JPH03179295A - Protective structure of reactor vessel against heat - Google Patents

Abstract

PURPOSE:To reduce generated stress by reducing the temp. difference between a gas dam and a reactor vessel by forming the gas dam so as to support the same in a state suspended from a shield plug closing the upper opening part of the reactor vessel or from the vicinity thereof. CONSTITUTION:A concentric circular gas dam 11 is provided on the inner wall side of a reactor vessel 9 using the under surface of a shield plug 7 as a support point 15. The upper part of the gas dam 11 is provided to the under surface of the shield plug 7 through a seal material 19 and a convection preventing plate 17 is interposed between the gas dam 11 and the reactor vessel 9 at the position above the free liquid level of the cooling material 8 therebetween. Therefore, the temp. difference between the shield plug 7 and the gas dam 11 in the vicinity of the support point of the gas dam 11 can be made small and a temp. change rate can be also reduced and the stress generated by the thermal expansion difference therebetween can be also reduced.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a reactor wall protection structure for a reactor vessel in a liquid metal cooled fast breeder reactor.

(Prior Art) A reactor wall protection structure for a reactor vessel of a conventional fast breeder reactor using liquid metal sodium as a coolant will be described with reference to FIG.

A reactor core 1 and a coolant 8 are housed in a reactor vessel 9 of a fast breeder reactor. The upper opening of the reactor vessel 9 is sealed by a jacket plug 7 to which the core upper mechanism 6 is attached. The reactor vessel 9 is equipped with an intermediate heat exchanger 3 and a circulation pump 5. Inside the reactor vessel 9, from top to bottom, there are a hot plenum 2, an intermediate plenum 12, and a cold plenum 4.
It is divided into A space between the liquid level of the coolant 8 in the hot plenum 2 and the lower surface of the shield plug 7 is filled with cover gas. The coolant 8 first enters the cold plenum 4, is then sucked in by the circulation pump 5, is fed into the core l, heated, enters the hot plenum 2, is further led into the intermediate heat exchanger 3, and is then drawn into the intermediate heat exchanger 3. After exchanging heat with the coolant circulating in the heat exchanger 3, it is returned to the cold plenum 4. Intermediate plenum 12 has hot plenum 2 and cold plenum 4.
In addition to isolating and insulating the reactor vessel 9
as well as thermally protecting its internal structures.

Further, inside the reactor vessel 9, a custom 11 having the same cylindrical shape as the reactor vessel 9 is supported by a Y-piece 14 from the reactor vessel 9 at an intermediate plenum portion. By providing a gas space between the high-temperature coolant 8 in the hot plenum 2 and the reactor vessel 9, the reactor vessel 9 is thermally protected from the effects of temperature changes in the coolant 8.

As shown in FIG. 6, a safety vessel IO is installed outside the reactor vessel 9 as a boundary in the event of a coolant leakage accident due to damage to the reactor vessel 9.
An inert gas is filled between the two.

Further, the outside of the safety container 10 is covered with a heat insulating structure such as a heat insulating material, and a concrete wall 13 is further provided on the outside.

(Problem to be Solved by the Invention) In the conventional reactor wall protection structure described above, the inner surface of the Y-piece 14 that supports the custom 11 is in contact with the high-temperature coolant 8, and the outer surface of the reactor vessel is almost insulated by a gas layer. . However, since the custom 11 and the reactor vessel 9 have a large temperature follow-up difference with respect to changes in the coolant temperature, a high stress is generated in the Y piece 14, which is the connecting portion of the mask, due to the difference in thermal expansion.

FIG. 7 is a partially sectional view showing the Y piece 14 in an enlarged manner. FIG. 8 shows the time history of the metal temperature when the coolant temperature changes at the portion shown in FIG. As is clear from Fig. 8, a maximum temperature difference d occurs between the joint C on the reactor vessel side and the technical part A on the custom side due to the delay in following the temperature of the reactor vessel, and due to the difference in thermal expansion between the two, the Y-piece joint A large stress is generated. Note that e in FIG. 8 indicates the coolant temperature.

If damage occurs in this high-stress area, not only will the coolant 8 invade the gas insulation layer and the reactor wall protection structure will become useless, but the reactor vessel 9, which is the coolant boundary that cools the reactor core, will also be damaged. There are challenges.

The present invention has been made to solve the above problems, and is a nuclear reactor that has a small temperature difference between the custom and the reactor vessel, generates small stress, and has a sound structure and does not break during operation. The purpose is to provide a thermal protection structure for the container.

[Structure of the invention] (Means for solving the problem) The present invention provides a concentric cylindrical custom inside the reactor vessel,
In a thermal protection structure for a reactor vessel, the custom is filled with gas to prevent temperature changes of high-temperature coolant in the reactor vessel from being transmitted to the reactor vessel, wherein the custom is used to close an upper opening of the reactor vessel. It is characterized by being suspended and supported from the drop-off plug or its vicinity.

(Function) The custom is suspended and supported from the underside of or near the gas plenum or shield plug, where the effects of temperature changes in the coolant above the free liquid level in the reactor vessel are slow. Since the custom support points are located in the gas plenum, temperature changes in the coolant are less likely to be transmitted to the support points, thereby reducing stress caused by differential temperature tracking.

(Embodiment) An embodiment of the thermal protection structure for a reactor vessel according to the present invention will be described with reference to FIGS.

In FIG. 1, a reactor core 1 is disposed within a reactor vessel 9, a hot plenum 2 is formed above the reactor core 1, and a cold plenum 4 is formed below. An intermediate plenum 12 is formed between the hot plenum 2 and the cold plenum 4.

A core upper mechanism 6 is disposed above the reactor core 1, and a circulation pump 5 that circulates an intermediate heat exchanger 3 and a coolant 8 is disposed on the side of the reactor core 1. The intermediate heat exchanger 3, the circulation pump 5, and the upper core mechanism 6 are inserted through a shield plug 7 that closes the upper opening of the reactor vessel 9, and are supported by the shield plug 7. A safety container IO is provided on the outside of the reactor vessel 9 to surround the vessel 9 and supported by a concrete wall. A concentric custom 11 is provided on the inner wall side of the reactor vessel 9, with the lower surface of the shield plug 7 as a support point 15. The upper part of this custom 11 is provided on the lower surface of the shield plug 7 via a sealing material 19, as shown in a partially enlarged view in FIG. A convection prevention plate 17 is interposed at a position above the free liquid level of 8. Further, an argon gas supply pipe 16, for example, is provided to pass through the shield plug 7 in order to supply gas into the custom ll from the lower end.

In this way, the custom 11 is suspended and supported from the shield plug 7, and is supplied from the custom 11 through the gas supply pipe 16 between the reactor vessel 9 and the custom.

Next, the operation of the thermal protection structure for the reactor vessel in the above configuration will be explained with reference to FIGS. 3 and 4.

In FIGS. 3 and 4, the temperature distribution near the support point 15 of the custom 11 with the breaker plug 7 is as shown in FIG.
The temperature time history at each point -i is as shown in FIG. Note that the f point is near the liquid level of the coolant 8 of the custom 11,
Point g is near the lower end of the shielding plug 7 of Custom 11, point h is near the upper end of Gustam 11, and point i is near the upper end of Custom 11.
The vicinity of the support point 15 for the Nojiyahei plug 7 is shown.

4 corresponds to f to i in FIG. 3, and j indicates the coolant temperature.

That is, although f in the coolant almost follows the coolant temperature j, the free liquid surface g to h of the coolant 8 changes in temperature mainly due to heat conduction from the lower part of the custom 11, so the temperature changes at the support point 15. As it approaches, the changes become slower and smaller. i is the temperature of the shielding plug 7, which is cooled to keep it constant. Therefore, the temperature difference between the shielding plug 7 and the custom 11 near the support point 15 of the custom 11 can be small, and the rate of change can also be made small. According to this embodiment, the temperature difference between the custom 11 and the shielding plug 7 that supports it can be reduced near the support point 15, and the stress generated due to the difference in thermal expansion can also be reduced.

FIG. 5 is a partial sectional view showing only the main parts of another embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals, and the explanation of the overlapping parts is omitted.

That is, in this embodiment, the custom 11 is located in the cover gas above the free liquid level of the coolant 8, and is provided in the reactor vessel 9 with the submerged Y piece 18 interposed therebetween.

Other parts are the same as in FIG.

According to this embodiment, the temperature difference between the custom and the reactor vessel 9 near the joint of the Y-piece 18 is small, and the stress generated can also be reduced.

[Effects of the Invention] According to the present invention, the temperature difference between the custom and the reactor vessel can be reduced, and the stress generated can also be reduced. Therefore, it is possible to provide a reactor wall protection structure that is structurally sound and undamaged even under various operating conditions of the nuclear reactor.

[Brief explanation of drawings]

1 to 4 are for explaining the first embodiment of the thermal protection structure for a reactor vessel according to the present invention, and FIG. 1 is a vertical cross-section schematically showing the structure of a fast breeder reactor. Figure 2 is a vertical cross-sectional view showing the main parts of the thermal protection structure, Figure 3 is a vertical cross-sectional view showing the heat measurement points in Figure 2, and Figure 4 is the temperature and time at the heat measurement points in Figure 2. FIG. 5 is a longitudinal sectional view showing the second embodiment of the present invention, FIGS. 6 to 8 are for explaining the conventional example, and FIG. 6 is a high-speed A vertical cross-sectional view to explain the configuration of the breeder reactor, FIG. 7 is a partial vertical cross-sectional view to explain the problem in FIG. 6, and FIG. 8 is a relationship between temperature and time at the heat measurement point in FIG. 7. FIG. 1... Core 2... Hot plenum 3... Intermediate heat exchanger 4... Cold plenum 5... Circulation pump 6... Core upper mechanism 7... Shielding plug 8... Coolant 9...Reactor vessel 10...Safety vessel 11...Custom 12...Intermediate plenum 13...Concrete wall 4...Y piece 5...Support point 6...Gas supply pipe 7 ... Convection prevention plate 8 ... Y piece in gas 9 ... Seal material

Claims (1)

[Claims] A thermal protection structure for a reactor vessel, in which a concentric cylindrical custom is provided in the reactor vessel, and the custom is filled with gas to make it difficult for temperature changes of high-temperature coolant in the reactor vessel to be transmitted to the reactor vessel. . A thermal protection structure for a nuclear reactor vessel, characterized in that the custom is suspended and supported from or near a shield plug that closes an upper opening of the reactor vessel.