JPS6182192A - Fast breeding type 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 fast breeder nuclear reactor (hereinafter referred to as a fast breeder reactor).

BACKGROUND OF THE INVENTION Generally, a nuclear reactor loses its reactivity due to the increase in output at reactor startup and the combustion of fuel after short-circuit output is achieved.

Therefore, in order to compensate for these reactivity losses, the reaction period is usually extended by loading extra fuel into the reactor at the early stage of combustion, and new fuel is added to the reactor core through fuel exchange after the stored combustion period has elapsed. This is to ensure that the reactor does not shut down due to a drop in reactivity until it is loaded.

On the other hand, during reactor operation, it is necessary to maintain the reactor at just the critical level to prevent nuclear runaway.

For this reason, nuclear reactors are equipped with control rods containing substances that absorb neutrons well, which are inserted into the reactor core to reduce excess reactivity and bring the reactor just over to criticality.

The core of a fast breeder reactor is loaded with fissile material and fuel parent material as fuel, and the core is usually cylindrical in shape. 4 and 5 are horizontal sectional views and vertical sectional views showing the configuration of the core of this example, and FIGS. 6 and 7 are horizontal sectional views and vertical sectional views showing the configuration of the core of another example. 1 is the inner core, 2 is the outer core, 3 is the radial blanket area, 4 is the axial blanket area, 5 is the adjustment rod, 6
indicates the starting rod, 7 indicates the backup system pile rod, and 8 indicates the main system rod.

These cores are composed of core fuel regions with different enrichments, indicated by an inner core 1 and an outer core 2, and an axial blanket region 4 and a radial blanket region 3 surrounding this,
The control R111 is inserted and removed from the upper axial blanket side.

These adjustment rods 5, starting rods 6, backup system pile rods 7, main system,
The control rods of fast breeder reactors such as No. 1 Ka 8 are often inserted from the top of the reactor core (the control rod drive mechanism is also located above the core), as in this example, but the insertion depth varies depending on the reactor startup. After the rated output is achieved, it decreases as combustion progresses.
It reaches its minimum at the end of combustion.

In the original nuclear reactor core, in the early stage of combustion after the rated power is achieved, fuel with a reactivity value sufficient to compensate for the reactivity loss due to combustion is loaded, and at the same time the excess reactivity is reduced. control rod is inserted. In this case, due to the strong absorption of neutrons by the control rods, the power density in the fuel region adjacent to the control rods is much smaller than the average power density of the core (which is approximately constant during rated power operation); Conversely, the power density increases in the fuel region away from the rod. The amount of distortion in the power distribution due to control rod insertion is highly dependent on the amount of control rod absorbing material, and the more ridges there are in the neutron absorbing material F↓, the greater the distortion in the power distribution becomes.

The power that can be extracted from the reactor is the maximum fuel power Wi
It is important to flatten the power distribution as much as possible since it depends on the +star. When determining the configuration or insertion pattern of the control rods J+Lll, the maximum power density in the control rod insertion state should be determined based on the core 1. It is necessary to ensure that the tolerance based on the thermal limitations of the first component is not exceeded.

The conventional fast breeder reactor shown in Figs. 4 and 5 has ζJ1
'4 Adjustment rod 5, startup A6, back-up system! It is equipped with 703 types of control rods 7. Adjustment rod 5 adjusts output and reactivity iH
The main control rod, the starting rod 6, is a control rod for starting the nuclear reactor, and the backup system payload 7 is a control rod for shutting down the reactor in the backup system.

In this way, in this fast breeder reactor, by providing separate control rods that are safe for reactor startup and operation, the reactivity value of the control rods (only the adjustment rods) inserted into the reactor core during operation can be reduced to a small value. , which reduces the distortion in power distribution caused by control rod insertion. However, since it is necessary to separately prepare starting rods (six in this example), there is a drawback that the number of control rods and the mechanisms for driving them increase.

On the other hand, in a conventional fast breeder reactor as shown in FIG. 6 and FIG. It is burial. The main system rod 8 has the reactivity value necessary for reactor start-up and power and reactivity control 1. Therefore, in this example, there is no need to prepare a separate starting stick, so Mrl'
The number of 11 rods may be smaller than in the fast breeder reactor shown in FIGS. 4 and 5. However, since the neutron absorbing substance ca in the control rods inserted into the reactor core during operation is high, there is a problem in that the power distribution is highly distorted when the control rods are inserted.

[Purpose of the invention]

An object of the present invention is to provide a fast breeder reactor that requires fewer control rods than conventional fast breeder reactors, and that also has less distortion in the power distribution when the control rods are inserted.

[Summary of the invention]

The present invention provides a high-speed reactor having a core region made of fuel enriched with fissile material, a blanket region mainly composed of fuel parent material, and an open end containing a neutron absorbing material and inserted into the core region from time to time. In a breeder atom, the length of the neutron absorbing material region 1 of the control frame is approximately twice the height of the reactor core, and the neutron absorbing material region is divided into multiple regions with black reactivity values. The region which is divided into regions and which is close to the first point (G) of the above-mentioned control system 1j bond is characterized by having a smaller reactivity value.

That is, the Asahi reactor according to the present invention has a reactor core,
having a blanket and a control fffl Y-,4,
The length of the neutron absorbing material region containing boron or tantalum, etc. in the control rod is approximately twice the height of the reactor core, and the neutron absorbing material region is divided into multiple regions, reducing the neutron absorption capacity up to the tip of the control rod. It is.

The present invention aims to minimize the reactivity value of the control rods (S1 rods) inserted into the reactor core during reactor operation, that is, to minimize the amount of neutron-absorbing material, and to minimize the power distribution due to control rod insertion. This study focuses on the fact that it is effective in improving the distortion of the nuclear reactor, and that the need for engine squeezing can be eliminated by installing a control rod (starting rod) above the adjustment rod that is used only for starting the reactor.

The nuclear reactor of the present invention is started by withdrawing the upper half of the control rod from the core, and the reactor is operated by gradually withdrawing the remaining lower half of the control rod from the core.

In the following explanation, based on the present invention, the control rod will be referred to as a "long adjustment/starting rod integrated control rod", whereas the conventional example shown in FIGS. The control rod is referred to as the "adjustment/starting rod separation type control rod", and the conventional control rod shown in FIGS. 6 and 7 is referred to as the "r:iM adjustment/starting rod combination type control rod".

[Examples of Yumei]

Hereinafter, the present invention will be explained in detail with reference to Examples.

In addition, the target fast breeder reactor core uses a mixed CD of plutonium and uranium as the core fuel, depleted uranium as the blanket (M', dilution material, B4C as the neutron absorbing material, and liquid sodium as the cooling T4). However, it is possible to apply the present invention to the case where LJ4 is used with external fuel, cooling blow, and neutron absorbing material.

2+rJ1) Actual examples are shown in 11'2+, Fig. 2, Fig. 3
m11 will be explained by the figure and FIG. Figure 1 is a structural diagram of the control rods, Figure 2 is a horizontal view of the reactor core, Figure 3 is a vertical cross-sectional view, and Figure 81 is a horizontal cross-sectional view of the reactor core. :li '7',
11: It is a diagram showing the operational status of gX. The same parts as in FIGS. 4 to 7 are given the same reference numerals.

In FIG. 2, the inner core 1 and the outer core 2 are loaded with depleted uranium enriched with plutonium, and the radial blanket 3 and the axial blanket 4 are loaded with depleted uranium. 9 is a long length adjustment method used in a fast breeder reactor based on the present invention.
It is a control rod with an integrated starting rod, and 7 is a back-up pile rod.

Table 1 shows the main core design parameters of the nuclear reactor. Reactor thermal output is approximately 2'500 MWX electrical output is approximately 10
100O, equivalent core diameter and core height are each 325c
rn, and 100 crri. Φ+i+ direction blanket thickness and radial direction blanket thickness are each 35c
nt and 40 an. Fuel smear density is 87 in the core
%TD, 91% TD with blanket. The refueling interval is one year, the capacity utilization rate is 80%, and the number of refueling batches is:
Both the core and the radial blanket are set to 3. nuclear fission E
f: Plutonium enrichment degree is 12% in <tar+ core
, 15% in the outer core.

The number of each assembly is 258 in the inner core,
Table 1 Main design parameters There are 162 cores on the side, 25 control rods (including 7 backup pile rods), and 250 radial blankets.

The design conditions are the same as the conventional examples shown in FIGS. 4, 5, 6, and 7.

FIG. 1 shows the structure and composition of an elongated control rod 9 integrated with an adjustment/starting rod. This control rod 9 is composed of a plurality of neutron absorption rods 10, an upper tie rod 11, and a lower tie rod 12.

The neutron absorption rod 10 connects both ends of the blowfish pipe 13 with end plugs 1.
4 and 15, and cover it with two types of Ba in the tube 8.
It is filled with C pellets 6A and 16B.

The total stack length of B4C pellets is twice the reactor core height, and among these, the stack lengths of 84C pellets 16A and 16B are both equal to the reactor core height (these are referred to as neutron absorption zones A and B, respectively). do).

The Bto element that absorbs neutrons well contained in Ba C pellet 16A is BI contained in B4C pellet 16B.
Bigger than G's heart. That is, the concentration of BIG in the former is 90%, and in the latter is 30%. Here BIO
The concentration of is (amount of B10)/(131°+amount of B11)
It is expressed as Btt is a substance that hardly absorbs neutrons. Therefore, the anti-calamity value is greater for the zone than for B.

Both ends of the r11 tron absorption rod are attached to the upper tie plate 1.
1 and the lower tie plate 12. It is fed through the upper tie plate 11, lower tie plate 12i, j, and cylindrical cover 17. The neutron absorption iron 10 is placed inside a cylindrical cover 17. Upper tie plate 1
1 has 18 joints at its upper end, which are connected to control rods,...
It is connected to an M device (not shown). The control rod drive device inserts the control rod into the reactor core or pulls it out from the reactor core using the rotating force of the motor. In FIG. 1, numeral 19 indicates an upper plenum, 20 a lower plenum, 21 a retainer, and 22 an orifice on the cooling side.

In the control rod according to the present invention, the total stack length of B4 C pellets is 200 crn, which is about twice that of the conventional control rod.

At the end of the cycle, the lower end of the neutron absorbing material is located above the upper end of the core, and at the beginning of the cycle, the upper end of the neutron absorbing material is located at the upper end of the core. The storage space for the neutron absorbing material inside the J-rod guide tube is 200 (7) vertically from the top of the core, a total of 4 spaces.
00mm sandwiched.

The dimensions of the fuel assembly in the 4711 direction in this example are schematically shown in FIG. The total length of the aggregate is 50
0Crn, the length from the top of the core to the bottom of the lower gas plenum is 215cm, and the length from the top of the core to the top of the assembly is 165Qn. From this, a space of 200 crn below the upper end of the reactor core can be easily secured. However, the space above the top of the core is fi 200 crn.
Since the neutron absorption material is less than K, the upper end of the neutron absorbing material section will be on the upper plenum of the core at the end of the cycle. Even when conventional control rods are used, the connecting rods connected to the control rod drive mechanism are located in the upper core plenum. Even if they are present in the plenum, the functionality and operability of the control rods will not be compromised. Also, the upper core glenum 1, usually these controls 1', i! (-7,N1"ζ can be sufficiently accommodated, so the conventional method for preventing disease in the reactor vessel is sufficient.

Next, effects based on such a 't=4 formation will be explained.

Figures (a), (b), (C), and (d) show the insertion states of the control rods into the core at the time of reactor shutdown, the beginning of the operating cycle, the middle of the operating cycle, and the end of the operating cycle, respectively. This is a schematic representation.

When the reactor is shut down, all control rods are 100% inserted into the reactor core. When starting a nuclear reactor, some control rods must be withdrawn to compensate for the loss of reactivity due to startup. In the present invention, as shown in FIG. 9(b), the reactivity is increased by completely pulling out zone A with high reactivity value above the core and simultaneously inserting zone B with low reactivity value into the core. One of the features is that the difference between the two is used to compensate for the starting reactivity. As in this example, the control rod is made long and divided into multiple regions in the axial direction (in this example, two upper and lower regions), and the starting rod and adjustment rod are integrated into one. As in the conventional example shown in Figure 5,
J17J M'9 There is no need to provide six starting rods separately from the rods, and the number of control rods and the number of control rod small movement mechanisms are reduced.

The operating cycle refers to the period from the time of fuel replacement to the time of the next conversion, but as the fuel burns during reactor operation, reactivity is lost, so to compensate for this, the period between the time of fuel exchange and the next conversion is , the control rods are gradually withdrawn from the reactor core. Control rod zone B, which was fully inserted into the core at the beginning of the operation cycle
At the end of the operating cycle, the reactor is completely pulled out above the core, as shown in FIG. 6(d). Control rod zone B needs only to have a reactivity value sufficient to compensate for the reactivity lost due to fuel combustion, so 1. Its reactivity value is the 6th
The control rod may be much smaller than the conventional adjustment/starting rod combination type control rod shown in FIGS. The breakdown of control rod reactivity is shown below.

(1) Combustion reactivity 3.0%Δk (2) Specific reactivity error 0.5%Δk (3) Operating margin
0.2%Δk(4) Safety margin 1.7
%Δk (5) Output temperature compensation 1.5%Δ
Total 6.9%Δ in Figure 6 and 41≦7
The required reactivity value of the conventional control rod shown in the figure is 6.9%.
In contrast, in the actual example according to the present invention, control rod zone A has a reactivity of (4), (5) of the above reactivity.
Since the total reactivity of 3.2% Δk is compensated for, the control rod zone B only needs to compensate for the total reactivity of 3.7% Δk of (1), (2), and (8).

Therefore, Bt is forced into the core during reactor operation.

Since the amount of the control rod is reduced compared to the conventional example shown in FIGS. 6 and 7, the distortion in the power distribution due to control rod insertion is reduced. In addition, the differential worth (control rod worth per unit insertion length) of the control frame during operation is reduced, so it can be used for control during earthquakes, etc.
There is also the advantage that the change in reactivity due to the relative change in the axial direction of the rod and the core is small.

In addition, a control rod in which the concentration of the neutron absorbing substance is changed in the axial direction has also been proposed, as in Japanese Patent Application No. 57-78380, but this control rod does not allow the control rod to be partially connected to the reactor core. It is effective in flattening the axial power distribution when inserted into a control rod or reducing distortion in the power distribution near the tip of the control rod. However, this control rod is not effective in reducing the number of control rods, which is one of the main objectives of the present invention, because the starting rods are reduced and the reactor starting reactivity is imposed on the adjusting rods. In this case, the reactivity value per control rod increases, and the amount of Blo contained in the control rods inserted into the reactor core during reactor operation increases, resulting in distortion of the power distribution due to control rod insertion. This is because it becomes larger.

A new effect of the present invention is that the number of starting rods can be reduced without increasing the amount of Blo contained in the control rods inserted into the reactor core during reactor operation.

The control rod of the second embodiment will be explained with reference to FIG. 1st
Figure 0 is a schematic diagram of a control rod integrated with an elongated adjustment/starting rod similar to that shown in Figure 1, and the same parts as in Figure 1 are given the same reference numerals. In this example, the B'' enrichments of 16A and 16C are the same in zone A and zone B;
By making the 4C pellets 16C hollow, the amount of B'4C loaded in zone B is less than 10 in zone A.

With this as well, the same effect as in the Q1 example can be expected.

The third embodiment 1 will be explained with reference to FIG. Figure 11 is a configuration diagram of a long adjustment/starting rod integrated control rod similar to Figures 1 and 10, and the same parts as in Figures 1 and 10 are given the same reference numerals. . Here, the B4C pellets) 16D in zone B are doped with a substance that slows down neutrons, such as carbon or beryllium. Due to the action of the moderator, the amount of B4C loaded into zone B is further reduced. This embodiment can also be expected to have the same effects as the other embodiments.

Alternatively, the moderator may be pelletized and mixed with B4C pellets.

The fourth embodiment will be explained with reference to FIGS. 12 and 13.

Figure 12 is a configuration diagram of a long adjustment/starting rod integrated type control rod similar to Figures 1, 10, and 11;
The same parts as Figure 0 and Figure @11 are given the same symbols,
23 indicates an internal blanket. In this example, the proposal of Japanese Patent Application No. 78380/1980 is applied to the Bto distribution of B4C Peretz) 16E and 16F in zone B.

That is, in FIG. 12, zone B is zone B1,
It is divided almost equally into zones B2, and the B10 concentration in B1 is about 10% higher than that in B2.

Note that the 7310 concentration in zone A is constant in the axial direction.

Also, the total reactivity value of zone B is the same as in the case of constant B10 enrichment. The core of this proposed fast breeder reactor is configured as an axially non-homogeneous core with axial and radial blankets, a cylindrical core, an internal blanket provided near the center of the core, etc., and the power distribution is flat. It is effective for

FIG. 13 shows the effect of using the control rod of this example, where (aL (bL) (C) and (d) are at the time of reactor shutdown and at the beginning of the operation cycle, respectively.

This figure schematically represents the insertion state of the control rods into the reactor core at the middle stage of the operation cycle and at the end stage of the operation cycle.

By lowering the BIG concentration in zone B on the lower side (the tip side of the control rod), there is an advantage that the axial power distribution, especially when the control rod is inserted halfway, is further improved. This embodiment is similar to the first to third embodiments in that the number of activation rods can be reduced.

The high speed i′? of the above embodiment? ! - In a breeding reactor, there is no need to separate the control rods for starting the reactor from the control rods for adjustment, so the number of control rods can be reduced.

In addition, control rods inserted into the reactor core during reactor operation include 8
Since the amount of 1° can be reduced, it is possible to improve the flatness of the output distribution when inserting the control rod.

〔Effect of the invention〕

The present invention makes it possible to provide a fast breeder reactor that requires fewer control rods and has less distortion in the power distribution when the control rods are inserted, compared to conventional fast breeder reactors. It is what it is.

[Brief explanation of drawings]

1. A cross-sectional view of a control rod of an embodiment of the fast breeder reactor of the present invention, Figure 2 is a horizontal cross-sectional view showing the ++r configuration of the reactor core, Figure 3 is a vertical cross-sectional view, and Figure 4 is a conventional 5 is a horizontal sectional view showing the core configuration of an example of a fast breeder reactor, FIG. 5 is a vertical sectional view, FIG. 6 is a horizontal sectional view showing the core configuration of another example, and FIG. A floor plan, Figure 8 is an explanatory diagram of the axial dimension of the fuel assembly of the fast breeder reactor in Figure 2, and Figure 9 is an explanatory diagram showing the relationship between the core and control rods of the fast breeder reactor in Figure V12. , FIG. 10, FIG. 11, and FIG. 12 are cross-sectional views of control rods of other different embodiments of the fast breeder reactor of the present invention, and FIG. 13 is a cross-sectional view of a fast breeder reactor using the control rod of FIG. FIG. 2 is an explanatory diagram showing the relationship between a reactor core and control rods. 1... Inner core, 2... Outer core, 3... Radial blanket, 4... Axial blanket, 7...
Backup system pile rod, 9... Control rod integrated with long length adjustment/starting rod, 10... Neutron absorption rod, 11... Upper tie rod, 12... Lower tie rod, 13... Covered pipe , 14゜15...end plug, 16A, 16B...B4C
Pellet, 17...Cylindrical cover, 18...Connection part,
19... Upper plenum, 20... Lower plenum, 2
1... Protection tube, 22... Coolant orifice. Na 7-Prisoner 40 Mori S Senryo 6th Ward Exit (Li CD-) 11th Exit (C) Ct)

Claims (1)

[Claims] 1. A core region consisting of fuel enriched with fissile material;
In a fast breeder nuclear reactor having a blanket region mainly composed of a fuel parent material, and a control rod containing a neutron absorbing material and inserted into the core region from time to time, the length of the neutron absorbing material region of the control rod is approximately twice the height of
A fast breeder nuclear reactor characterized in that the neutron absorbing material region is divided into a plurality of regions having different reactivity values, and the region closer to the tip of the control rod has a smaller reactivity value. 2. The neutron absorbing material regions have different reactivity values 2.
A fast breeder nuclear reactor according to claim 1, which is divided into regions. 3. The above two regions include a tip side region whose reactivity value is equal to the reactivity required for reactor power operation, and a tip side region whose reactivity value is more necessary for reactor startup than the reactivity value of the tip side region. 3. The fast breeder nuclear reactor according to claim 2, further comprising another region having a higher reactivity. 4. The fast breeder nuclear reactor according to claim 2, wherein the concentration of the neutron absorbing material in the two regions is high in the tip side region and low in the other regions. 5. The fast breeder nuclear reactor according to claim 2, wherein the volume ratio of the neutron absorbing material in the two regions is smaller in the tip side region than in the other regions. 6. The fast multiplication type atom according to claim 2, wherein the two regions consist of a front end region made of hollow pellets with equal pellet concentration of the neutron absorbing substance, and an other end region made of a central pellet. Furnace. 7. The two regions are composed of a distal region where a central pellet and a substance that decelerates neutrons are mixedly loaded, and the other end region consisting of a central pellet of the same type as the central pellet constituting the distal region. A fast breeder nuclear reactor according to claim 2. 8. The fast breeder nuclear reactor according to claim 2, wherein the tip-side region of the two regions has a neutron absorption capacity per unit length that decreases as it approaches the tip. 9. The fast breeder nuclear reactor according to any one of claims 1 to 8, wherein the control rod is part or all of the main system rod.