JPS5811891A - Stretch tube for underwater pump of 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 A submersible pump used to forcefully circulate the reactor primary cooling water within the reactor and control the output (1) has a structure as shown in FIG. An impeller 1 that circulates reactor water is directly connected to a pump shaft 2 and rotates.

The diffuser 3 forms a flow path for circulating water. Here, in order to prevent leakage of reactor water, pressurized purge water is flowed from below around the pump shaft, and a thin cylindrical stretch tube 4 is used to maintain the flow path and to fix the diffuser.

In order to perform this function, stretch tubes are required to have high strength at a reactor water temperature of around 300°C and thermal expansion characteristics comparable to those of the surrounding structural materials, such as martensitic stainless steel or ferritic stainless steel. Ru. In accordance with such requirements, conventional submersible pumps use Inconel 600, a Ni-based alloy containing about 16% Cr and about 7% Fe, as a stretch tube material.

However, as shown in FIG. 2, the present inventors focused on the fact that the stretch tube is used while bearing high stress with gaps formed between the inner and outer surfaces and surrounding structural materials.
As a result of evaluating the stress corrosion cracking (hereinafter referred to as SCC) of various materials under a high-temperature water gap environment (2), it was found that conventional stretch tubes made of Inconel 600 have the possibility of SCC failure during long-term use. It turns out that there is something. Therefore, in addition to the above-mentioned mechanical strength and thermal expansion characteristics, the stretch tube material has
It has been found that SCC resistance under high-temperature pure water gap conditions is required as an essential item to ensure its long life.

An object of the present invention is to provide a stretch tube with a long life without fear of SCC damage during many years of operation of a nuclear reactor.

As a result of the above-mentioned evaluation studies of various materials, the present inventors found that the Ni-based alloy according to the present claims is suitable as a stretch tube material. In particular, Cr is 20-25%, Mo
is preferably 4 to 10%, and C is preferably 0.1% or less. Further, in order to reduce the radioactivity of the nuclear reactor, it is preferable that Co be 0.2% or less, and for the same reason, it is preferable to suppress Ta contamination as much as possible.

The present invention will be explained below with reference to Examples.

Table 1 shows stretch tube materials, sample numbers (3) A to D indicate the chemical composition of the present invention agent, and sample numbers E and F indicate the chemical components of the conventional material Inconel 600. All of these materials were subjected to solution treatment at 1100° C. for 1 hour after hot forging.

Table 1 * The remainder is Ni ** excluding impurities. Inconel 600 Table 2 shows the mechanical properties and thermal expansion characteristics of these materials. All of the stretch tube materials of the present invention are heated to 300°C, which is the maximum temperature of the reactor water. From these points of view, it is a suitable material.

The SCC resistance test under high temperature underwater gap conditions was conducted using a plate with a thickness of 2 mm.
, using a rectangular specimen with a plate width of 10 mm and a length of 50 mm. The specimen was tightened with a stress applying jig to a radius of 100 mm, and a gap of 0.2 mm was formed on the tensile stress side surface with graphite wool interposed therebetween. In this state, the specimen was heated to 28
After being immersed in pure water containing 8 ppm (5) of dissolved oxygen at 8°C for 500 hours, it was released from the jig and the state of SCC generation was observed using a microscope. Table 3 summarizes the SCC test results.

Table 3 ○: No cracks ●: SCC generation Inconel 600 has some specimens that have SCC, whereas the material of the stretch tube of the present invention has no SCC.
did not occur.

As described above, it has been revealed that the stretch tube using the material described in the claims of the present invention maintains a long life in a submersible reactor pump and exhibits its functions.

[Brief explanation of drawings]

(6) Figure 1 is a cross-sectional diagram of the reactor submersible pump, and Figure 2 is the
It is an enlarged view of the vicinity of the stretch tube shown in the figure. 1 Impeller, 2 Pump Shaft, 3 Diffuser, 4 Stretch Tube Agent Patent Attorney Akio Takahashi

Claims (2)

[Claims] 1. In a stretch tube for a submersible pump that forcibly circulates reactor primary cooling water within the reactor, the stretch tube contains 15 to 25% Cr, 2 to 10% Mo, and 0% by weight.
．． A stretch tube for a nuclear reactor submersible pump, characterized in that it is made of an alloy containing 5% or less Al, 0.5% or less Ti, and 20% or less Fe, with the balance being Ni. 2. In a stretch tube for a submersible pump that forcibly circulates the reactor primary cooling water within the reactor, the stretch tube contains 15 to 25% Cr, 10 to 10% Mo, and Nb4 by weight.
．． 5% or less, Al 0.5% or less, Ti 0.5% or less, F
A stretch tube for a nuclear reactor submersible pump, characterized in that it is made of an alloy containing 20% or less of e and the remainder being Ni.