GB2594051A - Muon radiography - Google Patents
Muon radiography Download PDFInfo
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- GB2594051A GB2594051A GB2005156.1A GB202005156A GB2594051A GB 2594051 A GB2594051 A GB 2594051A GB 202005156 A GB202005156 A GB 202005156A GB 2594051 A GB2594051 A GB 2594051A
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- muon
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- 238000002601 radiography Methods 0.000 title claims abstract description 14
- 239000000463 material Substances 0.000 claims abstract description 86
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 36
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 34
- 239000010439 graphite Substances 0.000 claims abstract description 34
- 238000000034 method Methods 0.000 claims abstract description 30
- 239000003758 nuclear fuel Substances 0.000 claims abstract description 15
- 238000003384 imaging method Methods 0.000 claims abstract description 9
- 238000001739 density measurement Methods 0.000 claims description 18
- 238000001514 detection method Methods 0.000 claims description 15
- 238000004590 computer program Methods 0.000 claims description 6
- 230000003993 interaction Effects 0.000 claims description 4
- 238000012544 monitoring process Methods 0.000 abstract description 2
- 239000000835 fiber Substances 0.000 abstract 1
- 239000000446 fuel Substances 0.000 description 5
- 238000005259 measurement Methods 0.000 description 4
- 239000002826 coolant Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000011960 computer-aided design Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000003213 activating effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000007620 mathematical function Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000000053 physical method Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
- 230000032258 transport Effects 0.000 description 1
Classifications
-
- G01V5/26—
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T5/00—Recording of movements or tracks of particles; Processing or analysis of such tracks
- G01T5/02—Processing of tracks; Analysis of tracks
Abstract
A method of muon radiography, e.g. for monitoring of graphite moderator density in a nuclear reactor, comprises selecting a subset of determined muon tracks and determining density based on a ratio of incoming and outgoing muons traversing the subset. Muon detectors 202, 208 may comprise orthogonal layers of scintillating fibre 204, 205, 210, 212. The subset of muon tracks may be those within an acceptance region 222, 224 and selection of or the detectors may be arranged in relation to the monitored material 214 location (202, 208 fig. 3). This may be based upon calculating the location of material using muon imaging and e.g. selecting tracks not passing through nuclear fuel 216.
Description
MUON RADIOGRAPHY
Field of Invention
The present invention relates to a method of muon radiography and apparatus for density measurement In particular, the present invention has application in determining graphite density in a nuclear reactor.
Background of the Invention
Muon radiography is an imaging technique, which can be used to inspect properdes of matter, for example, thickness and density, by investigating the attenuation of cosmic-ray muons travelling through the matter.
A nuclear reactor generates energy from the process of neutrons interacting with nuclei in fuel elements. A coolant is used to remove excess heat produced as a result of the process. A moderator is also incorporated in the nuclear reactor to slow the neutrons down for controlled and efficient operation of the nuclear reactor.
Graphite is a key material in nuclear reactors such as the Advanced Gas-cooled Reactors (AG R) operating in the UK. It selves as a moderator, and at the same time it also is part of the mechanical construction. Ove r the lifetime of the reactor operation, the graphite is exposed to very high levels of neutron irradiation and where a carbon dioxide coolant is used, the graphite would lose weight due to oxidation (i.e. the coolant transports some of the carbon away). As a result the density of the graphite is reduced, leading to embritdement and strength reduction (e.g. developing cracks).
The density of the graphite is an important qua lifie r for the remaining reactor operation time defined by Government regulations. This density is therefore monitored and reported to the regulator. The conventional methods involve the collection of so-called trepanation samples that are then analysed in a laboratory. The resulting density measurements can only be made when the reactor is down for maintenance and they only reflect the samples that were necessarily taken close to the accessible surface of the graphite.
Summary of invention
It is desirable to have a method and associated muon radiography apparatus which accurately measure density of materials that are in close proximity to other materials. It is desirable to provide an improved method and apparatus which allows real-lime measurement and monitoring of graphite density in a nuclear reactor during its operation.
According to a first aspect of the present invention, there is provided a method of muon radiography for density measurement comprising the steps: -determining muon tracks incident on a sample comprising a first type of material and a second type of material; -selecting a subset of the muon tracks giving preference to those that pass through the first type of material but not the second type of material; -detecting incoming and outgoing muons traversing the subset of the muon tracks respectively before and after passing through the firsttype of material in the sample; and -determining density of the first type of material based on a ratio of the incoming to outgoing muons traversing the subset of the muon tracks.
Preferably, selecting the subset comprises selecting those that pass through the first type of material but not the second type of material.
Preferably, selecting the subset of muon tracks comprises selecting a subset of muon detection coordinates.
Alternatively, selecting the subset comprises arranging muon detectors in relation to the first and second types of material.
Preferably, selecting the subset comprises calculating geometric location of the first type of material relative to the second type of material in the sample.
Preferably, the geometric location is calculated by imaging the sample based on muon interactions with the sample.
Preferably, a muon detection system is used both for the imaging of the sample and for the detecting of incoming and outgoing muons for determining the density.
Preferably, selecting the subset comprises selecting a subset of the muon tracks giving preference to those that pass through the first type of material but not the second type and another type of material.
Preferably, selecting the subset comprises selecting those that pass through the first type of material but not the second type or another type of material.
Preferably, the sample comprises components of a nuclear reactor.
Preferably, the first type of material comprises a moderator.
Preferably, the moderator comprises graphite.
Preferably, the second type of material comprises nuclear fuel elements.
According to a second aspect of the present invention, there is provided a muon radiography apparatus for density measurement comprising the steps: -a muon detection system configured to determine muon tracks incident on a sample comprising a first type of material and a second type of material; and -a processor configured to: -select a subset of the muon tracks giving preference to those that pass through the first type of material but not the second type of material; -detect incoming and outgoing muons traversing the subset of the muon tracks respectively before and after passing through the first type of material in the sample; and -determine density of the first type of material based on a ratio of the incoming to outgoing muons traversing the subset of the muon tracks.
According to a third aspect of the present invention, there is provided a computer program product comprising a computer usable medium, where the computer usable medium comprises a computer program code that, when executed by a computer apparatus, determining density according to the method of the first aspect.
Brief description of drawings
Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a flowchart of a method of muon radiography for density measurement in accordance with an embodiment of the present invention.
Figure 2 illustrates, in schematic form, an application of the method of Figure 1 for density measurement of graphite in a nuclear reactor, in accordance with an embodiment of the present invention.
Figure 3 illustrates, in schematic form, an application of the method of Figure 1 for density measurement of graphite in a nuclear reactor, in accordance with another embodiment of the present invention.
Figures 4a and 4b illustrate a density measurement in a simulated nuclear reactor structure.
Figure 5 illustrates, in schematic form, a muon radiography apparatus for density measurement, in accordance with an embodiment of the present invention.
Description of embodiments
In the Figures, elements labelled with reference numerals found in the preceding Figures representthe same elements as described for the respective preceding Figure. For example, feature 202 in Figure 3 corresponds to the same feature 202 as described with reference to Figure 2.
Figure 1 illustrates a flowchart of a method of muon radiography for density measurement 100, in accordance with an embodiment of the present invention. The method has the following steps.
At step 102, muon tracks incident on a sample are determined, wherein the sample comprises a first type of material and a second (or more) type of material. This step may comprise using muon detectors to measure directions of muons incident on the sample.
At step 104, a subset of the muon tracks are selected, giving preference to those that pass through the first type of material but not the second type of material. For progressively more accurate density measurement preferably over 90%, more preferably over 95%, even more preferably over 98% and most preferably 100% of the tracks in the subset pass through the first type of material but not the second type of material. For a nuclear reactor application, to be able to measure the graphite density most accurately it is best to determine a "pure" sample of muon tracks (the subset) that only pass through the concrete shielding and the graphite, not the fuel elements. In general, the better the purity of the sample, the better the result However, to achieve a purer sample, the cuts (to the sample size) have to be more restrictive, which costs statistics, which means a larger statistical error, or a longer measurement time. In practice the aim is to find an optimum balance between the smallest statistical error (statistics) and the smallest systematic error (purity of sample) to getthe smallest overall error. Preference may be similarly given to those that pass through the first type of material but not the second type and not one or more other type of material. In principle there could be any number of materials, preferably with most (and at best all) selected tracks not crossing the avoided materials. Preferably, the second type of material (and the one or more other type of material) has a higher average atomic number than the first type of material.
This step 104 may involve selecting detection coordinates as described with reference to Figure 2. In another example, selecting the subset may involve arranging muon detectors in relation to the first and second types of material, as described with reference to Figure 3. In these examples, selecting the subset may comprise calculating geometric location of the first type of material relative to location of the second type of material in the sample. The geometric location may be calculated by imaging muon interactions with the sample.
At step 106, incoming and outgoing muons traversing the subset of the muon tracks respectively before and after passing through the first type of material in the sample are detected.
At step 108, density of the first type of material is determined based on a ratio of incoming to outgoing muons traversing the subset of the muon tracks.
Figure 2 illustrates, in schematic form, an application of the method 100 for density measurement of graphite in a nuclear reactor 201, in accordance with an embodiment of the present invention. The nuclear reactor 201 has a concrete casing 218 and the reactor contains nuclear fuel elements 216 inserted in vertical channels formed in a graphite moderator 214. Upper and lower muon detectors, respectively above 202 and below 208 the nuclear reactor 201, are used to determine muon tracks incident on the nuclear reactor 201. In this example, the muon detectors comprise four modules 204, 206, 210 and 212, each of which has two orthogonal layers of arrayed scintillatng fibres, wherein scintillation detectors are arranged with the scintillating fibres to detect photons generated by muons passing through the scintillating fibres. With their fibres, each of the modules (204, 206, 210,212) can detect the coordinates of a muon in two dimensions (e.g. x and y). With a known vertical separation z12 between a pair of modules, a 3D trajectory can be calculated from the muon detection coordinates (e.g. xi, yi, and x2, y2).
With reference to the cross section of Figure 2, muons are incident on the nuclear reactor 201. The muons travel along corresponding muon tracks. A subsetof the muon tracks incident on the nuclear reactor 201 is selected by selecting a subset of muon detection coordinates. The subset of muon detection coordinates define muon tracks that pass through graphite moderator material 214 but not the nuclear fuel element material 216. For example, a muon track 224 of a muon 220, which belongs to the subset is defined by muon detection coordinates including coordinates (xi, yi) of a first point 226, at which the muon 220 passes through the uppermost module 204, and coordinates (X2, y2) of a second point 228, at which the muon 220 passes through the next module 206.
For illustrative purposes, a muon track 232 is shown (for a muon 230) that is not a member of the subset It is not a member of the subset because the muon detection coordinates of its first 234 and second 236 points, at which the muon 230 passes through the upper modules 204 and 206 respectively, define a track 232 that passes through not only the graphite moderator material 214, but also the nuclear fuel element material 216. In the 2D cross-section plane illustrated in Figure 2, the subset of the muon tracks is restricted to an acceptance region defined by the boundaries 222 and 223. In 3D, the subset of the muon tracks is restricted to an acceptance volume. The shape of the acceptance volume will depend on the geometric location of the graphite relative to the nuclear fuel element material. The muon detection coordinates may be selected for example by filtering them out of a larger measured dataset, or by activating or reading from only a subset of available photodetectors.
With respect to Figure 3, selecting the subset of the muon tracks comprises arranging muon detectors in relation to the first and second types of material. In an example, the muon detectors above 202 and below 208 the nuclear reactor are configured with modules (304, 306, 310, 312) that have detector dimensions that fit within the acceptance volume that encloses the possible tracks that pass through the graphite but not the fuel elements. This configuration reduces the total number of the muons tracks to be detected by the muon detectors. However, because of its small detectors, it is not suitable for imaging the reactor, in the same way that a larger detector, as illustrated in Figure 2, would be. The detection arrangements of Figure 2 and 3 may be combined in different ways. One or more of the detector modules may be moveable. For example, it may be possible to put a large area detector on top of a reactor (as in Figure 2), but space constraints may mean only a small moveable detector (as in Figure 3) is used underneath the reactor.
Selecting the subset of the muon tacks may involve calculating geometric location of the firsttype of material relative to location of the second type of material in the sample. It is understood that the concrete wall 218 and the graphite moderator 214 shall not deflect cosmic-ray muons, whereas the nuclear fuel elements 216 (high-Z matter) can scatter or absorb the muons. In an example, a conventional tomographic reconstruction of the nuclear reactor 201 is created from imaging muon interactions with the nuclear reactor 201, based on which geometric locations of the graphite moderator 214 and the nuclear fuel elements 216 can be determined. Alternatively, a calibrated CAD (computer-aided design) model may be constructed from physical measurements and historical data. The subset of the muon tracks that pass through the volume corresponding to the geometric location of the graphite moderator 214 but not the volume corresponding to the geometric location of the nuclear fuel elements 216 can be selected.
Referring in Figure 2 in more detail, a number of incoming 221 and outgoing 225 muons traversing the subset of the muon tracks respectively before and after passing through the graphite moderator 214 in the nuclear reactor 201 are detected by muon detectors 202 and 208, respectively. The difference between the number of incoming 221 and outgoing 225 muons indicates muons that would have reached the detectors 208 in the absence of absorption by the graphite moderator 214. The absorption of those muons depends on the density of the graphite moderator 214, which is proportional to a mathematical function of the negative logarithm of a ratio of the number of incoming muons 221 (denoted by No) and outgoing muons 225 (denoted by N) as follows: p logN/No) Embodiments allow the application of this equation to measure the density of low-Z material (e.g. the graphite moderator 214) within the nuclear reactor 201, while advantageously avoiding scattering of muons in high-Z material (where Z is atomic number) like the nuclear fuel elements 216. This reduces errors in density measurement of the low-Z material.
Fluctuations in cosmic-ray muon flux, e.g. due to changes in atmospheric pressure, affect both the muon detectors above 202 and below 208 the nuclear reactor 201 in 30 the same way.
In embodiments, a subset of the muon tracks that pass through the nuclear fuel elements 216 but not the graphite moderator 214 is selected. Density measurement of the nuclear fuel elements 216 is achieved by determining a ratio of incoming and outgoing muons traversing the subset of muon tracks respectively before and after passing through the nuclear fuel elements 216. The density measurement of the nuclear fuel elements 216 can be used to inspect the nuclear reactor 201 during decommissioning for remaining fuel elements and to confirm that all fuel has in fact been removed. This will be of great importance for the Magnox reactors in the UK that are being decommissioned.
Figure 4a illustrates, in schematic form, a graphite structure simulated with the GEANT4 package, wherein the structure 401 comprises a 6-metre graphite block 404 placed between two layers of concrete 402, each of which is 3 metres in depth. Figure 4b is a graph depicting a correlation between density D (x-axis in g/cm3) of the graphite 404 and negative logarithms (y-axis) of ratios of incoming and outgoing muons traversing a subset of muon tracks (e.g. 424), which are determined by the muon detectors 402 and 408 respectively. Figure 4b is a generally representative result of a particular Monte Carlo study, i.e. for a particular thickness and statistics.
Figure 4b demonstrates that with a simple calibration the negative logarithms (y-axis) can be used as measurement of the graphite density (x-axis). The measurement of the graphite density can be analysed in terms of an overall average density of the graphite 404, a horizontal 2D density distribution or a 3D density distribution so long that the detectors are in sufficient dimensions in relation to the structure. In an example, a tessellation with several detectors above and/or below the nuclear reactor can be used to image nuclear reactors with a larger volume. In another example, a combination of two static detectors with one or several additional moving detectors may be used.
Figure 5 illustrates an apparatus of muon radiography for density measurement comprising a muon detection system 502 configured to determine muon tracks incident on a sample comprising a first type of material and a second type of material; and a processor 504 configured to a) select a subset of the muon tacks giving preference to those that pass through the first type of material but not the second type of material; b) detect incoming and outgoing muons traversing the subset of the muon tracks respectively before and after passing through the first type of material in the sample; and c) determine density of the first type of material based on a ratio of the incoming to outgoing muons traversing the subset of the muon tracks. The apparatus may be used in accordance with the methods described with reference to Figures 1 to 4.
S
A computer program product 506 is illustrated in Figure 5. It comprises a computer usable medium, in this example a memory card, where the computer usable medium comprises a computer program code that when executed by a computer apparatus (such as processor 504), determining density according to the method described with reference to Figures 1 to 4.
Claims (15)
- Claims 1. A method of muon radiography for density measurement comprising the steps: -determining muon tracks incident on a sample comprising a first type of material and a second type of material; -selecting a subset of the muon tracks giving preference to those that pass through the first type of material but not the second type of material; -detecting incoming and outgoing muons traversing the subset of the muon tracks respectively before and after passing through the first type of material in the sample; and -determining density of the first type of material based on a ratio of the incoming to outgoing muons traversing the subset of the muon tracks.
- 2. The method of claim 1, wherein selecting the subset comprises selecting those that pass through the first type of material but not the second type of material.
- 3. The method of claim 1 or claim 2, wherein selecting the subset of muon tracks comprises selecting a subset of muon detection coordinates.
- 4. The method of claim 1 or claim 2, wherein selecting the subset comprises arranging muon detectors in relation to the first and second types of material.
- 5. The method of any preceding claim, wherein selecting the subset comprises calculating geometric location of the first type of material relative to the second type of material in the sample.
- 6. The method of claims, wherein the geometric location is calculated by imaging the sample based on muon interactions with the sample.
- 7. The method of claim 6, wherein a muon detection system is used both for the imaging of the sample and for the detecting of incoming and outgoing muons for determining the density.
- 8. The method of any preceding claim, wherein selecting the subset comprises selecting a subset of the muon tracks giving preference to those that pass through the first type of material but not the second type and another type of material.
- 9. The method of any preceding claim, wherein selecting the subset comprises selecting those that pass through the first type of material but not the second type or another type of material.
- 10. The method of any preceding claim, the sample comprises components of a nuclear reactor.
- 11. The method of any preceding claim, the first type of material comprises a moderator.
- 12. The method of claim 11, the moderator comprises graphite.
- 13. The method of any preceding claim, the second type of material comprises nuclear fuel elements.
- 14. A muon radiography apparatus for density measurement comprising the steps: -a muon detection system configured to determine muon tracks incident on a sample comprising a first type of material and a second type of material; and -a processor configured to: -select a subset of the muon tracks giving preference to those that pass through the first type of material but not the second type of material; -detect incoming and outgoing muons traversing the subset of the muon tracks respectively before and after passing through the first type of material in the sample; and -determine density of the first type of material based on a ratio of the incoming to outgoing muons traversing the subset of the muon tracks.
- 15. A computer program product comprising a computer usable medium, where the computer usable medium comprises a computer program code that when executed by a computer apparatus, determining density according to the method of any of claims 1 to 13.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2005156.1A GB2594051B (en) | 2020-04-07 | 2020-04-07 | Muon radiography |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2005156.1A GB2594051B (en) | 2020-04-07 | 2020-04-07 | Muon radiography |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB202005156D0 GB202005156D0 (en) | 2020-05-20 |
| GB2594051A true GB2594051A (en) | 2021-10-20 |
| GB2594051B GB2594051B (en) | 2023-10-11 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB2005156.1A Active GB2594051B (en) | 2020-04-07 | 2020-04-07 | Muon radiography |
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| GB (1) | GB2594051B (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150279489A1 (en) * | 2014-04-01 | 2015-10-01 | Los Alamos National Security, Llc | Non-invasive in-situ imaging of interior of nuclear reactors |
| US20150287237A1 (en) * | 2014-04-04 | 2015-10-08 | Decision Sciences International Corporation | Muon tomography imaging improvement using optimized limited angle data |
| US20160041297A1 (en) * | 2014-08-11 | 2016-02-11 | Decision Sciences International Corporation | Material discrimination using scattering and stopping of muons and electrons |
| JP2018036156A (en) * | 2016-08-31 | 2018-03-08 | 株式会社東芝 | Heavy element inclusion measuring apparatus and measuring method thereof |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU2015264759B2 (en) * | 2014-02-26 | 2018-07-26 | Decision Sciences International Corporation | Discrimination of low-atomic weight materials using scattering and stopping of cosmic-ray electrons and muons |
-
2020
- 2020-04-07 GB GB2005156.1A patent/GB2594051B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150279489A1 (en) * | 2014-04-01 | 2015-10-01 | Los Alamos National Security, Llc | Non-invasive in-situ imaging of interior of nuclear reactors |
| US20150287237A1 (en) * | 2014-04-04 | 2015-10-08 | Decision Sciences International Corporation | Muon tomography imaging improvement using optimized limited angle data |
| US20160041297A1 (en) * | 2014-08-11 | 2016-02-11 | Decision Sciences International Corporation | Material discrimination using scattering and stopping of muons and electrons |
| JP2018036156A (en) * | 2016-08-31 | 2018-03-08 | 株式会社東芝 | Heavy element inclusion measuring apparatus and measuring method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2594051B (en) | 2023-10-11 |
| GB202005156D0 (en) | 2020-05-20 |
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