JPS6154193B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor using liquid metal as a coolant.

Generally, a liquid metal such as liquid sodium is used as a coolant in, for example, a fast breeder reactor.
This liquid metal is housed in a reactor vessel, and a cover gas such as argon is filled in a space above the liquid level of the liquid metal in the reactor vessel. By the way, heat is transmitted from the liquid metal almost uniformly to the part of the reactor vessel wall that is in contact with the liquid metal, and the temperature distribution is approximately averaged, but in the part above the liquid metal surface, heat is transmitted from the liquid metal to the surface. Heat is dissipated by radiation. Then, heat flows from the reactor vessel wall immersed in the liquid metal to the part exposed above the liquid surface, resulting in a temperature gradient near the liquid metal surface on the reactor vessel wall. ,
Since the liquid metal has good thermal conductivity, a large amount of heat flows through it, and the temperature gradient near the liquid surface becomes extremely large, creating a large thermal stress in this area, causing problems in maintaining the integrity of the reactor vessel. In addition, such thermal stress also occurs in the upper core mechanism and the like housed within the reactor vessel.

The present invention has been made based on the above circumstances, and its purpose is to reduce the thermal stress generated near the liquid metal surface of the reactor vessel and the members housed therein, and to improve the health of these members. The goal is to obtain a nuclear reactor that can improve performance.

The present invention will be described below with reference to an embodiment shown in the drawings. This embodiment is a sodium-cooled fast breeder reactor, in which 1 is a stainless steel reactor vessel and 2 is a reactor core. The reactor vessel 1 is suspended from a pedestal 3, and a heat insulator 4 is attached to its outer surface. Also,
A shielding plug 5 is provided at the upper end of the reactor vessel 1, and a core upper mechanism 6 is suspended from the shielding plug 5. Each part of this core upper mechanism 6 is made of stainless steel. A liquid metal 7 such as liquid sodium is contained within the reactor vessel 1, and a space above the liquid level 8 is filled with a cover gas such as argon. The core 2 and the lower part of the core upper mechanism 6 are immersed in this liquid metal 7. Radiation prevention plates 9 are attached to the inner surface of the reactor vessel 1 and near the liquid level 8 of the liquid metal 7 on the surface of the upper core mechanism 6, respectively. These radiation prevention plates 9... have an emissivity sufficiently lower than the emissivity (approximately 0.5 or more) of the stainless steel material forming the reactor vessel 1 and the upper core mechanism 6, for example, an emissivity of approximately
0.1 or less, such as aluminum, nickel, copper, etc., and its surface is polished to a smooth finish. These radiation prevention plates 9 are attached to the inner surface of the reactor vessel 1 or the surface of the upper core mechanism 6 via studs 10 made of the same material, and there is a small gap between them and these surfaces. 11... are formed.

In one embodiment of the present invention constructed as described above, heat is transferred from the liquid metal 7 to the parts of the reactor vessel 1 and the upper core mechanism 6 that are immersed in the liquid metal 7, and this heat is transferred to the liquid surface 8. It is transmitted to the upper exposed part and radiated to the outside. Incidentally, since radiation prevention plates 9 are attached to the inner surface of the reactor vessel 1 and the surface of the upper core mechanism 6 near the liquid level 8, the radiant heat hits these radiation prevention plates 9. And these radiation prevention plates 9...
... are made of a material with low emissivity, in other words, a material with high reflectance, so the radiant heat is reflected by these radiation prevention plates 9 and returned to the reactor vessel 1 or the upper core mechanism 6. As it is repeatedly reflected between the radiation prevention plates 9..., most of the radiant heat is absorbed into the reactor vessel 1 or core upper mechanism 6 side, which has a high emissivity, and eventually prevents future heat radiation. be done. Therefore, the thermal radiation from the reactor vessel 1 and the upper core mechanism 6 above the liquid level 8 decreases, and the temperature gradient generated near the liquid level becomes smaller.
Thermal stress is relieved. Incidentally, the results of an experiment conducted to confirm this effect are shown in FIG. In FIG. 3, curve A shows the temperature gradient of this embodiment, and curve B shows the conventional one in which the radiation prevention plate 9 is not provided. As is clear from this result, by providing the radiation prevention plates 9, the temperature gradient near the liquid surface 8 becomes extremely gentle, and the thermal stress is alleviated accordingly. In addition, since the radiation prevention plates 9 are installed with a small gap 11, heat is not directly transmitted from the reactor vessel 1 or core upper mechanism 6 to the radiation prevention plates 9. Prevented.

Note that the present invention is not limited to the above embodiment.

For example, the radiation prevention plate does not need to be provided all around the inner surface of the reactor vessel and the entire circumference of the core upper mechanism, but may be provided on a portion thereof, or may be provided on other members other than these.

Further, the radiation prevention plate may be one in which only the surface is covered with a material having a low emissivity.

As described above, in the present invention, a radiation prevention plate made of a material with a low emissivity is attached near the liquid metal surface on the inner surface of the reactor vessel and the surfaces of the members housed in the reactor vessel. Therefore, radiation from the parts exposed above the liquid surface is prevented, the temperature gradient in the parts near the liquid surface is reduced, thermal stress is alleviated, and the health of these parts is improved, among other effects. It's large.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a longitudinal sectional view, FIG. 2 is a longitudinal sectional view showing an enlarged main part, and FIG. 3 is a characteristic diagram of the temperature gradient near the liquid surface. 1... Reactor vessel, 5... Shielding plug, 6...
Upper core mechanism, 7...Liquid metal, 8...Liquid level, 9
...Radiation prevention plate, 11...Gap.

Claims (1)

[Scope of Claims] 1. In a system that uses a liquid metal as a coolant, at least a portion of the inner surface of the reactor vessel and the surface of the member housed in the reactor vessel near the surface of the liquid metal is provided with the reactor. A nuclear reactor characterized by being provided with a radiation prevention plate made of a material having a lower emissivity than the material of the vessel or the members housed in the reactor vessel. 2. The radiation prevention plate has a smooth surface,
2. The nuclear reactor according to claim 1, wherein the reactor is installed with a small gap between the inner surface of the reactor vessel or the surface of a member housed within the reactor vessel.