JPS6125114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fast breeder reactor, and more particularly to a fast breeder reactor having a free liquid level of coolant, in which the atmosphere around the reactor vessel is maintained at a predetermined relatively low temperature by means of an air conditioner. It is related to furnaces.

Since the reactor vessel of a fast breeder reactor is used at high temperatures exceeding 500°C, thermal stress associated with creep becomes a problem. In particular, in the reactor vessel of a nuclear reactor where the coolant liquid level is a free liquid level, heat transfer is good because the reactor vessel wall below the liquid level is in contact with the liquid metal coolant, and the temperature of the reactor vessel wall is lower than that of the coolant. It follows temperature changes with only a short delay, but since the coolant flow surface is a gas space filled with cover gas, heat transfer is poor, and the furnace vessel wall temperature follows changes in coolant temperature to a large extent. There will be delays. Therefore, in general, when the coolant temperature changes, a large thermal stress is generated in the wall of the furnace vessel near the coolant liquid level.

This thermal stress becomes particularly large during a nuclear reactor scram. In other words, during a scram, the coolant temperature drops rapidly, and the temperature of the part of the reactor vessel wall in contact with the liquid drops with a slight delay, but the delay in the temperature drop of the part of the reactor vessel wall in contact with the gas and the temperature of the coolant Volumetric contraction due to the drop is the main cause, creating a large temperature gradient on the wall of the reactor vessel near the coolant liquid level, generating high thermal stress.

In order to prevent the occurrence of such large thermal stress, there are two ways to lower the stress level during normal operation: to constantly cool the furnace vessel wall to lower its operating temperature, and to protect the gas space. There is a way to keep the temperature gradient small during normal operation by taking a long time. However, in the case of the cooling method, there is a waste of securing a large amount of cooling flow in addition to the core cooling flow, and in the case of the method of lengthening the gas space, the reactor vessel itself becomes long and expensive. Furthermore, forced cooling of the reactor vessel wall has been proposed, but in this case, this forced cooling must be performed in conjunction with the condition of the reactor coolant, and no rational solution has been considered.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fast breeder reactor in which the thermal stress generated in the wall of the reactor vessel due to changes in coolant temperature is effectively reduced by a simple structure.

Next, the present invention will be explained along with an embodiment of the present invention shown in the accompanying drawings.

FIG. 1 is a sectional view of a portion of the fast breeder reactor of the present invention related to the present invention. Portions not shown are the same as well-known fast breeder reactors. In FIG. 1, the fast breeder reactor of the present invention includes a reactor vessel 1, a shielding plug 2 provided at the top of the reactor vessel 1, and a shielding concrete structure 3 surrounding and supporting the reactor vessel 1. ing. A heat shield plate 4 is attached near the inner surface of the furnace vessel 1 to alleviate thermal shock. The liquid level 5 of a liquid metal coolant such as sodium is a free liquid level, the inner surface of the reactor vessel below the coolant liquid level 5 becomes a wetted part, and the space above the coolant liquid level 5 has a cover gas. Since it is sealed, the inner surface of the furnace vessel facing this space is in contact with the gas.

The furnace vessel 1 is installed in the shielding concrete structure 3 by placing the flange of the upper end opening on a sole plate 7 provided on the pedestal 6 of the shielding concrete structure 3. Furnace vessel 1
The space 8 between the outer surface of the shielding concrete structure 3 and the shielding concrete structure 3 is heated to a temperature of 50°C to 60°C by an air conditioner 11 including a pump 9 and a heat exchanger 10, as is well known.
The atmosphere is kept at a relatively low temperature of ℃. The low-temperature atmosphere from the air conditioner 11 is supplied into the space 8 through the nozzle 12, and is exhausted and circulated by an appropriate device (not shown).

Conduit 1 between nozzle 12 and air conditioner 11
A pipe 14 extends from an appropriate location of 3. The tip of the pipe 14 communicates with an annular header 16 provided at the lower part of the outer periphery of the annular closure body 15 . A flow path 17 extends from the header 16 through the lower part of the annular closure 15 and comes into direct contact with the lower part of the coolant liquid level on the outer surface of the furnace vessel 1 . In the operating state of the reactor shown in FIG. 1, this flow path 17 is closed because the protruding inner circumferential surface 18 of the annular closure body and the outer surface of the reactor vessel 1 are in close contact. . Above the inner peripheral surface 18, an annular space 19 is formed between the outer surface of the furnace vessel 1 and the annular closure 15, and this space 19 is filled with a low temperature atmosphere beyond the upper end of the annular closure 15. It communicates with space 8. To summarize, the conduit 13 from the air conditioner 11, the piping 14, the header 16,
The flow path 17 and the space 19 constitute a flow path 20 that directly supplies the low temperature atmosphere from the air conditioner 11 to the outer surface of the reactor vessel near the coolant liquid level of the reactor.

It is preferable that the annular closure body 15 is composed of a plurality of sections having an annular shape as a whole, as partially shown in FIG. 2, because manufacturing and installation are easy. That is, each compartment is a hollow, approximately box-shaped stainless steel member filled with a heat insulating material 21, as shown in the cross-sectional view of FIG. It has an inner circumferential surface 18 protruding from the portion. The inner circumferential surface 18 is made of a solid block 22 of stainless steel or the like having a coefficient of thermal expansion approximately equal to the coefficient of thermal expansion of the furnace vessel 1 and having a relatively large predetermined heat capacity.
This is one side of the story. In each section of the annular closure body 15,
to combine with each other to form an integral annular body.
A flange 24 with bolt holes 23 and tenons 25 and mortises 26 are provided, and a caul plate 2
7 is also provided. The annular closure 15 rests on a heat insulating material 28 provided on the outer surface of the furnace vessel 1 and is fixedly supported by the shielding concrete structure 3 by means of suitable fastening devices.

The annular closure body 15 has an inner circumferential surface 18 that protrudes into the flow path 20 and comes into contact with the outer surface of the reactor vessel below the coolant liquid level 5 during nuclear path operation, and the block 22 is approximately equal to the reactor vessel 1. It has a coefficient of thermal expansion and a predetermined heat capacity, and the annular closure 15 is supported by a structure outside the furnace vessel 1 . Therefore, during normal operation of the nuclear reactor, the flow path 20 is closed by the annular closure 15, and the low temperature atmosphere from the air conditioner 11 does not cool the reactor vessel 1 unnecessarily. On the other hand, when the operating conditions of the nuclear path change and the coolant temperature changes rapidly, the sudden and large change in coolant temperature and level creates a large thermal gradient on the reactor vessel wall near the coolant liquid level. appears and large thermal stress occurs.

For example, the thermal gradient that occurs during a nuclear reactor scram is shown in the graph of FIG. In this graph, during normal operation, the coolant in the reactor vessel 1 is at a coolant liquid level of 5.
It's filled to the brim. At this time, the temperature of the vessel wall below the coolant liquid level 5 of the furnace vessel 1 is approximately the same as the coolant temperature 529
℃ and is approximately uniform. The temperature of the vessel wall above the coolant liquid level 5 becomes lower as it moves upward away from the coolant liquid level 5. The temperature distribution on the wall of the furnace vessel 1 during such normal operation is represented by a solid curve 30 in FIG.

When a fast breeder reactor in such a state is scrammed, the coolant temperature reaches about 430°C in about 50 seconds after the scram, and 180°C after about 6 hours, as shown in Figure 4.
At the same time, volume shrinks due to temperature drop, level fluctuation ΔL occurs, and the liquid level drops to the coolant liquid level 29. Therefore, the wall of the furnace vessel 1 below the coolant liquid level 29 also has a low temperature of about 180°C.

However, in fast breeder reactors that do not have conventional thermal stress countermeasures, the wall of the reactor vessel 1 above the coolant liquid level 5 is in contact with the cover gas, so the temperature during normal operation is low. does not descend easily,
At the position of coolant liquid level 5, the temperature is about 450℃ even after about 6 hours.
This causes a large thermal gradient between the coolant liquid level 29 after the scram (approximately 180° C.) and the position of the coolant liquid level 29 after the scram. This state is shown by the dashed curve 31 in FIG.

On the other hand, in a fast breeder reactor equipped with the annular closure body 15 of the present invention, the coolant temperature after scram is approximately 180°C.
When the temperature decreases to 1, the furnace vessel 1 below the coolant liquid level 29
The temperature of the vessel wall portion also decreases, and the diameter of this portion of the furnace vessel 1 contracts. Therefore, a gap is created between the inner circumferential surface 18 of the annular closure body 15, which is supported by the support structure and has a predetermined heat capacity, and the outer surface of the furnace vessel, and the low temperature atmosphere from the air conditioner 11 is transferred to the outer surface of the furnace vessel. The supply channel 20 is opened. Therefore, the low-temperature atmosphere exists in the pipe 14, header 16, furnace vessel 1, and inner peripheral surface 1.
The coolant liquid level 5 flows through the space 19 between the reactor vessel 8 and the coolant liquid level 5, which includes the vicinity of the coolant liquid level in the reactor vessel 1, that is, the portion above the coolant liquid level 29 after scram.
The wall portion of the furnace vessel 1 in the vicinity of is cooled. Therefore, the temperature distribution of the conventional device shown by the broken line 31 in FIG. 3 has a peak of about 300°C as shown by the dashed line 32.
It becomes a curve with a smaller temperature gradient. Therefore, the thermal stress generated in the furnace vessel 1 is extremely small compared to the conventional one.

Cooling by the low-temperature atmosphere is stopped when the temperature difference between the furnace vessel 1 and the annular closure 15 becomes smaller, since the gap between them is closed.

As is clear from the above description, the fast breeder reactor of the present invention has a simple configuration and can effectively reduce the occurrence of thermal stress on the reactor vessel due to changes in coolant temperature.

[Brief explanation of the drawing]

Figure 1 is a partial sectional view of the fast breeder reactor of the present invention, Figure 2 is a perspective view of the annular closure shown in Figure 1, Figure 3 is a graph showing the temperature distribution on the wall of the reactor vessel, and Figure 4 is after scram. 3 is a graph showing changes in coolant temperature of FIG. DESCRIPTION OF SYMBOLS 1... Furnace vessel, 5... Coolant liquid level, 15... Annular closure body, 18... Inner peripheral surface, 20... Channel.

Claims (1)

[Claims] 1. The atmosphere around the reactor vessel is maintained at a predetermined relatively low temperature by an air conditioner,
In a fast breeder reactor having a free liquid surface of coolant, a flow path that directly supplies the low temperature atmosphere from the air conditioner to the outer surface of the reactor vessel near the coolant liquid surface, and a flow path that protrudes into the flow path. It has an inner circumferential surface that comes into contact with the outer surface of the reactor vessel below the coolant liquid level during reactor operation, has a coefficient of thermal expansion approximately equal to that of the reactor vessel, and has a predetermined heat capacity, an annular closure whose surface the inner peripheral surface directly contacts to close the flow passage, and which substantially remains in its original position to open the flow passage despite thermal contraction of the reactor vessel when the nuclear path is shut down; A fast breeder reactor characterized by being equipped with.