JPH032217B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a nuclear reactor material used in a neutron irradiation environment such as a light water reactor, a high temperature gas reactor, a fast breeder reactor, or a nuclear fusion reactor. This relates to 11B enriched nickel boron, which is added during melting and refining mainly in the production of nickel-based alloy materials, steel materials, etc., which contain ¹¹ ( ¹¹ B) at a higher proportion than the proportion found in nature. .

<Prior Art> Boron is added to nickel-based alloy materials, steel materials, etc. for the purpose of improving creep strength and tensile ductility. Furthermore, when these materials are used for welding and brazing, boron is added for the purpose of improving ductility and toughness, as well as increasing self-fluxability during construction.

The boron traditionally used for these purposes is natural boron, with an atomic weight of 10 ( ¹⁰ B)
It contains about 19.6% (by weight, the same hereinafter) and about 80.4% boron ( ¹¹ B), which has an atomic weight of 11. When a material containing natural boron is irradiated with neutrons,
A reaction in which only ¹⁰ B of the boron in the material absorbs neutrons and produces helium gas, i.e. ¹⁰ B
(n, α) ⁷ Produces transmutation of Li.

The generated helium is the main cause of deterioration of the mechanical properties of the material, such as a decrease in the high-temperature ductility of the material, a decrease in the creep strength, and an increase in the susceptibility to cracking.
Lowering the limit for use of structural members in the furnace. Therefore, nuclear reactor constituent materials that contain boron components with a higher proportion of ¹¹ B than natural boron and that prevent the production of helium by ¹⁰ B, as well as bonding materials for these materials, etc. (hereinafter collectively referred to as "atomic There is a growing need for the development of "furnace materials".

A method for adding ^11B to nickel-based alloy materials, steel materials, etc. is to melt and refine ^11B concentrated boric acid or metallic boron, which has a higher proportion of ^11B than natural boron, of the above-mentioned materials to which these are added. Sometimes, a method of directly adding 11B can be adopted, but the method of adding boric acid has a low yield of ^11B due to poor wettability with the molten metal and its small specific gravity, which makes it easy to float. It is extremely difficult to do so. On the other hand, the method of adding metallic boron to a molten alloy also has the disadvantage that the specific gravity is small and it tends to float, and that the manufacturing cost of metallic boron is high, which impairs the economic efficiency of the material.

In order to eliminate the above-mentioned drawbacks, ¹¹ B-enriched ferroboron has been proposed as a ¹¹ B-enriched compound particularly added to steel materials by the same applicant as the present application (Japanese Patent Application No. 123106/1982). When this ferroboron is added to molten steel during the melting and refining process during the production of steel materials, it melts in a short time, and since the specific gravity is substantially equal to the molten steel, the added feroboron does not float up and can be used uniformly and at a high yield. Can be melt mixed. In addition, because the obtained steel material has a high proportion of ¹¹ B in the total boron content ( ¹⁰ B + ¹¹ B), it is possible to reduce the production of helium due to the reaction between ¹⁰ B in the material and neutrons even in a neutron irradiation environment. , can maintain good creep strength and high temperature ductility.

However, since the ^11B enriched ferroboron according to the prior invention is mainly composed of iron, which was developed as an additive raw material for steel materials, it is necessary to use materials that do not require iron or precisely adjust the iron component. It cannot be used as an additive raw material for some materials. In addition, ferroboron, which contains about 10% or more boron and is effective as an additive raw material, has a relatively high melting point of about 1430°C or higher, so it can be used as a raw material that requires a low melting point. Not suitable for In addition, it contains concentrated ¹¹ B, is used with a relatively low melting point, has a nickel component as its main component, and does not contain a large amount of iron component.
The required additive raw material, which is characterized in that it does not contain harmful impurities such as aluminum to the extent that it has an adverse effect, has not been manufactured.

<Problems to be Solved by the Invention> Therefore, the main purpose of this invention is to reduce ^the (n, α)
When manufacturing nickel-based alloy materials, steel materials, etc. that generate little or no helium through reactions, the addition of ^11B improves creep strength in air under non-radiation conditions and at high temperatures. When manufacturing nickel-based alloy materials, steel materials, etc. that can maintain tensile properties, toughness, etc. even under neutron irradiation, it is possible to quickly, effectively, and economically add an optimal amount of ^11B to the materials. The object of the present invention is to provide a ¹¹ B concentrated additive raw material containing a nickel component as a main component, which can be used at a relatively low melting point.

<Means for Solving the Problems> According to the present invention, it contains 2 to 15% of boron B, 0.1% or less of aluminum as impurities, and 0.5% or less of carbon, with the remainder consisting of a nickel component, and the total boron content is 2 to 15%. Boron-11 ( ¹¹ B) for content
Provided is nickel boron, which can be added to nuclear reactor materials such as nickel-based alloy materials and steel materials, and has a melting point of 90% or more and a melting point of 1200° C. or less.

By adding the ^11B enriched nickel boron of this invention to molten metal in the melting and refining process during the production of nuclear reactor materials such as nickel-based alloy materials and steel materials, nuclear reactor materials with high ^11B content can be produced. can be obtained efficiently and economically. The material thus obtained has a total boron content of ¹¹ B relative to the total boron content ( ¹⁰ B + ¹¹ B).
Because of the high proportion of , it is possible to reduce the production of helium due to the reaction between ¹⁰ B in the material and neutrons even in a neutron irradiation environment, and it is possible to maintain good creep strength and high-temperature ductility.

Furthermore, when adding the nickel boron of this invention to the molten alloy, it dissolves in a short time after addition,
Further, since the specific gravity is substantially equal to the specific gravity of the molten metal, the added nickel boron can be uniformly melted and mixed into the molten metal without floating up.

Nickel boron is produced according to the nickel-boron equilibrium diagram shown in the attached drawing [Portnoi, KI and
“Binary constitution” by Romashov, VM
diagrams of system composition of vari−ous
elements and boron-A review”, Soviet
Powder Metallurgy & Metal Ceramics, 11
(1972), p. 378-384], the melting point is 1095°C at approximately 4% boron content, and 1100°C at 7% boron content.
℃, 10% is 1018℃, 13% is 1015℃, so
In the melting point range from 1000 to 1100°C boron contents of 4 to 13% can be selected. The relationship between these melting points and boron content varies slightly depending on the influence of impurities, but in the case of ferroboron according to the earlier invention, the melting point is usually about 1150 in the boron content range of about 4 to 13%. ℃ to 1500℃, and the melting point is about 1300℃ with a boron content of 7% or more, which is more cost effective.
℃ or more. An example of ferroboron, which is also included for comparison in the examples described below, showed a melting point of 1550° C. with a boron content of 11.5% ( ¹¹ B concentration 98%). In this way, the nickel boron of this invention is
A considerably lower melting point can be selected compared to ferroboron with a similar boron content. As a result, when the nickel boron of the present invention is added to a molten metal such as a nickel-based alloy material or a steel material, it can be uniformly mixed and dissolved in a shorter time than ferroboron.

The boron content in the nickel boron of the present invention is in the range of 2 to 15%, taking into account not only the relationship with the melting point described above, but also the specific gravity, impurity content, cost, etc. described later. Boron content is 2%
If less, the desired amount of ¹¹ B in the molten alloy
A large amount of nickel boron is required to contain this, which impairs economic efficiency. On the other hand, when the boron content in nickel boron is 15% or more, for example more than 20%, the melting point of nickel boron becomes higher than 1650°C, the specific gravity decreases, and even higher purity is obtained. It tends to get harder. Therefore, the boron content in nickel boron is 15% or less. The melting point of nickel boron is
When the temperature rises above 1650℃, it becomes difficult for the nickel boron added to the molten alloy to dissolve and mix uniformly in a short time, and when the specific gravity of the nickel boron decreases, the nickel boron added to the molten metal floats up, causing the surface layer of the molten metal to Problems arise when boron is absorbed by impurities or when the density of boron in the surface layer increases. These things are undesirable because they reduce the yield of ¹¹ B added to the added nickel-based alloy material, steel material, etc., and further impede uniform dissolution.

The reason why ¹¹ B is set to 90% or more of the total boron content in the nickel boron of the present invention is as follows. In other words, the material containing boron
¹⁰ The amount of helium produced per unit volume [cm ³ ] (number of helium atoms produced) by the B(n,α) reaction _is :
When the neutron irradiation conditions are constant, it is generally expressed by the following equation.

N _He = N _B-10 (1-e ^- 〓〓 ^t ) Here, N _B-10 is the number of ¹⁰ B atoms contained per unit volume [cm ³ ] of the material, and φ is the thermal neutron flux [n/cm ²・
sec], σ is the thermal neutron absorption cross section of ¹⁰ B [cm ² ], and t is the irradiation time [sec]. As can be understood from this equation, if the thermal neutron irradiation amount φt is the same, the thermal neutron absorption cross section of ¹⁰ B does not change, so the amount of helium produced from ¹⁰ B is proportional to the initial amount of ¹⁰ B component in the material. I will do it. In other words, with natural boron,
¹⁰ B is contained in 19.6% of the total boron component, but if this is reduced to about 2%, the amount of helium produced will be reduced to about 1/10 for the same irradiation dose. On the other hand, when examining the effect of neutron irradiation on high-temperature tensile elongation at break, which is a typical example of changes in material properties caused by neutron irradiation, we find that the amount of helium produced in the material is approximately 10 ^-8 to 10 ^-6 (the atomic fraction of helium relative to elongation). Atomic fraction range where the production amount dependence is noticeable)
In the case of the nickel-based alloy Hastelloy and for 304 stainless steel (Report
ORNL-TM-2019, Jan, 1968) There is an example of a decrease of about 6%. In the same atomic fraction range, if the atomic fraction of helium is doubled, the above Hastelloy
~2%, and for 304 stainless steel the elongation value decreases by about 2%. As an example of typical boron addition to nickel-based alloys and steel materials, if the total amount is 50 wppm, ¹⁰ B is contained in natural boron at 10 wppm. This 10 wppm of ¹⁰ B has a thermal neutron irradiation amount of 5
×10 ¹⁶ (n/cm ² ) with a helium atomic fraction of approximately 10 ^- ₈ ;
5×10 ¹⁸ (n/cm ² ), resulting in a helium atomic fraction of about 10 ⁻⁶ . Since these atomic fractions of helium are proportional to the content of ¹⁰ B in the initial material,
By reducing the initial content of 10 wppm to 1/2, it is possible to prevent the elongation value from decreasing by about 2 to 5% as described above.

In addition, the above-mentioned 5×10 ¹⁶ to 5×10 ¹⁸ [n/cm ² ]
The thermal neutron irradiation dose corresponds to the irradiation dose received during normal service life when nickel-based alloy materials and steel materials are used, for example, in nuclear reactor vessels, which are typical components of nuclear reactor structures. .

For the above reasons, in this invention, the proportion of ¹⁰ B to the total boron content is set to less than half of that of natural boron, that is, about 10% or less, and therefore the proportion of ¹¹ B to the total boron content [ ¹¹ B] /( ¹⁰ B+
¹¹ B)] is 90% or more. If the ratio of ¹¹ B to the total boron content is less than 90%, the amount of helium produced in a neutron irradiation environment by reducing ¹⁰ B in nickel-based alloy materials, steel materials, etc. obtained by adding nickel boron will increase. The economic benefits of producing such ¹¹ B concentrates, such as rational design and longer life of structures, are reduced.

The industrial method for producing nickel boron according to the present invention can be divided into two types depending on the method of reducing boron oxide. The first method is the so-called thermite method using aluminum as the reducing agent, and the second method is the electric furnace method using carbon as the reducing agent. When the thermite method is adopted, the content of aluminum as an impurity is about 3 to 5%, and when the electric furnace method is used, the carbon content is slightly higher, about 1%. Other impurity components that are undesirable as alloy additive raw materials for nuclear reactors include a large neutron activation cross section and a long half-life, making them a source of strong gamma radiation, which can cause equipment maintenance problems if migrated within the reactor. There are cobalt, tantalum, etc., but it has been found that by using purified raw materials for nickel boron, contamination as impurities can be avoided.

When aluminum is added as an impurity to a nickel-based alloy material, grain boundaries are eroded due to internal oxidation at high temperatures. From the viewpoint of internal oxidation, it is desirable that the aluminum content be 0.1% or less (Watanabe et al., Tetsu to Hagane 68, 682 (1982)). In addition, in austenitic stainless steel, the long-term creep rupture strength decreases due to a trace amount of aluminum content (0.1 to 0.03%) (Shintani et al., Tetsu-to-Hagane 71, 144
(1985)). As described above, since aluminum is undesirable to be added to nickel-based alloy materials and steel materials, the thermite method, which inevitably involves the inclusion of 3 to 5% aluminum, is not suitable as a method for producing the nickel boron of this invention. be.

As is well known, carbon is a dominant factor in improving the mechanical properties of nickel-based alloy materials, steel materials, etc. when added in appropriate amounts. When added, it reduces ductility and toughness, and also has unfavorable effects from the viewpoints of weldability and corrosion resistance. Adjustment of the carbon content of these reactor materials is
It is considered more efficient to do this separately from the addition of nickel boron, so the carbon content as an impurity in nickel boron should be kept as low as possible, and the value should be within a range where it has almost no effect when added or diluted. It is desirable to do so. When carbon is used as a reducing agent in the electric furnace method, in order to keep carbon as an impurity to a low level, one method is to reduce the carbon concentration by remelting, and another is to reduce the carbon concentration as a reducing agent. There is a method of reducing the amount less than the reduction equivalent, but the latter method deteriorates the yield of boric acid, which is the concentrated ¹¹ B raw material, for producing nickel boron. As a result of various studies on these points, in the present invention, the amount of carbon component as an impurity was set to 0.5% or less.

Therefore, the amounts of aluminum and carbon as impurities in the ¹¹ B concentrated nickel boron of the present invention are suppressed to 0.1% and 0.5%, respectively, taking into consideration the dilution effect when added.

In ferroboron, the iron isotope element ⁵⁴ Fe (natural abundance 5.84%) absorbs neutrons and becomes ⁵⁴ Fe (n,
p) The reaction produces radioactive ⁵⁴ Mn. this
⁵⁴ Mn has a long half-life and is a strong source of γ radiation, so if ⁵⁴ Mn migrates in the reactor,
This is a nuclide that poses a maintenance problem. From the viewpoint of nuclide generation in the radiation source, nickel boron does not cause any problems.

Further, according to the present invention, there is provided a silicon-doped nickel boron in which silicon Si is added in a range of 3 to 10% to the above-mentioned nickel boron.
In other words, this silicon-added nickel boron contains 2 to 15% boron B, 3 to 10% silicon Si, less than 0.1% aluminum as impurities, and carbon.
It contains 0.5% or less, with the remainder consisting of nickel components. Like nickel boron, this silicon-added nickel boron has a relatively low melting point, so it is not only effective as an additive raw material for nuclear reactor materials such as nickel-based alloy materials and steel materials, but also for joining nuclear reactor materials. It can also be preferably used as a brazing material. In other words, silicon has the effect of increasing its self-solubility when melted in relation to boron, so when silicon-added nickel boron is used as a joining brazing material, it reduces thermal distortion of the objects to be joined and increases heat resistance. This means that more effective joining construction with improved self-fusing properties can be carried out without causing damage. If approximately 1000° C. to 1200° C. is selected as the effective melting point range of silicon-doped nickel boron, the amount of silicon added is limited to approximately 7%, but the amount of boron in this case ranges up to approximately 4%. The silicon-added nickel boron in the examples described below had a melting point of 1040° C. when the silicon was 6% and the boron ( ^11B concentration 98%) was 4.8%. Considering the melting point, etc., the amount of silicon added to nickel boron is appropriately in the range of 3 to 10%, and the weight ratio of Si/B is preferably about 1.5.

Furthermore, considering the application of the bonding brazing filler metal made of silicon-added nickel boron of the present invention having a melting point of 1000°C to 1200°C to a nuclear reactor, for example, a fast breeder reactor, it is possible to Typical operating temperatures on the hot side of the structure are approximately 550
Since it can be regarded as ℃, the heat resistance as a brazing material is sufficiently maintained when used in a furnace.

<Examples> The present invention will be described in further detail with reference to Examples below.

Example 1 ¹¹ B concentrated boric acid (H ₃ BO ₃ ) powder with a value of ¹¹ B/( ¹⁰ B + ¹¹ B) of 98%, high-purity electrolytic nickel grains, and carbon powder for reduction necessary for refining were The mixture was mixed in the proportions shown in Table 1, and the mixture was reduced and dissolved in a high-frequency heating furnace filled with a high-purity argon atmosphere.

As a result of isotopic analysis of boron in nickel boron after melting, the ratio of ¹¹ B in total boron was 98.
It remained at %.

The melting point of the obtained nickel boron was 1027°C and the specific gravity was 7.5 [g/cm ³ ]. These characteristic values are sufficient for melting in a short time and uniformly mixing when added to a molten alloy as a raw material for a nickel-based alloy material or the like. Table 1 also lists these characteristic values.

In addition, the method for producing ^11B concentrated boric acid is as follows:
After precipitating boric acid from sodium borate, calcium borate, or crude boron, and purifying it by recrystallization, there is a method that utilizes the weight difference between ¹⁰ B and ¹¹ B, or a boron halide is prepared from boric acid. There are methods that make use of differences in chemical properties and other methods.

Table 1 Proportion of raw materials for manufacturing nickel boron Boric acid powder 40% (H ₃ BO ₃ , ^11B concentration 98%) Electrolytic nickel granules 55% Carbon powder 5% Characteristic values of nickel boron Total boron content (%) 10.6 ( 11.5) ^{* 11} B/( ¹⁰ B + ¹¹ B) (%) 98 (98) ^* Carbon content (%) 0.5 Aluminum content (%) 0.1 Melting point (℃) 1027 (1550) ^* Specific gravity (g/cm ³ ) 7.5 Note: *The numbers in parentheses are for feroborone prepared for comparison.

After degassing the nickel boron obtained above at the final stage of refining the nickel-based alloy material Hastelloy X,
45g was added per 100kg of molten metal. Nickel boron immediately began to melt after being added to the molten alloy. After the nickel boron was dissolved, samples for analysis were taken. As a result of boron analysis, the total boron content is
52ppm, and the proportion of ¹¹ B in the total boron is
It was 94%.

Example 2 The fine particles obtained by crushing the nickel boron obtained in Example 1, metal silicon particles and electrolytic nickel particles were mixed in the proportions shown in Table 2, and the mixture was heated in an electric atmosphere filled with a high-purity argon atmosphere. This mixture was reduced and melted in a furnace to produce an alloy ingot.

As a result of isotope analysis of boron in silicon-added nickel boron after melting, it was found that
The proportion of ¹¹ B remained at 98%.

The melting point of the obtained silicon-added nickel boron is
The temperature was 1014°C, the specific gravity was 7.85, and the boron and silicon contents were 4.1% and 6.0%, respectively. The amounts of aluminum and carbon as impurities were 0.04% and 0.01%, respectively. These characteristic values are sufficient for melting and uniformly mixing at a lower temperature in a shorter time than ferroboron when used as an additive raw material for nickel-based alloy materials and the like. It also has a melting point suitable for use as a nickel brazing material for joining nuclear reactor materials, and has a Si/B ratio (weight ratio) of approximately 1.5, a value that indicates good self-fluxability.

Table 2 Proportion of raw materials for manufacturing silicon-added nickel boron Crushed granules of nickel boron (Example 1) 40% Metallic silicon particles 6% Electrolytic nickel granules 54% Silicon-added nickel boron characteristic values Total boron content (%) 4.1 ¹¹ B/ ( ¹⁰ B + ¹¹ B) (%) 98 Silicon content (%) 6.0 Carbon content (%) 0.04 Aluminum content (%) 0.01 Melting point (℃) 1014 Specific gravity (g/cm ³ ) 7.85 <Effects of the invention> Above As can be seen from the description of ¹¹ B of this invention
By adding enriched nickel boron or silicon-added nickel boron to nuclear reactor materials used in neutron irradiation environments such as nickel-based alloy materials and steel materials, or by using it as a bonding material, ¹⁰ B in the material can be increased. It is possible to effectively contain ^11B without causing any oxidation.

In addition, instead of conventional addition of natural boron, the present invention's ^11B enriched nickel can be used in surface hardening alloys used in areas where self-fusion resistance and wear resistance are required, such as nickel-based Colmonoy alloys. By adding boron or silicon-added nickel boron as a raw material, the neutron irradiation resistance of the surface hardened alloy can be improved.

In addition, since the ^11B enriched ferroboron of the prior invention has iron as its main component, it could not be used in alloy materials for neutron irradiation environments, such as nickel-based alloys and steel materials, where addition of iron components is undesirable. By using the nickel boron and silicon-added nickel boron of the present invention, it becomes possible to effectively and economically add an appropriate amount of ¹¹ B to the above alloy materials. In particular, the nickel boron and silicon-added nickel boron of this invention have a lower melting point than ferroboron, so they can be easily mixed and dissolved into alloy materials in a shorter time, and furthermore, they can be used as a solder for joining parts in a neutron irradiation environment. When used as a material or its raw material, bonding can be performed under conditions with less thermal distortion.

In this way, in the ¹¹ B enriched nickel boron of this invention and the nickel-based alloy material obtained by adding silicon-added ¹¹ B enriched nickel boron, nuclear transmutation by the ¹⁰ B (n, α) reaction does not occur. Therefore, the favorable interaction between the added ¹¹ B and other component elements is maintained even in a neutron irradiation environment. Therefore, the addition of ¹¹ B to nickel-based alloy materials in neutron irradiation environments has become widely practiced, and this has accelerated the development of materials and structures with excellent neutron irradiation resistance. Become. By using such materials, it is possible to improve the safety and extend the lifespan of nuclear reactor internals used in a neutron irradiation environment as a key technology.

[Brief explanation of the drawing]

The accompanying drawing is a nickel-boron equilibrium diagram.

Claims (1)

[Scope of Claims] 1 Contains 2 to 15% by weight of boron B, 0.1% by weight or less of aluminum as impurities, and 0.5% by weight or less of carbon, with the remainder consisting of a nickel component, and the boron content is Nickel boron for addition to nuclear reactor materials such as nickel-based alloy materials and steel materials, characterized by containing -11 ( ¹¹ B) in an amount of 90% by weight or more and having a melting point of 1200°C or less. 2 2 to 15% by weight of boron B, 3 to 15% of silicon Si
Contains 10% by weight, 0.1% by weight or less of aluminum and 0.5% by weight or less of carbon as impurities, the remainder consists of a nickel component, and boron-11 ( ¹¹ B) is 90% by weight or more based on the total boron content. Nickel boron, which is characterized in that it has a melting point of 1200° C. or lower, and is used as an additive to nuclear reactor materials such as nickel-based alloy materials and steel materials, or as a brazing filler metal for bonding said nuclear reactor materials.