A validation of the possibility of developing and the basic advantages of a high-temperature nuclear reactor where the first-loop coolant is a solid are presented. The basic requirements for a solid coolant are formulated, a technology for fabricating spherical graphite particles by gas-phase pyrolytic deposition is developed, and three experimental batches are prepared. The experimental facilities for investigating the motion and heat transfer, including coolant flow stability, heat exchange, and durability, are described. The results of a determination of the heat-emission coefficient during the flow of the solid coolant in a 10-mm in diameter circular channel with warming-wall temperatures in the range 373-1073 K and flow velocities 0.1-0.22 m/sec in vacuum, argon, and helium are presented. The requirements for a 500-kW bench model, on which the basic parameters of the nuclear power system with a solid coolant are to be obtained, are formulated.If nuclear reactors are viewed as the main source of electricity and heat for purposes of global conservation of gas and oil and decreasing emissions of combustion products into the atmosphere, at least three problems must be solved:• the possibility of accidental emission must be eliminated and the escape of nuclides into the biosphere during operation of the entire chain of the nuclear cycle must be decreased; • the technological schemes for using the stores of nuclear fuel, which allow for economically competitive large-scale operation of nuclear power for a long period of time, must be validated; and • the possibility of using the nuclear components of power systems for producing nuclear weapons must be eliminated. The improvement of the currently widely used PWR is making these reactors more complicated and expensive, but nevertheless the probability of meltdown of the core of such a reactor is estimated to be 10 -5 yr -1 and the probability of radionuclides escaping over the last barrier in the form of a closed shell is 10 -7 yr. Estimates show that more than 10000 nuclear reactors will be needed to meet the world-wide demand for electricity. In this case, the probability of a serious accident with radionuclides escaping would be 10 -7 ·10 4 = 10 -3 , which is unacceptable for mankind. Accidents with escape of radionuclides beyond the last barrier must be eliminated if nuclear energy is to be used on a large scale.
The salient features of using a solid substance to cool the core of a nuclear reactor and the associated advantages and limitations are examined. Conceptual proposals concerning the core design and the arrangement of the in-reactor space of a high-temperature nuclear reactor with a solid coolant are presented. Evaluated data and some results for a model reactor are presented.The development of nuclear power requires an examination and development of innovative reactor designs which have enhanced safety due to the inherent properties of a reactor and are highly cost-effective. One interesting and promising proposal is to use a solid substance as the coolant [1].There are substantial advantages to using a solid coolant to cool the core of a nuclear reactor. These include the possibility of the coolant moving in the core under gravity and the absence of any need for excess pressure in the vessel. In turn, this means that the metal content of the system is low, the risk of accidents is lower, and the scale of the consequences of accidents is smaller. The core of a reactor can be cooled with a solid substance when certain conditions associated with the characteristic features of the solid coolant are satisfied. The most important requirements are uniform continuous motion of the coolant with minimum density fluctuations in all sections of the core, high mechanical strength and durability of the particles, and good heat-transfer indicators, i.e., the coolant material must have a high thermal conductivity and heat capacity under the working conditions characteristic for the core of a nuclear reactor.Studies of the possibility of using a solid coolant based on finely dispersed particles of graphite for cooling the core of a thermal reactor have revealed concrete conditions which are necessary in order to satisfy the main requirements for a solid coolant. A brief report on the results of such investigations is given in [2]. To prove that the proposed coolant can move under gravity as a dense layer with a high velocity and to study the durability of the particles, a complex of experimental works was conducted at the Research Institute and Scientific-Industrial Association Luch. The results of these investigations confirmed that a solid coolant consisting of spherical graphite particles with average diameter 1 mm coated with a pyrolytic carbon coating can move uniformly under gravity. When such a coolant is used, coolant velocities and heat-transfer coefficients which make it possible to obtain energy release density characteristic for high-temperature gas-cooled reactors can be
Questions of choosing a thermodynamic cycle and the working parameters for a high-temperature reactor with solid coolant are examined. The results of investigations showing that such a reactor can be used in a power-generating unit of a nuclear power plant with high unit capacity with well-understood turbine facilities operating on superheated steam are presented.The thermodynamic cycles and working parameters of a reactor facility for electricity generation based on an innovative design of a high-temperature nuclear reactor with solid coolant (HRSC) are examined in the present paper. A block diagram of a system with small, spherical, heat-carrying particles based on graphite and pyrolytic carbon and the technical aspects of such a scheme -proof that the coolant velocity can be acceptable under gravity only, experimental determination of the heat emission coefficients, preliminary studies of the durability and evaluation of the physical characteristics of the reactor facility -are presented in [1,2]. Microfuel and fuel compacts based on microfuel and graphite with dimensions adopted in the GT-MGR design (12.5 mm diameter, 50 mm height) were chosen as fuel at the first stage of the investigations. The conceptual questions concerning the engineering arrangement of the reactor setup, which make it possible to implement the advantages of solid coolant in the form of small heat-carrying particles moving through the core without special orientation, including passive cooldown, are presented in [2,3].It should be noted that using a solid coolant in reactors with coarse-elemental graphite coolant was studied in 1974-1988. The conceptual ideas presented in [4][5][6][7] proposed reactors constructed with massive elements which move along a circle in a horizontal plane on special rollers and cyclically heated in the core followed by heat transferred to a secondary coolant by means of radiation.The thermal diffusivity of a heat-carrying element with finite dimensions determines the characteristic heat transfer time and is inversely proportional to a squared characteristic linear dimension. It is difficult to make heat transfer by large elements cost-effective because of the high thermal inertia. The reactor construction examined employs small particles with thermal relaxation time ~0 .15 sec, moving through the core under gravity with direct contact with fuel elements, which fundamentally distinguishes it from previous designs [4][5][6][7]. We recall [3] that in accidents with complete loss of electrical power the reactor is cooled down using a standard scheme within ~100 sec as a result of excess coolant in the top hopper. The temperature of the fuel elements in an accident with protection actuated in 6 sec increases slightly above the nominal values. The concept provides for bottom hoppers for the coolant, which are designed to hold the entire coolant volume. If the protection is not actuated, the reactor is suppressed as coolant flows down into the bottom hoppers. Since the coolant is the main moderator, this occurs befor...
Large-scale production of parts from powders and powder steels, in which parts are shaped in presses is considered. The three processes for production of the parts are analyzed. At two of them preforms are formed from the powder, they are sintered and the parts are punched from the sintered preforms. In the first process is used hot forging, in the second process used cold forging. The advantage of cold forging is demonstrated. The durability of the tool during cold forming is not sufficient to produce of parts from powder steels. The ways to reduce of stresses in the tool are described. The third process comprises forming from powder of the final shape parts and their sintering. Such process is applied for parts from powder steels. However in this process the parts have large porosity, which reduces their strength and reduces the efficiency of heat treatment. The method for reducing of the parts porosity as they are formed is described.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.