Nuclear reactor fuel element simulator

FIELD: physics.

SUBSTANCE: fuel element simulator has a shell in which there is a column of natural fuel tablets with a centre hole, and an electric heater placed with clearance in the holes of the tablets. The heater is in form of pipe made of heat-resistant material on the outer surface of which is formed a microrelief which varies on the length of the heater and which provides optically variable properties on the length of the surface, which correspond to the simulated temperature profile. A shielding pipe made of heat-resistant material is also placed with clearance on the outside coaxial to the shell, the inner and outer surfaces of said pipe also having a varying microrelief which provides optically variable properties on the length of the heater.

EFFECT: high accuracy of simulating the thermal state of fuel elements under investigation by obtaining temperature levels, thermal flux and temperature profiles similar to those in full-scale conditions.

7 cl, 2 dwg

 

The invention relates to the field of thermophysical studies and can be used when studying the behaviour of fuel elements (cartridges) of nuclear reactors experimental modelling of thermal and gas-dynamic processes.

Known simulator fuel element of a nuclear reactor containing the shell, tablets natural fuel, the internal cylindrical heater located with clearance in the holes in the tablets, and the current-carrying nodes (see Gontar A.S., Kamnev A.A. and other uranium Dioxide with controlled restructuring as part of TVEL thermionic reactor Converter. International conference "Nuclear power in space", Moscow - Podolsk, March 1-3, 2005, proceedings, Vol.2, s-268).

A disadvantage of the known simulator is incomplete modeling, because the device does not allow to reproduce the profile of the change in heat flow along the length of a fuel rod, typical field operating conditions.

To simulate the temperature profile (heat flux) along the length of the simulator used heaters with variable length heat dissipation when current passes through the heater. Known simulator containing the tubular shell is placed inside the electric heating element made in the form of a filling of a mixture of powders of graphite and refractory IU is Alla, and separating the shell and the heater layer of insulating material (see Balashov S.M. and other Simulator fuel element of a nuclear reactor, RF patent 1499569, IPC6G21C 17/06, publ. 20.10.1999). The change in the ratio of powders of graphite and metal in a mixture of backfill required to reach a given temperature profile distributions of electrical resistivity backfill along the length of the simulator.

A disadvantage of such a simulator is the difficulty of obtaining fillings with a stable density at longer simulator and small diameters of the electric heating element; the violation of homogeneity of the density leads to overheating and destruction of the simulator.

Known simulator fuel element of a nuclear reactor containing the shell of stainless steel, internal heater with variable electrical and physical properties along its length, ceramic insulators and current-carrying nodes (see Boltenko E.A., Sevalkin SV and other Simulator fuel element of a nuclear reactor, RF patent №2168776, IPC7G21C 17/00, NV 3/48, publ. 10.06.2001). For modeling non-uniformity of heat dissipation along the length of the simulator ceramic insulators made in the form of sleeves of variable thickness at constant outer diameter, and the heater in the molten state fills the cavity of the bushing and therefore has p the value of diameter along the length of the simulator.

A disadvantage of the known simulator is the complexity of its filling of fusible material and the penetration of the liquid into the gap and cavity design. The latter excludes the possibility of research in this simulator behavior of full-scale pellet fuel, because the presence of liquid contact of the tablet shell is not consistent with the real operating conditions of the fuel element.

On the task being solved and essential features to achieve a technical result closest to the proposed simulator fuel element of a nuclear reactor containing the tubular sheath with the heater core or tube of electrically conductive material with a variable length cross-section, and the current-carrying nodes (see Boltenko E.A. electrically heated fuel elements for research and hydraulic characteristics of power plants. Atomic energy, t, issue 3, 2009, s-177). The heater is made of rods of different diameters, connected in series by welding. Due to the different temperature of the heater in areas with different resistivity select the distribution profile of the heat flux along the length of the simulator, simulate field.

The cross-sectional area of the heater in the known construction is changed stepwise, and the profile of the heat flux is a stepped, that does not correspond to the natural conditions of a fuel rod. In addition, distortion of the profile of the heat flux on the parts welded joints unacceptably large. Thus, the main disadvantage is selected as the prototype simulator is unsatisfactory accuracy of the simulation of field conditions.

The task of the invention is to improve the accuracy of modeling the natural thermal regimes of the fuel elements.

This object is achieved in that in the simulator fuel element of a nuclear reactor containing shell, a pillar tablets natural fuel with a Central hole and located with clearance in the holes tablets electric heater according to the invention, the heater is made in the form of a tube of refractory material, the outer surfaces of which are formed of alternating along the length of the heater microrelief, providing optically variable properties along the length of the surface, corresponding to a simulated temperature profile.

The task is achieved by the fact that the outside with a gap coaxial sheath is mounted a braided tube of refractory material on the inner and outer surfaces of which are formed of alternating micro, providing optically variable properties along the length of the heater.

In private versions displaced the tion along the length of the microrelief may be formed by the surface areas with different levels of roughness, the corresponding classes of roughness from the first to the fourteenth, or applied to the surface coating with variable density and thickness, or performed on the surface of the grooves of variable depth grooves to their diameter.

Shielding pipe can optionally be equipped with an Autonomous power source, and its outer surface may be provided along the entire length of the multilayer foil shields refractory material, made in the form of a winding with a variable number of layers.

Running a heater in the form of a tube of refractory material, the outer surfaces of which are formed of alternating along the length of the heater microrelief, provides a simulation of the temperature profile and heat flow corresponding to the standard fuel rods. Shielding pipe installed outside the shell, shaped along the length of the microrelief formed on inner and outer surfaces, performs the role of the first screen and allows to control the distribution of heat flow along the length of the simulator. Smooth change of the optical properties of the surface of the heater and a shielding pipe length, for example due to changes in roughness, allows you to get smooth, the corresponding field profile change heat dissipation and temperature of the studied items is now (shell, tablets of fuel) as opposed to a stepped characteristic of the simulator prototype. Extra foil shields reduces the load on the heater, i.e. allows to achieve a desired temperature of the studied elements at lower temperatures of the heater. The implementation of such screens, for example, in the form of expansions in terms of line before winding on the tube, owing to the varying number of layers along the length of the simulator to further control the distribution of heat flow.

Connecting a shielding pipe to a separate power source extends profiling of temperature fields in the investigated elements of a fuel rod, for example, allows to obtain the same temperature along the radius of the tablets of fuel at different temperature levels in the study of thermoprotect material.

The invention is illustrated by drawings.

Figure 1 shows the simulator fuel element

Figure 2 - example of the sweep of the foil shield.

Simulator, shown in figure 1, consists of a shell 1, a heater 2, the fuel pellets 3, the centering of the insulators 4, top 5 and bottom 6 of the current leads, a shielding pipe 7 and additional screens 8.

The heater 2 in the form of a tube of refractory metal with a variable external surface microrelief is installed inside the shell and coaxially with it. Between the shell 1 and the heater 2 is posted the column of fuel pellets 3. Centering the insulators 4 are installed on the ends of the fuel column 3, the heater is connected through openings in the insulators 4 upper 5 and lower 6 current leads. Shielding pipe 7 is installed coaxially with the shell 1 and the heater 2. On the screen pipe is wound several layers of foil 8 with gaps between the layers. The upper current lead connected to the flexible conductive cord that compensates for thermal expansion of the heater. Scan foil shield (figure 2) is shown for the case of symmetrical relative to the mid simulator profile of heat flow.

The simulator works as follows. The device is cooled in a sealed housing filled with an inert gas. By adjusting the magnitude of the current through the current leads 5 and 6 and the heater 2 set the required temperature levels of the heater. Heat flow from the heater comes on tablets of fuel 3 and next to the shell 1. Shielding pipe 7 and 8 screens limit the discharge of heat into the refrigerated case. The main mechanism of heat transfer through the gaps between the heater and tablets, pills and shell, and screens - rayed. The amount of radiant flux depends on the optical properties of the radiating surface, and the change of the microrelief surfaces of the heater and granitowa pipe can be obtained in each section of the simulator, heat flow, specified conditions of test.

The limits of the possible changes of the radiant heat flux due to changes in the optical properties of the surfaces of this construction simulator are determined using the known expression for the degree of blackness in the system of two coaxial cylinders of infinite length (see V. Adrianov., Fundamentals of radiation and complex heat transfer. M., "Energy", 1972):

εn=11ε2+(F1F21ε1-1)(1)

Here ε1and ε2- the degree of blackness, F1and F2square surfaces of cylinders of smaller and larger diameters. For example, consider the temperature range of the heater 1500 To 3000 K. the Integral degree of blackness heater surface (tungsten) has a value of 0.1 to 0.9, depending on the surface microrelief. Integrated degree of blackness of the surface of the fuel pellets (uranium dioxide) for the same conditions - 0.3 to 0.4. When the area ratio of surface tablets and heater 1,5-2,0 perhaps is the change shows degree of blackness, determining the change of the radiant heat flux to the fuel tablets, from 0.1 to 0.4, i.e. in ~ 4 times.

To modify the optical properties of surfaces along the length of the heater or shielding tube in different ways: by grinding and polishing to different levels of purity sections of pipe with the original large roughness (pipe obtained by the deposition of metal from the gas phase), getting regular roughness machining the original smooth tubes, for example by applying the marks with increasing length of pipe depth the risks to its width, sandblasting, coating the surface of the coatings with varying density and thickness, electrochemical milling holes (blind holes) with different ratio of depth to diameter. When defining the required characteristics of the surface microrelief (arithmetical mean deviation of the profile, i.e. the height of the roughness and the average step roughness, i.e. the distance between the projections) for the profiling of the heat flux along the length of the simulator can be used tabular data on the effective emissivity blind holes with the relationship of the depth of the holes to a diameter of from 1 to 12 in materials with different integral radiative properties (see Radiative properties of solid materials. The Handbook. Under the General editorship of A. Sandlin. M: Energy, 1974). These data provide satisfactory accuracy in the calculations of heat flow for materials with a regular microrelief (roughness), for calculations with arbitrary materials roughness data should be used integrated radiative abilities obtained experimentally.

Calculating values of emissivity for each radial cross-section of the simulator, based on which class is selected surface roughness heater (shielding pipe) in this section, is performed by using the expression:

εn=Q/σ(T14-T24)(2)

Here Q is the radial heat flow, in which the analyzed elements of a fuel rod are in this section in situ, σ - Stefan-Boltzmann constant, T2- estimated temperature value, converted to the heater surface of the investigated element, T1- set the temperature of the heater simulator. When calculating the required integral emissivity of the SPO is oblasti ε 1heater surface by the value of the integral capacity of the formulas (1) - valued ε2(the heated surface of the fuel pellets, shell) is taken for the temperature T2. On the basis of the obtained data on the integral emissivity is processed surface of the heater.

An example of a specific implementation.

As an example of a specific implementation of the device is considered a simulator designed to study the efficiency of fuel with new fuel materials at high temperatures, the radial and axial temperature gradients. The simulator consists of a shell of refractory alloy with the same field of TVEL, geometry, fuel pellets with a diameter of 8.2 mm with a Central hole with a diameter of 4.2 mm and heater tube of tungsten with a diameter of 3.2 mm and a wall thickness of 0.5 mm heater Length is 600 mm, the ends of the heater is connected by welding with rod current leads from molybdenum. The current leads are installed in centering the insulators, the upper current lead is connected to the inlet is screwed through a flexible copper harness that provides free elongation of the heater. Coaxial sheath over its entire length is set with a gap of 1 mm shielding pipe tungsten, on the outside of the pipe razmeshannoy foil shield. The simulator is installed in a sealed water-cooled enclosure, filled with helium.

The temperature profile of the surface of the fuel pellets along the axis of the fuel column, such as the conditions of the test must consist of three sections: mid - length of 300 mm with a constant length temperature (K), and extreme - 150 mm with decreasing temperature to the ends of the gradient 2K/mm (1900 To the edges). The specified radial heat flow in the cross sections in the Central zone and at the edges of respectively 1.3 MW/m and 0.4 MW/m, the desired temperature profile is provided with a heater temperature of 3000 K and the values of emissivity of 0.4 and 0.1. Integrated degree of blackness must be equal to 0.9 in the middle part and uniformly reduced to 0.4 at the edges of the heater. Such values are integral degree black tungsten surface can be obtained when the relationship of depth to diameter of from 5 (ε=0,9) to 1 (ε=0,4) forming the surface roughness of the recess.

The middle portion of the heater with a length of 300 mm is not processed after the pipe, the roughness of the surface after deposition of tungsten from the gas phase maximum. Areas adjacent to the middle, processed by grinding so that the length of 150 mm roughness gradually decreased by 6 points, corresponding to classes of roughness (see Anu is Lev VI Reference designer-mechanical engineer. Vol. 1. M: mechanical engineering, 1980, s-267).

Shielding pipe with a diameter of 17 mm obtained by gas-phase deposition of tungsten to copper pipe with pre-treated in accordance with the calculated data on the roughness of the surface. The surface of the Central section of copper pipe with a length of 300 mm was processed through 12th grade purity, cleanliness of the surfaces of the ends 150 mm gradually decreased from 12 th to 5 th grade. After removal by chemical etching of the copper substrate (pipe) the inner surface of the shielding pipe has maintained the required profile roughness. The external surface of the pipe after manufacturing had the 14th class of cleanliness, roughness profiling was carried out by mechanical processing.

The proposed simulator allows more accurate modeling of thermal state of the investigated fuel elements due to the receipt of the same, as in natural conditions, levels, temperature, heat flux and temperature profiles.

1. Simulator fuel element of a nuclear reactor containing shell, a pillar tablets natural fuel with a Central hole and located with clearance in the holes tablets electric heater, wherein the heater is made in the form of a tube of refractory material, on the outside the second surface of which is formed of alternating along the length of the heater micro, providing an optically variable properties along the length of the surface, corresponding to a simulated temperature profile.

2. The simulator according to claim 1, characterized in that the outside with a gap coaxial sheath is mounted a braided tube of refractory material on the inner and outer surfaces of which are formed of alternating micro, providing optically variable properties along the length of the heater.

3. The simulator according to claim 1 or 2, characterized in that the alternating along the length of the microrelief is formed by a surface with different levels of roughness, the respective classes of roughness from the first to the fourteenth.

4. The simulator according to claim 1 or 2, characterized in that the alternating along the length of the microrelief is formed by the surface coating with variable density and thickness.

5. The simulator according to claim 1 or 2, characterized in that the alternating along the length of the microrelief formed performed on the surface of the grooves of variable depth grooves to their diameter.

6. The simulator according to claim 2, characterized in that the outer surface of the shielding pipe is provided on the entire length of the multilayer foil shields refractory material, made in the form of a winding with a variable number of layers.

7. The simulator according to claim 2, characterized in that the shielding pipe is further provided with the auxiliary power source.



 

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2 dwg

FIELD: power engineering; evaluating burnout margin in nuclear power units.

SUBSTANCE: proposed method intended for use in VVER or RBMK, or other similar reactor units includes setting of desired operating parameters at inlet of fuel assembly, power supply to fuel assembly, variation of fuel assembly power, measurement of wall temperature of fuel element (or simulator thereof), detection of burnout moment by comparing wall temperatures at different power values of fuel assembly, evaluation of burnout margin by comparing critical heat flux and heat fluxes at rated parameters of fuel assembly, burnout being recognized by first wall temperature increase disproportional relative to power variation. Power is supplied to separate groups of fuel elements and/or separate fuel elements (or simulators thereof); this power supplied to separate groups of fuel elements and/or to separate fuel elements is varied to ensure conditions at fuel element outlet equal to those preset , where G is water flow through fuel element, kg/s; iout, iin is coolant enthalpy at fuel element outlet and inlet, respectively, kJ/kg; Nδi is power released at balanced fuel elements (or simulators thereof) where burnout is not detected, kW; n is number of balanced fuel elements; Nbrn.i is power released at fuel elements (or element) where burnout is detected; m is number of fuel elements where burnout is detected, m ≥ 1; d is fuel element diameter, mm.

EFFECT: enhanced precision of evaluating burnout margin for nuclear power plant channels.

1 cl, 2 dwg

FIELD: analytical methods in nuclear engineering.

SUBSTANCE: invention relates to analysis of fissile materials by radiation techniques and intended for on-line control of uranium hexafluoride concentration in gas streams of isotope-separation uranium processes. Control method comprises measuring, within selected time interval, intensity of gamma-emission of uranium-235, temperature, and uranium hexafluoride gas phase pressure in measuring chamber. Averaged data are processed to create uranium hexafluoride canal in measuring chamber. Thereafter, measurements are performed within a time interval composed of a series of time gaps and average values are then computed for above-indicated parameters for each time gap and measurement data for the total time interval are computed as averaged values of average values in time gaps. Intensity of gamma-emission of uranium-235, temperature, and pressure, when computing current value of mass fraction of uranium-235 isotope, are determined from averaged measurement data obtained in identical time intervals at variation in current time by a value equal to value of time gap of the time interval. Computed value of mass fraction of uranium-235 isotope is attached to current time within the time interval of measurement. Method is implemented with the aid of measuring system, which contains: measuring chamber provided with inlet and outlet connecting pipes, detection unit, and temperature and pressure sensors, connected to uranium hexafluoride gas collector over inlet connecting pipe; controller with electric pulse counters and gamma specter analyzer; signal adapters; internal information bus; and information collection, management, and processing unit. Controller is supplemented by at least three discriminators and one timer, discriminator being connected to gamma-emission detector output whereas output of each discriminator is connected to input of individual electric pulse counter, whose second input is coupled with timer output. Adapter timer output is connected to internal information bus over information exchange line. Information collection, management, and processing unit is bound to local controlling computer network over external interface network.

EFFECT: enabled quick response in case of emergency deviations of uranium hexafluoride stream concentration, reduced plant configuration rearrangement at variation in concentration of starting and commercial uranium hexafluoride, and eliminated production of substandard product.

24 cl, 5 dwg

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