JPS5853443B2 - Dendoutai - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical conductor, and particularly to an electrical conductor that reduces radiation-induced current generated in a cable that transmits signals from a neutron detector destined for a nuclear reactor, etc. .

In order to operate a nuclear reactor as safely and efficiently as possible, the neutron envelope within the reactor core must be closely monitored.

To provide information on these nuclear reactive particles, multiple detectors are placed at specific locations within the reactor core.

Detectors arranged in this manner generate electrical signals that indicate the near-instantaneous nature of the overall neutron fraction within the core as well as the local magnitude of the expected intensity in this outer can.

Typically, self-activated detectors of this type have a centrally located ``emitter'' that responds to neutron radiation by emitting relatively high energy electrons (beta particles).

The energy of these electrons is weak enough to traverse the IJ-blade or annulus of insulating material surrounding the centrally located emitter and strike the conductive outer shell or "collector."

Generally speaking, the intensity of the neutrons produced is related to the amount of beta particles produced.

As a result, the lightning, which represents the flow of electrons through the conductor per unit time, provides an indication of the neutron mass density at the measurement point within the reactor.

In either case, the detectors are linked by coaxial cables to a control panel to carry the detector signals out of the core.

Typically, these cables include a centrally located conductor that is electrically isolated or insulated from the outer conductive pair assembly.

In order to avoid the generation of neutron-induced electrons and thereby allow the entire length of the cable to be considered as part of the neutron detector, the cable material should be neutron-insensitive and therefore reduce the possibility of neutron-electron reactions occurring. Selected from a group of materials that are rarely represented.

Nevertheless, a considerable length of this connecting coaxial cable is exposed to gamma rays generated within the reactor core.

Naturally, this gamma ray is related to the neutron stocking density at each measurement point through the Compton electron generation mechanism and Pond's gamma ray-electron phenomenon (of which photoelectron friend and thermionic emission phenomena are representative). generates undesired current.

A number of techniques have been devised to compensate for or avoid the occurrence of these erroneous signals induced in the cable.

For example, in one example, a detector array housed within the reactor core was provided with at least one cable that was not connected to the neutron detectors.

This unconnected cable produces an amount of current that is to be subtracted from the in-core detector signal of the song.

The cable response signal, subtracted arithmetic or through automatic calculation from each observed detector signal, will approximately eliminate the portion of the uncorrected detector signal that is in error due to gamma-ray induced currents in the detector cable. .

Another technique to compensate for these induced cable currents is to utilize a single cable with two insulated conductors twisted together.

One of the conductors is connected to a neutron detector to provide a neutron detector and cable combination signal.

The enclosed conductor is not connected to the detector and therefore produces only the background Cable 2 signal.

The algebraic calculation of these two signals should give a result that is a practical guide to the neutron mass density at the measurement point in the core.

All of these correction devices require at least one extra lead and require the provision of an algebraic calculator or equivalent.

Thus, these approaches to the background signal compensation problem require additional materials, effort, and computational equipment.

The introduction of these factors makes the neutron density measurement system more prone to error.

Clearly, there is a need for a more reliable and efficient background cable signal compensation technique.

According to the present invention, the above-mentioned drawbacks found in the prior art are overcome by substantially eliminating gamma-ray-induced cable lightning through proper selection of the materials and dimensions of the conductors and pair assemblies to be used in the detector cable. Mostly overcome by offsetting.

A signal from a neutron detector coupled to a cable made in accordance with the principles of the present invention determines the core neutron density at the measurement point, which is induced in the cable through gamma-ray interactions with the conductors and the assembly material. Indicates that stray current has been eliminated.

Specifically, electrons emitted from the pair assembly and flowing into the conductor through the intervening insulator provide a negative total current.

Electrons flowing in the opposite direction from the conductor to the pair end up giving a positive total current as measured at the pair and the conductor terminals.

In accordance with a feature of the invention, it has been recognized that this gamma-ray induced electron radiation is approximately proportional to the area of the emitting surface.

Furthermore, it has been observed that this electron radiation is proportional to a certain power of the atomic number Z of the member receiving the gamma ray irradiation.

In the latter case, the photoelectron reaction is proportional to Z to the fifth power and the Compton electrons are simply proportional to Z.

In conclusion, the electron emissivity is related not only to the surface area of the pair assembly and the conductor, but also to the 1 to 5 powers of the atomic numbers of each of these cable components.

Thus, through application of the present invention, a relatively low Z value material is selected for the large surface area mating assembly and a high Z value material is selected for the small surface area conductor.

By doing this, the γ-ray induced currents in opposite directions are brought into a substantially balanced state, that is, in a canceling relationship,
This brings the background current close to zero.

These γ-ray effects are even more pronounced in high-density materials such as copper, nickel, etc., so r@ interactions with low-density insulating materials (e.g., magnesium oxide, alumina) occur relatively infrequently, and therefore cable makes a negligible contribution to background electron generation within

Under these circumstances, the current observed at the goople terminal is a measure of the neutron density in the vicinity of the detector, and is not a background current that may be induced through gamma interactions with the cable material. Stray currents are automatically eliminated.

A number of cables embodying this principle of the invention are 1.57
51n7It (0,062 inch) outer diameter and 1.016
Inconel 60 with an inner diameter of mm (0,040 inch)
0 outer sheath body.

A Norcaloy 2 conductor having a diameter of 0.279 mm (0.011 inch) and placed coaxially with an Inconel 600 pair assembly in an insulating matrix of, for example, magnesium oxide, has a diameter of approximately 1.6 x 1013 nV (wherein nv
represents the neutron flux in units of neutrons/- seconds) 2.76 x 1 per unit α of the cable
We found that it produced only background lightning of less than 0'' A/nv.

This current is 1720 times less than the lightning induced in a cable of comparable characteristics (with the exception of Inconel 600 conductor) at a similar neutron flux.

A similar reduction in background lightning is also achieved with a 1,346 inch (0,053 inch) outside diameter Inconel 600 outer shell (0,178 inch (0,00 inch) wall thickness), compressed magnesium oxide insulation and a .191mm (0,0075
It was also observed through experiments conducted using a coaxial zirconium conductor with a diameter of

From the results of experiments conducted to confirm the principle of the present invention,
It could be concluded that for a given outer ring size and material there may be a certain diameter conductor of higher atomic number material that provides cancellation of the gamma-induced background current.

Of course, the opposite can also be said.

Thus, for a given conductor diameter and material, γ
There is an outer ring of specific dimensions made of low atomic number material that provides cancellation of line-induced background currents.

The present invention will be explained in more detail according to its preferred embodiments.

For a more complete understanding of the invention, the following two considerations regarding gamma-ray induced background currents in neutron detector cables are provided.
Recall that there are two main physical properties.

(1) Area of the surfaces of the outer ring and the conductor that face each other,
and (2) the respective atomic numbers of the outer ring body and conductor material.

As a result of detailed analysis, the number of γ-ray induced electrons emitted from the centrally arranged conductor in the coaxial cable is proportional to 29 dl.

Here the subscript l represents the conductor, d represents the conductor diameter, and the index n depends on the relative contributions of photoelectric and Compton effects to the background current.

In this case, the index n must be a number between 1 and 5.

Z is of course the atomic number of the conductor.

Furthermore, the number of electrons leaving the cable sheath is proportional to Z"d.

Here the subscript S represents the exocycle S and m depends on the relative contribution of the photoelectric and Compton effects to the electron emission.

The index m is a number between 1 and 5.

The indices n and m are, as mentioned above, any number between 1 and 5 and depend on the relative contributions of photoelectric and Compton phenomena to electron emission under particular conditions.

In other words, the photoelectric effect is proportional to the fifth power of Z, and the Compton effect is proportional to the first power of Z, so the larger the contribution of the photoelectric effect, the closer n and m will be to 5, and the larger the contribution of the Compton effect, the closer to 1. approach.

In order to establish the mathematical identity of the current flowing in opposite directions between the outer ring and the conductor, the following relationship is necessary: This means that the atomic numbers of the materials are correlated such that the number of electrons emitted by the outer ring and conductor, respectively, in response to photoelectric and Compton phenomena is substantially equal.

Under these circumstances, for cables with smaller diameter conductors within a larger diameter outer ring, the atomic number (
Zl! , Z8) and the associated indices (n, m), it is clear that the zero condition can be given.

Specifically, in order to mutually cancel out the background currents generated in response to gamma rays, the overall effect of the atomic number and electron radioactivity index characterizing the outer ring material is must be smaller than the effect of the index.

In practice, first the outer ring material and dimensions are selected to withstand the core environment and to be suitable for the accommodation space within the core.

Of course, the outer ring body material must be made of a material that does not easily cause neutron-electron reactions.

Another material having an atomic number greater than that of the outer ring material and also less likely to undergo neutron-electron reactions is then selected as the conductor material.

Then, conductive wire materials of various diameters are made, combinations of conductive wires of various diameters and outer rings are tested in the reactor core, and a conductive wire diameter that generates almost no background current is selected.

Between the conductor wire of the selected diameter and the outer ring body, the
) is substantially satisfied.

As in almost all practical applications, the formula (
There are pond phenomena that tend to modify the simple physical relationships expressed in 1).

For example, some electrons will almost certainly be generated as a result of neutron interaction with the cable material.

However, the electrons generated through the neutron reaction go beyond the gamma ray phenomenon defined by equation (1).

Consequently, according to an additional feature of the invention, the cable material must be selected with a view to finding a material that not only satisfies equation (1), but also has a low probability of neutron-electron reactions occurring.

This is because, even with the greatest care in material selection, after equilibrium conditions are achieved within the cable, neutron reactions will almost certainly make a modest contribution to the overall electron emission.

Therefore, it is desirable to use a conductor diameter that is about 0.0254 mm (1/1000 inch) larger than the theoretical optimum diameter predicted through equation (1).

If the cable characterizes the reactor equipment, for example 316℃
If used at high temperatures (600'F), the thermally emitted electrons will also be lost to unwanted cable current.

To compensate for this additional error source, the conductor diameter must be
．． 0254 mm (171,000 inches) [11].

This single violet increase in wire diameter will result in a positive gamma-induced electron flow, which will offset the opposite flow of electrons thermionically emitted from the pair assembly.

Depending on the inherent nuclear properties of the cable material used, the formula (
In addition to considering deviations from the ideal relationship defined in 1), it is also necessary to select a material that is metallurgically and mechanically compatible.

For example, the properties of the pair assemblies and conductor materials vary so much that it is extremely difficult to anneal drawn or swaged cables.

In order to confirm the principle of the invention, as shown in the drawings,
1.575 mm (0,062 inch) outer diameter and 1.01
A mating assembly 10 formed from Inconel 600 having an inner diameter of 0.216 mm (0.216 in.)
A number of cables were made for use in conjunction with conductors 11 formed from zirconium (Zircaloy-2) having diameters ranging from 0.085 inches to 0.025 inches.

An insulator 12 consisting of magnesium oxide was tamped into the annular space between the conductor 11 and the envelope 10.

Naturally, neutron reactions with insulating materials must also be avoided for a long time.

As a result, representative materials such as aluminum (A1203) and magnesium oxide (MgOX) have particularly small neutron absorption densities of the order of 0.011 cm and 0.0034 cm, respectively, based on their theoretical densities. are often selected for this purpose.

Inconel 600 contains, by weight, 76.5 parts nickel, 14.5 parts chromium, 8.2 parts iron, 0.19 parts copper, 0.26 parts silicon, 0.007 parts sulfur, 0.01 parts chromium, 0.01 parts copper, 0.26 parts silicon, 0.007 parts sulfur. 2
It has a typical composition of 5 parts manganese and 0.03 parts carbon.

Preferably, the manganese concentration should be reduced to 0.1 parts by weight or less to minimize the primary source of undesired neutron-induced electron radiation and is not shown in the example compositions above. However, cobalt should also be avoided.

Naturally, there will also be trace elements of the song. Zircaloy-2 typically contains zirconium with the balance being 15 parts tin and 0.1 parts tin.
It consists of ferromagnetic metal, 0.11% chromium, (106% nickel) and trace amounts of up to 10 elemental elements (of which aluminum, boron, carbon, copper, and...fnium are typical examples).

Each of the cables is rated at 149'C (3000°C) in the neutron and gamma environment established within the IMW pool reactor.
F) Tested at the following temperatures:

The background current generated in each of the cables tested as a result of this neutron and gamma radiation exposure was observed for approximately 15 minutes.

A 0.279 mm (0.011 inch) diameter conductor cable exposed to an average neutron flux of approximately 1.6 × 10”' nv in the reactor atmosphere is 2.76
It was found that only the following current was generated.

This induced current is 0.223 mm (0,009 inch)
approximately 20 times lower than the background current generated in conventional cables containing Inconel conductors of the same diameter.

As mentioned above, powerful and unwanted sources of electrons, of which thermionic radiation and neutron-induced reactions are representative examples, occur at high temperatures.

Therefore, in order to compensate for this, an additional cost of 0 is added to the conductor diameter.
．． 051 (2/1000 inch) is the standard.

In this situation, 0.330 mm (0,013 inch)
It was found that the diameter of the conductor is appropriate.

Obviously, the principles of the invention can be applied to cable materials and cable geometries as well as curve pair assemblies and conductor size combinations.

As previously stated, for a particular pair assembly and conductor material system, there are particular pair assembly and conductor diameter combinations that provide the greatest amount of background current cancellation.

At this point, as mentioned earlier, 1.346 mm (0,0
An Inconel 6009 outer shell with an outside diameter of 0.178 mm (0.00 inch) and a wall thickness of 0.178 mm (0.00 inch) and then a magnesium oxide insulated
Recall as another example a coaxial cable consisting of a zirconium conductor having a diameter of 1.5 inches.

This cable was tested and this is 0.279
It exhibited gamma-induced background electron susceptibility similar to cables using 0.011 inch (7!2 m) conductors.

As previously indicated, 0.0254 mm (1/1000 inch) must be added to the conductor diameter to compensate for the neutron action toward equilibrium within the cable relative to the environment in which it is placed. .

Also, if use at high temperatures is intended, 0.0254
mm (1/1000 inch) should be added to the diameter.

Thus, a 0.241 mm (0.0095 inch) diameter conductor would be appropriate for these situations.

Furthermore, various neutron fluxes and associated r-ray activities can be traced to 1/2 and 1/3 with varying degrees of significance.
It should also be noted that there is a tendency to create auto-background current effects.

However, the general relationship disclosed in Equation (1) provides a broad basic optimization relationship between pair assembly and conductor dimensions and materials.

Although the atomic number Z is specific for each element on the periodic table, in the case of the alloy and composition compositions described herein, it applies to all individual components of the composition under consideration. means a weighted number based on the atomic number and relative proportion of

[Brief explanation of the drawing]

The drawing shows a part of a cable according to the invention in partial section. The components in the figure are as follows = 10: paired assembly, 11:
Conductor, 12: Insulator.

Claims (1)

[Scope of Claims] 1. A conductive pair assembly made of a material that is unlikely to cause a neutron-electron reaction and a conductive wire disposed within the pair assembly and made of another material that is also unlikely to cause a neutron-electron reaction. , in which case the conductor material has an atomic number greater than the atomic number of the pair assembly material, and the diameters of the conductor and the pair assembly and the atomic numbers of the conductor material and the pair assembly material are responsive to the photoelectric phenomenon and the Compton phenomenon. 1. An electrical conductor characterized in that the number of electrons emitted by each of the pair assembly and the conductive wire are correlated so as to be substantially equal. 2. An electrical conductor according to claim 1, characterized in that an electrical insulator having a low neutron absorption cross section is interposed between the paired assembly and the conducting wire.