JPH0361920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a boiling water nuclear reactor suitable as a multi-purpose small to medium-sized nuclear reactor installed, for example, around a city.

[Background of the invention]

Figure 1 shows an outline of a conventional boiling water reactor (hereinafter referred to as BWR). In Fig. 1, the output of the reactor core 2 loaded in the pressure vessel 1 is expressed by the control rod 3.
It is designed to be adjusted by operating the. The heat generated in the core 2 is removed to the upper part of the core 2 by a recirculation system 4 in the form of two phases of steam and water. 5 is a jet pump. The two phases of steam and water are separated by a steam separator 6 and a steam dryer 7, and only steam is supplied to the turbine 10 via a main steam line 8 and a steam control valve 9. The steam guided to the turbine 10 is reduced to water by the condenser 11 and returned to the pressure vessel 1 by the water supply pump 12.

On the other hand, Figure 2 shows an outline of a conventional pressurized water reactor (PWR). As shown in FIG. 2, in PWR as well, the output of the reactor core 2 loaded in the pressure vessel 1 is adjusted by operating the control rods 3. Heat generated in the reactor core 2 is carried away by cooling water and guided to a heat exchanger 14 via a recirculation system 4. The heat transferred from the primary side to the secondary side of the heat exchanger 14 is guided to a turbine or the like via the circulating water of the secondary system pump 15. Further, in a PWR, a pressurizer 13 is provided to control the pressure of the primary system to form a vapor phase, but the pressure vessel 1, heat exchanger 14, and recirculation system 4 are only in the liquid phase.

As described above, in both conventional BWRs and PWRs, when changing the output of the reactor core 2, it was generally done by operating the control rods 3.

However, in multi-purpose small and medium-sized reactors installed around cities, due to constraints on operation management (PCIOMR: break-in operation) to maintain the health of the reactor core, there is a possibility that the load may suddenly increase or decrease due to daily load fluctuations. It is difficult to respond. That is, from the standpoint of maintaining the integrity of the reactor core, it is undesirable to rapidly insert or withdraw control rods, and it is impractical to produce fuel that can withstand rapid load changes because it increases the cost of the entire plant. In addition, in conventional BWRs, flow control using a feed water pump or recirculation system pump could be considered as a means of adjusting output changes other than control rod operation, but this would result in complicated configurations and operations, making it impractical. Not.

[Purpose of the invention]

The purpose of the present invention is to provide a BWR that ensures sufficient reliability and safety, has a simple configuration, and can easily control the core output in response to sudden changes in load according to demand. do.

[Summary of the invention]

In order to achieve the above object, the present invention provides BWR
The present invention is characterized in that the amount of heat exchanged to the secondary system is controlled by adjusting the ratio of the liquid phase part and the vapor phase part in the primary system of the heat exchanger according to the liquid level.

That is, when the amount of exchanged heat is increased, the amount of subcooled cooling water returned to the pressure vessel increases, and the void ratio of the core decreases. This increases the power output of the core. On the other hand, if the amount of heat exchanged is reduced, the amount of subcooled cooling water returned to the pressure vessel will be reduced, increasing the void fraction of the core. This causes the core power to drop.

As described above, according to the present invention, by utilizing the void reactivity specific to BWR, the amount of heat exchanged according to the load and the core output can be controlled by the liquid level on the primary side of the heat exchanger.

[Embodiments of the invention]

Hereinafter, each embodiment of the BWR according to the present invention will be described based on the drawings.

FIG. 3 shows an embodiment of the present invention. In FIG. 3, the same parts as in FIG. 1 or 2 will be described below using the same reference numerals.

First, let's talk about the piping system. Heat generated from the reactor core 2 turns into steam within the pressure vessel 1 and is sent to the primary side of the heat exchanger 14. The heat of this steam is transferred to the cooling water on the secondary side in the heat exchanger 14,
The steam condenses. The heat transferred to the secondary side is supplied to each load by the secondary system pump 15. Further, the steam condensed in the heat exchanger 14 is accumulated on the primary side of the heat exchanger 14, and a liquid phase portion is formed. The accumulated cooling water is then returned to the pressure vessel 1 via the recirculation system pump 18 and the control valve 17 of the recirculation system 4. Thereafter, the same cycle is repeated to extract heat output.

Next, the output control of the BWR configured as above will be described. As a general characteristic of the heat exchanger 14, heat exchange in the form of "steam on the primary side and water on the secondary side" is better than heat exchange in the form of "water on the primary side and steam on the secondary side". It has been confirmed that the heat exchanger 14 is also larger (2 to 10 times).
By adjusting the ratio of the vapor phase to the liquid phase on the primary side of the reactor, the amount of heat exchanged can be controlled, and therefore the reactor output can be controlled.

The output control device includes a liquid level gauge 16 provided in the primary system of the heat exchanger 14, and a control device that controls the liquid level on the primary side of the heat exchanger 14 according to the measurement signal L. Ru. As a control device, the recirculation system pump 18 is used to control its discharge amount, or the control valve 17 is used to control its valve opening. By doing this, by measuring the liquid level on the primary side of the heat exchanger 14 using the liquid level gauge 16, the ratio of the vapor phase to the liquid phase can be determined. By controlling the control valve 17, a desired output can be obtained.

The characteristics of each part of the BWR constructed as described above are shown in FIGS. 4 to 9. As shown in FIG. 4, let L be the liquid level on the primary side of the heat exchanger 14, and let Q be the amount of heat exchanged on the secondary side, which is a function of this L. Also, the fifth
As shown in the figure, W is the primary system circulation flow rate of steam output from the pressure vessel 1, and H is the primary system outlet enthalpy. In addition, the subscript max in the figure indicates the maximum value, sat indicates saturation, and sub indicates subcool.

Now, as shown in FIG. 6, as the liquid level L rises, the proportion of the vapor phase decreases, so the amount of heat exchanged Q decreases. When the liquid level L is low, the amount of heat exchanged Q increases and the amount of steam condensed also increases. Therefore, in order to keep the liquid level L constant, it is sufficient to increase the circulation flow rate W to the pressure vessel 1, as can be seen from FIG. As the liquid level L decreases, the amount of heat exchanged Q in the vapor phase increases, and conversely, the amount of heat exchanged in the liquid phase decreases, so the enthalpy H at the exit of the heat exchanger 14 is as shown in FIG. , subcool increases. On the other hand, when the liquid level L increases, it approaches saturation. As shown in FIG. 9, as the liquid level L decreases, the recirculated water injected into the pressure vessel 1 approaches saturation, and as a result, the void ratio due to the core 2 increases.
Conversely, the output will decrease.

In this way, according to the BWR of the present invention, output can be controlled simply by controlling the liquid level in the heat exchanger when the load changes.

As described above, the gist of the present invention is to adjust the ratio between the vapor phase and liquid phase in the heat exchanger 14 using the devices 17 and 18.
Since the output control is performed by adjusting the output, various modifications can be made by taking advantage of this fact.
Each example will be explained below.

FIG. 10 shows an example in which an emergency water injection stage is provided for injecting cooling water into the pressure vessel 1 in the event of a loss of coolant accident (LOCA) due to pipe rupture. The emergency water injection means is composed of a liquid level gauge 19 that measures the amount of cooling water in the pressure vessel 1 and a recirculation system 4. A sudden drop in the amount of cooling water in the pressure vessel 1 is determined from the indication from the liquid level gauge 19, and the discharge amount of the recirculation system pump 18 is increased, or the opening degree of the control valve 17 is increased and the heat exchanger 14 is increased. By forcibly injecting the cooling water inside the pressure vessel 1, the reactor core 2 can be completely submerged with water. Furthermore, although the liquid level in the heat exchanger 14 decreases due to this water injection, a portion of the heat generated in the core 2 can be transferred to the secondary system.

FIG. 11 shows an example of a stopping means when the output suddenly increases or stops. The stopping means includes a neutron flux meter 20 (or manual 21) provided in the core 2 and a recirculation system 4. From the signal of the neutron flux meter 20 (or manual 21),
Determine whether it is necessary to stop the output, and restart the recirculation system pump 18.
The amount of water discharged into the pressure vessel 1 is set to zero, or the control valve 17 is completely closed to stop water injection into the pressure vessel 1. By doing so, the cooling water in the pressure vessel 1 moves to the heat exchanger 14 side, the reactor core 2 is exposed, and the coolant density decreases, so that the output is stopped. Since the power of the core 2 is low, it is sufficiently cooled by steam alone.

FIG. 12 shows an example in which recirculation water is moved to the pressure vessel 1 by its own weight without using a pump in the recirculation system 4. Therefore, the heat exchanger 14 is arranged at a higher position than the pressure vessel 1. In small and medium-sized reactors, the recirculation flow rate is small, so circulation by gravity fall is sufficient. By doing so, energy saving can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the ratio between the vapor phase part and the liquid phase part of the heat exchanger can be adjusted by controlling the liquid level. The output can be easily controlled in a follow-up manner, and in this case, reliability and safety are sufficiently ensured, and it can be realized with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an outline of a conventional BWR, Fig. 2 is a block diagram showing an outline of a conventional PWR, Fig. 3 is a block diagram showing an embodiment of a BWR according to the present invention, and Fig. 4 is a heat exchanger. An explanatory diagram of various quantities of the vessel,
Figure 5 is an explanatory diagram of various quantities of the pressure vessel and core, Figure 6 is a characteristic diagram showing changes in exchange heat amount with respect to liquid level, Figure 7 is a characteristic diagram showing changes in circulation flow rate with respect to liquid level, and Figure 8 9 is a characteristic diagram showing changes in outlet enthalpy with respect to liquid level, FIG. 9 is a characteristic diagram showing changes in void ratio and output with respect to liquid level, and FIG. 10 is a block diagram showing another embodiment provided with emergency water injection means. FIG. 11 is a block diagram showing another embodiment provided with output stopping means, and FIG. 12 is a block diagram showing another example of the recirculation system. 1...Pressure vessel, 2...Reactor core, 4...Recirculation system, 16...Liquid level gauge, 17...Control valve, 18...
Recirculation system pump, 19... liquid level gauge, 20... neutron flux meter.

Claims (1)

[Scope of Claims] 1. A pressure vessel loaded with nuclear fuel, a heat exchanger for condensing steam generated within the pressure vessel, and recirculation of cooling water condensed within the heat exchanger back into the pressure vessel. In a boiling water reactor equipped with a system,
A boiling water nuclear reactor characterized by comprising an adjustment device for adjusting the ratio of a liquid phase part and a vapor phase part in the primary system of the heat exchanger. 2. In the nuclear reactor described in claim 1, the adjusting means includes a liquid level gauge that measures the liquid level on the primary side of the heat exchanger, and a liquid level gauge that measures the liquid level on the primary side of the heat exchanger, and a liquid level meter that measures the liquid level on the primary side of the heat exchanger, and A boiling water nuclear reactor comprising: a liquid level control device for controlling a liquid level on the primary side of the reactor. 3. A boiling water nuclear reactor according to claim 2, wherein the liquid level control device is a recirculation system pump that returns cooling water from the heat exchanger into the pressure vessel. 4. A boiling water nuclear reactor according to claim 2, wherein the liquid level control device is configured by providing a heat exchanger at a higher position than the pressure vessel. 5. In the nuclear reactor according to claim 1, 2, 3, or 4, the adjusting means detects an abnormal decrease in the amount of cooling water in the pressure vessel and adjusts the amount of cooling water in the heat exchanger. A boiling water reactor characterized by being equipped with an emergency water injection means for injecting water into a pressure vessel. 6. In the nuclear reactor according to claim 1, 2, 3, 4, or 5, the adjusting means detects an abnormal increase in core power and controls the power from the heat exchanger to the pressure vessel. A boiling water nuclear reactor characterized by being equipped with an emergency stop means for stopping circulation of cooling water.