JPS60256092A - Measuring device for water level in nuclear reactor - 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 [Field of Application of the Invention] The present invention relates to a nuclear reactor water level measuring device, and particularly to a nuclear reactor water level measuring device suitable for use in a nuclear reactor of a boiling water nuclear power plant.

[Background of the invention J Conventional nuclear power plant reactor water level measurement equipment.

The pressure inside the reactor is extremely high, approximately 70 kg/a1g.

Because of the need to accurately measure the normal water level, we have adopted a differential pressure detection method in which pressure is detected from the upper and lower parts of the reactor, and the upper part is used as the reference water level. Here, the detection piping used as the reference water level is the reference leg (REF, LEG'), and the detection piping on the lower side is the barrier pull leg (VAR, LEG').
It is called.

In this differential pressure detection method, it is important to ensure a reference plane and the density difference between the reference leg and the barrier leg. In calculating the differential pressure, the nominal value under normal operating conditions is used, and very accurate measurement is achieved during normal operation at 100% output.

However, during startup tests (at low output) in the construction stage, plant startup and shutdown, etc., the environmental conditions change from those at 100% output, and the nominal value differs from the actual conditions, causing an error in the water level signal. There are drawbacks. In addition, in a nuclear reactor accident (especially a hypothetical accident such as a loss of coolant accident), conditions change significantly, so the error in the water level signal will be even larger than that at the time of plant startup and shutdown, and in the case of a loss of coolant accident, As a special phenomenon, vacuum boiling occurs near the gas phase of the reference leg, and experiments have shown that this boils at a water head of about 51 when using a condensing tank. Although these errors cannot accurately grasp the state of the reactor, they can be evaluated on the safe side from a functional point of view, but they are considered a drawback from the perspective of improving accuracy.

[Purpose of the invention]

The purpose of the present invention is to provide a system that is independent of reactor pressure and environmental conditions, regardless of the state of the plant, i.e., during start-up tests during the construction stage, during plant start-up and shutdown, during normal operation, during reactor accidents, etc. An object of the present invention is to provide a reactor water level measuring device that accurately measures the reactor water level.

[Summary of the invention]

The reactor water level measuring device in boiling water nuclear power plants uses a differential pressure detection method that has a reference water level as shown in Figure 1.1 The differential pressure generated is calculated from the water head difference between the reference leg and the barrier leg. But that is.

The density depends on the difference in water temperature in each part.

That is, from FIG. 1, the generated differential pressure is as follows.

ΔP=(L I) + (fl + Q4)9w +
CQss +Qs -Q-Qn)L■ ρs) -((Qt +fisriρ, +6ρLL)=
, ((LρLI Q sp,, J+ Q 4/)w
+ (Qn + n s n 4) × M - (ra ten ag
)ρ−):+−j1(ρ1−ρ, ), where.

ΔP: Differential pressure Q applied to the differential pressure transmitter 10, vertical distance between the two reactor lower measuring taps 16 and the lower instrumentation penetration 4 Ω12: Vertical distance between the upper instrumentation penetration 4 and the lower measuring tap 16 Q3: Standard Vertical distance from the reference plane of surface 13 to upper instrumentation penetration 4 Q4: Vertical distance ρ from lower measurement tap 16 to water level measurement reference point (level 0): Reference L inside reactor containment vessel 2 - Leg detection piping Density of water in 7 ρ: Density of water in barrier pull/H leg detection pipe 8 inside reactor containment vessel 2 ρ, : Density of steam with atoms in l ρW: Density of water in reactor 1 p , where the density of water in the detection pipe outside the two reactor containment vessels 2 is ρLL ("ρL) in ρL8, the term CQ, ρLfl-""ρLL) = ("l -Qs
)ρ.

When there is one party and = Ω3, the influence of ρ can be eliminated.

In the actual construction, this is difficult, so some items inevitably remain.

As you can see, the influence of density is large in the conventional technology.

The differential pressure generated is calculated by giving the density based on the temperature conditions during normal operation. Additionally, as mentioned earlier, construction efforts are being made to make Ql and Q3 as similar as possible.

Since the standard is based on normal operation, the actual situation is that when starting and stopping, etc., the operator must keep this in mind when operating, which puts some burden on the operator.

However, in terms of measurement, it is preferable to measure as accurately as possible even in the event of a nuclear reactor accident.

As a means to eliminate the water level detection that is affected by the plant status described above, (1) correct the density that changes depending on the plant status. For this purpose, install the following temperature/pressure detector and perform temperature and pressure compensation.

a) Reactor temperature b) M-7-heart tw-h C) Temperature inside the reactor containment vessel d) Temperature outside the reactor containment vessel It is not necessarily necessary to install all of the above.

(2) To compensate for reduced pressure boiling in the event of a nuclear reactor accident, the reference leg side is switched using a loss of coolant signal (referred to as the LOCA signal) using an automatic valve, and the low side of the differential pressure transmitter is opened to the atmosphere. By setting the standard to atmospheric pressure,
Eliminate the effects of reduced pressure boiling.

This is how it was done above.

[Embodiments of the invention]

Take out the reference leg detection pipe 7 from the upper measuring tap 15 of the reactor 1 and connect it to L of the differential pressure transmitter 10, and then take out the barrier pull leg detection pipe 8 from the lower measuring tap 16 and connect it to the differential pressure transmitter 10. Connect to the H side of the The reference leg detection pipe 7 is provided with a reference surface l13, and a reactor pressure detector 17 (PV) for detecting the reactor pressure is connected from the upper part of the reference surface device 3. In addition, the three-valve manifold 9 of the reference leg detection piping 7
An automatic isolation valve 22 and an automatic vent valve 23 are installed on the inlet side of the tank, and the automatic vent valve 23 is configured to discharge drain water into a drain funnel 25.

(See Figure 2) Furthermore, a reactor temperature detector 18 (T,) is attached to the reactor l to detect the reactor temperature, and the reference leg detection pipe 7 inside the reactor containment vessel Temperature detector 19 (TL) is installed on the detection pipe that can detect the average temperature,
Similarly, a temperature sensor 2 is installed on the barrier pull leg detection pipe 8.
0 (T,), and temperature detectors 21 are installed at representative locations outside the reactor containment vessel 2, and these signals are converted into temperature and
The water level signal 11 is inputted to the pressure compensation circuit 26 and is compensated to form a correct water level signal 27. The automatic isolation valve 22 is normally fully open, and the automatic vent valve 23 is normally fully closed.

At the time of a loss of coolant accident (LOCA), these valves are switched in response to the LOCA signal, and atmospheric pressure is applied to the L side of the differential pressure transmitter 10.

The pressure/temperature compensation circuit 26 has a circuit as shown in Fig. 3, and has three operation modes: (1) Normal operation (100% output) (2) Start/stop (less than 100% output) (3) There will be reactor accidents, and pressure and temperature compensation will be provided for each.

The configuration includes raw water level signal 1 from differential pressure transmitter 10.
1 is input to the manual changeover switch 28. In addition, temperature detectors (T,,TL,T,) for each part.

Signals from T, ) 18 to 21 and the reactor pressure detector (P, ) 17 are input to a temperature compensation circuit 29 and a pressure compensation circuit 30. The compensation circuit will be described later.

The temperature compensation circuit 29 is for the above-mentioned (2) start/stop mode, and is used when switched by the manual changeover switch 28, and is outputted through the automatic changeover switch 31. Since the output has been calibrated under normal operating conditions, it is output directly through the automatic changeover switch 31 without any particular correction.

In the event of an accident, the automatic changeover switch 31 is activated on the LOCA signal 24.
is automatically switched to the pressure compensation circuit 30 side and output.

Next, the contents of each compensation circuit will be explained.

(a) Temperature Compensation Circuit 29 In the first formula for calculating differential pressure generation, each density is as follows.

i) ρ = f+ (TL) L ii) ρ = ft (TH) 5I iii) ρ, = fg (T,,P,)iv) ρ-
"fs ('r-) V) p -= f - (Tll) (jB 2 formula)
However, L, f12: Density function with temperature and pressure as parameters.The density under normal operating conditions is given by each of the above formulas, and when starting and stopping, the temperature and pressure conditions change, so
’” to distinguish them.

From the first formula, during normal operation.

ΔP=f・(Q・ρLL'ρLH* I's r pw
*f'va) ρ□, ρIJ' ρ5. ρ1. ρ,
For simplicity, we represent ρ as ΔP=fA (Ω, ρ) From this, Ω”FA (ΔP, ρ) (3rd equation) When starting and stopping, Ω=FA (Δp /, ρ′) (4th equation) However, since the calibration is performed using the third equation, ρ""FA(Δp l, ρ)(AP' = fA(Q'
, ρ)), and Q' is the apparent water level.

In order to correct this, the actual water level a can be calculated using the fourth equation. That is, since ΔP' is the output of the differential pressure transmitter 10, the second equation is used to calculate ρ' and Ω.

(b) Pressure compensation circuit 30 The calculation formula for differential pressure generation is the differential pressure transmitter 1 using the LOCA signal 24.
Since the L side lining (reference leg) of 0 is separated and opened to the atmosphere, the first equation cannot be applied, and the following simple equation is used.

A P ” 72 t p LH+ (Q + El
4) /' w + (jl w + D 3Q Q4
) ρ9 +P.

” j' 1 ρLPI+ Q 4 P w + (Q
2+ Q 5 II 4 )ρ, +(ρ1−ρ9)+ρ
~ (Formula 5) This is for simplicity.

Δp=fll(u+　ρLH9ρ1.ρg)+P.

= f, (Q, P) = P ~ (Equation 6) Even though the automatic vent valve is currently open, the initial calibration was performed under normal operating conditions, so it is not suitable for reactor accidents. If we distinguish the temperature and pressure conditions by adding r', then from the 6th equation, Q=F8 (ΔP-P,,p) (7th equation), in the event of a reactor accident, Q=FII (ΔP'P ~, ρ′) (Equation 8), but the calibration is performed using f, (fl, ρ′) in Equation 6.
), AP' = fe (n'tρ
) 10P-, and a' is the apparent water level.

In order to correct this, the actual water level a can be calculated using equation 8, that is, ΔP' is.

Since it is the output of the differential pressure transmitter 10, using the second equation, ρ'
Ω can be calculated from the actual measured value P-.

According to one embodiment of the present invention, it is possible to correct the environmental conditions for any state of the plant, and to achieve the effect that the actual water level can be measured with high accuracy.

In FIG. 2, there are a total of four temperature detectors, but a sufficient effect can be expected even if the number is increased or decreased.

Further, although the density ρ is given as a constant as before during normal operation, the accuracy can be further improved by calculating the second equation from the actually measured temperature and calculating the actual water level.

[Effect of inspiration]

According to the present invention, it is possible to perform pressure/temperature correction on the reactor water level for all plant conditions, so accuracy can be improved, and in particular, sufficient accuracy can be obtained for reduced pressure boiling in the event of an accident. There is an effect that it can be done.

[Brief explanation of drawings]

Fig. 1 is a basic system diagram for measuring the reactor water level in a boiling water nuclear power plant using a differential pressure detection method, Fig. 2 is a system diagram of an embodiment of the present invention, and Fig. 3 is a temperature/pressure system diagram. FIG. 2 is a block diagram illustrating a compensation method. ■... Nuclear reactor, 2... Reactor containment vessel, 3... Reference plane device (condensation tank), 4... Instrumentation penetration, 5
...Detection source valve, 6...Overflow check valve, 10...
・Differential pressure transmitter, 15...Top measurement tap, 16...
Lower measuring tap, 23... Automatic vent valve, 24...
Coolant loss signal, 25...Drain funnel, 26.
...Temperature/pressure compensation circuit, 27...Water level signal after correction, 28...Manual changeover switch, 31...Automatic changeover switch. Agent Patent Attorney Akio Takahashi No. 1 Account 9 1-111 No. 2 (2)

Claims (1)

[Claims] 1. A nuclear reactor water level measuring device consisting of a differential pressure gauge having a reference water level, which is equipped with an automatic valve operated by a switching signal on the reference water level side, and an automatic valve with one side open to the atmosphere. Reactor water level measuring device.