US3435617A - Powerplant having radi active heat source - Google Patents

Description

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J- A. WAGLE POWERPLANT HAVING A RADIOACTIVE HEAT SOURCE Filed April 6, 1966 United States Patent 3,435,617 POWERPLANT HAVING A RADIOACTIVE HEAT SOURCE Joseph A. Wagle, New Augusta, Ind., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Apr. 6, 1966, Ser. No. 540,552 Int. Cl. G21d /04; G21c 15/00, 19/28 U.S. Cl. 60-105 5 Claims ABSTRACT OF THE DISCLOSURE My invention is directed to powerplants, particularly to heat energized powerplants suitable for use in remote or untended locations or where it is impracticable to supply fuel for combustion. The powerplant of my invention is particularly suited to generation of useful power, such as mechanical shaft power or electrical energy, from a source which generates heat constantly at a rather modest rate. Specifically, a powerplant according to my invention is useful to generate electrical energy, which may be stored, from the energy resulting from decay of a radioactive substance.

It has been previously proposed to generate vapor by the heat liberated by a radioactive substance and to drive a turbine by such vapor. It is also recognized that power plants may include means to generate electricity and to store it in suitable batteries.

The principal point of my invention is that it reduces the cost, improves the efficiency, and simplifies the control of such a power plant. These benefits are achieved by the incorporation in the power plant of controlling means operated to deliver vapor cyclically from the boiler to the turbine, each cycle consisting of a first phase in which flow of vapor is cut off and vapor is accumulated in the boiler, and a second phase in which vapor is supplied to the turbine at substantially constant pressure.

The nature of my invention and the advantages thereof will be apparent to those skilled in the art from the succeeding detailed description of a preferred embodiment thereof and the accompanying drawings thereof.

FIGURE 1 is a schematic diagram of a powerplant.

FIGURE 2 is a cross section of the boiler taken on the plane indicated by the line 2-2 in FIGURE 1.

FIGURE 3 is a graphical representation of the variations of pressure and power during the operating cycle.

FIGURE 4 is a somewhat schematic illustration of suitable vapor controlling valve means.

In the succeeding detailed description of the invention it will be assumed for conciseness that the cycle operates with water and the vapor will be refered to as steam, although it will be understood that other substances such as are used in vapor turbines may be employed, as desired.

Referring first to FIGURE 1, the powerplant includes a boiler 7, a steam flow control valve set 8, a steam turbine y, a condenser and a condensate pump 11. Steam generated in the boiler flows through the control valves and turbine to the condenser, which may be cooled in any desired manner. The steam condensed to water is returned by the pump 11 to the boiler. The pump 11 may be driven by the turbine through a shaft 13 and the turbine is further connected to an electric generator 14 by a shaft 15. The generator may charge a storage battery 17 through a suitable regulator 18, and the load is supplied from the generator and battery through leads 21 and 22. The turbine may include a suitable governor (not illustrated) and means may be provided if desired to operate the generator as a motor to drive the condensate pump 11 in response to accumulation of water in the condenser. In general, however, it is considered that drive of the pump by the turbine will be suflicient.

Considering first the preferred structure of the boiler 7 as illustrated in FIGURES 1 and 2, it includes a pressure shell 23 encased in heat insulating material 25. The heat supply is taken from a suitably encased or shielded body of radioactive material such as any of the suitable radioactive isotopes. The heat source 26 ordinarily is submerged in the water 27 in the boiler to which it can communicate heat directly. The heat source also delivers heat through a radiator 29 including fins 30. The radiator 29 may act to superheat the steam in the upper portion 31 of the pressure shell 23, which acts as a steam accumulator. The feed water is supplied to the lower part of the boiler through a pipe 33 and steam is delivered from the upper part of the boiler through a pipe 34 to the control valve group 8 which, as shown more clearly in FIGURE 4, includes a relief or pop-off valve 35 and a pressure regulating valve 37.

The detailed structure of these valves is not material to the invention, but a typical suitable structure is illustrated more or less schematically in FIGURE 4. As seen there, the relief valve 35 includes a case 38 within which is slida'bly mounted a valve piston 39. Piston 39 is biased into engagement with an annular seat 41 by a compression spring 42. Steam from the boiler enters the chamber 43 of the valve through line 34, and when the pressure is suflicient to overcome spring 42 and unseat the valve piston 39, flows through the annular seat 41 into a chamber 45 which discharges through a connection 46 into the regulating valve 37. It sould be noted that the area of piston 39 is substantially greater than that of the seat and that, when the relief valve opens, the steam pressure is exerted on the total area of the valve piston instead of the area exposed when the valve is seated. Thus, the closing pressure of the valve is substantially lower than the opening pressure and, in the preferred embodiment, the closing pressure is about one-third the opening pressure. Thus, when the pressure developed by the boiler reaches a value sufficient to open the relief valve, it will remain open until enough steam flows through the turbine to reduce the pressure of the accumulated steam by about two-thirds.

The turbine, however, works most efficiently at a substantially constant pressure ratio and, for this reason, the valve 37 is interposed between the relief valve and the turbine. The regulating valve 37 is of well-known type including a cylinder 47 and a spool 49 reciprocable in the cylinder. The spool 49 is biased by a compression spring 50 so that, in the absence of any pressure acting on the spool, it engages a stop '51. In this position, steam can flow freely from the inlet connection 46 between the lands of the valve spool to the valve outlet line 53 Line 53 leads direct to the turbine which, as previously stated, may include a suitable governor or power controlling valve (not illustrated). Unless the load on the turbine is reasonably constant, a governor may be necessary to limit turbine speed. A branch connection 54 leads from line 53 to the space 55 above spool 49 so that the delivery pressure biases the spool and, when the pressure is sufficient to compress spring 50, the spool moves downwardly as illustrated so that its upper land throttles flow between inlet 46 and outlet 53. The valve is balanced with respect to the inlet pressure and thus the discharge pressure remains constant.

The regulating valve 37 is set to deliver steam at a pressure very slightly below the closing pressure of relief valve 35. As a result, the turbine is supplied steam cyclically, the cycles involving a period of steam accumulation followed by a period of supply of steam at constant pressure to the turbine. The lower faces of the movable valve members 39 and 49, as illustrated in FIGURE 4, are vented to the condenser through a line 57 to minimize the back pressure on these members.

When the turbine is in operation, the steam discharged from it is condensed by the condenser and returned by the pump to the boiler. The operation of the turbine also energizes the generator 14 which charges the battery 17.

The cycle of operation may be made somewhat clearer by reference to the curves of FIGURE 3. The upper solid line indicated as Boiler represents the variation of boiler pressure with time and the broken line bearing the legend Turbine represents the variation of turbine supply pressure with time. The datum or zero is condenser pressure. Starting at the point at which the relief valve 35 closes as zero time, the turbine pressure remains at condenser pressure, which his substantially zero and the boiler pressure builds up to a point indicated as 60 at which the relief valve opens and the turbine pressure rises to the value determined by the regulating valve. The boiler pressure is reduced as steam flows to the turbine and when boiler pressure reaches approximately the value of controlled turbine pressure, the relief valve again closes at point 61 and the cycle repeats. Referring to the bottom curve, of power, it will be noted that turbine power output is zero until valve 35 opens, when it abnuptly rises to the maximum at 62 and remains essentially constant, decreasing slightly to point 63, at which the supply of steam to the turbine is cut off. There is a slight decrease in power ouput as a result of the diminished superheat of the steam because of the lessening of the throttling through the regulating valve as the accumulated pressure in the boiler diminishes.

It will be understood that the relative durations of the steam storing and power delivering phases of the cycle may vary widely and that these two need not be nearly equal as indicated in FIGURE 3. Particularly in the case of heat derived from radioactive decay, the rate of supply of heat will very slowly decrease with the progressive decay of the radioactive material. In the system of my invention this will not vary the condition of the steam supplied to the turbine but will merely increase the length of time of the energy accumulating portion of the cycle and slightly shorten the duration of the turbine operating portion.

The system may be operated so that some water remains in the boiler at all times or it could operate to evaporate the water in the boiler entirely and further heat the steam until the resulting pressure opens the relief valve. It will be seen that the turbine when operating will have substantially constant inlet and outlet conditions and can be designed for most efficient operation. Also, in installations providing a very small amount of power, the turbine need not be of undesirably small size. The generator and storage battery provide for constant available power during the entire cycle. For installations where intermittent availability of power is satisfactory, battery storage may be omitted.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, as many modifications may be made by the exercise of skill in the art.

I claim:

1. A powerplant comprising, in combination, a boiler containing a liquid, a heat source associated with the boiler effective to supply heat gradually and continuously to the liquid in the boiler to generate a vapor therefrom, a vapor turbine energized by the said vapor, a condenser connected to the exhause of the turbine, a pump effective to return condensate from the condenser to the boiler, and flow control means connected between the boiler and turbine and controlling the flow of vapor from the boiler operative to deliver vapor cyclically from the boiler to the turbine, each cycle consisting of a first phase in which flow of vapor is cut off and vapor is accumulated in the boiler and a second phase in which vapor is supplied to the turbine at substantially constant pressure, the flow control means comprising a relief valve supplied by the boiler having a predetermined opening pressure and a predetermined closing pressure significantly lower than the opening pressure and a pressure regulating valve supplied through the relief valve effective to maintain the pressure of vapor flowing to the turbine from the regulating valve substantially at a constant pressure.

2. A powerplant as recited in claim 1 in which the heat source is a substance subject to radioactive decay.

3. A powerplant as recited in claim 2 in which the heat source is contained within the boiler.

4. A powerplant as recited in claim 1 in which the lastrecited pressure is substantially the relief valve closing pressure.

5. A powerplant as recited in claim 1 including also a generator driven by the turbine and a storage battery charged by the generator.

References Cited UNITED STATES PATENTS 2,070,724 2/ 1937 Frickle -105 2,192,042 2/1940 Hofimann 13737 2,765,414 10/1956 Gendler et al. 60l05 2,968,600 l/1961 Allen 17656 3,061,533 10/1962 Shannon et al. 17656 REUBEN EPSTEIN, Primary Examiner.

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