JPH03105286A - Operating method of reactor - Google Patents

Abstract

PURPOSE:To enable execution of stable starting by operating a reactor in the range of density wherein reactivity decreases or the range of density wherein it does not change. CONSTITUTION:A control rod 4 is in an inserted state at the time of starting, and it is pulled out with a flow rate of steam increased by a steam generating system 5. In a stage when the flow rate of steam reaches a rated value, a steam blower 2 and a recirculation pump 3 are started, the system 5 is cut off by steam selector valves 6a and 6b and the density of a coolant is increased by adjusting the flow proportioning of the steam and water. Since the reactivity increases and an output rises at this time, criticality is maintained with the control inserted. At the same time with this switching, a turbine 8 is rotated by a steam generator 7, while the steam is sent to a primary condenser 9, and the water is supplied by the recirculation pump 3. The density of the coolant is made to approach the density in a steady operation from a lower level, and the steady operation can be reached from safe starting.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to nuclear reactors, in particular nuclear reactors, in which the reactivity increases with an increase in the volume ratio of steam contained in a unit volume of coolant (referred to as void fraction). The present invention relates to a method of operating a nuclear reactor having a characteristic range in which the void coefficient (including leakage of neutrons from the reactor core) is referred to as positive, and particularly relates to an operating method suitable for increasing or decreasing reactor power.

[Conventional technology]

Conventional nuclear reactors, such as boiling water reactors (IlltlR
As stated in "Nuclear Reactor Course" edited by Thermal Power Generation Association (1978), p. 101, when the reactor output increases for some reason, the reactivity increases due to the increase in steam bubbles. It has self-stability, which suppresses the increase in output.

Utilizing this effect, the reactor output can be increased or decreased by increasing or decreasing the reactor recirculation flow rate and the feed water flow rate. That is, by increasing the recirculation flow rate, the point of void generation in the reactor is moved upward, and the void volume in the reactor core is reduced, thereby increasing the reactivity. As a result, as the output increases, the amount of steam increases, that is, the voids increase,
Reactivity can be suppressed.

This characteristic also appears during the startup and shutdown of a nuclear reactor; regardless of the flow rate, the reactivity decreases (the void coefficient becomes negative) as the coolant density decreases due to an increase in void volume.

On the other hand, as light water reactors become more sophisticated, in order to further improve the utilization rate of uranium, steam and water are used as coolants to reduce the hydrogen to heavy metal atomic ratio. (SWPR, Steam-Water Pow)
ar Reactor) was announced at the 1988 Japan-Soviet Seminar.

In SWPR, there is a range of coolant densities in which the reactivity increases when the coolant density is lowered (the void coefficient is positive).
The characteristics are different from those of conventional boiling water reactors. This situation will be explained using FIG. 2.

Figure 2 shows the relationship between coolant density and reactivity for SWPR. As you can see from this figure, the coolant density is 140kg/
In a range where the coolant density is lower than m', that is, a high void ratio range, as the coolant density decreases (voids increase), the reactivity decreases (the void coefficient becomes negative). Also, in the density range higher than the coolant density, that is, in the range of low void fraction, as the coolant density decreases (voids increase), the reactivity increases (void coefficient is positive).
.

By setting the steady operating state to around this void coefficient O (coolant density 140 kg/rn'), SWPR
It has the inherent safety feature that the reactivity always decreases as the void increases or decreases.

However, a method for starting and stopping such a core has not yet been established. [Problem to be solved by the invention] As in the above SWPR, the steady operating state is a density range in which there is almost no change in reactivity with respect to coolant density, or the reactivity decreases as the coolant density decreases. range (with a void coefficient of O or a negative range), and if the coolant density at startup is higher than the steady-state operating state, similar to a conventional BWR, then from startup to steady-state operation, the void coefficient is The BWR will operate in the positive range, and the operating conditions at startup will be stricter than in conventional BWRs. That is, the output must be increased quasi-statically using control rods while monitoring the coolant density, and it takes a very long time to achieve steady operation.

The purpose of this invention is. The object of the present invention is to provide a safe and quick start-up device for a nuclear reactor with characteristics similar to SWPR.

[Means to solve the problem]

In order to achieve the above object, the present invention sets the coolant density state at startup to the same coolant density state as the steady operating state, that is, within the range where the reactivity does not change even if the coolant density changes.
Alternatively, the range is such that the reactivity decreases as the coolant density decreases.

It also supplies heat or steam from other systems to achieve moderator density during startup.

In addition, in order to control changes in reactivity due to startup, a control rod is inserted while maintaining steady operation.

Furthermore, when shutting down the reactor, in order to shut down the reactor quickly, the control rods are fully inserted and then the reactor is operated in a range where the reactivity increases as the density of the coolant decreases.

[Effect]

In other words, if the coolant density is in the void coefficient 0 or in the negative range at startup, the void coefficient is O even during steady operation.
or in the negative range, from startup to steady operation.
The vehicle always operates with a void coefficient of 0 or in a negative range, resulting in safe operation similar to the current BWR. Also,
Therefore, the time from startup to steady operation can be shortened.

In order to achieve this coolant density even during startup, when the reactor is not producing power, steam or a two-phase flow of steam and water can be delivered using other heat or steam generation systems.

Furthermore, when stopping, the operation is performed in the reverse order of normal starting, but by using the positive void coefficient range, it is possible to stop quickly. That is, first, when the control rods are fully inserted to lower the reactivity, the output decreases and the density of the coolant increases.

This further reduces the degree of reactivity, so it can be stopped quickly.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a system configuration suitable for applying the nuclear reactor operating method of the present invention to SWPR. S-PR is core 1,
It is composed of a steam blower 2, a ring pump 3, a control rod 4, etc. Also, when we look at the change in reactivity due to coolant density as a core characteristic, as shown in Figure 2, the void coefficient, where the reactivity increases as the coolant density increases, is in the positive range.
As the coolant density increases, the reactivity decreases and the void coefficient can take on both negative ranges. Also, during steady operation, the void coefficient is approximately 0, about 140kg/rn' (
The coolant density is 16 MPa).

This embodiment includes another steam generation system 5 in order to operate in this negative void coefficient range. The steam generation system 5 may be another type of furnace or a fossil fuel boiler.

At startup, the control rod 4 is in the inserted state, and the steam generation system 5 causes the control rod 4 to increase while increasing the steam flow rate.
I'm going to pull it out. When the steam flow rate reaches the rated value,
The steam blower 2 and recirculation pump 3 are started, the system 5 is shut off by the steam switching valves 6a and 6b, and the flow distribution of steam and water is adjusted to increase the coolant density. At this time, the reactivity increases and the output increases, so criticality is maintained while inserting the control rod. At the same time, the steam generator 7 turns the turbine 8 and sends steam to the primary condenser 9, and the circulation pump 3 sends water.

At this time, in FIG. 2, the lower coolant density approaches the density during steady operation. That is, in this embodiment, it is possible to reach steady operation from startup within the range where the reactivity decreases as the coolant density decreases (the range where the reactivity increases as the coolant density increases). Since it has a negative void coefficient in this range, it can be started safely and steady operation can be achieved.

Next, a first embodiment of the second nuclear reactor startup of the present invention will be described.
Illustrated using diagrams. In the first embodiment, complete steam (void ratio 100%) was sent by another steam generation system 5 at startup, but if the coolant density is in the negative void coefficient range, it is mixed with water from the beginning. It is also possible.

That is, in this embodiment, at the time of startup, the system 5 is operated and the circulation pump 3 is operated. At this time, in the injected mixed flow, the circulation pump flow rate is adjusted so that the mixing ratio of steam to water is greater than that during steady operation. This allows the coolant density to be lower than during steady operation, allowing safe startup.

The procedure from startup to steady operation in this embodiment is the same as in the first embodiment; first, the control rod is pulled out in a coolant density range in which the ratio of steam to water is greater than that during steady operation. Next, control rods are inserted to maintain criticality while increasing the ratio of water to steam. Since this method mixes water from the beginning, it has the effect of further shortening the time from startup to steady operation.

Note that if the moderator density is close to that during steady operation, the reactivity hardly changes and the void coefficient is approximately O, but even in such a case, the output coefficient is negative and safe.

Next, an embodiment of the first operating method regarding nuclear reactor shutdown of the present invention will be described using FIG. 1.

In a normal nuclear reactor with a negative void coefficient, shutdown is performed in the reverse order of startup, but in a core like this reactor where the void coefficient can be both positive and negative, the void coefficient is within a positive range in order to shut down even more quickly. It can be stopped in the range where the reactivity increases as the coolant density decreases.

That is, first, the control rod 4 is inserted to lower the reactivity to make it subcritical, and then the flow rate distribution is adjusted and the steam blower 2
We will reduce the supply from This increases the coolant density, further lowering the reactivity and allowing the reactor to be shut down quickly.

Although it is not quick, reactor shutdown can also be performed in the reverse order of startup as usual.

Although the present invention has been specifically applied to SWPR, it is applicable to all cores having similar characteristics.

〔Effect of the invention〕

According to the present invention, for a core with a coolant density range with a positive void coefficient that has not yet been established, it is possible to quickly and
It can be started and stopped safely.

[Brief explanation of drawings]

Figure 1 is a system diagram of an embodiment of the present invention, Figure 2 is a system diagram of an embodiment of the present invention.
FIG. 3 is a diagram showing a change in reactivity of R with respect to coolant density. DESCRIPTION OF SYMBOLS 1... Reactor core, 2... Steam blower, 3... Recirculation pump, 4... Control rod, 5... Steam generation system, 6
a, 6b...Steam switching valve, 7...Steam generator, 8.
...Turbine, Fig. 1 Fig. 2 Cold Ep material fermentation r(ri/π3冫

Claims (1)

[Claims] 1. As the density of the coolant flowing through the reactor core decreases, there is a density range in which the reactivity increases, and a density range in which it decreases or does not change, and the output becomes a nearly constant target output. During steady operation, in a nuclear reactor characterized by a density range in which the reactivity decreases due to the decrease in coolant density, or in a density range where it does not change, the output is increased to the target output by controlling the control rods and the coolant flow rate. A method for operating a nuclear reactor, comprising operating in a density range in which the reactivity decreases or does not change as the density of the coolant flowing through the reactor core decreases even during startup. 2. In claim 1, reducing the output of the nuclear reactor,
A method for operating a nuclear reactor, characterized in that when the reactor is shut down, the reactor is operated in a density range in which reactivity increases as the coolant density decreases. 3. A nuclear reactor operating method in which a mixed flow of steam and water is used as a coolant, characterized in that when the reactor is started up, the ratio of steam to water is higher than that during steady operation. 4. The nuclear reactor according to claim 3, wherein the control rods are pulled out at startup compared to during steady operation, and the control rods are inserted while increasing the ratio of water to steam until the target output is reached. How to drive. 5. A nuclear reactor operating method according to claim 2, characterized in that the flow rate is reduced after the control rods are inserted until the reactor becomes subcritical as a procedure from steady operation to shutdown. 6. At the time of startup of the nuclear reactor according to claim 1, heat or steam is supplied from another system to set a density range in which the reactivity decreases as the coolant density decreases. How to operate a nuclear reactor. 7. In claim 1, the density range of the coolant at the time of shutdown is the same as that at startup, and the shutdown procedure is a reverse procedure to the operating method at startup described in claim 1. How to operate a furnace.