Patent Number: 039869253
Section: description

Proceeding now to the detailed description of the drawings, there is illustrated a nuclear reactor 10, having a plurality of self-contained sections or portions such as 1, 1', 1" and others. Each reactor portion has its own nuclear fuel elements and control elements, subject to individual control as to each portion. However, neutron flux of the individual sections are inter-coupled due to proximity of disposition of the fuel element. Each reactor section pertains to a particular unit, 9 or 9' or 9" etc., serving individually as principal heat source for such a unit. Each unit, such as 9, includes its own closed circulation loop 20 for a heat exchange medium serving also as working fluid for MHD type electricity generation. Alkaline metal, such as sodium and/or potassium, circulates through loop 20. Nuclear reactor portion 1 is the principle heating source for the working fluid. Fluid leaving reactor portion 1 passes first through a two phase acceleration nozzle 2 with atomizer; next in the loop is a hollow jet condenser 3, feeding an inductively operating MHD-converter 4. Electric circuit lines 23 indicate schematically the withdrawal of electrical energy from the unit 9. Lines 23 are connected to a power output bus 33. Working fluid leaving MHD-converter 4 passes through a diffusor and shock condenser unit 8, to a heat exchanger 5, serving as cooling device for the principle working fluid in loop 20. A sub-loop 21 branches cooled working fluid off the main loop and couples same into the flow in the hollow jet condenser as part of the operation thereof. The principle return path passes through nozzle 2 for preheating of the working fluid. For the basic unit see, for example, "Electricity from MHD, 1968", Vol. III, page 1440 et seq., IAEA, Vienna 1968. The dashed line 22 in FIG. 1 denotes an open loop circulation path for air which passes through the heat exchanger 5 for receiving thermal energy from the working fluid, particularly for extracting residual thermal energy from the working fluid prior to entering the return branch of its circulation loop 20. Air is forced through loop 22 by means of a compressor 7 and passes through heat exchanger 5 to a gas turbine 6. The gas turbine extracts enthalpy from the air circulation and drives compressor 7. Gas turbine 6 and compressor 7 are combined as a driving aggregate of a type which is known from aerodynamics. As conceivably the air circulates in open loop, it is discharged from the turbine, for example, into a desalination plant 27, serving as prime heating medium for the desalination process. For this, the air flows for the several units 9, 9', 9" etc. are combined. The MHD working process that takes place in the system as shown in FIG. 1 is accompanied by temperature-entropy changes illustrated in the upper graph of FIG. 4. In FIG. 4 temperature T is plotted along the ordinate, entropy 5 is plotted along the abscissa on a suitable scale; the upper graph has particular validity for the working fluid in loop 20. Changes in state as between liquid and gaseous phases take place in the immediate vicinity of the characteristics of pure liquid (for the alkaline working fluid), and denoted as X = O (X) being the quality). Particularly, such changes of state occur partially in the liquid phase proper, partially in the wet steam area. Beginning with point d, that point defines the temperature-entropy state of the liquid metal as working fluid, upon leaving the nuclear reactor. The hot metal is depressurized in accelerator nozzle 2 along line d.fwdarw.e as continued along line e.fwdarw.f, whereby pursuant to the latter portion cooling is provided by means of already cooled, liquidious metal in the return branch 20' and having a relatively low energy content. The two phase stream is additionally cooled in hollow jet condenser 3, along line f.fwdarw.b, cooling resulting in a nearly complete condensation in the two phase flow. Cooling is provided particularly by operation of branch loop 21, returning some of the already cooled working fluid to the main stream. Pressure in the working fluid decreases throughout this process, while its kinetic energy is accordingly increased. Point b denotes entry into the MHD-generator 4 wherein energy is extracted from the fluid. The MHD-generator has windings for derivation of particular voltage and current. At this point, electrical energy is taken from the kinetic energy of the working fluid so that its temperature-entropy is not or only insignificantly changed. Subsequently, the working fluid is cooled in heat exchanger 5 the heat transfer being represented by branch b.fwdarw.a as to the working fluid in loop 20. Prior to heat exchange, as between air and working fluid, diffuser 8 regains pressure energy in the latter and thus completes, if necessary, condensation by a shock. Cooling of the working fluid in heat exchanger 5 and along line b.fwdarw.a is provided to render sufficiently cool fluid available for use in condenser 3, (sup-loop 2). The line b.fwdarw.c is almost identical with limit characteristics X = 0 and represents re-generative pre-heating of working fluid in nozzle 2 along a substantially isobaric characteristic. In other words, the branch b.fwdarw.c as to the returning working fluid is the heat exchange counter part for fluid entering nozzle 2 undergoing the change e.fwdarw.f. The working fluid re-enters the reactor at point c in the diagram, wherein it is heated and its state is changed to point d, completing the circulation. The lower portion of FIG. 4 illustrates, in a comparable scale, the concurrently occuring change of state of air as passing through heat exchanger 5. Air is compressed in the compressor 7 along the isentropic portion h.fwdarw.i. The air is heated (branch i.fwdarw.k) through heat exchange with the principal working fluid of the system. As to the working fluid, that corresponds to branch b.fwdarw.a. The air is decompressed in turbine 6 along the isentropic curve k.fwdarw.i and, possibly cooled, along line l.fwdarw.h. That latter branch is present only in case of a closed loop air circulation but is omitted for open loop circulation. The hot air at point 1 can be discharged, for example, into the desalination plant, and cool air (point h) may enter the system from the environment. Turning now to particulars of FIG. 2, an individual unit includes essentially all of the components as shown in FIG. 1 in form of a serial arrangement. The nuclear reactor 10 of the system as a whole is, therefor, divided into a plurality of subreactors such as 1, 1', 1", disposed respectively in the rear of each unit. The units are elongated in construction and extend parallel to each other. The reactor portions are aligned transversely to that direction of predominant extension of each unit. The particular two-phase nozzle 2 is disposed behind the fuel elements of subreactor 1'. Next in line is the hollow jet condenser 3, inductive MHD-converter 4, diffusor and shock-condenser 8 for self-energization, and heat exchanger 5 driving aggregate 11. All these components constitute a structural unit. As the other units, such as 9', 9", are similarly constructed, similar components are aligned transverse to the predominant extension of each unit. Elements 14, 15 and 18 provide shielding that encases the entire system. Unit 9 has power cable 23, unit 9' has a cable 23', unit 9" a cable 23" etc.; these cables are all connected in parallel and to the common bus system 33 that constitutes the electrical output of the plant. Reference numeral 13 denotes the control cable for unit 9 which includes signal lines providing signal in representation of the particular operational state of unit 9. There being similar cables 13', 13" and others respectively for units 9' and 9" and others. These signal lines included in cables 13 and others feed a process control computer 25, individually controlling the reactor and MHD-generator portions in accordance with a program that depends on the demand for power on bus 33. The control signals pass from the computer to the several units via control lines included in the several cables 13, 13' etc. The front end of each unit has a tube, such as tube 12 of unit 9. Cables 13 and 23 pass through tube 12. Additionally, cool air enters the system through tube 12. Hot air is discharged from unit 9 through opening 17. The arrows in the opening denote the path of air flow in the system. Hot air discharged from the several units combines in a collection chamber 26 and flows through openings to desalination plant, or chemical plant 27, for heating therein. FIG. 3 illustrates what can be described to be a cross section through a bundle of units of the type shown in FIG. 2 and arranged in a compact, honeycomb-type arrangement. The wall structure 19 establishes suitable support for the several units. The individual units are to some extent known per se as to their particular contribution to the operation as a whole. The invention resides in the construction of a power plant from such units as self-contained units with regard to the MHD-process. They ae electrically connected in parallel and their nuclear process is controlled, for example, by electronic computer 25, to optimize operation as to power requirement. Utilization of air as cooling medium for removal of thermal energy from the principal circulation yields a high degree of independence of the locaton of the power plant. Aggregate 11 comprised of gas turbine 6 and compressor 7 provides air at an elevated pressure to improve heat transfer from the working fluid so as to reduce the need for large cooling surfaces. The power for the compressor is produced in the gas turbine using residual thermal energy extracted from the circulating stream of alkaline working fluid (characteristics b.fwdarw.a and i.fwdarw.k). Each unit has its own aggregate so that the several units as they operate in parallel, are decoupled as to cooling. Cooling of each unit can be controlled to match the requirements for cooling of a particular unit in dependence upon its power output. The several units in a single power plant are coupled to each other three fold. First, neutron flux of the subreactor units 1, 1', 1" etc. is shared due to proximity. Secondly, the units operate on a common power bus 33. Thirdly, the control of the units is interrelated in accordance with a particular program. Each unit has two operational modes. In the cooling mode the respective MHD-converter takes electrical energy from the electrical circuit to pump liquid working fluid as cooling medium through the reactor, i.e., such a unit acts as a load on bus 33 and causes the working fluid to circulate through its loop. In the cooling mode the production of thermal energy in the particular reactor portion is rather low, too low to permit useful extraction of electrical energy from the MHD-generator. The second mode is the power mode in which electrical energy is produced by and can be taken from the unit when operated in that mode. A unit operated in the power mode can be shifted into the cooling mode through control of neutron flux in the particular unit. That control is particularly provided by the computer 25. In case the power requirement on bus 33 increases, a unit that is currently operated in the cooling mode can be shifted into the power mode, to participate in the production of electrical energy. The neutron flux decreases in the border zone of the reactor (e.g. in units 1'). This "natural" distribution in neutron flux is utilized by having the outer units operate under stand-by conditions to be normally in the cooling mode. A power plant controlled in such a manner operates particularly advantageous in comparison with a conventional power plant, as neither heavy masses such as rotors, flywheels, etc., nor stored energy steam volumes have to be considered upon change in power requirements. Thus, the response delay as to control operation of the system in accordance with the invention is considerably reduced, which, in turn, means that the power output of the plant may follow promptly even comparatively large, suddenly occuring variations in power requirements. It will be recalled that the electronic computer 25 supervises the reactors and MHD-converters in a process control operation and in dependence upon the power requirement. The program alluded to above refers specifically to the selection of power mode-cooling mode for the several units and to the selection of which unit is to undergo a change in mode. Another advantage of the invention is to be seen in the high degree of independence of each unit. Therefor, in case a defect occurs in one of them, the plant does not have to be shutdown as a whole. Instead, through appropriate control operations, the particular defective unit can be shutdown and replaced. The units do not only operate but are also constructed and manufactured as individual replacement units. Spare units may be kept as inventory, so that in case one of them is found to be defective, it can be replaced as a whole by readily available new one, while the removed, defective one is repaired. This, in turn, increases the availability of the plant as a whole, as the plant is not fully operationally only for the time it takes to replace a unit. If the plant has many units that exchange diminishes the available plant output only by a fraction of total output which is noticeable only if the plant operates at maximum capacity. On the other hand, testing as well as production of such units is simplified, as compared with conventional equipment. Also, rating of a power plant differs from others of similar construction merely in the number of units employed. The honeycomb arrangement, as shown in FIG. 3, permits not only indefinite increase extension of a plant, but different size plants are compact so as to differ little in overall size. The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.