Radiant energy – Calibration or standardization methods
Reexamination Certificate
2002-07-03
2003-12-16
Hannaher, Constantine (Department: 2878)
Radiant energy
Calibration or standardization methods
C250S491100
Reexamination Certificate
active
06664539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention concerns improvements in and relating to verification and/or calibration, particularly, but not exclusively, to verification and/or calibration in relation to characterisation of spent nuclear fuel.
2. The Relevant Technology
Nuclear power generation involves, the provision of fuel assemblies containing enriched fuel to a reactor; the residence of that fuel assembly in the reactor, during which time the fissile material is consumed; and the removal of the fuel assembly after a period of time for subsequent handling. The subsequent handling may include reprocessing, to recover fissile material for subsequent use, and/or storage and/or transportation of the fuel.
In such subsequent tasks it is desirable for a number of reasons to have information on the characteristics of the fuel in the fuel assemblies.
A variety of instruments for monitoring such characteristics to varying degrees are known, including high resolution gamma spectrometry (HRGS), low resolution gamma spectrometry (LRGS) and passive neutron counting.
A variety of actual emission forms can be monitored to calculate the burnup of the fuel, either according to the level of that emission form or the interrelationship of two or more emission forms to one another.
A frequently monitored emission is based on curium emissions from the spent fuel. To achieve a detailed measurement of burnup, however, this measurement requires information on the original enrichment of the fuel as the curium based count is not only based on the burnup of the fuel, but also its starting enrichment.
BRIEF SUMMARY OF THE INVENTION
The present invention aims to provide a technique for accurately verifying the consistency of operation of an instrument for measuring burnup. The invention also aims to allow the claimed history for the fuel to be independently verified by comparing a model based evaluation of the claimed fuel history against the independent measured value. The provision of improved sources for calibration and/or modelling purposes and/or of calibration and/or verification test rigs is also an aim of the present invention.
According to a first aspect of the invention we provide a method of investigating the response of an instrument to gamma emissions using a source package, the method comprising:
providing a source package on one side of a collimator including an aperture and a detector on the other side of the collimator relative to the source package, the collimator and detector positions defining an operating axis for the instrument;
moving the position of the source package relative to the collimator, with the response of the detector being measured for two or more of those different positions of the source package;
an aperture in the collimator having a first dimension measured in a first direction perpendicular to the operating axis;
the source package comprises one or more individual gamma emitting sources provided in a container, in use the individual source(s) having an overall extent in the first direction, the overall extent, during at least 10 seconds of use, being two or more times the first dimension of the collimator in that first direction.
The operating axis may be thought of as the centre line of the field of view defined by the collimator or collimators and detector and/or an axis generally corresponding to the direction of travel of gamma emissions detected by the instrument.
According to a second aspect of the invention, we provide a source of gamma emissions, the source comprising one or more individual gamma emitting sources provided in a container, the individual source(s) have an overall extent in a first direction, that extent being greater than 10 mm.
The first and/or second aspect of the invention may include any one or more of the following features, options and possibilities.
Preferably the overall extent of the individual source(s) in the first direction is less than 50 mm, more preferably less than 30 mm.
The individual sources have an overall extent in a second direction, for at least 10 seconds in use, ideally perpendicular to the first direction. The second extent may be less than 20 mm and preferably less than 10 mm. Preferably the extent in the second direction is at least 1.5 mm and more preferably at least 2 mm. The second extent is preferably the same in all directions perpendicular to the first.
The first and/or second extent of the source package during the at least 10 seconds of use may be provided by the actual dimension of the source or sources in that direction. The extent of the source package during the at least 10 seconds of use may be provided by oscillating a source or sources through that extent, the source or sources having an actual dimension in that direction less that the extent. Preferably a frequency of oscillation of greater than 10 Hz is provided.
A plurality of individual sources may be provided in the container. The plurality of sources maybe a number greater than 5, greater than 10 or even 15 or more.
The gamma emissions from the individual sources are preferably of the same energy and/or same energies and/or same range of energies as are used by the instrument in its measurements.
Preferably each of the individual gamma sources is of the same type. Preferably each of the individual gamma sources emits the same gamma emissions, in terms of their energy energies or range of energies. The individual sources may be or contain
137
Cs.
Preferably the level of emissions from each of the individual sources is substantially the same, for instance within 10% of one another. Preferably the level of emissions for an individual sources is substantially consistent from all directions, at least in all directions perpendicular to the axis on which the sources are aligned, for instance the second direction. Preferably the quantity of gamma emitter, ideally the quantity of the selected gamma emitter, such as
137
Cs, will be sufficient to give a nominal equivalent activity of at least 5 mCi and/or a nominal equivalent activity of at most 40 mCi.
Preferably each of the individual gamma sources is substantially the same shape. Preferably the individual sources are cylindrical.
The individual source or sources may be provided with an end face at one or both ends of the extent in the first direction. One or both of the end faces of one or more, ideally all, the sources are preferably planar and/or parallel to one another. Preferably at least the outside end face of the individual source defining one end of the overall extent and the outside end face of the individual source defining the other end of the overall extent are parallel to one another, ideally, they are also perpendicular to the axis on which the sources are aligned. The axis is preferably the first direction. One, preferably both, of the end faces of one or more of the individual source(s) may be perpendicular to the axis of the source and/or the cylindrical surface thereof.
The individual source or sources may be provided with an effective side edge. The effective side edge may be defined by a face, but is more preferably the extent of the cylindrical surface of the source when viewed in from the side, for instance, perpendicular to the axis of the cylinder. One, preferably both of the effective side edges of one or more, ideally all, the individual sources are preferably linear and/or parallel to one another. Ideally, the effective side edges are aligned with one another, at least in the second direction. Preferably the effective side edges are parallel to the axis on which the individual sources are aligned. The axis is preferably the first direction.
The sources are preferably aligned on a common axis with one another.
The individual sources, for instance as cylinders, may be between 0.5 mm and 1.5 mm in length. The individual sources may be between 1 mm and 4 mm in diameter.
The container may be of stainless steel. Preferably the container is cylindrical. The end faces of the container are preferably parallel to one another. One, preferably both, of t
Blundell Alan Stanley
Chesterman Andrew Stuart
Clapham Martin James
Merrill Lynda Elizabeth
Merrill Nolan Howard
British Nuclear Fuels PLC
Hannaher Constantine
Merrill Lynda Elizabeth
Moran Timothy
Workman Nydegger
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