JPS6346388B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in water supply nozzles for nuclear reactor pressure vessels.

Generally, although a single nozzle 2 of this type is shown in FIG. 1, a large number of water supply nozzles 2 are installed laterally in the body of the pressure vessel 1 of a nuclear reactor. This nozzle 2 has a pressure vessel 1
In order to protect the nozzle 2 from severe thermal stress when injecting cold water of approximately 10°C into the high temperature (289°C) reactor water inside the interior 6, a thermal sleeve is installed inside the annulus part 7 of the nozzle 2. The tip of the thermal sleeve is exposed to the inside 6 of the pressure vessel 1.

As shown in FIG. 2, this conventional nozzle employs an insert-type thermal sleeve 3 that is simply inserted into the annulus portion 7 of the nozzle 2. For this reason, when cold water is injected as shown by the arrow, the thermal sleeve 3 contracts rapidly, causing the thermal sleeve 3 to
A gap was created at the insertion point, and cold water leaked from this gap and mixed with high-temperature water at the nozzle corner 8, causing high cycle temperature fluctuations at the nozzle corner 8, causing thermal fatigue cracks. In the data obtained from experiments, these temperature fluctuations are
It has been confirmed that {(high reactor water temperature) - (cold injection temperature)} x 70% and the temperature fluctuation cycle is approximately 1 Hz, a phenomenon that can cause thermal fatigue.

The plug-in thermal sleeve 3 has a 0.2 to 0.5 mm gap between the nozzle 2 and the thermal sleeve 3.
A method has been considered to provide a certain degree of tightness and make the gap very small, but this does not prevent the thermal sleeve from shrinking when cold water is injected, resulting in cold water leakage.
The plug-in thermal sleeve is made of Inconel or stainless steel, but since the nozzle 2 body side is made of carbon steel, corrosion of the metal on the nozzle 2 side,
It is thought that aging is due to erosion, etc., and that cold water leakage is increasing due to the gradual increase in the gap between the mounting parts. There is also a concern that the thermal sleeve 3, which is supposed to provide the interference, may undergo so-called sag due to thermal cycles during operation, making it impossible to maintain the interference.

In order to prevent this cold water leak, recently a welded type thermal sleeve has been adopted in which the thermal sleeve 4 is directly fixed to the safe end of the nozzle 2 by welding 9, as shown in Fig. 3. Although there is no leakage of cold water, the "burst phenomenon" occurs because the thermal sleeve 4 is single-layered.
occurs, causing rapid temperature fluctuations on the inner surface of the nozzle 2. Additionally, water in the annulus replaces water in the furnace, causing thermal fatigue.

Incidentally, the "burst phenomenon" means that when the inner part of the thermal nozzle 4 is filled with cold water and the outer annulus part 7 is filled with high-temperature water as shown in FIG. The high-temperature water in contact with the thermal sleeve 4 forms a cold water layer 10 on the outer surface of the thermal sleeve 4, and when this cold water layer 10 grows to a certain extent as shown in C, it falls as shown by the arrow 11 due to the difference in specific gravity, and the nozzle 2 This is a phenomenon that causes rapid temperature fluctuations on the inner surface. And, even in the case of the welded type thermal sleeve 4 (the burst phenomenon can also occur in the plug-in type thermal sleeve), this temperature fluctuation range is {(reactor water temperature) - (feed water temperature)} x 20 to 30%.
It has been confirmed that the cycle time is approximately 1 cycle/30 seconds, and these are not thought to result in temperature fluctuations that would cause thermal fatigue.
However, for nozzles that inject cold water into the high-temperature reactor water (water supply nozzles, core spray nozzles, etc.), there is no leakage of cold water, the "burst phenomenon" is prevented, and nozzle thermal fatigue is sufficiently prevented. It is desired to develop a thermal sleeve that can prevent this.

The present invention was made in view of the above-mentioned situation, and an object of the present invention is to provide a highly safe water supply nozzle for a nuclear reactor pressure vessel that prevents temperature fluctuations at the nozzle corners and the inner surface of the nozzle and does not cause thermal fatigue. The requirements for the configuration of the present invention to achieve this objective are that a thermal sleeve is attached to the safe end of the nozzle of the reactor pressure vessel by welding with a distance from the inner wall surface of the nozzle,
The thermal sleeve has at least a double structure with an inner and an outer part, and the safe end and each of the inner and outer thermal sleeves are all attached by butt welding.

An embodiment of the reactor pressure vessel water supply nozzle according to the present invention is shown below with the same parts as the conventional one indicated by the same reference numerals.
This will be explained using figures. Reference numeral 5 denotes a double thermal sleeve attached by welding, and both the inner and outer thermal sleeves are fixed to the safe end of the nozzle 2 within the annulus portion 7 by butt welding. Since it is fixed by welding in this way, it completely blocks the leakage of cold water and prevents temperature fluctuations due to leakage, and since it is a double-walled thermal sleeve, it relaxes the thermal boundary conditions inside and outside the thermal sleeve. No burst phenomenon occurs on the outer surface of the thermal sleeve, and thermal fatigue on the nozzle corner 8 and the inner surface of the nozzle 2 can be prevented. In addition, thermal fatigue caused by water in the annulus being replaced with reactor water is also prevented. It is conceivable that this double thermal sleeve 5 may be made into three or more layers, and although the performance against burst phenomena may be improved somewhat, it is thought that there will not be much of a difference. In addition, in the double thermal sleeve 5, a method in which the outer sleeve is a welding type and the inner sleeve is a plug-in type is also considered, but regarding the burst phenomenon prevention effect of the present invention, it is difficult to The main reason for the effect is wrapping with double or more sleeves, but according to the above-mentioned insert type,
As described in the conventional example, leakage of cold water occurs from the insertion portion, and the cold water leaking from the insertion portion is wrapped in the single outer thermal sleeve. The conventional method of wrapping the cold water leaking from the insertion part in a single thermal sleeve is poor in preventing the burst phenomenon.

In this way, the reactor pressure vessel water supply nozzle of this embodiment prevents temperature fluctuations at the nozzle corners and inside of the nozzle of the reactor pressure vessel nozzle that injects cold water into high-temperature water, alleviates harmful thermal stress, and reduces thermal fatigue. Safety can be improved without causing any problems.

FIG. 6 shows another embodiment, which differs from the above embodiment in that the inner and outer thermal sleeves of the double thermal sleeve are connected to the nozzle 2.
In contrast, in this embodiment, the nozzle 2 has a single welded fixing part, and a double part is formed halfway to the inside 6 side. In this case, the outer thermal sleeve is indirectly fixed to the safe end of the nozzle 2 by two butt welds including butt welding to the inner thermal sleeve, and the same method as in the above embodiment is used. It has an effect.

As described above, according to the present invention, there is no need to bend and weld the end of the thermal sleeve toward the inner wall surface of the nozzle, and the multi-layered thermal sleeve prevents temperature fluctuations to the nozzle corners and the inner surface of the nozzle. The base of the multi-layered thermal sleeve is welded by butt welding, which is one of the most reliable types of welding, and water leakage is completely prevented, which prevents burst phenomena caused by water leakage, making it easier and more convenient to weld nozzle corners and nozzles. This has the effect of preventing inner temperature fluctuations and improving safety without causing thermal fatigue.

[Brief explanation of drawings]

Figure 1 is a sectional view of a water supply nozzle attached to a reactor pressure vessel, Figures 2 and 3 are sectional views of conventional water supply nozzles, and
C and D are explanatory diagrams of the burst phenomenon of the water supply nozzle in FIGS. 2 and 3, FIG. 5 is a sectional view of an embodiment of the water supply nozzle for a reactor pressure vessel of the present invention, and FIG. FIG. 3 is a sectional view of another embodiment of a water supply nozzle for a reactor pressure vessel. DESCRIPTION OF SYMBOLS 1... Pressure vessel, 2... Nozzle, 5... Double thermal sleeve, 7... Annulus part.

Claims (1)

[Claims] 1. A thermal sleeve is attached to the safe end of a nozzle of a reactor pressure vessel by welding with a distance from the inner wall surface of the nozzle, and the thermal sleeve has at least a double or more structure with an inside and an outside, A water supply nozzle for a nuclear reactor pressure vessel, wherein the safe end and each of the inner and outer thermal sleeves are all attached by butt welding.