JPS6232391A - Pressure vessel for 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 invention 1 The present invention relates to a nuclear reactor pressure vessel.

[Technical background of the invention and its problems 1 A nuclear reactor pressure vessel can be called the heart of a nuclear power plant, and the reactor core is housed inside the reactor pressure vessel.

The operating conditions for this reactor pressure vessel are approximately TO atmospheric pressure and 300°C for a boiling water reactor, and approximately 150 atmospheres and approximately 350°C for a pressurized water reactor. is exposed to high temperature and high pressure pure water. Since these reactor pressure vessels contain reactor fuel, their reliability is required to be high.

Generally, high-toughness materials are used as steel materials for reactor pressure vessels in order to prevent brittle fracture (a phenomenon in which NM structures break instantly without any warning).

On the other hand, as mentioned above, the reactor pressure vessel is used under high pressure conditions, so a certain level of strength (-tensile strength) is required, so the steel material for the reactor pressure vessel also has the function of a high-strength material. It becomes necessary. Furthermore, since the inner surface of the reactor pressure vessel is exposed to high-temperature pure water, this inner surface is lined with stainless steel, which has good corrosion resistance, to improve the corrosion resistance of the reactor pressure vessel. On the other hand, the design of the reactor pressure vessel R1 is based on Ministry of International Trade and Industry notification 5.
It is designed based on design standards such as No. 01 and the American ASME standard, and tolerance values are determined depending on the material so that there is a sufficient margin for its strength.

FIG. 5 shows an example of the structure of a currently used boiling water reactor pressure vessel. In the figure, 3 is a reactor pressure vessel, and 4 is a cladding. By the way, the plate thickness of a 1,100 MeW class nuclear reactor pressure vessel is 1,601,111 mm or more, so it must be handled as extremely thick steel, and extremely high quality is required. Normally, the plate thickness of the reactor pressure vessel is determined by the following formula.

Here, [: Plate thickness of the pressure vessel shell P: Internal pressure R: Radius of the pressure vessel shell: Constant α: Proof capacity of the material As can be seen from the above equation, the plate thickness of the reactor pressure vessel [is the internal pressure P
and inversely proportional to the tensile strength of the material.

Therefore, under conditions of the same internal pressure, that is, the maximum working pressure, high-strength materials I
The more 4r is used, the thinner the plate can be and the lighter the pressure vessel can be.

However, in general, when the strength of a steel material is increased, the toughness value tends to decrease. This indicates that if there are notches or defects in the material, there is a high possibility that unstable cracks will occur from these notches or defects.

[Object of the Invention] The present invention has been made in consideration of the above circumstances, and its object is to provide a nuclear reactor pressure vessel using a steel plate having material characteristics of high strength and high toughness.

[Summary of the Invention] In order to achieve the above object, the present invention uses high-strength steel as a base material and joins high-toughness materials such as mild steel or uncast steel to both sides of this base material, thereby achieving high strength and high toughness. This invention relates to a nuclear reactor pressure vessel using steel plates with special characteristics. and,
By using a material with a lower coefficient of thermal expansion than the base material for the bonding material, residual thermal stress of compression is generated on both the inner and outer surfaces during reactor operation, thereby reducing notch sensitivity.

[Embodiments of the invention] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross-sectional view of the steel material according to the present invention.
An example is shown in which stainless steel 2 is clad-welded on both sides of a high tensile strength steel 1 of ~100 kg/ll 1 m2 class.

In Figure 2, the stress-strain characteristics when using this steel material are shown as solid lines, and the stress-strain characteristics of steel materials commonly used for current reactor pressure vessels are shown as dashed-dotted lines. There is. As is clear from Figure 2, the yield stress that determines the plate thickness of the reactor pressure vessel is 41% higher than that of currently used steel.
It turns out that 1 material is much more expensive. Therefore, plate J of the steel plate for reactor pressure vessel is proportional to the upper back of this yield stress.
? can be made thinner. This makes it possible to reduce the weight of the reactor pressure vessel. For example, 1ffi of the reactor pressure vessel of a modern boiling water reactor is approximately 750 tons;
By using a material with twice the strength of VQ), it can be made approximately 370t. The broken line in the figure also shows the stress/strain relationship of the material depending on the cladding thickness, and as shown by the broken line, the larger the cladding thickness compared to the solid line, the greater the fracture strain, and the higher the ductility. to move to.

Note that FIG. 2 shows the results when clad welding was performed on high-strength steel as a base material and a current reactor pressure vessel material as a comparison material with the same plate thickness.

Figure 3 shows the stress/strain relationship of the material when the total plate thickness is kept constant for the same case as Figure 2. It can be seen that in all cases, the clad material exhibits higher strength. This shows that if the plate thickness is kept as it is, the strength and reliability will be improved by using the steel material according to the present invention.

FIG. 4 shows the stress distribution in the thickness direction of a steel plate coated with stainless steel. Both stress values are 0'' at room temperature, but the coefficient of thermal expansion is 12.90X for high-strength steel.
10-6 till/ll”c, 17 in stainless steel
．． 62 x 10-6 am/im"c, and due to the difference in coefficient of thermal expansion between high-strength steel and stainless steel cladding, compressive thermal stress is generated on the cladding side and tensile stress is generated on the base material side as the temperature rises. During reactor operation In addition to this thermal stress component, stress due to internal pressure is added, so tensile stress also occurs on the inner surface, but its magnitude is reduced due to compressive thermal stress.In this way, according to the present invention, the stress on the outer surface of the plate is reduced. Compressive stress can be added.

Generally, defects such as cracks often occur on the plate surface, and these defects develop due to tensile stress. Therefore, the use of the steel material according to the present invention can be expected to prevent the occurrence and propagation of cracks.

In addition, by using a material with high neutron absorption such as cadmium boron or lead with a high shielding effect for the outer cladding material of the reactor pressure vessel, it is possible to reduce radiation exposure.

Note that the stress-response strain relationship can be changed depending on the application, so it can be applied not only to nuclear reactor pressure vessels but also to other equipment.

[Effects of the Invention] As explained in 1-1 above, according to the present invention, a high-strength, high-toughness material can be made by joining a high-strength steel material to a high-toughness material. Reduce the plate thickness of
It can be made lighter.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the steel plate according to the present invention, Figure 2 is a stress-strain diagram of the steel plate of the present invention and the steel plate of a current nuclear reactor pressure vessel, and Figure 3 is a diagram of the stress-strain curve when the total plate thickness is kept constant. Stress-strain diagram of steel material,
Figure 4 is the thermal stress molecule fi diagram during reactor operation, Figure 5
The figure is a cross-sectional view of a current boiling water reactor pressure vessel. 1...High tensile steel 2...Stainless steel (8733) Agent Patent attorney Yoshiaki Inomata (and 1 others)
Name) Part 1 History g Figure 4 Figure 5

Claims (2)

[Claims] (1) By using high-strength steel as the base material and joining high-toughness materials such as mild steel or uncast steel on both sides of this base material, high strength and
A nuclear reactor pressure vessel characterized by using a steel plate with high toughness characteristics. (2) The nuclear reactor pressure vessel according to claim 1, wherein a material having a lower coefficient of thermal expansion than the base material is used as the bonding material.