JPS648795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-powered neutron flux and gamma flux detection device.

Self-powered neutron flux and gamma flux detection devices are used extensively in nuclear reactors. In some applications, these detection devices are used as primary detection devices in nuclear reactor safety systems, while in other applications they are used as primary detection devices in nuclear reactor control systems. In such applications, it is highly desirable to match the dynamic response of the detection device to the dynamic behavior of the nuclear fuel power. Although most of the thermal power in a nuclear fission reactor comes from the direct fission of the nuclear fuel, the so-called fission power, a significant proportion of the power comes from the beta- and gamma-ray energy released by the radioactive fission fragments, the so-called delayed firing. This is due to the output. In a CANDU-type natural uranium heavy water reactor, for example, about 93% of the equilibrium thermal power generated in the nuclear fuel is due to direct fission of the fuel, while about 7% is due to the decay of the fission fragments. ing. Said component follows changes in neutron flux quickly, while the latter component does not follow changes in neutron flux quickly. The reason is that fission fragments decay with a wide range of time constants, varying from seconds to days.

An ideal neutron flux and gamma flux detection device for use in nuclear reactor controls and safety systems would respond to changes in neutron flux in exactly the same manner as nuclear fuel responds.

Self-powered neutron flux and gamma flux detection devices usually consist of mineral insulated coaxial cables. The central electrode is called the emitter, while the outer electrode is called the collector. These two electrodes are electrically isolated from each other by a mineral oxide insulator. This insulator is usually MgO or
_Al2O3 , but other oxides can also be used _. In many applications, self-powered detection devices are used to measure power, ie, neutron flux and gamma ray flux, over a limited area of the reactor core. In these applications, the detection device is connected to a lead cable, which can also be a mineral insulated coaxial cable.
However, by appropriate selection of geometry and materials, and by lead cable compensation techniques, the self-output signal generated at the lead cable can be adjusted to be a small proportion of the signal generated at the detection device.

In a power reactor, the current generated in a self-powered detector is caused by three separate interactions: a beta radionuclide captures a neutron in the detector, usually an emitter electrode; (n, β) interaction, γ-rays generated by trapping neutrons in the detection device release free electrons by Compton and photoelectric processes, thus generating a net current between the two electrodes (n, gamma, e) interactions and reactor gamma rays generated in the fuel and reactor hardware interact in the detection device to produce a net current between the two electrodes. This is due to the (γ, e) interaction that causes Since (n, β) interactions are delayed, detection devices in which such interactions are the dominant current generation mechanism, such as detection devices with vanadium or rhodium emitters, are used in nuclear reactor control and safety equipment. It is not suitable for use as a primary detection device. Therefore, in these applications detection devices are used in which the current is essentially due only to (n, γ, e) and (γ, e) interactions. It is almost impossible to manufacture a detection device in which (n, β) interactions do not occur, and careful selection of materials can reduce the proportion of current generated by such interactions to a few percent of the total signal. It should be noted that it can be smaller than .

An idealized detector in which 100% of the signal is due to (n, gamma, e) interactions would respond effectively and instantaneously to changes in neutron flux. Such a detection device is 100% prompt. Therefore,
As mentioned above, the immediateness of the fuel output is only about 93%, so the response would be too fast for an ideal detection device. On the other hand, the signal
The response of an idealized detector that is 100% due to (γ, e) interactions would be too slow. The reason for this is that about one third of the gamma rays in a nuclear reactor are emitted late, and as a result about 67% of the signal component of such a detector is emitted immediately.

However, a detection device in which 21% of the signal is due to (γ, e) interactions and 79% of the signal is due to (n, γ, e) interactions has a prompt ratio of 93%, i.e. , this detection device would have the same immediate firing rate as the nuclear fuel output. Furthermore, since the delayed response of the detector is due to the delayed gamma rays of the reactor, the delayed response of the detector roughly matches the delayed output of the nuclear fuel. The reason is that delayed gamma rays result from the decay of fission products, which are the source of the nuclear fuel's delayed heat output.

Self-powered neutron flux and γ in a nuclear reactor
controlling the relative response of the flux detector to the reactor gamma flux and reactor neutron flux, such as to closely match the dynamic response of the detector signal to the dynamic response of the overall reactor fuel power; Attempts have been made to control the dynamic response of the detection device.

One method of controlling the relative response of detectors to reactor gamma-ray flux and reactor neutron flux is described in "Self-Powered Neutron Flux and Gamma Flux Detectors," published September 2, 1980, by Mr. CJALLan et al. Canadian Patent No.
As disclosed in US Pat. No. 1,085,066, the use of a relatively thick emitter coating layer of the order of 0.05 mm, for example made of platinum, completely covers the emitter core wire, for example INCONEL.RTM. The relative response of this type of detection device depends on the diameter of the emitter as well as the selection of the metal material of the emitter. The specific response is therefore determined by the particular geometry, which may be caused by, for example, the manufacturing method or the limited space during assembly used to house the detection device. A problem may arise that is incompatible with one or more constraints on the size of a certain detection device. If, for example, it is necessary to provide a detection device with an emitter with a platinum-coated “INCONEL” core a dynamic response that matches that of the fuel power of a heavy water-moderated natural uranium reactor. For example, the emitter of the detection device must have an overall diameter of approximately 2.9 mm. Such a detection device would have an outer diameter of approximately 5 mm;
Additionally, housing such a large detection device in an existing heavy water-moderated natural uranium reactor poses various problems.

Another method of controlling the relative response of the detector to the reactor gamma ray flux and the reactor neutron radiation is the "Self-powered Neutron Detector" issued to Mr. LOJOHANSSON on October 31, 1978. As disclosed in US Pat. No. 4,123,658, the use of very thin (less than 5 microns) cladding of, for example, platinum on a cobalt core. By adjusting the thickness of this cladding layer,
It is possible to control the response of the reactor to gamma rays, and therefore the dynamic response.
Although the detection device proposed by JOHANSSON is useful, it suffers from manufacturing problems in that it is very difficult to adjust the thickness of the necessary very thin cladding layer. Therefore, it is difficult to adequately control the dynamic response of the detection device.

Thus, for example, it is possible to provide a dynamic response that closely matches that of the fuel power, which can be easily accommodated in existing heavy water-moderated natural uranium reactor detection equipment assemblies and which does not pose particular manufacturing problems. There is a need to obtain a self-powered neutron flux and gamma flux detection device with.

The present invention includes an emitter core wire, an emitter outer layer made of a different metal attached around the emitter core wire, a metal collector formed around the emitter core wire and the emitter outer layer, and a metal collector formed around the emitter core wire and the emitter outer layer. and an electrical insulator electrically insulating the outer layer from the metal collector, the self-powered neutron flux and gamma flux detection device having an overall diameter of the emitter core wire and the emitter outer layer of at least 0.4. mm, the emitter outer layer covers a range of only about 10% to about 90% of the surface area of the emitter core wire, and has at least one band around the emitter core wire, and has a width of about 0.02 mm to 0.07 mm. the metal of the emitter core wire, the metal of the emitter outer layer, the metal of the metal collector, the overall diameter of the emitter core wire and the emitter outer layer, and the emitter covered by the emitter outer layer; The device for detecting the surface area of the core wire has a prompt firing ratio in the range of about 90% to about 96% and has a dynamic response that substantially matches the power response of the nuclear fuel output of the reactor in which the detection device is to be used. The present invention provides a self-power supplying neutron flux and gamma ray flux detection device characterized by the following selections.

In an embodiment of the invention, the emitter core wire is made of a material selected from the group consisting of nickel, iron, titanium, chrome, cobalt, and alloys based on at least one of these metals; The outer layer is comprised of a material selected from the group consisting of platinum, palladium, tantalum, osmium, molybdenum, cerium, tin, ruthenium, niobium, zirconium and alloys based on at least one of these metals. .

In another embodiment of the invention, the emitter outer layer has a number ranging from 5 to 10 bands having equal widths along the length of the emitter core and equally spaced longitudinally. It is equipped with

In other embodiments of the invention, the emitter outer layer comprises 40% to 60% of the surface area of the emitter core wire.
% is placed above it.

In another embodiment of the invention, the emitter core wire is comprised of a nickel-based alloy, typically containing 76% by weight nickel, 15.8% by weight chromium, and 7.20% by weight iron, and the emitter outer layer is comprised of platinum. has been done.

In embodiments of the invention for use as fuel output detection devices in heavy water-moderated natural uranium nuclear reactors, the emitter core wire is typically 76% nickel by weight, chromium.
Preferably, it is composed of a nickel-based alloy containing 15.8% by weight and 7.20% by weight of iron, or of high-purity iron or high-purity nickel, and the emitter outer layer is of platinum or tin or molybdenum. It is preferable to configure
Further, the overall diameter of the emitter core wire and the emitter outer layer is preferably about 2 mm or less.

In another embodiment of the invention, the emitter core is comprised of substantially solid nickel and the emitter outer layer is comprised of platinum.

In one embodiment of the present invention, the emitter core wire is made of a material selected from the group consisting of nickel, iron, titanium, chrome, cobalt, and alloys containing at least one of these metals as a main component, and The outer layer comprises at least two different materials selected from the group consisting of platinum, palladium, tantalum, osmium, molybdenum, cerium, tin, ruthenium, niobium, zirconium and alloys based on at least one of these metals. Equipped with a band.

FIG. 1 shows an emitter core wire 1, an emitter outer layer formed of a different metal and generally indicated by the reference numeral 2 attached around the emitter core wire 1, and an emitter outer layer formed around the emitter core wire 1 and the emitter outer layer 2. metal collector 4 and emitter core wire 1
and an electrical insulator 6 electrically insulating the emitter outer layer 2 from the metal collector 4, the self-power supplying neutron flux and γ-ray flux detection device comprising:
The overall diameter of the emitter core wire 1 and the emitter outer layer 2 is at least about 0.4 mm, and the emitter outer layer 2 covers a range from only about 10% to about 90% of the surface area of the emitter core wire 1, and the emitter core wire 1 at least one, typically 5 to 10, bands around the
The metal of the emitter core wire 1, the metal of the emitter outer layer 2, the metal of the metal collector 4, the emitter core wire 1, and the emitter outer layer 2 are shown as 4 and 15 and have a thickness of about 0.02 mm to 0.07 mm. and the surface area of the emitter core wire 1 covered by the emitter outer layer 2, if the detection device has a prompt firing ratio in the range of about 90% to about 96% and the detection device is of the reactor fuel to be used. A self-powered neutron flux and gamma flux detection device is shown characterized in that it is selected to have a dynamic response that substantially matches that of the output.

In one embodiment of the invention, the emitter core wire is made of Inconel and includes several platinum tubes drawn from several oversized tubes to form an emitter band, as shown at 12, 13, 14, and 15. As a result, the emitter core wire 1 and the emitter bands designated by reference numerals 12, 13, 14, and 15 are brought into conductive contact along the length direction. Emitsuta core wire 1 and collector 4
A device 8 for measuring the strength of the current flowing between the electrodes is connected by a coaxial extension cable 10 to these electrodes. The electrical insulator 6 is in this embodiment a compressed metal oxide powder, for example a magnesium oxide powder. The electrical insulator 6 is the collector electrode 4
The cable 10 is sealed by a closed end 20 and an electrically insulating epoxy resin seal 22 at the end of the cable 10.

The dynamic response of such a detection device depends on the ratio of the emitter core wire 1 that is covered; the higher the ratio, the slower the dynamic response; it also depends on the diameter of the emitter; the smaller the diameter of the emitter, the slower the response. It also depends on the atomic number of the metal in the bands 12 to 15, and the smaller the atomic number, the faster the response. For a given emitter diameter, a given core wire 1 material, and a given band 12 to 15 material, the emitter should be shielded so that the dynamic response of the detection device best matches the delayed output of the nuclear fuel. There is generally an optimum value for the surface area ratio of the core wire 1. This ratio was determined by experimentally measuring the dynamic response of a detection device with a core 1 without an outer emitter layer 2, and the dynamic response of a detector with an emitter core 1 completely covered by an outer emitter layer 2. It can be easily determined by measurement. Thus, for example, F ₁ is an emitter of the first type, i.e.
is the immediate firing ratio of a detection device with an emitter without an emitter outer layer 2, and F ₂ is the emitter of the second type, i.e. an emitter in which the emitter outer layer 2 completely covers the emitter core 1; This is the promptness ratio of the detection device that the company has, and
If F _fuel is the ratio of fuel output that is prompt, then
A sensing device in which the emitter outer layer 2 covers a ratio X of the emitter core 1 will have a prompt ratio equal to the prompt ratio of the fuel output if X is given by:

X=F ₁ −F _fuel ／F ₁ −F _2From the experiment, the overall diameter of the emitter is approximately 1.5mm.
, a collector made of nickel 4, an emitter core wire 1 made of nickel, and an emitter outer layer 4 made of platinum.
For a 3 mm diameter detector _with
1.02 and _F2 was found to be approximately 0.90. Therefore, in order to obtain a prompt-fire ratio of 0.93, which is the ratio of fuel power that is prompt-fire in a CANDU-type natural uranium deuterium moderated reactor, approximately 75
A detection device is used which has a nickel core wire 1 covered with an emitter outer layer 2 of % platinum. For use in a nuclear reactor safety system, it is desirable that the response of the detection device be slightly faster than the fuel output so that a slightly smaller proportion of the emitter core wire 1 is preferably shielded.

The dynamic response of a detection device with a given type of emitter also depends on the material used for the collector 4. Thus, for example, if the nickel collector 4 of the above detection device were replaced by a Zircaloy collector 4, F ₁ would be approximately
1.04, F ₂ is about 0.80, and thus in order to obtain a prompt ratio of about 0.93 with a detection device having a Zircaloy sheath, about 46% of the Nickel emitter core wire 1, assuming an overall diameter of the emitter of 1.5 mm. Preferably, a detection device is used which is only covered by the platinum emitter outer layer 2.

In practice, matching the prompt ratio of the sensing device to the prompt output of the fuel using a single material of the emitter outer layer 2 does not necessarily result in perfect matching of all late components. The reason is that it is generally not possible to manufacture a detection device that contributes zero from the (n, β) interaction. For example, using the above emitter materials, ie, nickel and platinum, the small slow current is attributable to the β-decay of 199pt with a half-life of 30.8 minutes and the β-decay of 65Ni with a half-life of 2.57 hours.
Nevertheless, it becomes possible to closely match all of the dynamic responses of the sensing device to the dynamic responses of the fuel output.

According to the above-mentioned Canadian Patent No. 1085066, the gamma ray sensitivity of an emitter with a core material and a covering material is approximately
It is known that saturation can be achieved with a coating thickness of 0.02 mm. By using one or more bands such as 12 to 15, the thickness of bands 12 to 15 may be at least about 0.02 mm, thereby increasing the sensitivity of the detection device to said bands. It is possible to avoid variations that occur during manufacturing due to changes in the thickness of the material. Moreover, by changing the total percentage of surface area of the emitter core 1 covered by the bands 12 to 15, the emitter core 1 and the band 1 have a specific overall diameter and are of a specific metal.
A specific dynamic response can be obtained in a detection device with 2 to 15. Therefore, in a detection device in which the emitter core wire 1 and the bands 12 to 15 have a particular overall diameter and are constructed of a particular metal, the total percentage of the surface area of the emitter core wire 1 covered by the bands is equal to the emitter core wire 1. can be selected for the practical overall diameter and desired dynamic response. Since the overall sensitivity of the detection device decreases as the diameter of the emitter becomes smaller, there is a practical lower limit to the overall diameter of the emitter that can be used;
It is about 0.4mm.

As previously mentioned, the proportion of the surface area of emitter core 1 covered by bands 12-15 is the most important factor influencing the dynamic response of emitter core 1 and bands 12-15 to a given metal. However, if 1
If only one or two bands cover the emitter core wire, the position of the band should be the second one to be introduced.
It brings about the action of position. Therefore, in order to minimize this second-order effect, the emitter core 1 is divided into a relatively large number of bands, i.e., of equal width and with the emitter core 1 in order to obtain the desired shielding ratio.
preferably 5 to 10 longitudinally spaced
It is preferable to cover the area with two bands.

In FIG. 2, parts similar to those shown in FIG. 1 are given the same reference numerals, and the above description applies directly to this embodiment.

Referring to FIG. 2, for a given material of the emitter core wire 1, the materials of the second set of bands indicated by numerals 18 and 19 are compared to the materials of the first set of bands indicated by numerals 16 and 17 made of different materials. Bands can be used to improve alignment. Therefore, for example, in combination with the nickel emitter core wire 1, the first set of bands 16 and 17 are made of Pt, and the second set of bands 18 and 19 are made of Mo.
could be used. The prompt firing ratio is expressed by the following formula.

_{F cpn =} F _Ni (1- _{X Pt} -X _Mp ) + X _Pt ^{F Pt} _{Ni +}
is the prompt ratio obtained by a detection device with a bare nickel emitter core 1, i.e. without bands 16 to 19, F ^Pt _Ni is Pt
F ^Mo _Ni is the prompt ratio of a detector with a Nickel emitter core 1 completely covered with a layer of Mo, X _pt is the prompt ratio of a detector with a Nickel emitter core 1 completely covered with a layer of Mo, and the ratio of the Nickel emitter core wire 1 covered by 17,
And X _Mp is the ratio of the nickel emitter core wire 1 covered with Mo bands 18 and 19.

Similarly, the delayed component will be a linear combination of the delayed responses obtained by three arch-shaped representative emitters. Optimal response is usually X _pt
may be determined by a progressive error method by comparing the dynamic response obtained for a given set of values of and X _Mp with the dynamic behavior of the fuel power.

It should be noted that the thickness of bands 16 and 17 need not be the same as the thickness of bands 18 and 19. Similarly, the width of bands 16 and 17 need not be the same as the width of bands 18 and 19.

There are several methods of manufacturing emitter cores with bands according to the present invention, but the method depends to a large extent on the metal used for the emitter core and the band.

If the emitter core is composed of a very highly ductile metal, such as nearly pure nickel, and the band metal is relatively hard compared to the hardness of the emitter core, one or more of the band materials A number of tubular members can also be placed over an oversized emitter core and the assembly passed through a swaging die to press the band onto the surface of the emitter core and reduce the emitter core to the desired diameter.

However, if the emitter core is constructed of a metal that is relatively hard compared to the metal of the band, each band may first include metal in the form of a wire, strip, or sheet along the longitudinally extending portion of the emitter core. The bands can be formed by winding a layer of metal and then stretching each metal band flat on the surface of the emitter core wire. In this case, the band may at least partially protrude from the surface of the emitter core.

A third method of manufacturing emittee core wires with bands is to wrap a thin metal foil or wire in a closed or open helix around the emittee core wire as each band and, for example, by welding, peening or creasing. The ends of the helical metal foil or wire are fastened together and the collector and electrical insulation are then stretched by swaging to press and secure the band in place.

In nuclear reactors, it is desirable to use detection devices that respond slightly faster than nuclear fuel;
Nuclear fuel output is typically 93% prompt, so it is preferred that the detection device be 93% to 95% prompt.

From the foregoing description of the invention, it can be seen that generally the same techniques can be used to obtain self-powered neutron flux and other dynamic responses of the gamma flux detection device to override delayed responses due to gamma radiation in a nuclear reactor, for example. It will be clear that the neutron flux response can thereby be substantially matched.

[Brief explanation of drawings]

Fig. 1 is a side view of a broken section of a self-power supplying neutron flux and gamma-ray flux detection device, and Fig. 2 is a side view of a cutaway cross-section of the self-power supplying neutron flux and gamma-ray flux detection device, which is different from that shown in Fig. 1. be. 1...Emitsuta core wire, 2...Emitsuta outer layer,
4... Collector, 6... Electric insulator, 8... Current measuring device, 10... Cable, 12, 13, 1
4, 15, 16, 17, 18, 19...band,
22...Seal.

Claims (1)

[Scope of Claims] 1 (a) an emitter core wire, (b) an emitter outer layer of a different metal attached around the emitter core wire, and (c) an emitter outer layer formed around the emitter core wire and the emitter outer layer. A self-power supplying neutron flux and gamma ray flux detection device comprising: a metal collector; (d) an electrical insulator electrically insulating an emitter core wire and an emitter outer layer from the metal collector; the overall diameter of the core wire and the emitter outer layer is at least about 0.4 mm; at least 1 in
(g) the metal of the emitter core wire, the metal of the emitter outer layer, the metal of the metal collector, the entirety of the emitter core wire and the emitter outer layer; The detection device determines the diameter of the emitter core wire and the ratio
X _{is determined by _ _ _} self-power supply neutron flux and γ, characterized in that F _fuel is the prompt ratio of the detection device covered by
Ray flux detection device. 2. In the self-power supplying neutron flux and γ-ray flux detection device according to claim 1, the emitter core wire is made of nickel, iron, titanium, chrome,
The emitter outer layer is made of a material selected from the group consisting of cobalt and alloys containing at least one of these metals as a main component, and the emitter outer layer is made of platinum, palladium, tantalum, osmium, molybdenum, cerium, tin, ruthenium, niobium. , zirconium, and alloys containing at least one of these metals as a main component. 3. The self-powered neutron flux and gamma ray flux detection device according to claim 1, wherein the emitter outer layer has an equal width along the length of the emitter core wire and is spaced equally apart in the longitudinal direction. 1. A self-powered neutron flux and gamma flux detection device characterized in that it comprises a number of bands ranging from 5 to 10 arranged in a range of 5 to 10 bands. 4. In the self-power supplying neutron flux and γ-ray flux detection device according to claim 1, the emitter outer layer has a surface area of 40% of the emitter core wire.
A self-power supplying neutron flux and gamma ray flux detection device, characterized in that the self-power supplying neutron flux and gamma ray flux detection device is arranged on the self-power supplying neutron flux and γ-ray flux. 5. In the self-power supplying neutron flux and γ-ray flux detection device according to claim 1, the emitter core wire is usually made of 76% nickel and 15.8% chrome.
and a nickel-based alloy containing 7.20% iron, and the emitter outer layer is composed of platinum. 6. In the self-power supplying neutron flux and γ-ray flux detection device according to claim 5, which is used as a fuel output detection device for a heavy water-moderated natural uranium nuclear reactor, the emitter core wire is normally made of nickel 76%,
The emitter outer layer is made of platinum, and the overall diameter of the emitter core wire and the emitter outer layer is about 2 mm or more. A self-power supplying neutron flux and gamma ray flux detection device characterized by having a small size. 7. In the self-power supplying neutron flux and gamma ray flux detection device according to claim 1, the emitter core wire is made of substantially pure nickel, and the emitter outer layer is made of platinum. A self-power supplying neutron flux and gamma ray flux detection device characterized by: 8. In the self-power supplying neutron flux and γ-ray flux detection device according to claim 1, the emitter core wire is made of nickel, iron, titanium, chrome,
The emitter outer layer is made of a material selected from the group consisting of cobalt and alloys containing at least one of these metals as a main component, and the emitter outer layer is made of platinum, palladium, tantalum, osmium, molybdenum, cerium, tin, ruthenium, niobium. , zirconium and alloys based on at least one of these metals. .