JPS5890197A - Reactor water level meter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The non-invention relates to a water level gauge for a nuclear reactor.

Generally, in a boiling water reactor, as shown in FIG. 1, a reactor pressure vessel 1 is installed inside a containment vessel 21.

During normal operation of the reactor, the pressure cuff inside the reactor pressure vessel 1 is 0.
The inside of the containment vessel 21 which houses the reactor pressure vessel 1 is maintained at an atmospheric pressure and a temperature of f&285U, and a pressure of 1 atmosphere and a temperature of 60C or less.

By the way, when evaluating reactor safety equipment, it is assumed that the suction side piping of the recirculation/increase system 6 will break as 1. and 7. Location 2 in e.g. rf1 recirculation system 6
When the pipe ruptures at 6, the high temperature, high pressure (285r, 70atm) coolant inside the reactor pressure vessel 1 flows:
The temperature and pressure inside the dry well 22 rise. There is a ura in the dry well 22, and the steam released is subrection no boule 2.
The large amount of cooling water filled in the
It is condensed by water sprinkling from the containment vessel Sergei 24.

In this way, the temperature inside the dry well 22, the FF force,
It is maintained below cutting A straight. In the event of such an accident, a large amount of cooling water is supplied from the emergency core cooling system 5 into the reactor pressure vessel to maintain cooling of the reactor core 7.

In order to fully control the flow rate of the water supply system 9 so as to keep the water level in the reactor pressure vessel 1 constant during normal operation of the reactor, the reactor pressure vessel 1 is provided with ``!''! A water level gauge 10 is installed in order to detect a low water level Tk in the reactor pressure vessel 1 and activate the emergency core cooling system 5 in the event of an accident in the Takonshi reactor.

The water level gauge 10 consists of three pressure conduits 1.1. ．． 12 and 13
, a reference plane 14 and a differential pressure gauge 15, and is adapted to measure the water level 27 in the annulus section 3 surrounded by the reactor pressure vessel 1 and the shroud 2. Steam in the steam dome (space above the liquid level in the reactor pressure vessel 1) 4 flows into the base diverter 14 through the pressure conduit 11. This steam condenses in the reference vessel 14, and the condensed water flows back through the pressure conduit 11 and into the reactor pressure vessel 1. Therefore, a reference surface 28 of a constant level is always formed within the reference surface device 14. The water level gauge 10 detects the water level in the reactor pressure vessel 1 based on this reference surface 28 according to the following principle. That is, the pressure kP in the reactor pressure vessel 1 at the connection part of the pressure conduit 11. , when the pressure on the pressure conduit 12 side acting on the differential pressure gauge 15 is Pl and the pressure on the third pressure conduit side is P2, the pressures P and Pt are as follows, P, =Po + (h2h+ lρ1+h, ρ, +h3
ρs −−−−−−old −<1) p, = po + h2ρ
2+h, ρ, , -, -...- (2) Differential pressure ΔPfl, ΔI) acting on the differential pressure gauge 15 = P, -P.

=h, (ρ2-ρ,)-h, (ρ1-ρ1)...
......(3). As a result, water level gauge 10
For the water level h1 measured at h, -[ρ2-ρ1)h2-ΔP)/(ρ1-ρ1)・
......(4). However, in the above equation, h is the water level in the reactor pressure vessel 1 consisting of 12 pressure conduits, and h2 is the reference plane 2 in the pressure conduit 12 and the reference plane 14.
8, h, l-1: pressure conduit 12 and differential pressure gauge 1
5, ρ1 is the vapor density in the reactor pressure vessel 1, ρ1 is the density of water in the reactor pressure vessel 1, ρ2 is the density of water in the upper part of the pressure conduit 13, and ρ is the density of water in the pressure conduit 12. and 13 is the density of water at the bottom.

(4) In 2, ρ and ρ1 are the pressures P in the reactor pressure vessel 1. is a function of pressure P. is known because it is measured independently, and h is determined and known when the water level gauge 10 measures it. Further, the temperature inside the dry well 22 is set to 1]160tr, and the density of water at 60C is used as ρ2. Therefore, by measuring the differential pressure ΔP acting on the differential pressure gauge 15, the water level in the pressure vessel 1 can be determined from equation (4).

Therefore, what is important in water level measurement is that the reference surface 28 in the reference surface device 14 is maintained at a constant level, that the water temperature above the pressure conduit 13 is constant at 60C, and that the water density ρ2 does not change.

It has been confirmed that during normal operation of a nuclear reactor, the water level can be measured with an accuracy of within ±3%. However, in the event of a loss of coolant accident in which the cooling water in the reactor pressure vessel 1 flows out, the following problem occurs.

That is, when the high-temperature, high-pressure coolant flows out, the pressure and temperature outside the reactor pressure vessel 1 (inside the dry well 22) rise as shown in FIG. The outflow flow rate of the cooling water decreases over time, and due to steam condensation in the suppression pool 23 and operation of the containment vessel spray 24, the dry well 2
The pressure and temperature of 2 decrease. Due to this temperature change in the dry well 22, the water temperature in the pressure conduits 12 and 13 is
It is expected that the temperature will change as shown in the figure and reach a maximum of 140C. Since the density of water changes with temperature as shown in Figure 4, and ρ2 in equation (4) changes, equation (
Letting the error ε of the water level shown in 4) and the density of water in the pressure conduit when the temperature rises be ρ2', the following equation is obtained.

ε=(ρ, −ρ, 'l/(ρ1−ρ1)・・・・・・・
...(5) The measurement error ε shown in equation (5) is as shown in Figure 5, and when the temperature of the water in the pressure pipe reaches 140C, the measurement error of the water level in the reactor pressure vessel 1 is It reaches 6%.

The purpose of the present invention is to provide a water level gauge that can prevent temperature rise in the pressure conduit of the water level gauge even in the most severe accident assumed in the evaluation of nuclear safety equipment, and has measurement accuracy comparable to that during normal operation. It's about doing.

In order to achieve the above object, the present invention provides: (1) 60% or more of the total length of the vertical portion of the pressure conduit is installed outside the containment vessel;
The vertical section of the pressure conduit installed inside the containment vessel has a total length of 4
0% or less.

FIG. 6 shows an embodiment of the present invention, in which a water level gauge 10 includes a reference level gauge 14 and a differential pressure gauge 15, and a pressure guide Wll,
The reactor pressure vessel 1 is connected to the reactor pressure vessel 1 by 12 and 13. The pressure conduit 13 connecting the reference plane 14 and the differential pressure gauge 15 is arranged horizontally at a distance h below the reference plane 28, and most of the vertical portion of the pressure conduit 13 is installed outside the containment vessel 21.

Of the 3% error of the water level gauge 10 during normal operation of the nuclear reactor, 0.5% is due to instrument error, and 2.5% is due to temperature change within the pressure conduit. Therefore, in order to maintain the same error range in the event of an accident as in normal operation, the pressure conduit 13
The effect due to the change in the density of water within the tank should be 22.5% or less. Since the temperature outside the containment vessel 21 does not change even in the event of an accident, in the water level gauge 10 of this embodiment, the measurement error ε' in the event of an accident is expressed by the following equation.

ε' − (h/h21 ((ρ2−ρ2')/(ρ, −
ρ1))...(6) When the measurement error ε of the conventional water level gauge shown in equation (5) is substituted into equation (6), equation (7) is obtained.

ε'=(h/h,) ・ε・・・・・・・・・
...(7) From FIGS. 3 and 5, the maximum error εBlue at the time of an accident is 6%, so the maximum error ε'□ by the water level gauge 10 of this embodiment shown in FIG. 6. In order to make 25% or less, the condition of equation (8) is required.

ε′□a=0. Q 6 (h/h2) <0.025,
', h(0,4h2 ・・・・・・・・・
(8) That is, the height h2 of the vertical portion of the pressure conduit 13 installed in the containment vessel 21 is 40% or less of the height h2 between the pressure conduit 12 and the reference surface 28. h and water level gauge 10
Figure 7 shows the relationship between the measurement error and the measurement error. A shows the maximum error during normal reactor operation, and B shows the instrument error.

Figure 8 shows the dry well 22 at the time of the accident shown in Figure 2.
5 shows another embodiment of the present invention based on the measurement error of the water level gauge due to the temperature change in the pressure conduit shown in FIG. The water level gauge 10 includes a reference level gauge 14 and a differential pressure gauge 15.
1. 2゜Pressure conduits 11, 12.1 in Fig. 3
3 to the pressure vessel 1, and a heat insulating material 16 is installed in the portion of the pressure conduit 13 that is installed in the internal containment container 21.

Considering the meter error of 0.5%, the water level gauge at the time of the accident was 10.
To keep the total error within 3% during normal operation, the fifth
As shown in the figure, the temperature inside the pressure conduit 13 should be set to 100C or less. The temperature T inside the pressure conduit 13 is the initial temperature T. When the temperature of the dry well 22 is T, it is as follows.

In the above formula, t is time, Rh is thermal resistance of the heat insulating material 16,
S is the surface area of the pressure conduit 13, and C9 is the heat capacity inside the pressure conduit 13. From Figure 2, T, = 14 QC, To =
Is 60C, t=300 seconds?

For T<100C, it is sufficient to satisfy the condition of equation (10).

Equation (10) is a condition when h=h, but Equation (10
), taking into account the effect of h, we get the result shown in Figure 9, (
9) This equation can be expressed as an approximate equation as follows.

In this way, the pressure conduit 13 installed inside the containment vessel 21
By insulating the pressure with the heat insulating material 16, hl can be increased, and the restrictive conditions for installing the pressure conduit can be relaxed.

The present invention has the above-described configuration 1, and 60% or more of the vertical piping portion of the pressure conduit that communicates the reference plane of the water level gauge and the differential pressure gauge is installed outside the containment vessel, or c.
By insulating the pressure conduit installed in the containment vessel, there is an effect that even in the event of an accident, the water level in the reactor vessel can be detected at the same n degree as during normal operation.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of a conventional nuclear reactor water level gauge, Figure 2 is a characteristic diagram showing changes in dry well pressure and temperature assuming the most severe accident, and Figure 3 is a conventional water level gauge (10). FIG. 6 is a longitudinal sectional view of a water level meter according to a preferred embodiment of the present invention, and FIG. 7 is a characteristic diagram showing the maximum error characteristics of the water level meter shown in FIG. 6. , FIG. 8 is a vertical sectional view of another embodiment of the present invention, and FIG. 9 is a characteristic diagram showing the thermal resistance of the heat insulating material of the pressure conduit 13 in the embodiment shown in FIG. 1... Reactor pressure vessel, 3... Annulus section, 4...
...Steam dome, 10...Water level gauge, 11, 12.13
...Pressure conduit, 14...Reference plane device, 15...Differential pressure gauge, 16...Insulating material. Agent Patent Attorney Akio Takahashi (11) Drawings 1 and 7 (2 dimensions ≧ no changes) / Bacteria (), Fu 41k Tsu 4 I (D ≦ k4) Europe
Mi ・ ~ ＼ (nctu) U 54(x pl;, A()・n
Anμ! Tomoe 1Δ4 晦ムj11()7＄4 Low-temperature soaking (°C) 7 and false pickling (°C) 6th day 1. H71'z Procedural amendment (method) April 19, 1980 Commissioner of the Japan Patent Office Haruki Shimada Case Indication 1982 Patent Application No. 188549 Title of the invention
Relationship with the Case of Person Who Corrects Water Level Gauges in Nuclear Reactors Patent Applicant: 5-1 Marunouchi-chome, Chiyoda-ku, Tokyo Name: 51O) Manufactured by Hitachi Co., Ltd. Representative: 3 1) Shigeyo Katsu Address: Marunouchi-5-1, Chiyoda-ku, Tokyo Supplementary JX
E') Contents of the 7-dimensional application, 9 drawings of the specification, and amendment to the power of attorney (1) Engraving of the application, specification, and drawings (no changes to the contents). (2) Submit a separate power of attorney.

Claims (1)

[Claims] 1. First and second pressure conduits connected to the reactor vessel installed in the containment vessel, a certain fishing vessel attached to the first pressure conduit, and connected to the base vessel The third
and a differential pressure gauge attached to the second and third pressure conduits and disposed outside the containment vessel, in which % or more of the water level gauge for a nuclear reactor, wherein the water level gauge is installed outside the containment vessel.