DE1265882B - Arrangement for the continuous measurement of the neutron flux in a reactor core - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN W7WWS PATENT OFFICE Int. Cl .:

G21d

EDITORIAL

Number:
File number:
Registration date:
Display day:

German: 21g-21/31

G 39947 VIII c / 21g
February 26, 1964
April 11, 1968

The invention relates to an arrangement for continuously measuring the neutron flux in one Reactor core with pipelines penetrating the core through which an activatable substance flows and those outside the core with radiation detectors to measure the activity of the effluent Substance are provided.

To monitor the behavior of nuclear reactors under various operating conditions To be able to do so, it is absolutely necessary to determine the temporal distribution of the neutron flux in the reactor core to measure continuously.

For this purpose, different methods and arrangements are currently in use, in which one uses small ionization chambers, thermocouples or wires or bands made of metal, which are activated and then checked point by point. In reactors with a large neutron flux, measurements of this type are carried out discontinuously or intermittently, both because of their principle and because the thermocouples or ionization chambers only have an extremely short life. For example, an ionization chamber with a boron deposit in a flow of thermal neutrons of 10 ¹⁴ n / cm ² s loses 4% of its sensitivity per day of operation, and an ionization chamber with a uranium deposit loses 0.7% of its sensitivity under the same conditions.

Furthermore, from the Austrian patent specification 220 256 a method is known in which a by Neutron activatable gas is sent through the reactor core and the activity of the exiting Gas is measured. The flow rate is pressed through narrow channels Gas changed. The result of the reactivity measurements during a period of change in the Flow velocity is differentiated and provides a measure of the flow distribution. This too known measuring method works discontinuously in principle.

The invention is therefore based on the object of specifying an arrangement that has a continuous Measurement of the neutron flux also permitted in high-power reactors.

According to the invention, this object is achieved in that two each other except for a line section of the one line at the location of the measuring point the same lines are run parallel to each other through the reactor core, one of which is connected to the Measuring point in its cross section to increase the dwell time of the activatable substance at this point Activation chamber is expanded, and that

Arrangement for continuous measurement
the neutron flux in a reactor core

Applicant:

Groupement Atomique Alsacienne Atiantique,

Le Plessis-Robinson, Seine (France)

Representative:

Dipl.-Ing. R. Beetz

and Dipl.-Ing. K. Lamprecht, patent attorneys,

8000 Munich 22, Steinsdorfstr. 10

Named as inventor:

Yves Wilmart, Paris;

Jean Laxague,

Chatenay-Malabry, Seine (France)

Claimed priority:

France of February 26, 1963 (926 106)

Outside the core, two radiation detectors are arranged in a differential circuit on the lines are.

With this arrangement, the circulating activatable substance is retained in the activation chamber during a time equal to the volume of this chamber in relation to that Throughput of the substance in the entire circulation within the reactor; the activation of the substance is proportional to the neutron flux that surrounds it; consequently the activity of the substance at the exit from the core of the reactor basically depends on the size of the neutron flux in the area of the Activation chamber dependent.

In the core of the reactor there are two circulations fed in the same way with the substance, in where the flow medium flows at the same speed. Make the two circuits through the core of the reactor; however, one of the circuits contains an activation chamber, through which the substance must flow and in which it is subjected to the effect of the neutron flux which is present in the region of the chamber or surrounds this chamber. The presence such an activation chamber is the only difference between the two circuits; every The difference in the activity of the substances emerging from the reactor in the two circulations is due to this.

809 538/426

based on the presence of one of these substances in the activation chamber.

This difference is measured immediately when the substances emerge from the reactor and makes it is possible at any time to determine the size of the neutron flux at the point where the activation chamber is is located. If you use a differential measurement system, for example with a Device for immediate display or a recording device is provided, one can determine the value of the neutron fiow read at any moment as the measurement and display are continuous.

Depending on the number of points at which the neutron flux is to be measured, and accordingly the position of these measuring points, several circuits, each provided with an activation chamber, can be used be built into the reactor core; each of these circuits is a direct flow circuit assigned. In certain cases, if the measuring points are sufficiently close to one another, you can the activities of the substances in the corresponding circulations one after the other with the activity of the Substance can be compared to a single circulation with direct flow through the nucleus flows through.

According to a further embodiment of the arrangement, the differential measuring system that measures the activities is gaseous Compares substances, formed by a differential ionization chamber with two structural units, F i g. 1, 2 and 3 three schematic longitudinal sections through different versions of activation chambers,

F i g. 4 an ionization chamber, one half in vertical section, the other half in external view,

F i g. 5 an arrangement of several measuring channels,

F i g. 6 a different arrangement of the measuring device,

F i g. 6 a shows a section along the section line VI-VI of FIG. 6,

F i g. 7 shows a vertical section through measuring channels arranged symmetrically around a single feed line,

F i g. 8 on a larger scale one of the activation chambers of FIG. 7,

9 shows an assembly diagram of a measuring device with recirculation of the gaseous fluid.

As one can see from FIG. 5 recognizes, the measuring arrangement exists from two lines 17, 17 a of small diameter, which are side by side and parallel to each other are arranged in the reactor core; in the course of one of these lines 17 a there is an activation chamber 18 at the measuring point. Furthermore, means (not shown) are provided which serve to use equal amounts of the same activating substance at the same speed through similar

Flow media emerging from the ionization chambers are returned via the collecting line 23 discharged.

Each of the ionization chambers 20, 21 is connected to a display system or a registration system (not shown) connected, which indicates the value of the output current of the chamber in question, so one Value from which the size of the neutron fluaee can easily be determined

Pass parts of each of the lines through. Further

each of which by the substance in one of the lines 30 are each made up of two units 20 and 21 consisting of donations is traversed and the high voltage ionization chambers are present, their openings opposing polarity fed each means of that in one of the cable runs are provided, wherein means are provided in order to control the outflowing activatable substance, which in the following read the input current of the ionization chamber or be referred to as flow medium for short, register it; there is also a collection device for the 35 flows; these ionization chambers are made with escaping gases provided. Voltages of opposite polarity fed. the

At the electrical output of the "double" ionization chamber, an output current is detected its current strength proportional to the difference in the current strengths of the output currents of each of the two Units of the ionization chamber, d. H. proportional to the difference between that of the activity of the Substance in the first circulation or the first conduction dependent current strength (this substance

has flowed through the activation chamber) 45 can be determined in the area of the activation chamber and the strength of the current that can depend on the activity of the sub-.

punch in the second cycle depends, which only so far The activation chamber can, for example, a

has been activated, like the substance in the other cylinder with optionally conical inlet and Cable run or circulation in the lines alone - outlet part or a cylinder with built-in guiding influence became. For the sake of simplicity, sheets or a cylinder with a screw are used be the two circulation lines and the activation line-shaped partition that denotes the flow chamber with the expression "measuring channel". flow through the chamber.

According to a variant, a difference can be made. The F i g. 1, 2 and 3 each show a simple ©

Assign ionization chamber to several measuring channels; cylindrical activation chamber 1 (FIG. 1) with, in this case, switching valves are provided, one chamber (FIG. 2) with 55 conical inlets and outlets 2 and 3 for the flow of measuring channels in succession to the ionization chamber symmemer to "switch". One can also take advantage of it
a same vertical axis around activation chambers at different altitudes together
arrange with their lines and such 60
Arrangement a single direct passage circulation
or assign "compensation cycle", where one
then the changeover only with the lines
the activation chambers.

Further advantages and features of the arrangement will become apparent from the detailed description of a Embodiment of the invention clearly, which is illustrated in the drawing. In this show trically arranged in the cylinder baffles 4 and finally (Fig. 3) a cylindrical chamber with a helical guide coil 5.

The flow of the flow medium within the activation chamber can also be through others Internals or means are performed, as is the case, for example, with the embodiment according to FIG. 8 shows which is described below.

The line in which the activation chamber is located and the line without the activation chamber for direct flow of the flow medium are each provided with a structural unit of the ionization chamber

bound, which in turn expediently and in particular with low throughputs a The gaseous flow medium consists of a cylinder equipped with transverse plates, the plates of which are alternately connected to a high voltage electrode and to a collecting electrode; the cylinder has an inlet and outlet opening for the flow medium from the corresponding Duct comes from. The differential ionization chamber is by a combination formed two such units, the electrical output signals of which are fed to a recorder after appropriately amplifying them by known means if necessary.

The ionization chamber according to FIG. 4 includes two identical units 6, one of which is shown in section in the drawing.

A cylindrical unit 6 comprises: an axial inlet 7 for the gas or flow medium coming from one of the lines of the measuring channel, and an outlet 8 for the same flow medium, a cover 9 through which the outlets 8 and the electrical feed lines 10 as well the measuring lines 11 pass through and which, via retaining and protective rings 12 and insulating parts 13, carries a cylindrical high-voltage electrode 14 with plates 14 '; An axial collecting electrode 15 with further plates is arranged centrally in the cylinder. A preamplifier 16 is built onto the cover 9, to which the signal coming from the collecting electrode 15 is fed via the electrical line 11.

The entire arrangement as shown in FIG. 5 comprises a plurality of measuring channels provided in the core A of a reactor; Each of these measuring channels consists of a "compensation" line 17a and a measuring line 17 in which an activation chamber 18 is located; the two cable runs are connected to a differential ionization chamber 20, 21. The gas is fed to the measuring channels via the distributor line 22; The medium flows from the ionization chambers 20, 21 (which each supply the measured variable for the flow to be detected by the relevant channel) via outlet lines into the collecting line 23.

In FIG. 6 shows an arrangement which has a differential ionization chamber 20, 21, which several channels 17 are common to which a common compensation channel 17 α is assigned is, while the other channels 17 each contain an activation chamber 18. Changeover valves 29 are provided together with corresponding detour lines to the channels 17 in each case Request directly with the manifold 23 or with the one unit of the differential ionization chamber 21 to connect, while the other unit is permanently connected to the channel 17 a and over the outlet 32 is connected to the manifold 23.

Such an arrangement can contain as many measuring channels as there are measuring points in the reactor core on which one would like to determine or monitor the size of the neutron flux.

The entire arrangement of measuring channels as shown in FIG. 7 illustrated consists of a cylindrical Sleeve 33, which is permeable to neutrons and whose hollow axis 34 for the supply of the gas is used. The central axis is with the activation chambers, each arranged at different heights 35 connected via measuring pipes 36; a compensation pipe 37 is the whole Arrangement together, and the outflow of the gases from the activation chambers 35 takes place via the pipes 38. In this embodiment, there are three in the illustrated arrangement Measurement channels combined.

The F i g. Fig. 8 shows, on a larger scale, an activation chamber 35 within the cylindrical shell 33; it also shows the hollow shaft 34 serving as a distributor. The chamber 35 has a double bottom 3S ₁ and 35 ₂ at each of its two axial ends, so that at each end of this chamber partly disc-shaped and partly annular cavities 39 are formed, which are in its annular part are provided with passage openings 40 through which the gas coming from the supply line 36 flows into the interior of the chamber and the gas emerging from the interior can first enter the cavity 39 and then flow out through the pipeline 38. The compensation pipeline is denoted by 37.

The F i g. 9 schematically shows an arrangement with a closed gas circulation; of this Arrangement is shown a measuring channel 41, a compensation circuit and a measuring circuit with a Activation chamber 18 contains the two parallel lines 17a and 17 through the kernel of the reactor and via shut-off valves 29 to the two units of the differential ionization chamber 20, 21 are connected. The ionization chamber supplies the electrical signals or measured values at their output 46, and each of these chambers provided in a larger number can via a shut-off valve 47 each in a z. B. cyclic sequence can be connected to a deactivation container 48, from which the gas passes through a compressor 49 and a shut-off valve 50 in a buffer pressure vessel 51, from which it is fed back to the measuring channels via the pipeline 52.

The gas flowing out of the ionization chamber (or the ionization chambers) is in a Collectors collected and reintroduced into circulation. One has an interest in the time until following recirculation relatively large in relation to the lifetime of the activated isotopes do; because the activity remaining when the flow medium is reintroduced into a measuring channel but is the same for each of the pipelines that make up the measuring channel, the ionization current, which can be traced back to such residual activity, through the difference principle of measurement balanced, thereby eliminating its influence on the measurement result.

The circulating gas can be argon or any other gas that is opposite to the special conditions of neutron fluxes and ionization is compatible. Generally will the measurements are carried out using beta radiation, but you can also use the Gamma radiation work. When using argon, its isotope 40 gives by the reaction: Neutron, Gamma an isotropic 41, which turns into potassium after emitting beta and gamma rays 41 converts.

The volume of the activation chamber is always dependent on the time throughput of the Gas and the sensitivity of the ionization

chamber set. This volume is generally 10 to 20 cm ³ .

Instead of an ionization chamber, Geiger-Müller counters, proportional counters, Flow meters, scintillation detectors or semiconductor detectors can be used.

The arrangement can of course not only be used for measuring neutron fluxes, as they do occur in the core of reactors, but also outside the reactor core.

Instead of passing the gas through an ionization chamber, it can also be passed through a very thin one Partition wall, which delimits the chamber, taking the measurement for example is carried out using beta rays.

Claims (11)

Patent claims: 1. Arrangement for continuously measuring the neutron flux in a reactor core with the core penetrating pipes through which an activatable substance flows and which are provided outside the core with radiation detectors for measuring the activity of the substance flowing out, characterized in that two to one line section of the a line to lines (17, 17 a) which are identical to one another at the measuring point are led parallel to one another through the reactor core (/ 4), one of which (17 a) at the measuring point in its cross-section to one the dwell time of the activatable substance on this Place increasing activation chamber (18) is expanded, and that outside of the core (A) two radiation detectors (20 and 21) are arranged in a differential circuit on the lines (17, 17 a). 2. Arrangement according to claim 1, characterized in that several groups of two Lines (17, 17 a) are connected for the circulation of the activatable substance, in each of which in which a line (17 a) an activation chamber (18) is turned on, and that each group to a difference measuring system (20, 21) for measuring the difference in the activities in the Pairs of lines circulating activatable substance is connected. 3. Arrangement according to claim 1, characterized in that in addition to the reactor core (/ 4) traversing line (17 a) without activation chamber several lines (17), each with an activation chamber (18) at different Locations included in the core, and means (29) for selectively connecting one of the lines at a time (17) with activation chamber and the line (17a) without activation chamber with a Difference measuring system (20, 21) for the activity of the activatable ones circulating in the lines Substances are provided. 4. Arrangement according to claim 1, characterized by one of two identical units (6) existing differential ionization chamber. 5. Arrangement according to claim 4, characterized in that one of the ionization chamber Signal registration device is connected. 6. Arrangement according to claim 3, characterized in that there are several coaxially one above the other arranged activation chambers (35), a row of each in one of the chambers having opening lines (38) and a line (27) extending through all chambers. 7. Arrangement according to claim 1, characterized in that it has a cylindrical activation chamber (1) each with a conical one and outlet (2 and 3, respectively). 8. Arrangement according to claim 7, characterized in that the activation chamber (1) is provided with guide plates (4) for guiding the circulating substance that can be activated. 9. Arrangement according to claim 7, characterized in that the activation chamber \ 1) contains a guide helix (5) for guiding the circulating activatable substance. 10. Arrangement according to claim 1, characterized in that the activation chamber (35) is cylindrical and contains an entry space and an exit space (39), which with the central space of the chamber via peripheral passages (40). 11. The arrangement according to claim 4, characterized in that it has a collector (23, 30) for has the activatable substance coming from the ionization chambers. Considered publications:
Austrian patent specification No. 220 256. 1 sheet of drawings 809 538/426 4.58 © Bundesdruckerei Berlin