JPS6138828B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wastewater monitor for measuring the radioactivity concentration of radioactive wastewater discharged from a nuclear power plant or the like. In the drainage monitor, in order to eliminate the influence of radiation from radioactive substances adhering to the inner wall of the pipe, the waste water is passed through the inner wall of the pipe in a non-contact manner in the pipe where radiation measurement is performed. However, with drainage monitors that pass water through the inner wall of the pipe without contact, the effective volume for radiation measurement changes depending on the drainage flow rate.
Accurate measurement is difficult. Countermeasures include keeping the drainage flow rate constant, or assuming that it will change within a certain flow rate range and treating it as an error. The former requires a control mechanism to maintain a constant flow rate;
The equipment becomes complicated. Additionally, the latter had the disadvantage of poor accuracy as a monitor. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the conventional techniques described above and to provide a wastewater monitor that can accurately measure the radioactivity concentration in wastewater regardless of fluctuations in flow rate. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an embodiment of the present invention, and FIG. 2 is a diagram for explaining the effects of this embodiment. In FIG. 1, waste water is sent by a water pump 1, passes through a flow meter 2, a rectifier pipe 3, and a water discharge nozzle 4, and is passed through the inner wall of a pipe 5 of a measuring section without contacting it. The waste water 6 that has passed through the measuring section is drained in the direction of the arrow 7. Cleaning water is always passed at a constant flow rate along the inner wall of the pipe 5 of the radiation measurement section through the supply pipe 8 and the guide plate 9. The radioactivity of the waste water discharged from the water discharge nozzle 4 is measured by a radiation detector 11 surrounded by a shield body 10 and a counting device 12. The shape of the drainage water discharged from the water discharge nozzle 4 changes depending on the flow rate of the drainage water. This results in a change in the effective volume of wastewater that is measured by radiation, and requires correction of the measured value. For this correction, a correction calculation section 14 is provided in the counting device 12, and the output of the flowmeter 2 is transmitted through the signal line 13.
A correction calculation is performed based on the signal. This corrected value becomes the output of the counting device, that is, the output of the drainage monitor. If a rectifier pipe or the like is provided in the water discharge nozzle section to make the discharge pressure of the water pump approximately equal to atmospheric pressure, Bernoulli's equation will hold in the water discharge nozzle section and its downstream side. That is, the speed and shape of the water discharged from the water discharge nozzle can be determined by the head position relative to the water discharge nozzle. From this, the relationship between the flow velocity and the water discharge shape in the water discharge nozzle section and its downstream is as follows. R: Radius of the water discharge shape at the radiation measurement position R ₀ : Radius of the water discharge nozzle v ₀ : Drainage flow velocity at the water discharge nozzle g: Acceleration of gravity h: Water head from the tip of the water discharge nozzle to the radiation measurement position Here, R ₀ and h is a constant value due to the design of the drainage monitor, and the radius R of the water discharge shape is determined by the flow rate v ₀
It is found as a function of This relationship has also been experimentally proven. Figure 2 shows the relationship between the calculated value and the actually measured value of the water discharge radius R. As an actual correction value, if R is 1 when v ₀ is 2 m/sec, then v ₀ is 1 m/sec
In this case, R is 0.78 (however, h is 30 cm). Based on this value, the effective volume is corrected. When measuring from the side with sufficient collimation of the radiation from the discharged wastewater, the effective volume of the measured wastewater is determined by the length of the central axis of the discharge shape as expected by the radiation detector and the radius of the discharge shape at the center position of the radiation detector. It can be approximated by a cylindrical volume consisting of . The length H of the central axis of the water discharge shape that the radiation detector can see does not change even if the radius R of the water discharge shape changes. Therefore, the effective volume can be corrected approximately by multiplying the measured value by ² (R/R'), where R is the radius of the reference water discharge shape and R' is the radius of the water discharge shape at the time of measurement. can. If the nozzle flow velocity of the standard water discharge type is v ₀ and the nozzle flow velocity at the time of measurement is v ₀ ', then the correction coefficient F is

[Formula] becomes. here

[Formula] C ₂ = 2gh, both of which are constant values. Based on the output signal of the flowmeter 2, v ₀ ' and F are calculated to correct the effective volume. A specific example of the correction calculation section 14 shown in FIG. 1 calculates the flow velocity v ₀ ' of the water discharge nozzle section from the measured flow rate value of wastewater, calculates the above-mentioned correction coefficient F, and multiplies it to the measured value of radioactivity. Become. In the above example, if the flow velocity v ₀ ' at the time of measurement is 1 m/sec with respect to the standard v ₀ of 2 m/sec, this correction will be 1.64 times the count value. FIG. 2 shows the relationship between actually measured values and theoretically calculated values according to the apparatus of this embodiment. In the figure, double circles indicate actual measured values, and solid lines indicate calculated values. According to the present invention, the radiation detector is adjusted based on the flow velocity V ₀ of radioactive wastewater in the water discharge nozzle portion, the radius R ₀ of the water discharge nozzle, the gravitational acceleration g, and the water head h from the lower end of the water discharge nozzle to the set position of the radiation detector. Since the effective volume of radioactive wastewater at the installation location is corrected and the corrected effective volume of radioactive wastewater is used to correct the output signal of the radiation detector,
Since there is no need for a flow rate control device that constantly maintains the flow rate of radioactive wastewater supplied to the water discharge nozzle within a predetermined range, the wastewater monitor has a simple structure, and radioactivity detection accuracy can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention, and FIG. 2 is a diagram for explaining the effects of the present invention. In Fig. 1, 1... Water pump, 2... Flow meter, 3... Rectifier pipe, 4... Water discharge nozzle, 5... Piping, 6... Drainage, 7... Arrow, 8... Supply pipe, 9
. . . Guide plate, 10 . . . Shape body, 11 .

Claims (1)

[Claims] 1. A cylindrical body disposed substantially vertically, and a water discharge nozzle disposed in the center of the cylindrical body, extending in the axial direction of the cylindrical body, and opening downward. a radioactive drainage conduit that guides radioactive wastewater to the water discharge nozzle; and a radioactive drainage conduit that supplies cleaning water to a space between the cylindrical body and the water discharge nozzle above the lower end of the water discharge nozzle to drain the inner wall of the cylindrical body. A drainage monitor comprising means for forming a cleaning water flow along the water discharge nozzle, and a radiation detector disposed outside the cylindrical body in a portion where the radioactive wastewater flow flowing out from the water discharge nozzle and the cleaning water flow exist, The flow velocity V ₀ of the radioactive waste water at the water discharge nozzle part is determined based on the flow meter provided in the radioactive waste water conduit and the output signal of the flow meter, and the flow velocity V 0 of the radioactive waste water at the installation position of the radiation detector is determined by the following formula. Find the radius R of the radioactive wastewater, and use the radius R of the radioactive wastewater as a base. Here, R ₀ is the radius of the water nozzle, g is the gravitational acceleration, and h is the water head from the bottom of the water nozzle to the installation position of the radiation detector. and means for correcting the effective volume of radioactive wastewater at the installation position of the radiation detector and correcting the output signal of the radiation detector using the corrected effective volume of the radioactive wastewater. Drainage monitor.