JPH0587797B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides an automatic reactor startup device that automatically operates control rods during the temperature and pressure increase process after criticality is achieved during reactor startup operation. Regarding.

(Prior art) Generally, the startup of a boiling water reactor is performed by first withdrawing the control rods in a predetermined sequence to inject reactivity into the reactor core. After reaching a state where 1, that is, criticality is achieved, the control rods are further withdrawn to increase the neutron flux, promote heat generation, and heat the reactor cooling water. At this time, the turbine control valve and the turbine bypass valve are simultaneously closed to isolate the turbine and the reactor, and the temperature and pressure are increased until the reactor pressure reaches the rated value.

The graph in Figure 13 shows that during the temperature and pressure increase process from the rise in neutron flux after criticality, with conventional manual control rod operation, the reactor cycle was approximately 100 seconds, and the rate of change in reactor water temperature was
This shows an example of changes in major parameters when operating at a temperature of 55°C/hr or less. Note that the reactor cycle is also called a period, and the neutron flux level is e.
(=2.71) is the time to double, and is defined by the following equation.

T ^-1 = |n {φ (T ₂ ) / φ (T ₁ )} / (T ₂ - _{T 1} ) where, T: Furnace period (unit: seconds) φ: Neutron flux level T ₂ , T ₁ : Time The driving operations in the figure are explained as follows.

That is, first, the reactor cycle is set to 100 seconds from the time when the operator determines criticality, and the neutron flux is increased at a constant reactor cycle. The rate of increase in neutron flux begins to be suppressed due to thermal feedback, which causes a decrease in the multiplication factor due to the Doppler effect due to the rise in reactor water temperature associated with the increase in neutron flux, and a decrease in the neutron multiplication factor due to a decrease in coolant density. It operates while maintaining the neutron flux level (nuclear heating level).

During this period, control rod operations are suspended, and the SRM is mainly used in the region with a neutron flux of ¹⁰⁴ to 2× ¹⁰⁹ .
(Source Range Monitor: Neutron source range detector)
By pulling out the neutron flux and replacing it with this SRM, the neutron flux becomes
^IRM ( ^Interme-
The neutron flux is monitored by a diate Range Monitor (intermediate range neutron flux detector).

In addition, the IRM functions to prevent control rod withdrawal when 108% is indicated in the 125% range, and 120 in the 125% range.
%, a scram trip signal is generated. Therefore, in the above process, in order to avoid missing the timing of IRM range switching, it is necessary to increase the neutron flux to the nuclear heating level at a certain appropriate reactor cycle.

When the neutron flux reaches the nuclear heating level, which is about 0.1% of the rated value, and thermal feedback occurs,
Periodically, the rate of increase in reactor water temperature begins to change approximately in proportion to thermal output, and the reactor water temperature begins to rise. When the thermal output is lower than this, the reactor water temperature remains constant or gradually decreases due to heat leakage from CUW (Clean Up Water). After that, as the reactor water temperature rises, the heat loss from the reactor increases, and to compensate for this, the control rods are gradually withdrawn until the rated pressure is reached. The temperature and pressure are increased until the temperature is reached.

During this temperature and pressure increase process, it is stipulated that the rate of increase in reactor water temperature must be kept within 55°C/hr in order to avoid applying thermal shock to the reactor pressure vessel. Therefore, if the control rods are withdrawn too early, the rate of rise in the reactor water temperature will become too high.In such a case, the control rods should be inserted to reduce the calorific value, or the turbine bypass valve should be opened to release energy. need to be released.

(Problems to be Solved by the Invention) The following problems occurred in the operation of the temperature and pressure increasing process according to the conventional method described above. In other words, during the neutron flux increase process before temperature increase, the reactor cycle is kept constant due to IRM range switching, but the initial increase in reactor water temperature due to the reactivity with this reactor cycle is
This does not necessarily mean that the limiting condition of a temperature increase rate of 55°C/hr is satisfied. Therefore, as shown in FIG. 13, the rate of change in reactor water temperature may exceed this limit.

In order to avoid the above problem, the above furnace cycle should be changed to
It may be possible to set the rate of change in reactor water temperature in advance to a value that does not exceed the limit value. However, as the furnace cycle increases, the time required for startup increases, making it inefficient and difficult to evaluate off-line in advance.

Furthermore, if the rate of change in reactor water temperature is likely to exceed the limit value, a method of inserting control rods to suppress the increase in the rate of change in reactor water temperature may be considered. However, heat transfer from fuel to reactor water takes time. Furthermore, it is necessary to perform a constant time averaging operation to remove noise components, and it also takes time to evaluate the rate of change in reactor water temperature. Furthermore, the control rod value varies depending on the coordinates and position of the control rod. For this reason, if control rod withdrawal or insertion is determined only based on the rate of change in reactor water temperature, there may be cases where the rate of change in reactor water temperature is not controlled in time by control rod operation, and the rate of change in reactor water temperature exceeds the limit value. In order to raise the temperature efficiently without causing any problems, the operator must be highly skilled.

The present invention has been made in response to such conventional circumstances, and is capable of automatically starting a nuclear reactor by automatically controlling control rods during temperature and pressure increases from the rise in neutron flux after criticality. The aim is to provide equipment.

[Structure of the Invention] (Means for Solving the Problems) That is, the automatic nuclear reactor startup device of the present invention includes a reactor cycle calculation unit that inputs a neutron flux measurement signal and calculates a reactor cycle, and a reactor cycle calculation unit that inputs a neutron flux measurement signal and calculates a reactor cycle, and a reactor cycle calculation unit that inputs a neutron flux measurement signal and calculates a reactor cycle. The reactor water temperature change rate calculation unit inputs the reactor water temperature change rate and calculates the reactor water temperature change rate, and the reactor cycle and reactor water temperature change rate are inputted from the reactor period calculation unit and the reactor water temperature change rate calculation unit, respectively, and are calculated in advance. When the reactor water temperature starts to rise and the rate of change is small, the predetermined reactor period is maintained, and thereafter the control rod operation amount is increased according to the control rule that increases the reactor period as the rate of change of the reactor water temperature increases. and a control rod operation determination section that determines the control rod operation command signal and outputs a control rod operation command signal, and operates the control rods to raise the reactor water temperature until a predetermined reactor pressure is reached.

(Function) In the automatic reactor startup system of the present invention, control rules based on the reactor water temperature change rate and reactor cycle are determined in advance to determine control rod operations such as withdrawal, interruption, and insertion, and the calculated reactor cycle and reactor cycle control rules are determined in advance. The water temperature change rate is compared with the mutual set values of the reactor water temperature change rate and reactor period set in this control rule, and the control rod operation amount is calculated according to the deviation, and the control rod operation command signal is Output. Broadly speaking, this control rule is
When the rate of change at the beginning of the rise in reactor water temperature is small, a predetermined reactor cycle is maintained, and thereafter, as the rate of change in reactor water temperature increases, the reactor cycle is increased. Then, the control rods are automatically operated to raise the reactor water temperature until a predetermined reactor pressure is reached.

(Example) Hereinafter, details of the present invention will be described with reference to the drawings.

FIG. 1 shows an automatic reactor startup system according to an embodiment of the present invention. The automatic reactor startup system 1 of this embodiment includes a reactor period calculation section 2, a reactor water temperature change rate calculation section 3, , a limit condition setting section 4, a control rod operation determination section 5, and a display device 6.

The reactor cycle calculation unit 2 receives a neutron flux measurement signal from the neutron flux detector 11 disposed in the nuclear reactor 10, calculates the reactor cycle from this signal, and outputs it to the control rod operation determination unit 5.

In addition, the reactor water temperature change rate calculation unit 3
The reactor water temperature measurement signal from the reactor water temperature detector 12 and the reactor pressure measurement signal from the reactor pressure detector 13 are input, and the rate of change in reactor water temperature is calculated from these signals to the control rod operation determination section. Output to 5.

In addition to the above-mentioned reactor cycle and reactor water temperature change rate, a neutron flux measurement signal is input to the control rod operation determination unit 5.
Furnace cycle set value input from the limit condition setting unit 4,
Compare with the reactor water temperature change rate set value and nuclear heating level neutron flux value.

Then, according to the results of these comparisons, the amount of control rod operation is calculated to efficiently increase the neutron flux and the reactor water temperature, and the control rod operation amount and operation amount are calculated to determine how many notches to insert or withdraw. A control rod operation command signal, which is the coordinates of the control rod to be controlled, is output to the control rod position control device 14.

The control rod position control device 14 operates the control rod drive mechanism 15 based on this control rod operation command signal, and inserts and withdraws the control rods into the reactor 10 .

Further, the position and coordinates of the control rods to be operated and the parameters representing the above-mentioned core state are displayed on the display device 6.

Here, control during temperature and pressure increase after criticality is performed as follows.

In other words, as shown in the graph of Figure 2, where the horizontal axis is the reactor period and the vertical axis is the rate of change in reactor water temperature, the dotted line indicates the reactor cycle and rate of change in reactor water temperature from criticality to temperature and pressure rise. become.

When criticality is achieved, the reactor period is from infinity to a large positive value, the neutron flux level is low and the thermal output is negligible, and the reactor water temperature change rate is zero or a negative value (point A). Note that the decrease in reactor water temperature is due to circulation of feed water with the outside of the core or heat dissipation.

The increase in neutron flux after criticality is due to the neutron multiplication factor being 1.
This is done by withdrawing the control rod several notches from the point at which physical criticality is achieved and maintaining the reactor period at about 100 seconds (point B).

As the reactor water temperature increases as the neutron flux increases, the reactor water temperature change rate becomes a positive value and shows an increasing tendency. On the other hand, in the reactor period, the reactivity decreases due to the negative nuclear feedback associated with the rise in reactor water temperature, and shows a tendency to increase. The reactor water temperature change rate increases due to the reactivity introduced when the neutron flux increases, but if it is determined that the reactor water temperature change rate is likely to exceed the limit value of 55°C/hr, control rods are inserted. Then, increase the reactor period to suppress the increase in neutron flux and the rate of change in reactor water temperature (point C).

After the control rods are inserted, the reactor period increases rapidly, but there is a slight time lag in the rate of change in reactor water temperature, and it rises for a short time (point D). After the rate of change in reactor water temperature settles down to a constant level, the neutron flux decreases due to the rise in reactor water temperature, and the rate of change in reactor water temperature also decreases (point E).

Therefore, the control rod is withdrawn through the notch to raise the reactor water temperature. At this time, by withdrawing the control rod, the reactor period increases instantaneously, but control rod operation is interrupted during this time (point F).

The increase in neutron flux increases the rate of change in reactor water temperature, and the rate of change in reactor water temperature is controlled at a value close to 55°C/hr without exceeding the limiting conditions (point D).

However, in this case, the rate of change in reactor water temperature of 55°C/hr was set as the target value and limiting condition, but the target value of the rate of change in reactor water temperature during temperature rise can be set arbitrarily as long as it is around 55°C/hr and is positive. The value of is sufficient.

The control rules for control rod operation during temperature and pressure increases based on the increase in neutron flux after criticality can be expressed as follows.

When the rate of change in reactor water temperature is small, control rod positions are adjusted to maintain an appropriate reactor cycle target value, for example, about 100 seconds.

When the rate of change in reactor water temperature is large, evaluate the reactor cycle and rate of change in reactor water temperature at the same time, and if the reactor cycle is positive and the rate of change in reactor water temperature is likely to exceed the limit value, or has exceeded the limit value temporarily. In such a case,
Insert the control rod.

If the reactor water temperature change rate is below the limit value and within the set range, control rod operations will be interrupted.

In addition, FIG. 2 shows the above control rod operation rules divided into areas based on the relationship between the reactor period and the rate of change in reactor water temperature.

In other words, on the map of reactor period and reactor water temperature change rate in the same figure, the reciprocal of the reactor period and the peak value of the reactor water temperature change rate when neutron flux increases are almost proportional, so the peak value of the reactor water temperature change rate is the limit value. The relationship between the reciprocal of the reactor period and the rate of change in reactor water temperature so as not to exceed 55℃/hr and to settle at the target rate of change in reactor water temperature is determined at point _B1 .
→C ₁ →D is determined as a guideline, and control rods are inserted and withdrawn according to this guideline, that is, according to a control rule that increases the reactor period as the rate of change in reactor water temperature increases.

These boundaries for withdrawal/insertion/interruption can be obtained from a map of the reactor water temperature change rate and reactor cycle as a result of actual operation.

Furthermore, when increasing the neutron flux with a larger reactor period, the target value of the reactor period when the neutron flux is increased is changed depending on the neutron flux level.

In other words, when the neutron flux level is low and the contribution of thermal output to the reactor water temperature is completely negligible, the target value of the reactor cycle may be increased by withdrawing the control rods.
B Drive at points like ₂ . Next, when the neutron flux level reaches the level of nuclear heating that affects reactor water temperature changes, control rods are inserted and operation is performed at point B, which is referred to as B → C → C ₁ → D. Drive. It is sufficient to set the neutron flux level for this nuclear heating to about 0.1% of the rated output.

In Fig. 2, the control rod is withdrawn and inserted in the third
It represents two notches at the upper part of the control rod 31 on the inner circumference of the reactor core 30 as shown in the figure. For control rods of low value, such as the outermost control rod 32 and the control rods at the bottom of the core, as shown by diagonal lines in the figure, the ratio of control rod values is determined and the number of operation notches is corrected.

In the temperature and pressure increase range from criticality, the thermal output is less than a few percent of the rated value, and the amount of voids generated is small.
Changes in output distribution are small. In addition, since the control rod value is approximately proportional to the power distribution, we calculated the three-dimensional power distribution of the core during temperature rise by off-line calculation, and averaged it in the radial and axial directions as shown in the graphs of Figures 4 and 5. This is further averaged in each region, and the reciprocal is used as the gain of the control rod operation amount. That is, the scores shown in the graphs of FIGS. 4 and 5 are the control rod values in the axial and radial directions of the control rod, respectively, and the actual number N of control rod operation notches is determined by the following equation.

N= _W ≦ _R 〓 ΔN W (k, i, j) = 1/WZ (k)/WZmax・1/WR(
i, j)/WRmax・ΔN where, WZ(k): Value of axial control rod worth at k notch WZmax: Maximum value of axial control rod worth WR(i, j): At coordinate (i, j) Control rod worth WRmax: Maximum value of radial control rod worth W (k, i, j): Control rod value at (k, i, j) coordinates ΔN: Number of notches operated at one time It represents the number of control rod notches required for the control rod value to reach the calculated number of operation notches R by integrating from the position along the sequence. However, the value of N is rounded off to an integer of 2 notches.

The above is based on the control rod value based on the three-dimensional calculation of the reactor core.
Although each bundle is weighted, the control rod value may be weighted by dividing it into two areas: the inner circumference, the outer circumference, and the upper and lower areas. Furthermore, all control rods may have the same weight. In this case, since the value of the control rods at the outer periphery and the lower part of the core is low, reactivity will be applied as the control rods are operated more frequently.

FIG. 6 is a flowchart showing the operation of the control rod operation determination section 5.

The control rod operation determination unit 5 first checks whether the control rod operation command signal outputted by the control device has been achieved (a), and if the control rod operation command signal has been executed, resets the timer (b). , updates the time and counts the elapsed time after the operation (c).

If this elapsed time is longer than a predetermined waiting time, inference is made to determine the amount of control rod operation, and if the waiting time has not elapsed, the estimation calculation of the amount of control rod operation is bypassed. (d). This is because the core state does not change immediately after control rod operation. This waiting time is sufficient time for core state changes to occur, but short enough to accommodate sudden changes.

After this certain period of time has elapsed, the reactor water temperature and neutron flux are input (e), the rate of change in the reactor water temperature and the reactor period are calculated, and the control rod operation amount is inferred and determined based on the control rules given in advance (e). ).

Next, the obtained control rod operation amount is weighted with respect to the radial and axial positions of the control rod to determine the actual control rod operation amount (g).

The procedure for determining control rod operation using fuzzy inference is shown below. FIG. 7 shows the control rule in FIG. 2 expressed as a fuzzy control rule. Also,
The membership functions for each variable are shown in FIGS. 8 and 9. The reactor period and reactor water temperature change rate are divided into fuzzy variables such as positive and large (PB) and negative and small (NS), and there are control rules for each variable. The number of withdrawal notches for the control rod in the figure is 2 notches for C2, and operation interrupted for C1.
C0 is a fuzzy quantity representing two-notch insertion. In other words, an individual control rule may be, for example, ``If the reactor period T is positive and small (PS) and the reactor water temperature change rate DT is positive and small (PS), withdraw the control rod through the C0 notch.'' It can be expressed as

In general, if the reactor period T is Ai and the reactor water temperature change rate DT
If is Bi, pull out the control rod through the Ci notch. '', i=1, 2,...n. However, i is the number of the rule,
n is the total number of control rules.

A fuzzy inference method using this control rule will be explained below. FIG. 10 illustrates this inference method.

Now, if the input to the inference section is that the reactor period is TO and the reactor water temperature change rate is DTO, first,
The degree of conformity of the input to the conditions of each of the above control rules is determined. Antecedent “T is Ai”
The goodness of fit of the input “T is TO” is Ai
(TO) In other words, it is the membership value in TO of the fuzzy set Ai, and the antecedent parts are connected by AND, so Wi=min[Ai(TO), Bi(DTO)], i=1, 2,
...N. Therefore, the inference result based on the i-th rule is C is Wi×Ci. The inference result based on these n rules is: C= _o U ⁱ⁼¹ Wi×Ci However, the above equation is an operation that takes the union of fuzzy sets. Find the centroid of the membership function of C,
The control rod manipulated variable _c2 is determined.

c ₂ = ∫cC (c) dc / ∫C (c) dc An example of the results of automatically operating the control rods and raising the temperature and pressure from criticality using the automatic reactor startup system of this embodiment described above is shown below. This is shown in the graph of Figure 11.

As shown in this graph, after criticality, the reactor is operated at a constant period and the neutron flux increases exponentially. As the neutron flux increases, the rate of change in reactor water temperature increases, and when it becomes a positive value, control rods are inserted according to the control rules shown in Figure 7, and the reactor period approaches infinity and the rate of change in reactor water temperature becomes constant. Become. After that, the control rods were gradually withdrawn and the temperature was raised efficiently after satisfying the limit condition of 55°C/hr.

In addition, the graph in FIG. 12 shows the results of increasing the temperature and pressure from a furnace pressure of 38 KG and a reactor water temperature of 247°C. 55
Efficient temperature rise is achieved without exceeding ℃/hr.

[Effects of the Invention] As described above, according to the automatic reactor startup system of the present invention, the rate of change in reactor water temperature can be controlled safely and efficiently from the rise in neutron flux after criticality without exceeding the limit conditions. Control rod operations can be performed automatically during temperature and pressure increases, contributing to more efficient and labor-saving nuclear power plant operations, as well as improved safety.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an automatic reactor startup system according to an embodiment of the present invention, Fig. 2 is a graph showing the reactor cycle from criticality to temperature rise and pressure rise and the rate of change in reactor water temperature, and Fig. 3 is a control rod 4 is a graph showing the radial power distribution, FIG. 5 is a graph showing the axial power distribution, FIG. 6 is a flowchart showing the operation of the control rod operation determination section, and FIG. 7 is a graph showing the radial power distribution. An explanatory diagram showing fuzzy control rules, FIGS. 8 and 9 are explanatory diagrams showing membership functions, FIG. 10 is an explanatory diagram showing a fuzzy inference method, and FIGS. 11 and 12 are an explanatory diagram showing the atoms shown in FIG. 1. FIG. 13 is a graph showing changes in reactor parameters when an automatic reactor startup device is used, and FIG. 13 is a graph showing changes in reactor parameters using a conventional method. DESCRIPTION OF SYMBOLS 1...Reactor automatic startup device, 2...Reactor cycle calculation unit, 3...Reactor water temperature change rate calculation unit, 4...Limit condition setting unit, 5...Control rod operation determination unit, 10...Reactor , 11... Neutron flux detector, 12... Reactor water temperature detector, 13... Reactor pressure detector, 14... Control rod position control device, 15... Control rod drive mechanism.

Claims (1)

[Claims] 1. A reactor period calculation unit that inputs the neutron flux measurement signal and calculates the reactor period; a reactor water temperature change rate calculation unit that inputs the reactor water temperature measurement signal and calculates the reactor water temperature change rate;
The reactor cycle and reactor water temperature change rate are inputted from the reactor cycle calculating section and the reactor water temperature change rate calculating section, respectively, and if the change rate at which the reactor water temperature starts to rise is small, the predetermined reactor cycle is calculated. and a control rod operation determination unit that determines the control rod operation amount and outputs a control rod operation command signal in accordance with a control rule that maintains the temperature of the reactor and thereafter increases the reactor cycle as the rate of change in reactor water temperature increases. An automatic nuclear reactor startup device characterized in that the temperature of reactor water in a nuclear reactor is raised until a predetermined reactor pressure is reached by operating a control rod.