Safety measures when using nuclear batteries. Disadvantages of an atomic power source

Back in the 50s of the last century, betavolta - a technology for extracting the energy of beta radiation - was considered by scientists as the basis for creating new power sources in the future. Today, there are real grounds to confidently assert that the use of controlled nuclear reactions is inherently safe. Dozens of nuclear technologies are already being used by people in Everyday life, radioisotope smoke detectors are an example.

And so, in March 2014, scientists Jae Kwon and Baek Kim, working at the University of Missouri, Columbia, USA, reproduced the world's first working prototype of a compact power source based on strontium-90 and water. IN this case the role of water is an energy buffer, which will be explained below.

A nuclear battery will operate for years without maintenance, and will be able to produce electricity through the process of decomposition of water molecules when they interact with beta particles and other decay products of radioactive strontium-90.

The power of such a battery should be entirely enough to power electric vehicles and even spacecraft. The secret of the new product lies in the combination of betavoltaics and a fairly new physical trend - plasmonic resonators.

Plasmons have been actively used in the last few years in the development of specific optical devices, including ultra-efficient solar cells, perfectly flat lenses, and special paint to print at a resolution many times greater than the sensitivity of our eyes. Plasmonic resonators are special structures capable of both absorbing and emitting energy in the form of light waves and other forms of electromagnetic radiation.

Today, radioisotope power sources already exist that convert the energy of the decay of atoms into electrical energy, but this does not happen directly, but through a chain of intermediate physical interactions.

First, the tablets of radioactive substances heat the body of the container in which they are located, then this heat is converted into electricity by means of thermocouples.

Lost at every step of the transformation great amount energy, from this the efficiency of such radioisotope batteries does not exceed 7%. Betavolta was not used in practice for a long time due to the very rapid destruction of parts of the batteries from radiation.

Research has shown that these decomposed portions of water molecules can be used to directly extract the energy absorbed by them as a result of collision with beta particles.

In order for a water nuclear battery to work, a special structure of hundreds of microscopic columns of titanium oxide coated with a film of platinum, similar in shape to a comb, is needed. In its teeth and on the surface of the platinum shell there are many micropores through which the named products of water decomposition can penetrate into the device. So in the process of battery operation, a series of chemical reactions- there is a decomposition and formation of water molecules, while free electrons appear and are captured.

The energy released during all these reactions is absorbed by the "needles" and converted into electricity. Due to the plasmons that appear on the surface of the columns, which have special physical properties, such a water-nuclear battery reaches a maximum efficiency, which can be 54%, and this is almost ten times higher than classical radioisotope current sources.

The ionic solution used here is very difficult to freeze even at fairly low temperatures. environment, which allows the use of batteries manufactured according to new technology, to power electric vehicles, and with the right packaging, in spacecraft for various purposes.

The half-life of radioactive strontium-90 is about 28 years, so Kwon and Kim's nuclear battery can operate without a significant loss in power for several decades, with a decrease in power of only 2% per year. Such parameters, scientists believe, open up a clear prospect for the widespread distribution of electric vehicles.

NUCLEAR POWER SOURCES

Energy application nuclear decay gives, in contrast to, for example, solar power sources, qualitatively different types of long-term space power plants. The fact is that the energy sources of space nuclear installations (a reactor or a radioactive isotope) do not receive this energy from space, but are, as it were, batteries. At the same time, a nuclear reactor is not a direct source of electricity. A reactor or isotope is a powerful source of heat. Receipt electric current in a nuclear power source is reduced to the conversion of thermal energy into electrical energy.

The nuclear power source will be located directly on board the OCS, and this makes it possible to receive energy almost continuously and regardless of any external factors.

Here we will not dwell on the principle of operation and the design of a nuclear reactor; quite a lot and in detail has been written about this. Consider only some ways of converting thermal energy into electrical energy.

Turbine generator set with a nuclear reactor is considered one of the most promising systems for long-term use in space, so we will consider it in more detail.

On fig. 31 shown circuit diagram such an installation, with a heat transfer agent and the working medium of which is a liquid.

Rice. 31. Diagram of a nuclear turbine generator set:

1 - reactor; 2 - boiler; 3 - pump; 4 - turbine; 5 - electric generator; 6 - refrigerator; 7 - pump

The heat released in a nuclear reactor is absorbed coolant primary circuit. The liquid heated to a high temperature enters the heat exchanger - boiler, where it gives off its heat working body secondary circuit. After that, the primary coolant pump high pressure is distilled back into the reactor.

The main operating cycle of the installation is carried out in the secondary circuit. The working fluid (also liquid) is first heated to the boiling point in the boiler, and then completely evaporates here. The steam that enters the working blades of the steam turbine drives an ordinary machine electric generator. The exhaust steam, after leaving the turbine, enters the refrigerator, where it is completely condensed, i.e., it turns into a liquid again.

As we have already said, the only way to release heat into the surrounding space in space is radiation. Therefore, the refrigerator of any space installation is a heat emitter. The working fluid, which has come to its original liquid state, is distilled by the pump back into the boiler. This completes the cycle of the main working circuit.

A scheme in which the main working fluid is not heated directly in the reactor, but receives heat through an intermediate coolant, is called double-circuit.

It is possible to use and single-loop a heat transfer scheme in which there is no primary circuit and the working fluid is heated and evaporated not in the boiler, but directly in the channels of the reactor fuel elements.

It is obvious that the single-circuit scheme is simpler and lighter, since it does not have a heat exchanger - a boiler and primary circuit lines. In addition, with such a scheme, it would be possible to significantly increase the heat removal from the heat-releasing surface of the reactor, to obtain a higher cycle temperature, and, consequently, a higher efficiency. But despite all these advantages, a single-circuit scheme cannot be applied to OKS. main reason- contamination of the system coolant with radioactive decay products and the occurrence of the so-called induced activity in the structural elements of the installation. And this entails an increase in the weight of anti-radiation protection for the crew and, in addition, makes it largely impossible to repair and preventive maintenance of the installation under operating conditions. With a two-circuit scheme, the main working fluid does not have direct contact with the nuclear reactor, and the secondary circuit of the system is quite accessible for maintenance.

The actual implementation of a space electrical turbine plant with a nuclear reactor is associated with the choice of a suitable working fluid for the main (secondary) circuit.

In ground nuclear power plants with a turbogenerator, water is used as a working fluid. But high corrosiveness, high vapor pressures (up to 280 atm and more), high induced radioactivity, and most importantly, low maximum cycle temperatures (not higher than 300 °C) make water completely inapplicable for space power plants.

The best properties are liquid metal coolants. Liquid metals: mercury, sodium, potassium, rubidium, cesium and some others have very high thermal conductivity, high latent heat of vaporization, low vapor pressures at high temperatures, which justifies their widespread use in the design of nuclear turbine generators. Anticorrosive properties and induced activity are also quite acceptable.

In principle, a turbogenerator circuit can be carried out not only on vapors of liquid metals, but also with gas as a working fluid - according to the so-called Brayton cycle, that is, as a gas turbine plant, which includes a compressor instead of a pump. But such a scheme, with some advantages (higher temperatures and high performance), has very significant drawbacks, in particular, a very large specific gravity.

The constructive solution of a turbogenerator nuclear installation can be considered using the example of the SNAP-2 system developed in the USA with an electric power of 3 kW (Fig. 32).

Rice. 32. Power plant SNAP-2:

1 - condenser tube; 2 - emitter; 3 - reactor core; 4 - additional heater; 5 - coolant pump; 6 - reactor reflector; 7 - load management; 8 - payload; nine - expansion tank; 10 - mercury pump; 11 - plain bearing and thrust bearings; 12 - stator of the electric generator; 13 - turbine; 14 - plain bearing; 15 - pump

The primary coolant is sodium-potassium alloy, the temperature of which at the outlet of the reactor is 650 °C. The coolant of the secondary circuit is mercury. Maximum temperature duty cycle 621 °C. Turbine - two-stage. The area of ​​the radiation cooler - emitter - 9.3 m 2 . The electric generator provides alternating current with a voltage of 110 V, a frequency of 2000 Hz.

The total efficiency of SNAP-2 is only 6.5%. This means that out of 50 kW of the thermal power of the reactor, about 47 kW is dissipated by the emitter or is used to heat the structure. Total weight SNAP-2 systems without biological protection - 270 kg (of which 90 kg falls on the reactor), i.e. the unit weight without protection is 90 kg/kW.

But even this rather high specific gravity of a nuclear installation will noticeably increase due to the weight of biological protection, which to a large extent depends on the location of the power plant at the station, as well as on the operating conditions, in particular, on the place where the reactor is launched - whether it will be produced on Earth or after launching the OCS into orbit.

The ground launch of a nuclear installation complicates the maintenance of the launch site, but provides conditions for full check operation of the entire power system.

Launching in orbit is associated with a decrease in the reliability of the entire energy system and quite difficult to implement. In the case of a launch on Earth, the crew, at the time of preparation for launch and in flight when passing through the atmosphere, must be completely protected not only from directed radiation, but also from its “splashing” by ambient air molecules, i.e., in practice, the protection must be circular, continuous. In orbit, only the so-called shadow protection of the crew is enough, the weight of which, obviously, is much less. In addition, in orbit, the power plant can be removed from the main structure of the OCS at a certain distance, for example, using a retractable telescopic rod or in another way. And since the thickness of the protection depends on the distance to the source of radiation, the weight of the shadow protective screen can be made even less. How much should the biological protection for the SNAP-2 turbogenerator weigh? It is calculated based on the allowable radiation dose for the crew. If we assume that the total dose for the OCS crew for three months should not exceed 15 roentgens, then the weight of protection when the reactor is crushed from the crew by 15 m will be from 200 to 450 kg, depending on the mutual layout of the reactor and the cockpit.

Thus, the total weight of the installation can reach 720 kg, and the specific gravity - 240 kg/kW. It should be noted, however, that with an increase in the power of the installation, these figures decrease significantly.

Turbine generator plant is not the only way to use the energy of a nuclear reactor in space. There are other ways to convert it into electricity. We will discuss these methods in the section on non-machine methods of energy conversion.

The energy of nuclear decay can be obtained not only in a reactor, but also with the help of radioactive isotopes. The main advantages of this energy source, applicable for small powers up to 0.5 kW), are low weight and long time continuous and stable operation.

The principle scheme for the use of isotopes is no different from the scheme of a turbogenerator plant with a reactor - the coolant is pumped through a special boiler with tubes made of a material saturated with an isotope, such as strontium-90 or cesium-144. But the scheme used in solar batteries can be used: a phosphor layer irradiated with heat from an isotope emits photons that fall on a silicon element similar to a solar battery. It is very difficult to obtain high electrical power with the help of radioisotopes, and hardly profitable, given the difficulty in obtaining isotopes and their high cost.