OF BEACHHEADS, ENERGY DEPOTS, AND LUNAR BASES.
NASA / ARMY / NAVY OVERLAPPING REQUIREMENTS
A- NASA SPACE BASES AND LUNAR BASES
In September of 1963, Westinghouse Astronuclear was awarded a six month contract from the U. S. Army Corps of Engineers to perform an engineering study of both chemical and nuclear systems for lunar base power supplies. This report is written to show the extent to which the current SNAP-50/SPUR powerplant development program is directly applicable to the LUBAR nuclear powerplant concept recommended by Westinghouse Astronuclear in the interim report of the Lunar Base Study. The general ground rules for the nuclear portion of this study, as set forth in the request for proposal, were:
1. Initially an average power demand of under 100 Kwe with growth to approximately 1 Mwe.
2. Target date for launch to the moon of 1972.
3. Powerplant and necessary support equipment must be transportable to the moon using a single Saturn
The lunar base study is divided into two phases. The first phase is to survey the status of existing technologies and to recommend a most applicable concept. The second phase is to perform extensive studies based on the recommended concept of developing the powerplant, delivering, starting, and operating the powerplant on the lunar surface. The first phase has been completed and an interim report (WANL-PR(S)-004, Volume I and Volume II, Parts 1, 2, and 3) issued.
An initial concept, designated as LUBAR I (Lunar Base Reactor), was recommended in the interim
report to be followed by LUBAR II, later generation system of the same concept but with higher oper ating temperatures .
From a comparison of the LUBAR systems with the SNAP-50/SPUR system, the similarity of the technologies is readily apparent. This similarity is especially evident in the following sections through a description of the components for both concepts and a discussion of the component development program in progress for the SNAP-50/SPUR powerplant. The program which would be required to develop the LUBAR powerplant would be nearly identical to that in progress to develop the SNAP-50/SPUR powerplant. The major exception would be the main heat rejection system which in the lunar base application could utilize lunar gravity to provide natural circulation of the radiator fluid.
In general, it is concluded that the LUBAR concept represents the lower temperature range of the SNAP-50/SPUR technology. However, as growth capabilities of this system to higher operating temperatures are realized, the operating conditions of the lunar base systems would be expected to become nearly identical to those of the SNAP-50/SPUR powerplant.
DISCUSSION
1-Similarity of Requirements for Space and Lunar Base Powerplants
The general requirements for a space powerplant and a lunar base powerplant are similar. The power output for both systems ranges from less than 100 Kwe to about 1 Mwe and for lifetimes of at least one year. Specific weight must be minimized and the system reliability must be high for both applications. The environment of space is that of hard vacuum, meteoroids, and zero gravity. The environment of the lunar surface does, however, differ from space by having a lunar gravitational force approximately 1/6 that at the earth's surface.
The mode of heat rejection is by thermal radiation for both applications, however, in the lunar environment, the effective sink temperature is altered due to reflection and radiation from the lunar surface. At the operating temperatures of the main and auxiliary radiators, this higher sink temperature is not a serious concern. However, cooling of solid-state electronic devices to the vicinity of 150F is a serious problem on the lunar surface during the daylight periods and requires more elaborate systems.
Shielding is provided on the unmanned space powerplant to protect the electronic components of system. However, in the lunar base application, sufficient shielding must be provided to protect personnel against nuclear radiation from the reactor system. Due to the extreme cost associated with delivering a payload to the lunar surface, the utilization of lunar material is highly attractive. However, for the early application, the site preparation equipment and manpower required to move
this material into a shielding configuration would be prohibitive. For the earlier low power systems,
it does appear that sufficient shielding can be carried along with the powerplant without exceeding the capabilities of Saturn V booster.
2-SNAP-50/SPUR Development Program
The objective of the SNAP-50/SPUR development program is to provide a powerplant which produces a net electrical power output of 300 Kwe with an unshielded specific weight of approximately 20 lbs/ Kwe and a lifetime of 10, 000 hours. A powerplant of this type is adaptable to a variety of space missions such as electric propulsion, military applications, communications, and lunar base or space station power supplies. This program is currently in the design and component development phase. Design studies of all major components are in progress. A large number of materials tests have been completed and additional tests are continuing. Programs for the development of subcomponents have been initiated. In support of the reactor design, an extensive fuel irradiation program is in progress. Upon completion of subcomponent tests and component designs, testing of individual components, subsystems, and the complete powerplant will be performed.
Major milestone objectives of the SNAP-50/SPUR program include the reactor and non-nuclear powerplant tests. The SNAP-50/SPUR Project Office has recently established that the target dates for the start of both of these tests will be mid-calender year 1969 .
The development program for a lunar base nuclear electric powerplant, of the type recommended in the Westinghouse Astronuclear Interim Report, would roughly parallel that of the SNAP-50/SPUR development program. Over-all powerplant component tests for both systems would be expected to have the same general objectives, encounter similar problems, and require comparable facilities.
B- US NAVY - FACT SHEET ON BEACHHEAD OPERATIONS
TYPICAL CRITERIA
NUCLEAR POWER - BEACHHEAD PLANT
Title — Beachhead Plant, 100 KWE
Proposed Use — There are requirements within the Navy for portable nuclear power plants with electric power outputs of approximately 100 kw. Examples of military operations requiring a power source without dependence on continuous fuel or cooling water supply are: support of beachhead operations and tactical missile systems, air head operations including field hospitals, remote locations. Their requirements are very similar to the Army Mobile Energy Depot own portable nuclear reactor - the MCR: military compact reactor.
1. The power plant will reject heat to the surroundings by means of an air-cooled heat exchanger.
2. Beachhead, landing and tactical operations will be completed within three days. Base development will be initiated after the first day of beachhead operation. Base development will be a continuous effort for 30 to 60 days.
3. Requirements for power plants during tactical operations include dispersion, quietness of operation, portability (trailer or truck-mounted) and ship-to-shore delivery systems for fossil fuel.
4. Power plant size will be limited to 100-kwe output. Power plant weight will not exceed 2500 pounds.
5. Tactical airfields, maintenance facilities and conmunicatlons systems represent the major power demand for the beachhead power plant. All equipment utilized in these facilities requires a high degree of portability.
6. Total electric power requirements for services during beachhead operations are of the order of 1000 kw.
7. During combat operations, power supplies are required to have a high degree of reliability. Reliance on a single power source is difficult to justify and a multiplicity of units is indicated.
8. Transportability during beachhead operations is limited by the lifting capacity of helicopters. Helicopters for beachhead operations are capable of carrying 2500 pounds. Five-ton trucks represent the upper limit of ground-vehicle load-carrying capability.
9. Electric power is also required for hospitals, lighting, refrigeration and water purification during initial beachhead operation.
10. Approximately 10 days after beachhead establishment, base development and electric power demand will Justify the utilization of a larger power plant such as the advanced base plant. The stringing of transmission wire for load distribution will be feasible at that time.
The object of the current Systems for Nuclear Auxiliary Power (SNAP) program is to develop power plants with weights of 10 lb per kwe, including reactor, power conversion unit, radiator and any necessary shielding. Usually the shielding considered for these space power plants consists of just enough material to protect sensitive equipment in proximity to the reactor from radiation damage. If it is desired to provide shielding on the beachhead plant reactor, adequate to allow personnel access to the plant after reactor shutdown, the total weight of the unit will be substantially greater than that of 'a similar unit used unshielded for space power.
The power conversion system must match the reactor in compactness and light weight. At the present time, three systems show promise for this application. All are under development but none is ready yet for efficient practical application.
The heat rejection requirements of the beachhead plant are somewhat less stringent than those of a comparable space power unit. The latter can reject heat only by radiation in the space vacuum. For beachhead operations, heat rejection will, in general, be to air or ground to enhance the plant mobility and render the plant independent of a water supply.
The space reactors will become lighter and more compact as they develop, from SNAP-2 to SNAP-8, to the ORNL Intermediate Reactor, to SNAP-50 and the thermionic reactor. At what point these power plants will become small enough for beachhead plant applications is not immediately apparent.
The selection of a power plant for beachhead operations depends on the following:
a. Advancement of the technology of nuclear fuels, reactor control, efficient power conversion systems, materials, etc.
b. The development of a nuclear reactor system, including reactor and power conversion system, capable of 100-kwe output, which weighs 25-50 pounds per kwe or less, including appropriate shielding and which does not require highly trained personnel or setup time in the field.
c. The development of a military requirement for such a plant in beachhead operations which will justify the replacement of diesels.
It is concluded that:
a. There is no nuclear power plant that will be available in time to meet the original schedule stipulated for this plant in the Scope of Work statement.
b. There is a good chance that such a plant will become available within the next 20 years, due to the space nuclear power development effort.
C- THE ARMY MOBILE ENERGY DEPOT
Army attention was initially directed toward the use of a SNAP-50/SPUR type reactor as an advanced Mobile Compact Reactor for the Mobile Energy Depot. Since the reactor power levels required for both SNAP-50/SPUR and the MCR are in the same range, both applications required high temperature liquid metal coolants to achieve light weights, and both applications used fast spectrum reactors.
The high temperatures attainable with a SNAP-50/SPUR type reactor, as compared with those of the present MCR powerplant, could make possible higher power outputs and efficiencies. In reviewing MCR requirements it became apparent that an attractive alternative which could be realized much sooner would be the use of the LCRE reactor, coupled with an engine already developed to achieve the goals of the present LCRE program. This reactor could be run at reduced temperature to supply heat to the Pratt & Whitney Aircraft FT-12 free turbine engine, using a liquid metal-to-air heat exchanger of the type developed by Pratt & Whitney Aircraft in the Aircraft Nuclear Propulsion Program.
The proposed powerplant consists of a lithium-cooled reactor, identical to that to be used in the Lithium-Cooled Reactor Experiment (LCRE), which was scheduled for test in late 1965, and the Pratt & Whitney Aircraft FT-12 engine, a marine development of the JT-12 engine. This engine employs the open Brayton (gas turbine) cycle with a liquid metal-to-air heat exchanger replacing the usual burner. A generator, driven by the gas turbine, provides a net electrical output of 2250 Kw of 3-phase, 60-cycle current. Overall weight of the proposed powerplant, including shielding is estimated to be 125,000 pounds.
This approach to the Mobile Compact Reactor Program has tremendous appeal, since it makes use of both a reactor which was being designed as part of the SNAP-50/SPUR program and of an existing FT-12 engine used to power the Sikorsky Sky Crane helicopter (currently being constructed for the U.S. Army) and which is also under development for a Naval application.
Other components, such as EM pumps, are state-of-the-art. The only additional development program required would be that needed to marry the components into an integrated system.
COMPLIANCE WITH DESIGN OBJECTIVES OF THE MILITARY COMPACT REACTOR
The following compares the LCRE mobile plant characteristics with a condensed version of the requirements:
1. Requirement
The powerplant must be in one, self-sufficient package, including shielding, with the exception of an internal control module. It must be capable of startup, shutdown, control, and monitoring without recourse to external power sources.
Comment - The powerplant includes a self-contained auxiliary power unit for startup and shutdown power. It has a self-contained shield which reduces radiation doses to 10 mr/hr or less, outside a 450-foot radius.
2. Requirement
Maximum protection against small arms fire and against the effects of large bursts of neutron and gamma rays are to be provided.
Comment - The reactor and primary loop are protected from small arms fire by their radiation shielding. The turbine engine and generator are believed to be invulnerable. Circuit breakers and other switchgear will be protected by local armor plate. The thickness of secondary piping and tankage will be chosen to resist small arms fire damage.
To avoid damage from radiation bursts, the control system will be designed without radiation-sensitive solid state devices and, if possible, vacuum tube amplifiers will be replaced by magnetic amplifiers or similar devices. If appropriate, radiation-sensitive switches will be provided for momentarily shutting off critical circuits.
3. Requirement
The minimum power level is to be 2 Mwe net
4. Requirement
The powerplant weight should allow disassembly into packages for air shipment, none of which should exceed 40500 pounds. The maximum dimensions of any package should permit shipment on C-124 and C-133 aircraft. The powerplant should be carried on a standard military trailer as an integral unit. In March, 1963, it was recommended that the transportation requirements be relaxed to require the use of one trailer only on paved highways.
Comment - Studies of the best method of packaging for air shipment are still in progress, but the heaviest and largest package undoubtedly will include the reactor, inner gamma shield, primary liquid metal loop and secondary liquid metal loop (including the liquid metal-to-air exchanger). The weights of these components are estimated to be 25, 000 pounds. It would be necessary to rearrange or augment the shielding to obtain adequate protection during shipping, raising the weight of the package to about 35, 000 pounds . The maximum dimensions of the package are 8 feet, 6 inches in height and 20 feet in length, both with in the allowable load dimensions. The powerplant was laid out to fit the XM524 military trailer specification. Recent communication indicates that the Army will not purchase trailers to this specification but will purchase commercial trailers of like capacity for the XM524 requirement. The Fruehauf model CD-120WD-16 drop-deck trailer appears to have the desired capacity and size for the powerplant on paved highways.
5. Requirement
The powerplant should be transportable by rail, ship, overland, and by C-124 and C-133 aircraft, taking due account of the shock-loading encountered.
Comment - The package sizes suitable for aircraft can readily be loaded into ships, railroad cars, or semi-trailers. The LCRE was designed for 2-g loading and will require reinforcement at the juncture of the reflector outer container with a mounting skirt, in order to survive the 15-g shock condition associated with rail transporation. The reinforcement can be applied in the form of external doubler plates. The use of a shock-absorbing material between the reactor mounting and the skids would also ease the problem. Other components are de signed for rail, ship and air transportation and do not require modification.
6. Requirement
The powerplant should be capable of operating without appreciable loss of power on a 60 percent fore and aft slope and a 30 percent lateral slope.
Comment - The liquid metal circuits employ EM pumps not requiring control of liquid metal level or attitude. Therefore, the liquid metal loops will operate at the slopes specified. The en gine will present no problem, since it is designed for aircraft attitudes and accelerations. The generator will be furnished with a thrust bearing, making it capable of operating at the 60 percent fore and aft attitude .
7. Requirement
The basic powerplant life should be 50, 000 hours; the interval between major overhauls should be 10, 000 hours, and the reactor core life should be 5000 full power hours.
Comment - As discussed in detail in the Appendix, available information on 1500F liquid metal systems contained by iron or nickel base alloys indicates that measurable mass transfer occurs in 1000 hours. The prospects are poor that this system, or any other using the same materials and temperatures, would survive 50, 000 hours. A realistic goal is 10, 000 hours. The period between major overhauls would probably be determined by the engine. GG-12 engines (the gas generator section of the FT-12) are being developed for approximately this period between overhauls and one such engine has operated for most of this time period without overhaul. The reactor core is capable of operating for 7500 full power hours.
8. Requirement
The system should be capable of a transition from shutdown to full power in 30 minutes and a transition from full power to readable shutdown (all fluids left in place) in 15 minutes.
Comment - The shutdown requirement poses no problem, because the primary loop containment material has a high thermal diffusivity combined with a low Young’s modulus and low coefficient of thermal expansion. Even a scram does not result in severe thermal stresses and rapid shutdowns are feasible. Most of the time would be taken up by transferring electrical load to the APU and reeling in cable. The time required to transfer load could be virtually eliminated by allowing the APU generator to float on the line as a synchronous condenser and by causing the APU to start automatically to maintain APU generator speed. Assuming the startup to occur with liquid metal coolants in place, the startup time would be determined by the safe reactor period. Assuming reactor startup time to be the same as in similar aircraft propulsion systems studied in the past, a 30 minute startup time is possible.
CONCLUSION
A portable reactor derived from the SNAP-50 could be useful, altogether: to Navy beachhead operations; to the Army mobile energy depot; and to a NASA space station and lunar base. Other applications might be a reborn nuclear aircraft with modified JT-12 engines; a nuclear electric lunar freighter and robotic probe.