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The shut-down of the Barseback 1 BWR: A unique opportunity to measure the power distribution in nuclear fuel rods
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, Nuclear Physics.
2006 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 33, no 13, 1091-1101 p.Article in journal (Refereed) Published
Abstract [en]

Reactor poolside measurements of gamma radiation specific for the fission product La-140 (1596 keV) have been used for an experimental determination of axial power distributions in 55 nuclear fuel rods irradiated in the Barseback 1 BWR nuclear power plant. The measurements take advantage of the unique situation of a very short last reactor cycle of only three months due to the out-phasing of the reactor unit at November 30 1999. La-140 whose decay is controlled by the mother nuclide Ba-140 with the half-life 12.75 days reflects an average power distribution, representative for the latest weeks of core operation (in this case basically during November 1999). The measured intensities have been transformed into a 25 nodal representation to allow a precise and direct comparison with the corresponding calculated power distribution. The 55 rods were selected from two different fuel assemblies with average burn-ups of 1.9 and 9.7 MWd/ kgU, respectively (that is one fresh bundle and one slightly more than one cycle bundle). The stability and the linearity of the measurement system were evaluated. The linearity was checked using the two-source method. The stability was checked by recurrent measurements on a reference fuel rod. The results have been used in the validation of the pin power reconstruction model of Westinghouse 3D core simulator POLCA-7. The deviation between measured and calculated Ba-140 concentration (expressed as radial error) is typically a few percent on rod level. Results indicate that also Gd-rods are properly modelled over a broad range of conditions. It is indicated that predictions for fuel rods in their first month of operation are less accurate than for the rest of the rods.

Place, publisher, year, edition, pages
2006. Vol. 33, no 13, 1091-1101 p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-94563DOI: 10.1016/j.anucene.2006.07.007ISI: 000242114100003OAI: oai:DiVA.org:uu-94563DiVA: diva2:168451
Available from: 2006-05-16 Created: 2006-05-16 Last updated: 2011-05-13Bibliographically approved
In thesis
1. Studies of Nuclear Fuel Performance Using On-site Gamma-ray Spectroscopy and In-pile Measurements
Open this publication in new window or tab >>Studies of Nuclear Fuel Performance Using On-site Gamma-ray Spectroscopy and In-pile Measurements
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Presently there is a clear trend of increasing demands on in-pile performance of nuclear fuel. Higher target burnups, part length rods and various fuel additives are some examples of this trend. Together with an increasing demand from the public for even safer nuclear power utilisation, this implies an increased focus on various experimental, preferably non-destructive, methods to characterise the fuel.

This thesis focuses on the development and experimental evaluation of such methods. In its first part, the thesis presents a method based on gamma-ray spectroscopy with germanium detectors that have been used at various power reactors in Europe. The aim with these measurements is to provide information about the thermal power distribution within fuel assemblies in order to validate core physics production codes. The early closure of the Barsebäck 1 BWR offered a unique opportunity to perform such validations before complete depletion of burnable absorbers in Gd-rods had taken place. To facilitate the measurements, a completely submersible measuring system, LOKET, was developed allowing for convenient in-pool measurements to be performed.

In its second part, the thesis describes methods that utilise in-pile measurements. These methods have been used in the Halden test-reactor for determination of fission gas release, pellet-cladding interaction studies and fuel development studies.

Apart from the power measurements, the LOKET device has been used for fission gas release (FGR) measurements on single fuel rods. The significant reduction in fission gas release in the modern fuel designs, in comparison with older designs, has been demonstrated in a series of experiments. A FGR database covering a wide range of burnup, power histories and fuel designs has been compiled and used for fuel performance analysis. The fission gas release has been measured on fuel rods with average burnups well above 60 MWd/kgU. The comparison between core physics calculations (PHOENIX-4/POLCA-7) and the in-pool measurements of thermal power indicates that the nodal power can generally be predicted with an accuracy within 4% and the bundle power with an accuracy better than 2%, expressed as rms errors.

In-pile experiments have successfully simulated the conditions that occur in a fuel rod following a primary debris failure, being secondary fuel degradation. It was concluded that massive hydrogen pick-up takes place during the first few days following the primary failure and that a pre-oxidized layer does not function as a barrier towards hydriding in an environment with a very high partial pressure of hydrogen. Another series of in-pile experiments clearly indicate that increased UO2 grain size is an effective way of suppressing fission gas release in LWR fuel up to the burnup level covered (55 MWd/kgUO2).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 103 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 191
Nuclear physics, fission gas release, nuclear fuel, core physics, gamma-ray spectroscopy, LOKET, thermal power, burnup, fuel failure, validation, cladding, Kärnfysik
urn:nbn:se:uu:diva-6912 (URN)91-554-6582-X (ISBN)
Public defence
2006-06-07, Sal 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:30
Available from: 2006-05-16 Created: 2006-05-16Bibliographically approved

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