Nuclear fast reactor liquid metal cooled

 

(57) Abstract:

Usage: the invention relates to the field of nuclear technology and can be applied mainly for energy or research facilities using nuclear fast reactor. Essence: active area and side screen fast reactor liquid metal cooled, made the type of reactor in the form of a set of fuel reproducing and irradiation channels, located in the nodes of a regular or irregular lattice and separated that weakly absorb and subsumesa neutrons environment, for example, with an inert gas. Step placement of the channels is selected to provide close to zero (less than the effective delayed neutron fraction) or negative void coefficient of reactivity. As a result, significantly improves the security of fast reactor due to the guaranteed supply of negative values void reactivity effect, and improve reliability and performance system CPS. 3 Il., table 1.

The invention relates to the field of nuclear technology and can be applied mainly for energy or issledovatelskiy case of fast reactors with liquid metal coolant. The use of liquid metal, usually sodium, helps to provide a high energyproject fuel, high reproduction rate, increased the efficiency of thermodynamic cycle and does not require high pressure, which increases the safety of the reactor. The specific problem of rapid large reactors, primarily sodium cooled is large (in the above bn-800 5-6 EF) positive sodium void reactivity effect (NPAR), which negatively affects its safety in emergency situations with the devastation of the active zone or the boiling of sodium. The main reason for the positive NPAR is a small leakage of neutrons from the core due to the large size of the last reactor of high power (600 MW and above). The problem of positive NPAR compounded if the fast reactor is used for burning minor actinides (MA) isotopes of neptunium, americium, curium. It is shown that the increase in the content of MA in the active zone of 2% leads to an increase in the positive sodium reactivity at 20% Obvious and used in practice by solving the positivity NPAR is an increase in the leakage of neutrons from active), refusal end screens, placing special sodium cavity over the active area or inside the organization of gas volumes in the active zone (a project of the advanced liquid metal reactor ALMR based on the concept of PRISM).

In the invention (patent SU 1799178 A1, class G 21 C 1/02) the design of fast reactor liquid metal cooled with a porous active area. In this application to "deficiencies in the prototype (the bn-800 approx. ed.) with a dense arrangement of fuel assemblies containing the beam sterzenbach fuel rods to the coolant flow, the active area is made of materials, including fuel, having a small average cell density, i.e., increased effective porosity, and the porosity achieved by education in the core is empty (gazonapolnennyh) volumes in one of the following options nutritiona porosity or nutritiona in combination with midvalley or marcassite, and the porosity calculated in advance depending on the reactor power". Thus, for the implementation of the proposed patent N 1799178 design requires the creation of a special porous TVEL, which when compared with traditional fuel rod dimensions, will have a material is a, as a Cabinet-type fast reactor bn-800 with integrated layout that will lead to a significant increase in the size of the reactor vessel. The increase in the size of housing is particularly undesirable in the case of a heavy fluid, because it increases the seismic hazard for the reactor. The proposed method of introducing midvalley and marcassite porosity type reactor bn will lead to increased sodium and steel in the composition of the active zone and, consequently, to mitigate the spectrum and reduce the replacement rate. So in the variant with a porous active zone of reactor bn-800 [6] the volume of the active zone increased to 15600 l compared to 4840 l in bn-800 with a traditional layout, i.e., 3.2 times. Accordingly, and housing dimensions dimensions-reactor storage and storage for long-term spent fuel assemblies. Reproduction rate of the porous active zone (KVA) fell to 0.31, i.e., was one and a half times less than even the VVER.

As a prototype of the present invention describes the design of a nuclear reactor-fast breeder reactor bn-800 liquid metal (sodium) cooled. The reactor consists of an active area, the content is the totype are:

1. The presence of a positive sodium void effect at full load MOX fuel and in the presence of reproducing side and end screens.

2. Communication agencies cor circulation of the coolant, thus reducing the potential danger of the release of the bodies of CPS from the active zone.

3. A large amount of liquid metal coolant, concentrated in a single volume of the reactor vessel, creating increased seismic hazard and high hazard damaged casing.

The main technical problem to be solved in this invention is the elimination of the above disadvantages when:

any question at present and for the foreseeable future reactor power (up to 2000 MW El.) and for any physically justifiable share of MA in the fuel;

traditional for fast reactors worked well sterzenbach rods with large effective density of the fuel composition is adopted in the present loading of heavy atoms per unit length of fuel rod;

To solve the above problem is proposed fast reactor liquid metal cooled channel type. The layout of active areas, each individually to the BMC, CANDU, PGE-6, etc. For fast reactors with liquid metal cooling scheme of the reactor is still not used. Meanwhile, for this type of reactor channel layout seems to be the most simple and attractive compared to the channel layout of a thermal reactor.

First, the channel in thermal reactors, the space between the channels is filled with a moderator usually graphite or heavy water. For fast reactor this is not required, here the space between the fuel channels should be filled with that weakly absorb neutrons environment, for example, with an inert gas under low pressure, which greatly facilitates the design of the active zone, alleviates problems associated with overheating, burning, swelling, deformation of graphite or the production of tritium in the heavy water moderator.

Secondly, high energyproject fuel provided through the use of liquid metal coolant, allows for the same with thermal reactor power to decrease the number and height of the channels. Estimates show that when the power of the fast reactor of 1000 MW (e) will be enough to 160 channels with height actively the height of the active zone 700 see This allows to simplify the system inlet and outlet pipes.

Thirdly, the liquid metal coolant does not require high pressure, there is no boiling of the coolant, which allows for the manufacture of covers, fuel channels, inlet and outlet piping to use thin-walled tube, thus minimizing the parasitic capture of neutrons in the core and overall metal structure. Greatly simplified, and the problem of sealing the case.

In General, the design of the active channel zone, the system inlet and outlet pipes for fast reactor liquid metal cooled it seems much simpler (less bulky, less bulky) than the design of the operating channel reactors on thermal neutrons. Design and manufacturing technology of the latter are well tried and tested by many years of practice. This experience can be used to create channel of the reactor on fast neutrons.

The main advantages of fast reactors channel-type front hull (and the latter applies to the prototype fast reactor bn-800) are sleeky, energonapryazhennosti fuel becomes possible to optimize the leakage of neutrons from the active zone by choosing the size of the fuel channels and channels playback screen, and most importantly, through their step placement, achieving desired by the magnitude of the void coefficient of reactivity.

The physical reason for this phenomenon is the increase in the leakage of neutrons from the active zone with the vacuum lattice channels, i.e., the same as when using other known methods of reducing NPAR described above (flattening of the zone, refusal end of the screens, the introduction of sodium and gas cavities in the active zone, nutritiona porosity, supplemented by midvalley and marcassite porosity).

2. Channel layout is the possibility of individual adjustment of the coolant flow in the fuel channels, providing the optimum temperature for the fuel rods.

3. The space between the channels can be used for hosting CPS agencies and irradiation devices. Significant positive aspect is the independence of the organs of CPS from the first cooling circuit of the reactor, the control rods may not be actively ejected from the space can be used for ultrafast quenching of the reaction by introducing under pressure He-3.

4. The absence of a completed cooled reactor gives an important advantage of the channel reactor from the point of view of seismic stability especially when using lead-bismuth coolant. In case of damage to the reactor consequences from the devastation of the active zone or from the combustion of sodium will be much more severe than the damage to a single channel. Resource casing is limited by its radiation and thermal resistance. Replacement case energy installation is almost impossible, while the covers of channels can regularly as necessary, be replaced by a new and thus the lifetime of the reactor can be greatly increased.

5. There is a principal possibility (at least for the side of the screen) overload the reactor at power, thereby increasing its economic indicators.

6. Channel arrangement facilitates removal of residual heat in the event of termination of the circulation of the coolant in the first circuit, and also greatly simplifies the solution of the dispersion of the corium in the case of meltdown to prevent the formation of secondary Christmassy.

NH channels, sector 60 deg. where: 1 - the fuel channel 2 playback channel 3 irradiation channel, 4 - pin SMT, 5 biological protection; Fig.2 is an example of arranging the active zone channel fast reactor with a square lattice of the fuel channels, sector 90 deg. where: 1 fuel channel 2 playback channel, 3 - irradiation channel 4 pin SMT, 5 biological protection; Fig.3 - the dependence of the sodium void reactivity effect and critical plutonium content in MOX fuel from the spacing of the channels in the channel fast reactor with a triangular lattice of channels, with a capacity of 1000 MWe sodium cooled, where: 1 the dependence of the sodium void reactivity effect of the step location of the fuel channels, 2 the dependence of the critical plutonium content in MOX fuel from the spacing of the fuel channels.

Example link channel fast reactor with a triangular lattice placement of the fuel, reproducing and irradiation channels (not necessarily of equal diameter) and bodies CPS placed in the channel space, shown in Fig.1. A similar example for the channel reactor with a square lattice occupancy of the channels shown in Fig.2.

Topl is or natural uranium, thorium) is placed in the reproducing channels 2. Irradiation channels 3 are used for producing isotopes, burn actinides or long-lived fragments, irradiation of various materials. The cooling channels is performed by using liquid metal coolant supplied individually to each channel and pumped through them in the required quantity and at the required rate. The space between the channels are filled with an inert gas such as argon. Control of the chain reaction is carried out by using control rods placed in the space between the channels and independent of the first path. As a fast-acting emergency protection can be used for rapid filling of interchannel space absorbing gas such as He-3. The reactor is sealed in a concrete pit, lined with steel.

Thanks razrezhennogo placement of the fuel channels is increased leakage of neutrons from the core, thus providing a negative value sodium void reactivity effect.

Conducted computational studies of neutron-physical characteristics of variant channel fast), confirmed the possibility of achieving negative values of sodium void reactivity effect an appropriate step placement channels.

In Fig.3 shows the calculated dependence of NPAR from step placement of the channels for one of the alternative channel fast reactor with capacity of 1000 MW (e). The main parameters of the reactor are given in table.

The figure shows that with increasing step of placing channels the value of NPAR drops to zero and then becomes negative. Thus, for the above-described channel fast reactor when the spacing of the channels in a triangular lattice 48 cm, provided required by the rules of nuclear safety negative value sodium void reactivity effect.

It is important to note that this is an important security property is achieved using waste and spent long practice in existing fast reactors the size and design of fuel elements, at a moderate to fast reactors energonapryazhennosti fuel.

Nuclear fast reactor liquid metal cooled containing the active zone, side and end view for fuel, reproducing and irradiation assemblies placed in the nodes of a regular or irregular lattice and separated by a gas environment or vacuum.

 

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