JPS58155383A - Nuclear 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 [Technical Field of the Invention] The present invention relates to, for example, a boiling water nuclear reactor, and particularly to a nuclear reactor that can increase reactivity and improve fuel utilization efficiency.

Technical Background of the Invention In general, in a boiling water reactor, a reactor core 2 is housed in a reactor pressure vessel 1, as shown in FIG. A large number of fuel assemblies (not shown) are loaded between them. The reactor core 2 is immersed in water as a reflector.

In the boiling water reactor configured as described above, the hydrogen used as a reflector has an atomic weight of 1, so the deceleration of neutrons due to elastic scattering is large, but the deceleration due to inelastic scattering is large. Since this does not occur, the number of collisions required for a fast neutron to become a thermal neutron increases. Furthermore, since hydrogen has a large absorption cross section for thermal neutrons, many of the neutrons that are decelerated in the water region, which is a reflector, are absorbed by water.

Therefore, in the conventional boiling water reactor configured as described above, the proportion of thermal neutrons that are decelerated by the reflector and returned to the reactor core is not sufficient, and it is not always possible to obtain sufficient reactivity and fuel utilization efficiency. There wasn't.

[Object of the invention] The present invention has been made in response to such conventional circumstances,
The objective is to provide a nuclear reactor in which more of the fast neutrons emitted from the reactor core are reflected back to the reactor core, thereby increasing neutron utilization efficiency and fuel utilization efficiency.

[Summary of the Invention] That is, the present invention is characterized by comprising a reactor core loaded with nuclear fuel and a reflector made of a material having a macroscopic thermal neutron absorption cross section smaller than that of light water and arranged around the reactor core. This is a nuclear reactor.

EMBODIMENTS OF THE INVENTION The details of the present invention will be described below with reference to embodiments shown in the drawings.

FIG. 2 shows a boiling water nuclear reactor according to an embodiment of the present invention, and in the figure, reference numeral 5 indicates a reactor pressure vessel.

A reactor core 8 is formed between an upper grid plate 6 and a core support plate 7 disposed in the reactor pressure vessel 5, and this reactor core 8 has a reflector 9 containing beryllium (Be), carbon ( C),
Zirconium (Zr>, lead (Pb), bismuth (Bi
), their oxides, and hydrogen compounds.

In the boiling water reactor configured as described above, some of the fast neutrons generated by nuclear fission in the reactor core 8 are not slowed much, but fly into the reflector 9 at high speed, and are absorbed within the reflector 9. It is slowed down by scattering. Note that since the reflector 9 is made of a material that has a large removal cross section for fast neutrons, the neutrons are very well decelerated.

The neutrons that have been decelerated to the thermal region in this way are transported to the core 8.
The darkness is divided into those that re-enter the reactor core 8 and those that leak out into the water region.Except when the reflector 9 is extremely thin, the darkness of those that return to the core 8 and those that leak out into the water region are approximately equal. Therefore, if the heat of the neutrons absorbed by the reflector 9 decreases, the number of neutrons returning to the reactor core 8 increases.

In other words, in a boiling water reactor configured as above,
Among the fast neutrons that jumped out from the reactor core 8 to the reflector 9 region, the amount of them that is decelerated by the reflector 9 material and returns to the reactor core 8 increases, so of the neutrons generated in the reactor core 8, the amount of neutrons that do not participate in nuclear fission increases. neutron utilization efficiency can be improved. This improvement in neutron utilization efficiency makes it possible to increase the combustion efficiency of nuclear fuel, making it possible to use the fuel effectively.

FIG. 3 shows another embodiment of the present invention, in which reference numeral 7 indicates a core support plate, into which a fuel support fitting 10 is inserted; A fuel assembly 11 is fixed. Then, the fuel assembly 11 formed on the upper surface of the core support plate 7 and the fuel assembly 11
A reflector 12 is arranged in the gap between the two. This reflector 12 is made of the same material as the reflector 9 described in FIG. 2, and can achieve the same effect as the reflector 9 shown in FIG. Therefore, fast neutrons ejected downward from the reactor core 8 can be decelerated and reflected, thereby improving the efficiency of neutron utilization.

FIG. 4 shows still another embodiment of the present invention, in which reference numeral 6 indicates an upper lattice plate, into which a fuel assembly 11 is inserted. A reflector 13 is arranged in the gap between the fuel assemblies 11 on the lower surface. This reflector 13 is made of the same material as the reflector 9 shown in FIG. 2, and can decelerate and reflect fast neutrons ejected downward from the reactor core 7, thereby improving the efficiency of neutron utilization. .

The embodiment shown in FIG. 5 shows an example in which a reflector is inserted into the fuel rods constituting the fuel assembly 11. In the figure, reference numeral 14 indicates a cladding tube constituting the fuel rod. A fuel filling part 16 that accommodates a large number of fuel pellets 15 is formed in the middle part of the pipe 14, and a reflector is inserted into an upper plenum part 17 formed above this fuel filling part 16. has been done. This reflector 18 is made of the same material as the reflector 9 shown in FIG.

Fuel assembly 11 consisting of fuel rods configured as described above
The sii water-form original atoms housed in the reactor core 8 fly upward from the fuel rods. The intermediate trons are reflected in the direction of the reactor core 8 by the reflector 18, making it possible to improve the efficiency of neutron utilization.

[Effects of the Invention] As described above, according to the nuclear reactor of the present invention, the reactivity of the reactor can be increased and the utilization rate of nuclear fuel can be improved.

Figure 6 shows the increase in the actual increase rate when water, beryllium, beryllium oxide, and lead are used as the reflector of the boiling water reactor shown in Figure 2. By using it as a liquid, the effective multiplication factor can be significantly improved compared to the conventional case using water.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a conventional boiling water reactor, FIG. 2 is a longitudinal sectional view showing a boiling water reactor according to an embodiment of the present invention,
FIG. 3 is a longitudinal sectional view showing the core support plate of the nuclear reactor of the present invention;
FIG. 4 is a longitudinal sectional view showing the upper grid plate of the nuclear reactor of the present invention;
FIG. 5 is a longitudinal sectional view showing the fuel rod of the nuclear reactor of the present invention, and FIG.
The figure is a graph for explaining the effect of the nuclear reactor shown in FIG. 2. 6・・・・・・・・・Upper lattice plate 7・・・・・・
......Core support plate 8......Core 9.12.13.18...Reflector 10... ...Fuel support fitting 11...
・・・・・・・・・Fuel assembly agent patent attorney Su
Yamasa - Figure 1 Figure 2 Figure 3 Figure 4゜1<) Figure 6 Surplus W (knowledge)

Claims (3)

[Claims] (1) A nuclear reactor comprising a reactor core loaded with nuclear fuel and a reflector made of a material having a macroscopic thermal neutron absorption cross section smaller than that of light water and arranged around the reactor core. (2) The nuclear reactor according to claim 1, wherein the reflector has a macroscopic fast neutron removal cross section that is larger than or at least the same as that of light water. (3) The reflector is made of one or more materials selected from heavy water, beryllium, carbon, zirconium, lead, bismuth, and their oxides and hydrogen compounds. The nuclear reactor described in item 2.