JPH0338553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a neutron and gamma ray measuring device for measuring radiation levels within a nuclear reactor.

(Technical Background of the Invention) In order to measure and monitor the levels of radiation, ie, neutrons and gamma rays, generated within a nuclear reactor, each detector is equipped with its own detector, if desired.

In other words, to measure the gamma ray level inside the reactor, a gamma ray detector is loaded inside the reactor, and to measure the neutron flux level, neutron detectors are loaded inside the reactor, and the output of each detector is The gamma ray level and neutron level are measured from the signal level.

FIG. 1 shows a conventionally widely used neutron detector, which is a fission chamber-type neutron detector that detects neutrons generated by fission of nuclear fuel in order to monitor the output of a nuclear reactor.

In FIG. 1, openings 2 and 3 at both ends of a cylindrical envelope 1 made of titanium or the like are hermetically closed by, for example, alumina porcelain split end plates 4 and 5 having good electrode insulation properties.

An anode 6 made of a conductive material such as stainless steel is fixed to the shaft portion of the envelope 1 .

A lead wire 7 is connected to this anode 6, and the end plate 4
It is led out from a through hole provided in the.

The envelope 1 also serves as a cathode, and a predetermined voltage is applied between the lead wire 7 and the envelope 1 by a power source (not shown).

Further, on the inner circumferential surface of the envelope 1, a fissile material 8, such as uranium, which is fissionable by irradiation with neutrons,
235 is attached.

The space between the anode and the cathode is filled with an inert gas 9, such as argon gas.

When such a detector is irradiated with neutrons, uranium-235 absorbs the neutrons and causes a nuclear fission reaction, and the fission fragments generated thereby ionize the inert gas 9 sealed in the space. .

At this time, if a voltage is applied between the anode and the cathode, electrons and ions in the gas generated by ionization can be taken out as an electric current.

The interelectrode current flowing due to the ionization effect of this gas is proportional to the amount of neutrons irradiated to the envelope 1, so the output of the reactor can be determined by multiplying the above current value by an appropriate coefficient. .

As shown in FIG.
Since the measurement is carried out by installing the DC power supply 25 and the ammeter 26 outside the reactor 33, the conductor connected to the anode and cathode inside the ionization chamber 21 is connected to the guide cable. 24 to the outside of the furnace for measurement.

Here, the signal component of the neutron detector that measures the neutron flux level naturally includes not only a signal due to neutron flux but also a signal due to gamma rays inside the nuclear reactor.

This gamma ray signal component directly becomes a measurement error.

In other words, gamma rays in the furnace enter the detector,
The ionized gas within the detector is ionized.

The signal component due to this ionization is also added to the signal due to neutrons, and becomes an output signal.

For this reason, if all the output signals of the detector are measured as signals due to neutrons, an error corresponding to the proportion of the signal component due to gamma rays will occur, and the measurement accuracy will decrease.

Furthermore, gamma ray detectors can be thought of as having almost the same structure as neutron detectors, with the fissile material removed.

In other words, only the ionization in the gas due to gamma rays is extracted as an output signal, not the ionization in the gas due to nuclear fission fragments.In this case, the signal is proportional to the gamma ray level at the detector position and can be measured with high accuracy.

However, in order to improve measurement accuracy, it is necessary to correct the gamma ray signal mentioned above, and in fast breeder reactors where the gamma ray level inside the reactor is high, the error component is high and it is difficult to perform sufficient correction. It was hot.

(Objective of the Invention) This invention was made in consideration of the above problems, and uses one detector to process the signal in two measurement methods, thereby measuring the neutron level and gamma ray level. The present invention provides a neutron and gamma ray measuring device that can measure neutrons and gamma rays simultaneously.

(Summary of the Invention) That is, the present invention includes one neutron detector inserted into a nuclear reactor, an input circuit that separates the output signal of this neutron detector into an alternating current component and a direct current component,
a Campbell amplifier that AC amplifies and squares the AC component separated by the input circuit; a DC amplifier that amplifies the DC component separated by the input circuit;
A first differential amplifier receives outputs from the DC amplifier and the Campbell amplifier and selects a neutron output, and a second differential amplifier receives outputs from the DC amplifier and the Campbell amplifier and selects a gamma ray output. This is a neutron and gamma ray measurement device characterized by comprising a dynamic amplifier.

(Embodiment of the Invention) An embodiment of the invention will be described below with reference to FIG.

In FIG. 3, numeral 30 is a neutron detector (fission type ionization chamber), which has almost the same configuration as the detector shown in FIG.

A coaxial cable 31 is connected to the output side of this detector 30.
is connected to the coaxial cable 31, and an input circuit 32 is connected to the coaxial cable 31.

This input circuit 32 includes a high input impedance circuit consisting of an input resistor R ₁ and a coupling capacitor C ₁ .
It has a high-voltage power supply HV and a power supply circuit with a protective resistor _R2 .

A Campbell amplifier 33, which is a high input impedance type low noise intermediate frequency band amplifier, is connected to the high input impedance circuit side, and a DC current amplifier 34 is connected to one power supply circuit side.

Also, Campbell amplifier 33 and current amplifier 3
Two differential amplifiers 35 and 36, each having a different processing method, are connected to the output end of the amplifier 4.

Next, the operation of the neutron and gamma ray measuring device configured as above will be explained.

The neutron signals and gamma ray signals output from the neutron detector 30 are transmitted through the coaxial cable 3.
1 to a predetermined location, the input circuit 32 connected to the end of the coaxial cable 31 separates the signal into alternating current and direct current components.

Here, the AC component is input to the Campbell amplifier 33 and amplified, and the DC component is input to the DC component amplifier 34.
are amplified and output respectively.

At this time, the DC current component I _DC is the current component I _o due to neutrons, as described above.

Claims (1)

[Claims] 1. One neutron detector inserted into a nuclear reactor, an input circuit that separates the output signal of this neutron detector into an alternating current component and a direct current component, and a A Campbell amplifier that amplifies the AC component and averages the square of it, a DC amplifier that amplifies the DC component separated by the input circuit, and the outputs from this DC amplifier and the Campbell amplifier are input to select a neutron output. A neutron and gamma ray measurement device comprising a first differential amplifier and a second differential amplifier that receives outputs from the DC amplifier and the Campbell amplifier and selects a gamma ray output. 2. The neutron and gamma ray measuring device according to claim 1, wherein the neutron detector is a fission type ionization chamber type neutron detector.