JPS6126019B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plugging meter for measuring impurity content in liquid metal.

In liquid metal cooled breeder reactors, it is necessary to monitor the impurity concentration in the cooling liquid metal to keep it low due to problems such as blockage of cooling liquid metal piping, corrosion problems, or improving the sensitivity of water leak detection. For this reason, a Plucking meter is often used as an impurity concentration meter. Plagging meter uses liquid metal for cooling.
For example, by cooling sodium and depositing impurities in the orifice, the pressure loss at the orifice increases.The resulting decrease in the flow rate of the liquid metal is detected by a flowmeter, such as an electromagnetic flowmeter, and the fluid temperature at the time of the decrease is measured. The impurity concentration is measured by measuring the impurity concentration.

As shown in Figure 1, the conventional Plagging meter
A branch circuit 2 connected to a main pipe 1 through which liquid metal, such as sodium, flows; a bypass 3 in which the inlet pipe of the branch circuit 2 is connected to the outlet pipe; a bypass 3 having a bypass orifice 9 in the middle; It consists of an electromagnetic pump 4, an electromagnetic flowmeter 5, a cooler 6, a heat exchanger 7, a plugging orifice 8, and a thermometer 10, which are attached to the pump.

Various proposals have been made to improve the measurement accuracy of plugging meters and to prevent orifice clogging.
Examples include a valve-type variable flow cross-sectional area orifice, an orifice plate with a plurality of holes, and a modified orifice hole. However, conventional plugging meters require a measurement period of 20 minutes or more, and have problems with response and measurement accuracy.

Among these conventional devices, plugging uses an orifice plate 27 for the piping 19 as shown in FIG. An example of actual measurement of the meter will be explained. A large hole 22 with a diameter of 2 mm with a wide taper on the downstream side of the center of the orifice plate 27 is for preventing complete blockage, and four holes 22 with a diameter of 1.2 mm with a tapered taper on the upstream side provided around the center of the orifice plate 27 are for preventing complete blockage. The holes 23 to 26 are for depositing impurities. In this case, the flow rate flowing through the central large hole 22 increases the background of the orifice flow rate of the plugging meter and lowers the S/N ratio of the flow rate change. As a result, actual measurement results showed that the measurement cycle was only shortened by about 10 minutes, and it became difficult to measure changes in flow rate.

An object of the present invention is to provide a plugging meter that has a measurement period of 5 minutes or less, has better measurement accuracy than conventional ones, and does not cause complete blockage.

The state of precipitation of impurities in the conventional plugging meter is as shown in FIG. 4, 11.

Figure 5 shows the relationship between the orifice blockage rate due to precipitated impurities and the liquid metal flow rate in a Plagging meter [Mc Pheeters CCNuclear Applications
6, PP573 (1969). ] If the orifice pressure loss is large and the pressure loss of piping other than the orifice is negligible in comparison, a flow rate decrease will occur that is approximately proportional to the orifice blockage rate, as shown by line a in FIG. 5.

If the pressure loss at the orifice and the pressure loss at other piping sections are the same, a flow rate change as shown by curve b will occur.

If the pressure drop in other parts of the pipe is greater than the pressure drop in the orifice, or if the flow rate at the orifice is adjusted by a flow control valve in the flow path, the flow rate changes as shown by curve c. In other words, the flow rate begins to change significantly only when the orifice is approximately 80% blocked and the pressure loss there overcomes the pressure loss in other parts of the piping.

Further, it can be seen that the orifice shown in FIG. 2 causes a flow rate change as shown in FIG. 6, and has low sensitivity.

In addition, as a result of detailed experiments and analysis of changes in flow rate on one side, it was found that such considerations for the plugging meter orifice and its piping alone were insufficient. In other words, as mentioned above, in order to increase the flow rate change of the plugging meter, it is necessary that the pressure loss in the parts other than the part where the change in pressure loss occurs due to the adhesion of impurities be as small as possible. However, even if a plagging meter is carefully designed with these considerations in mind, the measurement cycle requires more than 10 minutes, and it is not possible to obtain a flow rate change proportional to the orifice blockage rate. This indicates that impurities were attached to the orifice and pressure loss occurred in areas other than those where pressure loss changes were caused by the impurities. However, the pipes have been carefully designed so that the pressure drop can be ignored. However, when we calculate the pressure drop in the plugging orifice section in detail, we find that the sudden contraction and expansion of the orifice flow at the entrance and exit of the orifice plate causes a very large pressure drop, which is equivalent to the large pressure drop in the piping section. If a normal orifice plate is used to serve as
It was found that the flow rate change as shown by line a in FIG. 5 never occurred.

Therefore, as shown in FIG. 7, we thought of providing tapered and widening tapers at the entrance and exit of the orifice hole, respectively, to eliminate sudden contraction and expansion. When this orifice plate is used, only the straight pipe inside the orifice shown in Figure 7, that is, the part where the pressure drop changes due to the precipitation of impurities, has a pressure drop in the sodium passage of the plugging meter. The change in flow rate due to precipitated impurities is much larger than in conventional plugging meters.

A plugging meter according to this invention having an orifice shown in FIG.
As shown in the figure.

As a result, the measurement cycle was shortened to 1.5 minutes.

[Brief explanation of the drawing]

Fig. 1 is a general configuration diagram of a Plagging meter, Fig. 2 is a sectional view of a conventional orifice plate having a central hole with a wide tapered portion on the exit side and a plurality of orifices with a tapered portion on the inlet side. Fig. 3 is a plan view of the orifice plate shown in Fig. 2, Fig. 4 is a sectional view showing how precipitated impurities adhere to the orifice of a conventional plugging meter, and Fig. 5 shows the relationship between orifice blockage rate and flow rate. The diagram, Figure 6, is a diagram showing the relationship between the blockage rate and flow rate of the orifice in Figure 2, and Figure 7
The figure is a sectional view of the orifice plate according to the present invention, No. 8.
The figure shows the actual measurement results of the plugging meter according to the present invention. 8...Plugging orifice, 1...Main piping, 2...Diversion circuit, 3...Bypass, 4...Electromagnetic pump, 5...Electromagnetic flowmeter, 6...Cooler, 7
... Heat exchanger, 9 ... Bypass orifice, 10
... Thermometer, 11 ... Precipitated impurity.

Claims (1)

[Claims] 1. Measure the impurity content in the liquid metal by passing the liquid metal cooled by a cooler placed upstream through an orifice formed on an orifice plate and depositing impurities on the inner surface of the orifice. In the liquid metal plugging meter, the orifice has one plate on the orifice plate.
1. A plugging meter for liquid metal, characterized in that the shape of the inflow side is formed into a tapered shape and the shape of the outflow side is formed into a widening taper shape.