RU2519063C1 - Titanium-based alloy for absorption of heat neutrons - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed alloy comprises the following elements, in wt %: carbon - 0.03-0.10; iron - 0.15-0.25; silicon - 0.05-0.12; nitrogen - 0.01-0.04; aluminium - 1.8-2.5; zirconium - 2.0-3.0; samarium - 0.5-5.0, titanium and impurities making the rest.

EFFECT: higher efficiency of absorption, better working and bonding properties.

3 tbl, 1 ex

Description

The invention relates to the field of metallurgy, to the development of new non-radioactive materials and can be used in the nuclear energy industry. The traditional non-radioactive metals used in nuclear power plants for more than 50 years are zirconium alloys (∋125, ∋225), corrosion-resistant steel (08Х18Н10Т) and boron steel ChS82 (04Х14Т3Р1Ф). The latter due to the content of boron has the property of absorption of thermal neutrons. Currently, hexagonal pipes are made from it for the assembly of fresh nuclear fuel racks and spent fuel pool holding pools.

This steel was widely used in nuclear engineering, TU14-1-3689-83, TU14-1-4599-89 were developed and approved for the production of pipe billets from ChS82 steel. Also, a technology has been developed for the production of hot-rolled pipes from this steel (TU14-242-275-89), which serve as a blank for producing hexagonal pipes (TU14-3-1630-89).

Modern requirements for materials that are capable of absorbing thermal neutrons from radioactive elements dictate an increase in the level of absorption. An increase in boron content in ChS82 steel from the traditional content (1.5-1.8)% according to TU14-1-4599-89, for example, up to 2.5%, makes ChS82 steel brittle and unsuitable for the intended use. Known alloy based on titanium for absorption of thermal neutrons (RF patent No. 2483132, BI No. 15 of 05/27/13), where the boron content is in the range of (1.5-3.5)%. To increase the absorbing properties, it is necessary to increase the boron content in the alloy according to modern requirements - up to 10%. However, the boron element and its 10 V isotope, which has a maximum absorption capacity, significantly “embrittle” not only iron-based steels, but also titanium-based alloys. This is a common property of borides.

In table 1, on the basis of known data from the directory: Element properties: Ref. Edition in 2 books. / Ed. Dnitsa M.E. - M.: Publishing House "Ore and Metals", 2003, presents the values of effective cross sections for thermal neutron capture for natural isotopes of titanium, aluminum, zirconium, boron and samarium.

From Table 1 it follows that the natural isotope of samarium (149Sm) absorbs thermal neutrons an order of magnitude more efficiently than the boron isotope of 10 V.

The purpose of the present invention is the development of a material that would not only have a high level of absorption of thermal neutrons, but also have high operational and plastic properties, which generally ensures the safety of storage of spent nuclear fuel.

The closest to the described by the technical essence and the achieved effect is an alloy based on titanium PT7M (GOST 19807-91), which is also used in nuclear energy (see article Ushkova S.S. et al. - Materials Science, 2009, No. 3 ( 59), p. 172-187.). The chemical composition of the alloy PT7M, weight. %:

Carbon 0.03-0.10 Iron 0.15-0.25 Silicon 0.05-0.12 Nitrogen 0.010-0.040 Aluminum 1.8-2.5 Zirconium 2.0-3.0 Titanium and impurities rest

This goal is achieved by the fact that in the well-known alloy PT7M based on titanium, a rare-earth element is added - samarium - in the following volume, weight. %: 0.5-5.0. The range of content in the samarium alloy is determined by the optimal level of absorption of thermal neutrons and economic feasibility. Below 0.5% - the alloy does not provide the necessary minimum level of absorption of thermal neutrons, more than 5% - the cost of the alloy increases significantly.

To obtain titanium-based alloys, electron beam remelting (EBM) is used in vacuum furnaces. Sponge titanium (grades TG100, TG110) with a titanium content of (99.7-99.7)% according to GOST 17746-96 is used as the main raw material. In order to evenly distribute alloying elements (Al, Zr, Sm), a double remelting is performed in the ingot. The neutron absorption control of the obtained alloy in the ingot and pipes is controlled using the UKPN-1 domestic facility.

An example of obtaining a titanium-based alloy for absorption of thermal neutrons. Sponge titanium TG100 in the form of discrete pieces (20-45) mm in size is mixed with a ligature: from aluminum, zirconium and samarium (TU48-4-207-72) in the ratio - 1 kg (TG100) +0.025 kg (Al) +0, 03 kg (Zr) +0.01 kg (Sm) in a total volume of 20 kg and is supplied to the experimental setup (ELP). After double remelting, we get an ingot ⌀100 mm 500 mm long. After turning and rotational forging of the ingot with a diameter of 65 mm, we obtain the microstructure of the alloy with a grain size of 5-6 points. Hot pressing allows you to get a pipe billet for subsequent cold redistribution.

Table 2 shows the chemical composition of the obtained alloy (SPS-1,0; SPS-1,5), and Table 3 shows the mechanical properties of the forged wheel ⌀65 mm from the alloy SPS-1,0; SPS-1.5 at + 20 ° С together with the absorption value of thermal neutrons at a samarium content of 1.0% and 1.5%. For comparison, Table 2-3 shows the chemical composition and mechanical properties of a forged ⌀65 mm circle made of PT7M alloy manufactured at VSMPO AVISMA OJSC (V. Salda), according to GOST 26492-85,

As follows from table 1-3, the claimed alloy has a high level of absorption of thermal neutrons compared with the prototype PT7M while it has high strength properties.

It should be noted that the introduction of samarium during the smelting of an alloy based on titanium is not necessarily in the form of technically pure metal (Sm), manufactured according to TU48-4-207-72. To maintain the regulatory requirement for the distribution of samarium in the alloy, where the distance between the Sm particles is not more than 15 microns, it is sufficient to use samarium dioxide in the melting, which significantly reduces the cost of the alloy and its products.

Thus, reducing the titanium content in the PT7M alloy by (0.5-5.0)%, replacing it with samarium (0.5-5.0)%, we obtain an alloy with a high level of absorption of thermal neutrons, which is in demand in nuclear engineering .

Table 1 Values of effective cross sections for thermal neutron capture of natural isotopes of titanium, aluminum, zirconium, boron, samarium (n _ρ · 10 ^-28 m ² ) No. Isotope n _ρ No. Isotope n _ρ No. Isotope n _ρ one 46 Ti 0.6 3 90 Zr 0.10 5 149 Sm 50,000 47 Ti 8.0 91 Zr 1,50 152 Sm 5600 154 Sm 5600 2 27 Al 0.21 four 10 V 3838 11 V 757

table 2 The chemical composition of the experimental melts of titanium alloys with samarium (SPS-1,0; SPS-1,5) and the prototype PT7M No. alloy Sm FROM Fe Si N Al Zr Ti impurities one SPS-1,0 1,0 0.08 0.20 0.10 0.02 2,5 3.0 main 0.34 2 SPS-1,5 1,5 0.08 0.20 0.10 0.02 2,5 3.0 main 0.34 3 PT7M - 0,07 0.15 0.08 0,03 2.1 2,5 main 0.28

Table 3 Strength limit (σ _b ), yield strength (σ ₀₂ ), elongation (δ ₅ ) and thermal neutron absorption (n _ρ · 10 ^-28 m ² ) for titanium alloys СПС-1,0; SPS-1.5; PT7M at + 20 ° C No. ALLOY σ _b σ ₀₂ δ ₅ N _ρ (MPa) (MPa) (%) one SPS-1,0 730 510 thirty 109 2 SPS-1,5 790 543 25 355 3 PT7M 610 490 21 0.7

Claims (1)

A titanium-based alloy for absorbing thermal neutrons, containing carbon, iron, silicon, nitrogen, aluminum, zirconium and titanium, characterized in that it additionally contains samarium at the following component content, wt.%:
Carbon 0.03-0.10 Iron 0.15-0.25 Silicon 0.05-0.12 Nitrogen 0.010-0.04 Aluminum 1.8-2.5 Zirconium 2.0-3.0 Samarium 0.5-5.0 Titanium and impurities rest