by its lack of fission gas content; reconstruction of the rod-wise fission product distributions in the fuel stack and plenum regions of the assembly; and determining the rod-wise fission gas release fractions.

In the experimental demonstration, the rod-wise distributions of the fission products 137Cs and 85Kr in the fuel stack and plenum regions of the assembly were reconstructed, as well as the distributions of the activation products 60Co and 178mHf in the plenum region, revealing the plenum springs and tie rods, respectively. The reconstructed data was in the form of images, useful for qualitative assessment of the fuel.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 94 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1201
Keyword
Nuclear fuel performance, Nuclear fuel assemblies, Gamma emission tomography, Gamma spectroscopy
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-235124 (URN)978-91-554-9099-7 (ISBN)
Public defence
2014-12-16, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2014-11-25 Created: 2014-10-29 Last updated: 2015-02-03

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