Evaluation of the technological parameters of a high-temperature reactor with solid coolant in the electricity generating regime

Abstract

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...

Investigation of the thermal inertia and thermal stresses of heat-transferring elements in a solid-coolant nuclear reactor

“…The effect of turning of the particles can be even greater, but no simple methods of evaluating it have been found. On the basis of calculations and the arrangement of the experimental facility, it can be concluded that the experimentally determined heat-emission coefficients for particles with diameter about 1 mm do not contain any errors due to thermal inertia, and the effect of thermal inertia is negligibly small in computational assessments of a power reactor [3]. However, thermal inertia and internal stresses in heat-carrying elements grow very rapidly as the size of the elements increases.…”

“…The basic ideas of the reactor design and assessment of the actually attainable technological parameters are presented in [2][3][4], and the experimental results of a study of the thermophysical characteristics of the flow of heat-carrying particles are presented in [5]. The particulars of the proposed nuclear reactor are as follows:…”

“…Heat-carrying particles with diameter 0.85-1.1 mm and nominal thermal constant 0.1-0.15 sec for experimental work were also fabricated at the Luch. The experimental results were used for computational evaluations of nuclear reactors [2,3] as well as estimates of the wear of the heat-carrying particles.…”

“…The change of temperature and rate of heating and cooling is taken for the reactor parameters of [3] -temperature 370°C at the entrance into the core and 760°C at the exit, velocity of the particles in 6-m high core 0.15-0.17 m/sec, which presumes an average and maximum heating rate 20°C/sec and 30°C/sec, respectively, and rate of decrease of the temperature in the steam generator 5°C/sec. The power distribution over the height is assumed to be nearly nonuniform with K z = 1.6.…”

“…The heat emission coefficient in the core was taken to be 600-1000 W/(m 2 ·°C), which corresponds to the experimental heat emission coefficient for coolant velocity 0.1-0.22 m/sec in helium as the medium. The passage time of the coolant through the core was assumed to be 20-40 sec, the maximum time corresponds to core height 6 m with velocity 0.15 m/sec, and the minimum time corresponds to 0.2 m/sec at height 4 m. The cooling conditions in the steam generator are based on an analysis of the experimental heat-emission coefficients at low velocity of the heat-transmitting particles and nominal characteristics of the steam generator [3]. The passage time of the heat-transmitting particles through the steam generator is taken for the two variants as 100 and 50 sec, respectively.…”