Nuclear fuel shell with high specific heat conductivity and method of its production. RU patent 2504030.

FIELD: power engineering.

SUBSTANCE: shell is fully or partially made of a composite material with a ceramic matrix containing fibres of silicon carbide (SiC) as reinforcement of the matrix and a phase-to-phase layer between the matrix and fibres. The matrix contains at least one carbide selected from titanium carbide (TiC), zirconium carbide (ZrC) or triple carbide of titanium-silicon (Ti₃SiC₂). The method to manufacture a shell of nuclear fuel includes, in particular, manufacturing of a fibre pre-mould, application of a phase-to-phase layer on it with chemical steam infiltration, application of the matrix.

EFFECT: reliable mechanical retention of products of nuclear fuel fission inside a shell during radiation, at the same time optimal transfer of heat energy to coolant is provided.

2 cl, 2 dwg

FIELD OF THE INVENTION

This invention in General relates to the field of nuclear fuel and, in particular, it refers to the shell of the nuclear fuel for cooled helium «high-temperature nuclear reactors, as well as to method of its production.

BACKGROUND OF THE INVENTION

Among the nuclear reactors of the future can be noted fast reactor (FNR), which uses helium as a gas carrier (the so-called reactor "He-GFR"). This reactor is a so-called «high temperature» of the reactor, as during job temperature it the active zone, as a rule, is in the range between 800 degrees C and 1 200 C

As described in the patent application EP 1913600, shell nuclear fuel used in such reactors could be completed in the form of plates, cylinder, sphere or network cavities.

At influence of temperature conditions above, this shell requires the use of high-melting refractory materials (to provide sufficient mechanical stability for holding the fuel inside containment) and must have a high specific heat conductivity under irradiation (for the optimal transfer the generated heat energy in the direction of the gas coolant during operation of a nuclear reactor).

Ceramics, although it meets those criteria, usually is too fragile to withstand working conditions shell nuclear fuel.

Indeed, the reaction of fission in nuclear fuel generate solid and gaseous fission products, causing swelling of the shell. When exposed to such loads ceramics, forming a shell, can break down and cause a loss of sealing fuel.

To prevent such a loss could benefit from composite material on ceramic matrix (CMC) type SiC f /SiC to achieve enhanced mechanical properties. Such material is usually made from a two-dimensional or three-dimensional structure of fibres, of silicon carbide (SiC-called f ), which contributes to hardening of ceramic matrix SiC, in which it is included.

However, for any given temperature, thermal conductivity CMC type SiC f /SiC can be significantly reduced after he will be subjected to irradiation.

During operation of a nuclear reactor "He-GFR", exposed to high temperatures, such CMC has proved that they are unsuitable for transfer of thermal energy from the shell of nuclear fuel to gas heat carrier.

SHORT DESCRIPTION OF THE INVENTION

Therefore, one of the purposes of this invention is to provide a wrapper nuclear fuel, fully or partially made of composite material, which when exposed to radiation and temperatures between 800 degrees and 1200C C can mechanically keep the fuel inside the shell, while providing an optimal transfer of the generated thermal energy of the gas heat-carrier.

Thus, the subject matter of the invention refers to the shell of the nuclear fuel, fully or partially made of composite material on ceramic matrix, including carbide silicon SiC, fiber as reinforcement for the matrix and the interphase layer provided between the matrix and filaments, and the matrix includes at least one carbide, selected titanium carbide TiC, carbide zirconium ZrC or triple titanium carbide-silicon Ti 3 SiC 2 .

As shown below, and irradiation temperatures between 800 degrees C and 1200C C (preferably between 800 degrees C and 1,000 degrees Celsius, or even equal to 800 degrees C) shell nuclear fuel on a given invention has specific thermal conductivity that improves heat transfer to the heat carrier, at the same time keeping thermomechanical (high melting point) and mechanical (reduced fragility) properties inherent to the CMC and provide optimum sealing fuel inside the shell.

According to their preferred option for implementation of a composite material, on ceramic matrix additionally includes silicon carbide SiC. For example, the number of silicon carbide SiC less than 50% (typically 1% to 50%) by volume matrix, preferably less than 25% (typically from 1% to 25%)and an even more preferably less than 10% (typically from 1% to 10%). Adding variable quantities SiC allows to optimally adapt the matrix properties (such as thermal conductivity) under the prevailing conditions. The inclusion of SiC in the matrix also allows to improve its compatibility with the fibers of the SiC: for example, matching coefficients of thermal expansion allows us to reduce the effects of relative expansion between the matrix and filaments, which can lead to the destruction of the shell of nuclear fuel.

In a preferred embodiment silicon carbide SiC in the matrix is between 5% and 15% on a volume of a matrix (especially if the matrix contains TiC). As shown below, the composition of the matrix allows to achieve optimal thermal conductivity.

Optional matrix has a bar microstructure.

Fiber, they can be fully or partially ordered. So, they tend to come from the fibre pre-form that is most often made of fibers instead be randomly ordered. So, in particular, the fibers can be in the form such as two-dimensional fabric (for example, basketry), fabric (such as woven fabric, which is then sewn), three-dimensional fabric, knitted fabric or felt.

Preferably fibers are in the shape of plaiting or voylokov when the shell of nuclear fuel has the form of tubes or plates, respectively.

With respect to their composition, the fibers are made of SiC, so that they are especially suitable to the situation of this invention, since the SiC has excellent resistance to neutrons and heat.

In addition, between fibers and matrix provides the interphase layer.

This layer can be fully or partly made of the connection, including several of superimposed layers, this connection is preferably pyrolytic.

Imposed by the nature of these layers can be:

- is caused by the structure inherent connection (namely, because this combination of nature has this type of structure as in the case of pyrocarbon, which is necessarily composed of graphite planes: such a structure is then called lamellar), or

- obtained through the method of production connection (method, which can be, for example, pulse method CVI described below: such a structure is then called the structure of wafer).

The interphase layer can have an average thickness in the range between 10 nm and 500 nm, preferably between 10 nm and 50 nm, and even more preferably between 10 nm and 30 nm, in accordance with the decrease of the thickness often leads to the improvement of the mechanical properties.

The porosity of a composite material, forming the whole or part of the skin of nuclear fuel on the invention, preferably 10% or even 5%) by volume or less, to contribute to the high thermal conductivity.

An additional objective of this invention is to provide a method to shell production of nuclear fuel on a given invention. This method includes the preparation of a composite material according to the following consecutive stages:

a) the manufacture of fibrous preprinted form of fibers,

b) application of the specified interphase layer through a chemical steam infiltration in preliminary form,

c) application of this matrix by means of chemical steam infiltration to the specified preliminary form, covered by a specified interphase layer.

Preliminary form of fiber typically has a geometry, close to the geometry of the shell of nuclear fuel, which must be made. So after it carried out a way of the invention, this shell often is in its final form or requires a maximum of several operations regrinding.

Preferably, chemical steam infiltration stage C) carry out, using a mixture of initial substances, including (i) at least one compound selected from the compounds based on titanium, zirconium, or silicon, ii) hydrocarbons and iii) hydrogen.

More preferably these substances are those that:

connection titanium is at least one connection, selected from TiCl 4 , TiBr 4 or Ti[CH 2(CH 3 ) 3 ] 4 ,

connection of zirconium is at least one connection, selected from ZrCl 4 , ZrBr 4 or Zr[CH 2(CH 3 ) 3 ] 4 ,

- a compound of silicon is at least one connection you selected from the SiCl 4 , SiH 2 Cl 4 or CH 3 SiCl 3 ,

- hydrocarbon is at least one connection you selected from the CCl 4 H 2 , CH 4 , With 4 N 10, or 3 N 8 .

Preferably at least one of the chemical steam infiltration (namely, infiltration, carried out for the manufacture of interphase layer according to the stage of (b) or carried out for the application of the matrix as in step C)is impulsive type.

Other objects, peculiarities and advantages of the present invention will become more apparent from the following description which is given by a non-limiting example.

SHORT DESCRIPTION OF THE SHAPES

Figure 1 shows the change in thermal conductivity of ceramic materials on the basis of TiC as a function of temperature for different shares of SiC.

Figure 2 shows the change in thermal conductivity at 800 degrees irradiated ceramic materials on the basis of TiC as a function of the share of SiC.

THE DETAILED DESCRIPTION OF INDIVIDUAL EMBODIMENTS OF THE INVENTION

The following examples illustrate the part of the production method according to the present invention, in which prepared a composite material on ceramic matrix (CMC)intended for introduction into the composition of the shell of nuclear fuel.

As discussed above, the application of the fibre pre-form, having the form and the sizes close or identical to those of shell nuclear fuel, allows to receive at the end of the mode of production on a given invention such a membrane in the form of work or even in its final form.

Applying CVI, carbide can be formed from the initial substances and then applied on fiber preliminary form. Such substances are typically available in gaseous form.

A particular case of the CVI is pulse CVI, such as is described in the EP 0385869 or "T.M. Besmann, Ceram. Trans., vol. 58, pages 1-12, 1995".

In the pulse CVI source substances carry a sequence of pulses to the reaction vessel (e.g. microwave). For each pulse pressure of initial substances inside the furnace varies over time according to the following three phases:

phase 1: increase pressure to the working pressure (usually a few kPa)to enter the initial substances;

- phase 2: maintenance of working pressure (stage during which put carbide);

- phase 3: reduce the pressure to unload excess of the original substances.

1.1 - Production of CMC type SiC f /TiC

Applying the method of CVI, fiber preliminary form, made of ordered fibers silicon carbide SiC cover the interphase layer, with an average thickness of several tens to several hundreds of nanometers, which consists of a plate connection such as pyrolytic (Rus).

Lament advance form then placed in an oven at 1050°With walls and expose the pre-evacuation.

After that, applying pulse CVI, produce CMC matrix by means of drawing under the operating pressure of 5 kPa titanium carbide 1 through reaction, starting with gaseous initial substances TiCl 4 , CH 4 and N 2 , originally contained in a vessel for mixtures under pressure 40 kPa.

To obtain a more uniform coverage carbide, depending on the composition and microstructure preferable to limiting the speed of operation at low temperatures (typically in the range between 900 C and 1200 degrees C) and under the low working pressure (typically in the range between 1 kPa 10 kPa).

It should be noted that the parameters are different from the temperature and pressure, can also influence the uniformity carbide coating. In particular, it is the nature of hydrocarbon, carbon fraction, and the dilution factor.

So, for example, for the application of TiC:

- carbon fraction m C/Ti , equivalent to a ratio of the number of carbon atoms to the amount of titanium atoms in gaseous mixture of initial substances, although it varies depending on the hydrocarbon in General should be in the range between 1 and 18;

- dilution ratio corresponding to the ratio of the total concentration of initial substances concentration TiCl 4 , expressed in mol/l (or alpha=([TiCl 4 ]+[CH 4 ]+[H 2 ])/[TiCl 4 ]), should normally be in the range between 15 and 100.

Consumption of carrier gases, CH 4 and, especially, N 2 , and managing the temperature of boiling TiCl 4 allow you to control the flow TiCl 4 and, thus, a dilution factor and carbon fractions m C/Ti .

The pressure in the furnace also depends on the flow rate, as well as from the time of opening the stop valve.

In this case, the application parameters are the following:

average consumption carrier gases=30 l/h,

- opening the stop valve (phase 1)=0.2 to 0.3 seconds,

- exposure time (phase 2)=4 to 5 seconds

- time pumping (phase 3)=1 second,

- thickness of coating on the pulse=1.5 nm,

m C/Ti =9,

- application speed=approximately 1 m/hour.

So received CMC type SiC f /TiC, in which the matrix is made of stoichiometric TiC and has a bar microstructure and average thickness of 40 microns.

1.2 - Production of CMC type SiCf/ZrC

Working conditions similar to those described in the previous example, can be used for the preparation of the CMC, in which the matrix contains carbide zirconium ZrC. The only specific parameters in this case are the following:

- ZrCl 4 , With 3 N 6 , gas N 2 and Ar in equivalent amounts /1600 OC/ m C/Zr =0,5 (speed of less than 14 m/hour); or

- ZrBr 4 , CH 4 , N 2 , Ar / 1,000 degrees C-1500 C / 1-10 kPa.

1.3 - Production of CMC type SiC/TiC-SiC.

In this case prepare CMC, in which the matrix has a mixed composition, such that it contains and titanium carbide TiC, and silicon carbide SiC.

Pulse CVI is especially well suited for the production of mixed matrices due to a slight change in the proportion of TiC to SiC through changes, for example, the number of pulses depends on the source of substances for each of these carbides. This feature is used to prepare three mixed SiC f /TiC-SiC CMC, in which the matrix had the following composition TiC/SiC volume%: 90/10, 75/25, 50/50.

Consider a few of the modes of application of impulse CVI.

In the first variant of the implementation of the number of pulses in each of the sequences of the application of TiC and SiC reduced so that the coat was not continuous.

Application conditions in TiC the same as those mentioned in the preceding example.

For the application of SiC and conditions similar to those applying TiC, except for the following settings:

- gaseous substances: N; and MTS ( formula CH 3 SiCl 3 ),

- temperature of 900 C to 1050°C,

- operating pressure of 1.5 kPa up to 5 kPa,

- alpha SiC (P H2 /P MTS ) 1/4 to 5 (1/4 to 1/2 visible education of residual carbon, and above 3 no no residual carbon. However, the application speed increases with the α sic ).

It should be noted that the speed of drawing a layer of SiC proportional to the shown values of temperature and pressure.

In this case parameters, effectively used for the application of SiC are the following:

- temperature = 1050°C,

- working pressure=4 kPa,

- alpha sic (P H2 /P MTS ) = 0,5,

- the average thickness of coating on the pulse = 3 nm,

- application speed = approximately 0.3 to 1 m/hour.

The structure of the pulse sequence is the following: 2 pulses for the application of TiC, then one impetus for the application of SiC.

Received mixed matrix made from stoichiometric SiC and TiC and has an average thickness of 40 microns.

In the second variant of implementation are made consistent application of nanolayers, namely the application, in which the layers with different characteristics, have an average thickness of 10 to 100 nm, applied consistently. With this purpose consistently produce pulses of initial substances, separately intended either for a TiC, or SiC (for example, 40 impulses for the SiC and 80 pulses for a TiC, or 20 pulses for the SiC and 40 impulses for TiC).

In the third variant of the implementation of the initial substances for the SiC and TiC are administered together. As a rule, the starting materials and the operating conditions in this case, choose from the following:

- TiCl 4 , SiCl 4 , CCl 4 H 2 /950°-1150 C/100 kPa,

- TiCl 4 , SiCl 4 , C 3 H 8 , N 2 /950°-1150 C/4-40 kPa,

- TiCl 4 , SiCl 4 , CH 4 , H 2 /950°-1150 C/7 kPa,

- TiCl 4 , SiH 2 Cl 4 , With 4 N 10 , N 2 / 950°-1150 C/100 kPa,

- TiCl 4 , CH 3 SiCl 3 , H 2 / 950°-1150 C/1 kPa-100 kPa,

- TiCl 4 , SiCl 4 , C 3 8 H , H 2 / 950°-1150 C/100 kPa.

2 Thermal properties of composite materials on ceramic matrix (CMC), containing TiC

Ceramic materials (without fibers and interphase layers) with the same composition, and the matrix of four CMC on the basis of TiC made earlier, produce sintering under pressure.

Four ceramic material have the following composition TiC/SiC volume%: 100/0, 90/10, 75/25, 50/50.

These ceramic materials allow to determine relative specific conductivity four manufactured earlier CMC on the basis of TiC, because even despite the fact that the absolute value of their specific differs from that of the corresponding CMC, their relative values comparable. In other words, the behavior of thermal conductivity of these ceramic materials in relation to each other like and indicate the behavior of four previously prepared CMC.

In practice, the measured thermal diffusivity of ceramic materials at different temperatures.

Given the density and mass heat capacity (identified Cf) these ceramic materials, the specific thermal conductivity is calculated by the formula k=a·ρ·Cp, where:

- k is thermal conductivity (W·m -1 K -1 ),

- a is thermal diffusivity (m 2 ·-1 ),

= - density (kg m -3 ),

- Cp is the specific heat capacity (j kg -1 ·-1 ).

Formula Cp(T) for the TiC and SiC are the following:

P =0,7415+0,00114T-1,57655 X 10 -6 T 2 +1,14714 X 10 -10 T 3 +7,05467 x 10 - 13 T 4

If the ceramic material has a mixed composition (for example, 75% TiC + 25% SiC), its mass heat capacity is a weighted average mass of heat capacity of each of the carbides.

After the calculation of gain change of thermal conductivity (trend curves) depending on the temperature, as shown, for example, in figure 1.

From Figure 1 we can conclude that the addition of the increasing number of titanium carbide TiC in a matrix of unirradiated CMC type SiC f /TiC-SiC allows thermal conductivity of such CMC to grow despite the temperature increase, in particular for temperatures ranging between 800 degrees and 1200 OC and to the content of TiC more than 50%.

The following measurement of thermal conductivity have confirmed this behavior ceramic material after irradiation.

These measurements were carried out according to the same procedures on five irradiated ceramic materials, namely four previous ceramic materials and one ceramic material made from 100% SiC (that is, for ceramic materials with the following bulk composition TiC/SiC: 100/0, 90/10, 75/25, 50/50, 0/100).

Irradiation was modeling of neutron flux through the implementation of Kr ions with energy 74 MeV, so as to achieve the irradiation dose 1 dpa (substitution per atom), to create two zones of damage namely, one for nuclear interactions (which simulates damage neutron) and one for the electronic interactions. Specific thermal conductivity was measured at 800 degrees C in nuclear interactions.

The results are summarized in figure 2. They show that thermal conductivity at 800 degrees C irradiated ceramic materials containing TiC and SiC, improved by increasing the share of TiC. Found that the ceramic material having a bulk composition 90% TiC + 10% SiC (typically, material, consisting of 95%-85% TiC, while the remainder is SiC, by volume) is the optimal specific conductivity.

Additional results also showed that after ion irradiation Au (4 MeV, 8 dpa) thermal conductivity at 800 degrees C ceramic material made of TiC, more than ceramic material made of SiC.

Thus, it appears that for the production of casings of nuclear fuel application of composite material on ceramic matrix containing fiber SiC, phase transfer layer, and the matrix, comprising of at least one carbide, selected titanium carbide TiC, carbide zirconium ZrC or triple silicon carbide titanium Ti 3 SiC 2 , allows to improve specific thermal conductivity of the specified shell under the action of radiation at temperatures usually in the range between 800 degrees C and 1 200 C

During reactor operation, "He-GFR" shell nuclear fuel according to the present invention may accordingly, thus, mechanical withhold nuclear fuel and to ensure heat transfer to the gas heat more effectively than in the case of a cover made of CMC type SiC f /SiC.

1. Shell nuclear fuel, fully or partially made of composite material on ceramic matrix, including silicon carbide SiC, fiber as reinforcement for the specified matrix and phase transfer layer provided between the matrix and these fibers, thus, the matrix contains at least one carbide, selected titanium carbide TiC, carbide zirconium ZrC or triple titanium carbide-silicon Ti 3 SiC 2 .

2. Shell nuclear fuel according to claim 1, where the specified matrix additionally contains silicon carbide SiC.

3. Shell nuclear fuel in paragraph 2, where the specified silicon carbide SiC is less than 25% of the volume specified matrix.

4. Shell nuclear fuel pursuant to clause 3, where silicon carbide SiC is less than 10% of the specified matrix.

5. Shell nuclear fuel pursuant to clause 3 of the silicon carbide SiC is between 5 and 15% of the volume specified matrix.

6. Shell nuclear fuel according to claim 1, where the specified matrix has a bar microstructure.

7. Shell nuclear fuel according to claim 1, wherein said fiber fully or partially ordered.

8. Shell nuclear fuel according to claim 1, the phase transfer layer fully or partially consists of compounds containing several superimposed layers.

9. Shell nuclear fuel according to claim 1, the phase transfer layer has an average thickness of between 10 and 500 nm.

10. Shell nuclear fuel according to claim 1 of the composite material porosity 10% or less.

11. Method of production of casings of nuclear fuel on any one of claims 1 to 10, including the preparation of a specified composite material according to the following consecutive stages: a) make a lament the preliminary form of the fibers, b) cause the specified phase transfer layer through a chemical steam infiltration to the specified preliminary form, c) put the specified matrix through chemical steam infiltration to the specified preliminary form, covered by a specified layer.

12. Production method according to claim 11, where specified chemical steam infiltration stage c) carry out, using a mixture of the original substance, containing (i) at least one compound selected from the connection on the basis of titanium, zirconium, or silicon, ii) hydrocarbons and iii) hydrogen.

13. Method of production by 12 where: - the connection specified titanium is at least one connection, selected from TiCl 4 , TiBr 4 or Ti[CH 2(CH 3 ) 3 ] 4 , - specified connection zirconium is at least one connection, selected from ZrCl 4 , ZrBr 4 or Zr[CH 2(CH 3 ) 3 ] 4 , - specified connection silicon is at least one connection you selected from the SiCl 4 , SiH 2 Cl 4 or CH 3 SiCl 3 .

14. Method of production according to paragraph 12 of the hydrocarbon is at least one connection you selected from the CCl 4 H 2 , CH 4 , With 4 N 10, or 3 N 8 .

15. Production method according to claim 11, where at least one of the chemical steam infiltration infiltration is impulsive type.