JPS6259885A - Underwater radiation monitor - Google Patents

Abstract

PURPOSE:To measure the radiation concentration of gamma rays in water even at a deep water-depth position by charging a liquid scintillator in a thin metallic container, arranging a bellows, and holding the pressure in the container equal to ambient hydraulic pressure. CONSTITUTION:When an underwater radiation monitor is arranged in water, the bellows 5 deforms owing to the hydraulic pressure. Then, the liquid scintillator 1 in the thin container 2 made of metal having low gamma-ray cutoff ability is pressed and then the pressure in the container 2 is held as high as the ambient hydraulic pressure. Then, a pressure-resistant optical window is provided to the thin metallic pressure-resistant container 6 and a photoelectron multiplier tube and a data processor are stored in the container 6, so the radiation concentration of gamma rays is measured at a place where the hydraulic pressure is high and the depth of water is large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an underwater radiation monitor that measures radioactivity concentration in water.

[Technical background of the invention and its problems] In general, in nuclear power generation plants such as nuclear power plants, the radioactivity concentration in the wastewater used and discharged within the facility and the river water and seawater around the facility where the wastewater is discharged are Continuous monitoring of radioactivity concentration is required. For this reason, underwater radiation monitors are installed.

Conventional underwater radiation monitors that continuously monitor the radioactivity concentration of gamma rays in river water and seawater from which wastewater is released around nuclear facilities include NaI (Tβ) scintillators, which have the advantages of small size and high sensitivity. , this NaI (Tfl
,) A detection section containing a photomultiplier tube that detects the light emission of the scintillator, a high-voltage distribution resistor that processes the electrical signal from the photomultiplier tube, and a preamplifier housed in a pressure-resistant container, and a detection section located on land or on a ship. The external recording method is to electrically connect the data processing unit, which consists of a recorder, etc., with a pressure-resistant cable, and the data processing unit, which consists of a detection unit and a recorder, is housed in a pressure-resistant container and suspended from a ship, etc. There are two types of underwater radiation monitors: a self-recording method that lowers

With such conventional underwater radiation monitors, the depth of water that can be measured is limited to several hundred meters due to the electrical resistance of the voltage-resistant cable that connects the detection unit and the data processing unit. Measurements at deeper depths are carried out using a self-recording underwater radiation monitor. However, in this self-recording underwater radiation monitor, Na1 (T
°C) Since the scintillator is housed in this pressure-resistant container, it acts as a shield for gamma rays, resulting in low sensitivity, especially to low-energy gamma rays, which poses the problem of not being able to perform highly sensitive measurements of gamma rays in deep water. be.

[Object of the invention] The present invention has been made in response to such conventional circumstances,
The present invention aims to provide an underwater radiation monitor that can measure the radioactivity of gamma rays in water even at deep water depths and has higher sensitivity to gamma rays with lower energy than conventional ones. .

[Summary of the Invention] That is, the underwater radiation monitor of the present invention includes a container having an opening and filled with a liquid scintillator, and a container that seals the opening and deforms according to the pressure difference between the inside and outside of the container. It is equipped with a pressure adjustment mechanism that keeps the pressure inside the container equal to the pressure around the outside, and a photodetector housed in the pressure-resistant container and connected to the liquid scintillator through a pressure-resistant optical window. It can measure the radioactivity concentration of gamma rays in water even in deep places, and has higher sensitivity to low-energy gamma rays than conventional methods.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the underwater radiation monitor of the present invention, and in the figure, reference numeral 1 indicates a liquid scintillator. This liquid scintillator 1 is filled in a spherical outer shell container 2 made of thin metal, and the outer shell container 2 is provided with an air hole 3 and an opening 4, and the opening 4 is connected to a bellows 5. is sealed by. Further, a spherical pressure-resistant container 6 made of thick metal is suspended in the center of the outer shell container 2, and a pressure-resistant optical window 7 made of tempered glass is disposed in this pressure-resistant container 6. A photomultiplier tube 8 is disposed inside this optical window 7. Furthermore, as shown in FIG. 2, inside this pressure-resistant container 6, there is a photomultiplier tube drive device consisting of a battery 9 for operating the photomultiplier tube 8, a high voltage supply circuit 10, and a photomultiplier tube drive device consisting of a battery 9 for operating the photomultiplier tube 8. A data processing device consisting of a preamplifier 11, a linear amplifier 12, an adder 13, and a count rate meter 14 for processing electrical signals is housed.

The underwater radiation monitor configured as described above is suspended underwater from a ship or the like and continuously monitors the radioactivity concentration of gamma rays. At this time, when the underwater radiation monitor is placed underwater, the bellows 5 is deformed by water pressure, and the outer shell container 2
By pressing the liquid scintillator filled inside, the pressure inside the outer shell container 2 is maintained at the same level as the water pressure around the outside. In this state, light emission from the liquid scintillator 1 due to gamma rays is detected by the photomultiplier tube 8 disposed through the optical window 4, and counted by the data processing device.

In other words, in the underwater radiation monitor configured in this way,
Outer shell container 2 made of thin metal with weak gamma ray shielding ability
is filled with a liquid scintillator 1, and a bellows 5 is arranged so that the pressure inside the outer shell container 2 is equal to the surrounding water pressure,
Since the photomultiplier tube 8 and the data processing device are housed in a pressure container 6 made of thick metal and having a pressure-resistant optical window, it is possible to measure the radioactivity concentration of gamma rays in deep water locations with high water pressure. Moreover, it has high sensitivity even to low-energy gamma rays.

In addition, although the liquid scintillator 1 has inferior sensitivity compared to the same volume of NaI (T, 2> scintillator) used in conventional underwater radiation monitors, the outer shell container used in this example was designed with pressure resistance in mind. Since there is no need to do this and the size can be freely designed, the capacity of the liquid scintillator 1 can be increased, and the sensitivity can be increased more than that of conventional underwater radiation monitors.

Although this embodiment is a self-recording underwater radiation monitor in which a data processing device is housed in the outer shell container 2, the present invention is not limited to such an embodiment. Of course, an external recording method may also be used.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing an embodiment of the underwater radiation monitor of the present invention, and FIG. 2 is a block diagram showing a photomultiplier tube drive device and data processing device housed in the underwater radiation monitor shown in FIG. 1. It is a diagram. 1...Liquid scintillator 2...
... Outer shell container 4 ...... Opening 5 ... Bellows 6 ...... Pressure-resistant container 7 ...・Optical window 8...Photomultiplier tube applicant Japan Atomic Energy Corporation applicant
Toshiba Corporation Patent Attorney Satoshi Suyama - Continued from page 1

Claims (1)

[Claims] (1) A container that has an opening and is filled with a liquid scintillator, and the opening is sealed and deformed according to the pressure difference between the inside and outside of the container, so that the pressure inside the container is equal to the pressure around the outside. What is claimed is: 1. An underwater radiation monitor comprising: a pressure adjustment mechanism for maintaining the liquid scintillator; and a photodetector housed in a pressure-resistant container and connected to the liquid scintillator through a pressure-resistant optical window.