JPH0240996B2 - JIDORIMONITASHISUTEMUNOKANDOHOSEIKAIRO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sensitivity correction circuit for an automatic RI monitor system, particularly a sensitivity correction circuit for automatically correcting detection sensitivity in an automatic RI monitor system that monitors radioactive contamination in a controlled area where RI substances are handled. Regarding circuits.

RI of nuclear power plants or radiation medical facilities, etc.
Radioactive contamination must be constantly monitored in facilities that use radioisotope (radioisotope) substances in order to prevent contamination accidents for workers and others due to radiation. In internally controlled areas, automated systems are used to measure radiation levels within the area and monitor radioactive contamination.
A RI monitoring system is provided. These monitoring systems include area monitors that monitor the air dose rate in controlled areas, gas monitors or dust monitors that monitor the radioactivity concentration in exhaust gas, and water monitors that measure the radioactivity concentration in wastewater. or a combination of multiple devices to constantly measure radiation levels within controlled areas. In addition, one or more monitors are installed at facilities using RI substances within these controlled areas, and these monitors are automatically
It not only monitors the entire system as a monitor system, but also plays the role of issuing an alarm or activating an appropriate control device in the event of an abnormality.

The radiation detectors used in each of the above monitors include current detection type radiation detectors such as ionization chambers, scintillation counters, proportional counters, or
A pulse-output radiation detector such as a GM tube is used, and the radiation dose within the controlled area is reliably measured using a detector compatible with the RI substance used.

The automatic RI monitor system described above is operated continuously to constantly monitor the radiation dose within the controlled area, but the sensitivity of the monitor system may fluctuate during this operation period, and these fluctuations are mainly due to the sensitivity of the radiation detector. Due to the fluctuations and the sensitivity fluctuations of the processing circuit, the detection signal suddenly or over time contains a large error, resulting in a problem that the monitor system cannot operate normally. For example, in the case of an ionization chamber, the causes of fluctuations in the radiation detector include fluctuations due to the pressure and temperature of the filled gas, and in other detectors, fluctuations due to temperature are the main cause. Furthermore, in processing circuits, there is a problem in that the temperature characteristics of circuit elements or changes over time occur, and the sensitivity is significantly distorted due to these causes.

In conventional automatic RI monitor systems, in order to perform the sensitivity correction described above, the monitor administrator must correct the sensitivity of the system at appropriate intervals, which makes fully automatic operation of the automatic RI monitor system difficult and The drawback was that a skilled administrator was required for continuous operation of the system.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an improved sensitivity correction circuit that can operate an RI monitor system fully automatically and continuously by automatically performing sensitivity correction. There is a particular thing.

In order to achieve the above object, the present invention provides an automatic RI monitoring system that measures the radiation dose in a predetermined controlled area and monitors radioactive contamination in the controlled area. a shutter drive device that opens and closes the shutter; a shutter controller that controls the shutter drive device to irradiate the radiation detector with reference radiation; and a standard corresponding to the detection value of the radiation detector and the reference radiation when the reference radiation is irradiated. A correction value output circuit that outputs the ratio to the sensitivity correction value as a sensitivity correction value, and a correction that updates the sensitivity correction value by automatically operating the shutter controller and correction value output circuit at an arbitrary time predetermined by a timer. A control circuit is included, and the detection signal of the radiation detector is automatically corrected using a correction value.

Preferred embodiments of the present invention will be described below based on the drawings.

In the figure, the radiation detector installed in a predetermined controlled area consists of an ionization chamber 10, and its high-voltage electrode 1
2 is supplied with a high voltage from a high voltage source 14, and the charge collected on the collector electrode 16 is converted into a voltage value by an electrometer 18 and output as a detection signal. The output of electrometer 18 is
It is converted into a digital signal by the AD converter 20, and after sensitivity correction is performed at any time by the sensitivity correction circuit 22, it is outputted from the output terminal 22a to a display, printer, totalizer, etc. (not shown), Radiation levels within the controlled area will be continuously monitored at all times.

In the present invention, the radiation detector, the ionization chamber 10 in the embodiment, is provided with a reference radiation source 24 for irradiating reference radiation, and the reference radiation source 24 is the ionization chamber 10 in the embodiment.
The ionization chamber 10 is housed in a shielding chamber 26 located adjacent to the ionization chamber 10, and a shutter 28 for shielding radiation is provided between the shielding chamber 26 and the ionization chamber 10. Therefore, when the shutter 28 is closed, the reference radiation from the reference radiation source 24 does not irradiate the ionization chamber 10, while when the shutter 28 is open, the reference radiation from the reference radiation source 24 does not ionize. box 1
Irradiated within 0. A shutter drive device 30 is connected to the shutter 28 to open and close the shutter 28.

A shutter controller 32 is provided in the sensitivity correction circuit 22 for supplying a drive signal to a shutter drive device 30, and a reference radiation source control device controls the irradiation of reference radiation to the ionization chamber 10 together with the shutter drive device 30 and the shutter 28. Work as.

After the detection signal of the ion chamber 10 is converted into a digital signal by the AD converter 20, a predetermined sensitivity correction is performed by the arithmetic unit 34 of the sensitivity correction circuit 22, and the signal is output from the output terminal 22a. Arithmetic unit 3
In order to perform the sensitivity correction in step 4, the sensitivity correction circuit 22
is provided with a correction value output circuit that calculates a detection signal of the ionization chamber 10 during reference radiation irradiation and a reference value corresponding to the reference radiation and outputs a sensitivity correction value, and the correction value output circuit in the embodiment is a register 36. ,38
and a computing unit 40. That is, AD converter 2
The output of 0 is supplied to the arithmetic unit 34 or the register 36 through contacts 42 and 44, one of which is selectively controlled on and off, and as will be described later, when the sensitivity is corrected, the detection signal is generated by turning on the contact 44. is temporarily stored in the register 36 as b. A reference value a corresponding to the reference radiation of the reference radiation source 24 is stored in advance in the register 38, and a sensitivity correction value a/ b as operator 3
It is possible to output to 4.

In order to perform the sensitivity correction at an arbitrary time, the sensitivity correction circuit 22 is provided with a correction control circuit, and the correction control circuit in the embodiment includes a timer 46 and a flip-flop (hereinafter referred to as FF) 48. The timer 46 outputs an inverted signal to the FF 48 at any time, for example, once a day or at a predetermined time interval.
The sensitivity correction is controlled by the Q output or output of. That is, the Q output of the FF 48 supplies a control signal to the shutter controller 32,
At the same time, the contact 44 is turned on to supply a detection signal to the register 36. Furthermore
The Q output of the FF48 supplies a signal to the OR gate 52 via the delay circuit 50, and the output of the OR gate 52 is connected to the sampling input terminal of the AD converter 20, so the Q output of the FF48 supplies the signal to the OR gate 52.
The converter 20 will sample and output the detection signal once after a predetermined delay time has elapsed.

Note that the sampling signal of the AD converter 20 during normal measurement is obtained from the pulse oscillator 54,
The output of the pulse oscillator 54 is supplied from the OR gate 52 to the AD converter 20 via the AND gate 56, but the AND gate 56 is controlled by the Q output of the FF 48, and only generates a pulse when there is an output from the FF 48. From oscillator 54 to AD converter 2
The sampling signal will be output to 0.

The embodiment of the present invention has the above configuration, and its sensitivity correction action will be explained below.

During normal monitor operation, the Q output of the FF48 is "0" and the output is "1", so as shown in the figure, the contact 42 is on or the contact 44 is off, and the AD converter 20
The detection signal converted into a digital signal is subjected to sensitivity correction by a predetermined correction value in the arithmetic unit 34, and then outputted from the output end 22a. At this time, since the AND gate 56 is opened at the output of the FF 48, the AD converter 20 is supplied with a sampling signal of a predetermined sampling period from the pulse oscillator 54. Further, since the Q output of the FF 48 is "0", the shutter controller 32 is in an inactive state, the shutter 28 of the ionization chamber 10 is closed, and the reference radiation of the reference radiation source 24 is transmitted to the ionization chamber 10.
will not be irradiated.

Next, when the timer 46 reaches a sensitivity correction time set at a preset arbitrary time, for example, once a day, an inverted signal is supplied from the timer 46 to the FF 48, and the sensitivity correction action is started.

When the FF 48 is inverted, its output becomes "0", so the contact 42 is turned off, and the AND gate 56 is closed, so that the conversion action of the AD converter 20 is stopped. Then, since the Q output of FF48 becomes "1", the shutter controller 3
2 is activated, and the shutter 28 is opened using the shutter drive device 30. As a result, the reference radiation from the reference radiation source 24 is irradiated onto the ionization chamber 10, and since this reference radiation is set to a significantly larger value than the radiation to be measured, the ionization chamber 10 outputs a substantially constant detection signal. Q output of FF48 is delay circuit 5
After being delayed for a predetermined time by 0, the OR gate 5
2 to the AD converter 20 as a sampling signal, the AD converter 20 converts the detection signal of the ionization chamber 10 at the time of sampling into a digital signal. This delay time is set as the time until the ionizing effect of the reference radiation in the ionization chamber 10 stabilizes, and when the monitor sensitivity is normal, the AD converter 20 sends a nearly constant signal value to the sensitivity correction circuit 22. Output. At this time, contact 44 is FF
Since it is turned on by the Q output of 48,
This detection signal is stored in the register 36 as b. Then, this detection signal b is calculated with a predetermined reference value a in a calculation unit 40, and is supplied to a calculation unit 34 as a sensitivity correction value a/b.

After the sensitivity correction value is updated as described above,
FF48 is reversed again and returns to normal monitor operation. Since the above-mentioned updated sensitivity correction values a/b are inputted to the calculator 34, the sensitivity correction is performed according to this correction value, and the sensitivity correction is performed based on the pressure, temperature, or change over time of the radiation detector or processing circuit. It becomes possible to accurately correct errors and continuously monitor radiation doses.

As described above, in the embodiment, by setting the operation interval of the timer 46 once a day or at an appropriate interval, the sensitivity correction value can be automatically updated at any time to obtain an accurate detection signal at all times. becomes possible.

The sensitivity correction circuit 22 in the embodiment is preferably formed by a microcomputer or the like,
It has the advantage that the device can be miniaturized and a sensitivity correction circuit that can be applied to various automatic RI monitoring systems can be obtained.

In each of the embodiments described above, an ionization chamber is used as a radiation detector, but in the present invention, not only such a current-powered radiation detector but also a scintillation counter, a proportional counter tube, a GM tube, etc. It is also possible to apply the present invention to a pulse output type radiation detector. However, in this case, it is necessary to replace the AD converter 20 with a counting circuit.

As explained above, according to the present invention, the reference radiation source is irradiated automatically by the shutter drive device, and the sensitivity is automatically corrected using the sensitivity correction value. It has the advantage of being able to operate fully automatically and continuously and not requiring a skilled manager.

[Brief explanation of the drawing]

The figure is a circuit diagram showing a preferred embodiment of the sensitivity correction circuit of the automatic RI monitoring system according to the present invention. DESCRIPTION OF SYMBOLS 10... Ionization chamber, 22... Sensitivity correction circuit, 24... Reference radiation source, 28... Shutter, 30... Shutter drive device, 32... Shutter controller, 34... Arithmetic unit, 36, 38... Register, 40... Arithmetic unit, 46
...Timer, 48...Flip-flop.

Claims (1)

[Claims] 1. In the automatic RI monitoring system that monitors radioactive contamination in a controlled area by measuring the radiation dose in the controlled area using a radiation detector installed in the controlled area, A shutter drive device that opens and closes the shutter, a shutter controller that controls the shutter drive device and irradiates the radiation detector with reference radiation, and a detection value of the radiation detector during reference radiation irradiation and a reference value corresponding to the reference radiation. A correction value output circuit that outputs the ratio of A sensitivity correction circuit for an automatic RI monitor system, comprising a circuit and automatically correcting a detection signal of a radiation detector using a correction value.