JPH045847Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an improvement of a water level detection device in a steam generator of a nuclear power plant.

The primary coolant that has passed through the reactor core in the reactor vessel and is heated is guided from the primary coolant circulation system piping through the water chamber of the steam generator into the heat transfer tubes, and is then transferred to the secondary cooling water ( In pressurized water nuclear power plants, which heat and evaporate the fluid (outside the tube) and guide it to the turbine to drive the generator, when the water level of the secondary cooling water in the steam generator becomes low, the heat of the primary coolant is transferred to the secondary cooling water. This prevents the heat from being transferred to the cooling water side, and the heat from the reactor side accumulates on the primary side, causing accidents such as fuel melting.
The water level in the steam generator must be maintained at a set point.

The conventional water level control in a steam generator is
When the output of the generator is 0 to 15% and the flow rate of steam taken out from the steam generator is small, the water level inside the steam generator is detected by a narrow range water level detector (2 in Figures 1 and 2).
The detection signal obtained there is sent to the deviation detector (see 8 in Fig. 2), and the deviation from each other is calculated based on the water level setting value (see 1 in Fig. 2). The temperature difference ΔT at the steam generator inlet and outlet of the material is detected by the steam generator inlet and outlet temperature difference detector (first,
The water supply flow rate of the secondary cooling water supply system piping (the water supply flow rate of the bypass water supply pipe (see e ₁ of Figure 1)) is detected by the water supply flow rate detector (see 4 of Figures 1 and 2). ), and furthermore, the detection signals obtained by each of the above-mentioned detectors 8, 3, and 4 are sent to the water level control device in the steam generator, and calculations are performed to zero the difference between the actual water level and the set water level. The resulting control signal is sent to the bypass water supply valve (see 15 in Figure 1) to control the opening of the bypass water supply valve to maintain the water level in the steam generator at the set value. When the output of the steam generator is 15 to 100% and the flow rate of steam taken out from the steam generator is large, the water level in the steam generator is detected by the narrow range water level detector, and the detection signal obtained there is used as the deviation The flow rate of steam taken out from the steam generator is detected by the steam flow rate detector, and the flow rate of the water supplied to the secondary cooling water supply system piping ( The water supply flow rate of the water supply pipe (see e in Figure 1) is detected by the water supply flow rate detector, and the detection signals obtained by each of the detectors are sent to the water level control device in the steam generator, and the actual water level and Performs calculations to make the difference with the set water level zero, and sends the resulting control signal to the main water supply valve (see 16 in Figure 1).
The water level in the steam generator is maintained at a set value by controlling the opening degree of the main water supply valve. The secondary cooling water supply system piping is equipped with two water supply valves, a bypass water supply valve and a main water supply valve.The reason for this is that the secondary cooling water with a small flow rate and the secondary cooling water with a large flow rate are This is because it is difficult to control with the same water supply valve in terms of accuracy. When the flow rate is small (), the bypass water valve is used and () the generator output is
15 to 100%, and when the flow rate of steam taken out from the steam generator is large (when the flow rate of secondary cooling water is large), the main water supply valve is used. In addition, in the case of () above, the detection signal obtained by the primary coolant steam generator inlet and outlet temperature difference detector is used to control the bypass water supply valve, and in the case of () above, the detection signal obtained by the steam flow rate detector is used to control the bypass water supply valve. The reason for using a detection signal is that when () above, the amount of steam extracted from the steam generator is large, the steam flow rate is stable, and the steam flow rate does not reflect the load of the steam generator. In contrast, in case () above, the amount of steam taken out from the steam generator is small and the steam flow rate is The steam flow rate is unstable and does not accurately reflect the steam generator load, and the detection signal obtained by the primary coolant steam generator inlet and outlet temperature difference detector is used instead of the steam flow rate detector. are doing. The detected value of this steam generator inlet/outlet temperature difference detector also indicates the load fluctuation of the steam generator. In other words, this nuclear power plant is operated by keeping the primary coolant flowing through the primary coolant circulation system at a nearly constant flow rate, and the load on the steam generator is Q, and ΔT is the temperature difference between the primary coolant inlet and outlet of the steam generator. , F is the flow rate of the primary coolant, then Q
=ΔT×F holds true, and ΔT indicates the variation in the load of the steam generator.

The water level control device in the steam generator of the nuclear power plant had the following problems. In other words, since the temperature difference ΔT of the primary coolant between the inlet and outlet of the steam generator is proportional to the flow rate of steam taken out from the steam generator, the temperature difference ΔT is the leading element in controlling the secondary cooling water supply system (bypass water supply valve). Become. However, a time delay occurs before the load fluctuation (steam flow rate change) of the steam generator is reflected in the temperature difference ΔT. This is because heat, which has a slow response, is used as a medium. When the load of the steam generator changes, the narrow-range water level detector detects the water level L (inside the downcomer) between the outer shell and the inner shell (see b ₆ in Figure 1) of the steam generator, and The water level inside the shell is not detected. Inside the steam generator, there are 4th and 5th
As shown in the figure, there are many bubbles, and when the load of the steam generator fluctuates and the internal pressure of the steam generator changes, the specific volume changes, which causes the gap between the outer shell and the inner shell of the steam generator to change. The water level changes significantly. For example, when the load on the steam generator decreases, the internal pressure of the steam generator increases due to excess steam, and P ₁ < P ₂ ,
Water level L decreases from L ₁ to L ₂ . That is, the water level L responds to changes in specific volume. A narrow-area water level detector detects the actual water level in this area, and the bypass water supply valve is controlled based on the detection signal obtained by the narrow-area water level detector, so water level control when the steam generator load fluctuates is controlled. It takes time to settle, lacks stability, and when a large deviation occurs between the actual water level of the steam generator and the set water level, control of the heat exchange area becomes a problem.

This proposal addresses the above-mentioned problems by keeping the primary coolant heated after passing through the reactor core inside the reactor vessel at a nearly constant flow rate, and directing the heated primary coolant from the primary coolant circulation system piping to the water chamber of the steam generator. while guiding it into the heat exchanger tube,
The secondary cooling water is guided from the secondary cooling water supply system into the steam generator, and the secondary cooling water flowing inside the steam generator as extra-tube fluid is heated and evaporated by the primary cooling water. In a nuclear power plant where water is guided to a turbine to drive a generator, a narrow-area water level detector detects the water level of secondary cooling water in the steam generator, and a water level detection value obtained by the narrow-area water level detector. and a steam generator outlet temperature difference detector that detects a temperature difference of the primary coolant at the outlet and outlet of the steam generator;
a water supply flow rate detector that detects the flow rate of water supplied to the steam generator; and a wide area water level detector that detects the water level of secondary cooling water in the steam generator in place of the narrow area water level detector when the load of the steam generator changes. A water level detector is installed in the secondary cooling water supply system based on the control signal obtained by calculating the amount of secondary cooling water supplied to the steam generator based on the detection signals from each of the detectors. A nuclear power plant characterized in that it is equipped with a water level control device in a steam generator that controls a bypass water supply valve to maintain the water level of secondary cooling water in the steam generator at a set value. To provide a water level control device in a steam generator of a nuclear power plant that can stably control a bypass water supply valve even when the load of the steam generator fluctuates when the output of the generator is as low as 0 to 15%. At the point.

Next, the water level control device in a steam generator of a nuclear power plant according to the present invention will be explained using an _embodiment shown in _FIGS . Water chamber b, b ₂ is an inverted U-shaped heat transfer tube extending from the same water chambers b ₁ and b ₃ to the heat exchange area b ₄ of steam generator b, b ₅ is a steam extraction pipe, and b ₆ is an inner cylinder. , f is a water supply ring disposed in the upper part of the steam generator b, c is a primary coolant circulation pipe connecting the reactor a and the water chambers b ₁ and b ₃ of the steam generator b, and d is the main water supply pump, e is a pipe extending from the main water supply pump d to the water supply ring f, 16 is the main water supply valve provided in the pipe e, and 15 is a bypass pipe that bypasses the main water supply valve 16.
e Bypass water supply valve installed in ₁ , 1 is the water level setting value of steam generator b, 2 is a narrow range water level detector, 3 is a primary coolant steam generator inlet/outlet temperature difference detector, 4 is a feed water flow rate detector, 5 is the first-order lag element (high-frequency filter) that excludes high-frequency periodic noise of the water level, 6 is the leading/lag element (high-frequency filter + differential element + load (equivalent to steam flow rate)), and 7 is the high-frequency period of the feed water flow rate. 1st-order delay element (high-pass filter) that removes noise, 8 is an adder (water level deviation detector), 9 is a proportional-integral controller, 10 is an adder, 11 is a wide area water level detector that is the most distinctive feature of this project, 12 is a Phase lead/lag element (high-pass filter + differential element), 13 is proportional-integral controller, 14 is automatic -
It is a manual switch.

Next, the operation of the nuclear power plant will be explained. The actual water level detection signal obtained by the narrow range water level detector 2 is sent to the first-order delay element 5, where noise is removed and sent to the adder 8 together with the water level setting value 1.
Here, the mutual deviation is calculated and sent to the proportional-integral controller 9, where the correction described later is performed and sent to the adder 10, and also obtained by the steam generator outlet and outlet temperature difference detector 3. The signal is sent to the phase lead/lag element 6, where the control advance signal is created and noise removed, and sent to the adder 10, and the signal obtained by the water supply flow rate detector 4 is sent to the first-order lag element 7. is sent to adder 1, where it undergoes noise removal and is sent to adder 1.
Sent to 0. Further, the actual water level detection signal obtained by the wide area water level detector 11 is sent to the phase advance/delay element 12, where the control advance signal is created and noise removed, and then sent to the adder 10, where it is mutually The deviation is calculated and sent to the proportional-integral controller 13. The equal proportional-integral controller 13 has a generator output of 15
~100%, and when the flow rate of steam taken out from steam generator b is large, the actual water level detection signal from narrow area water level detector 2 is used to control the main water supply valve 16, but the When the output is 0 to 15% and the flow rate of steam taken out from steam generator b is small, due to the difference between the lead/lag element 6 and the primary lag element 7 and the differential element of the lead/lag element 12, The water level in steam generator b is calculated to match the set value. Although it is preferable that no deviation occurs in the water level in the steam generator b based on this calculation result, a deviation normally occurs. The proportional-integral controller 9 is provided to correct this deviation. The control signal obtained by the proportional-integral controller 13 is transferred to the automatic-manual switch 1
4 to the bypass water supply valve 15, and the opening degree of the bypass water supply valve 15 is controlled. A specific example of the wide area water level detector 11 is shown in FIG. In Fig. 3, 17 is a differential pressure transmitter, r _s is the specific weight of the gas phase, r _w is the specific weight of the liquid phase, r _f is the specific weight of the piping, ΔP is the pressure drop in the downcomer, ΔP .oo is 100%
The pressure applied to the detector when the water level is 0%, ΔPo is the pressure applied to the detector when the water level is 0%, and each of the above pressures is as follows: ΔP.oo=H(r _f −r _w )+ΔP …… ΔPo=H(r _f − r _s )+ΔP... The wide area water level detector 11 is calibrated with r _f = r _w = 1, r _s = 0, ΔP = 0, and ΔP.oo = 0, ΔPo = H. The reason why the wide-area water level detector 11 responds more accurately and quickly than the narrow-area water level detector 2 when the load of the steam generator b changes at low output is as follows. As already mentioned, there are many bubbles in steam generator b, and when the load on steam generator b fluctuates and the internal pressure of steam generator b changes, the specific volume changes, and as a result, the steam generator The water level between the outer shell and the inner shell (inside the downcomer) of b changes significantly. For example, when the load on steam generator b decreases, the internal pressure of steam generator b increases due to excess steam, P ₁ < P ₂ , and the water level L decreases from L ₁ →L ₂
decreases to The narrow-area water level detector 2 detects the actual water level in this area, and the narrow-area water level detector 2 responds to changes in specific volume, but the wide-area water level detector 11 measures r×H. and does not respond to changes in specific volume. Therefore, the wide area water level detector 11 responds more accurately and quickly than the narrow area water level detector 2 when the load of the steam generator b changes at low output. Further, if the manual/automatic switch 14 is set to manual, the proportional integral controller 1
Any control signal can be taken out from 3, and if it is set to automatic, it will be automatically controlled as shown in the block diagram of FIG.

The proposed nuclear power plant is configured as described above, and the actual water level is detected by a wide-area water level detector that accurately and quickly responds to the changing water level of the secondary cooling water when the load of the steam generator changes at low output. Since it is incorporated into the signal as a control precedent element, the output of the generator is 0~
When it is as low as about 15%, the bypass water supply valve installed in the secondary cooling water supply system can be stably controlled even if the steam generator load fluctuates. That is, the secondary cooling water flow path in the steam generator b is separated into an outer part and an inner part by a wall part. The secondary cooling water is fed into the outer part of the steam generator and starts boiling in the inner part of the steam generator. The boiled steam is taken out of the steam generator from the inner upper part of the steam generator, and the non-boiled secondary cooling water flows again to the outer part of the steam generator and is circulated. This flow rate is called the circulation flow rate. Further, the point at which the secondary cooling water starts boiling inside the steam generator is called the boiling start point. In this state, the narrow area water level detector 2 measures the differential pressure between the upper detection end and the lower detection end. The differential pressure ΔP _N detected by the narrow-range water level detector 2 determines the specific gravity of water in the can by
When the height is h _N , the circulating flow rate is Q, and the pressure loss coefficient is K _i , ΔP _N = PH _N −PL _N = (Po + γh _N ) − Po−KQ ² = γh _N −K _N Q ² .... The wide area water level detector 11 also measures the differential pressure between the upper detection end and the lower detection end. The differential pressure ΔP _W detected by this wide-area water _level detector 11 is calculated as follows _, as shown in FIG _. = PH _W − PL _W = (Po + γh _W ) − Po − K _W Q ² = γh _W − K _W Q ² ……. In this way, the measurement procedures of the narrow-area water level detector 2 and the wide-area water level detector 11 are the same, but the steam generator b has a circulating flow rate inside it, unlike a normal tank, etc. It is necessary to consider the pressure loss due to As already mentioned, the inside of the steam generator b is separated by a wall into an outside part and an inside part, but due to its structure,
The flow path area outside the wall is the upper part (narrow area water level detector 2
(measurement range) is wide, while at the bottom,
As shown in Fig. 7, it has become narrower. That is, the wide-area water level detector 11 has a pressure loss term that is higher than that of the narrow-area water level detector 2.
The impact is so large that it cannot be ignored. Therefore, the above formula and the above formula can be rewritten as follows.

Narrow area ΔP _N = γh _N ... Wide area ΔP _W = γh _W −K _W Q ² ... From the above, it can be seen that the indication of the wide area water level detector 11 changes depending on fluctuations in the circulating flow rate.

The water level of the steam generator b is controlled based on the detection signal of the narrow range water level detector 2. However, it is the circulating secondary cooling water that controls the water level in the steam generator b, and the amount of circulation depends on the amount of water inside. For example, as shown in FIG. 8, if the gas phase capacity of the two-phase flow decreases, secondary cooling water will flow from the outside to the inside to compensate for the decrease.
Therefore, the level of the secondary cooling water in the steam generator b decreases. That is, the range in which the gas phase exists governs the behavior of the water level of the secondary cooling water. As a result of the above, the narrow-range water level detector 2 is easily influenced by fluctuations in the boiling start point of the secondary cooling water.

To summarize what has been said above, (2) The narrow range water level detector 2 is susceptible to changes in the boiling start point.
() The wide area water level detector 11 is susceptible to changes in the circulating flow rate. For example, the boiling point increases. That is,
Assuming an event where the narrow area water level detector 2 falls,
(A) ΔP _N of the narrow-area water level detector 2 appears as a decrease in the water level as h _N decreases. (B) As for ΔP _W of the wide area water level detector 11, although h _W decreases, the circulating flow rate also decreases, making it difficult for ΔP _W to decrease. For example, when the water supply is increased, the water capacity in the can increases, but the boiling start point temporarily rises due to the thermal influence of the cold water supply, and the narrow area water level temporarily falls. On the other hand, since the wide area water level detector 11 is not easily affected by the boiling start point, it rises by the amount of increase in capacity (see FIG. 9).
As described above, the wide-area water level detector 11 does not affect parameters other than capacity, unlike the narrow-area water level detector 2, and thus expresses the capacity relatively accurately. Therefore, it is easy to predict the behavior of the narrow area water level detector 2 from the behavior of the wide area water level detector 11, and by correcting the detection signal of the narrow area water level detector 2 with the detection signal of the wide area water level detector 11, The bypass water supply valve 15 of the secondary cooling water supply system is difficult to fluctuate greatly, the amount of overflow can be reduced, and the bypass water supply valve 15 provided in the secondary cooling water supply system is stably controlled.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of a nuclear power plant according to the present proposal, Fig. 2 is a system diagram of a water level control device in a steam generator, and Fig. 3 is an explanatory diagram of a wide area water level detector.
FIGS. 4 and 5 are explanatory diagrams showing detection parts of the narrow area water level detector, and FIGS. 6, 7, 8, and 9 are explanatory diagrams explaining the effects of the nuclear power plant according to the present invention. a...Reactor vessel, b...Steam generator, c...
Primary coolant circulation system piping, A...Primary coolant, B...
...Steam, 1...Water level setting value, 2...Narrow area water level detector, 3...Steam generator inlet/outlet temperature difference detector, 4...
...Water supply flow rate detector, 8...Difference detector, 11...
Wide area water level detector.

Claims (1)

[Scope of utility model registration request] The primary coolant heated after passing through the reactor core inside the reactor vessel is guided from the primary coolant circulation system piping to the heat transfer tubes via the water chamber of the steam generator while maintaining a nearly constant flow rate. is guided into the steam generator from the secondary cooling water supply system, and the secondary cooling water flowing as extra-tube fluid in the steam generator is heated and evaporated by the primary cooling water, and then guided to the turbine. hand,
In a nuclear power plant that drives a generator, a narrow-range water level detector detects the water level of secondary cooling water in the steam generator, and a water level detection value obtained by the narrow-range water level detector and a water level setting value. a deviation detector that detects a deviation; a steam generator inlet/outlet temperature difference detector that detects a temperature difference between the primary coolant at the inlet and outlet of the steam generator; and a feed water flow rate detector that detects the flow rate of water supplied to the steam generator. and a wide-area water level detector that detects the water level of the secondary cooling water in the steam generator in place of the narrow-area water level detector when the load of the steam generator changes, and the detection from each of the detectors is provided. Based on the signal, the amount of secondary cooling water supplied to the steam generator is calculated, and the control signal obtained as a result controls the bypass water supply valve provided in the secondary cooling water supply system. A nuclear power plant characterized by comprising a water level control device in a steam generator that maintains the water level of cooling water at a set value.