Reaktor Nuklir untuk Aplikasi Antariksa

"Everything is becoming science fiction. From the margins of an almost invisible literature has sprung the intact reality of the 20th century."
 ~J. G. Ballard, 1930.~

The Martian Surface Reactor: An Advanced Nuclear Power Station for Manned Extraterrestrial Exploration

A. Bushman, D.M. Carpenter, T.S. Ellis, S.P. Gallagher, M.D. Hershcovitch, M.C. Hine, E.D. Johnson, S.C. Kane, M.R. Presley, A.H. Roach, S. Shaikh, M.P. Short, and M.A. Stawicki




Add and Edited By:

Arip Nurahman
Department of Physics, Faculty of Sciences and mathematics
Indonesian University of Education
and
Follower Open Course Ware at MIT-Harvard University. M.A. USA.

Abstract

As part of the 22.033/22.33 Nuclear Systems Design project, this group designed a100 kWe Martian/Lunar surface reactor system to work for 5 EFPY in support of extraterrestrial human exploration efforts. The reactor design was optimized over the following criteria: small mass and size, controllability, launchability/accident safety, and high reliability. The Martian Surface Reactor was comprised of four main systems: the core, power conversion system, radiator and shielding.

The core produces 1.2 MWth and operates in a fast spectrum. Li heat pipes cool the core and couple to the power conversion system. The heat pipes compliment the chosen pin-type fuel geometry arranged in a tri-cusp configuration. The reactor fuel is UN (33.1w/o enriched), the cladding and structural materials in core are Re, and a Hf vessel encases the core. The reflector is Zr3Si2, chosen for its high albedo. Control is achieved by rotating drums, using a TaB2 shutter material. Under a wide range of postulated accident scenarios, this core remains sub-critical and poses minimal environmental hazards.

The power conversion system consists of three parts: a power conversion unit, a transmission system and a heat exchanger. The power conversion unit is a series of cesium thermionic cells, each one wrapped around a core heat pipe. The thermionic emitter is Re at 1800 K, and the collector is molybdenum at 950 K. These units, operating at 10+% efficiency, produce 125 kWe DC and transmit 100 kWe AC. The power transmission system includes 25 separate DC-to-AC converters, transformers to step up the transmission voltage, and 25 km of 22 gauge copper wire for actual electricity transmission. The remaining 900 kWth then gets transmitted to the heat pipes of the radiator via an annular heat pipe heat exchanger that fits over the thermionics. This power conversion system was designed with much redundancy and high safety margins; the highest percent power loss due to a single point failure is 4%.

The radiator is a series of potassium heat pipes with carbon-carbon fins attached. For each core heat pipe there is one radiator heat pipe. The series of heat pipe/fin combinations form a conical shell around the reactor. There is only a 10 degree temperature drop between the heat exchanger and radiator surface, making the radiating temperature 940 K. In the radiator, the maximum cooling loss due to a single point failure is less than 1%.

The shielding system is a bi-layer shadow shield that covers an 80º arc of the core. The inner layer of the shield is a boron carbide neutron shield; the outer layer is a tungsten gamma shield. The tungsten shield is coated with SiC to prevent oxidation in the Martian atmosphere. At a distance of 11 meters from the reactor, on the shielded side, the radiation dose falls to an acceptable 2 mrem/hr; on the unshielded side, an exclusion zone extends to 14 m from the core. The shield is movable to protect crew no matter the initial orientation of the core.

When combined together, the four systems comprise the MSR. The system is roughly conical, 4.8 m in diameter and 3 m tall. The total mass of the reactor is 6.5 MT.

Nuclear Reactors for Space Applications 

With the renewed interest in deep space applications, Professor A. Kadak has instituted several studies on nuclear power systems for space applications using the nuclear engineering design course offered for both graduate and undergraduate students. The first such study considered the design of nuclear electric power for propulsion and a terrestrial power station for manned Mars missions. This project was presented to NASA senior project planners in Washington DC in 2003.

Following that meeting and a subsequent meeting with Naval Reactors engineers, feedback was used to redesign the reactor from a highly efficient spent fuel Plutonium core to a highly enriched uranium core by a Master’s thesis student. This year, due to President Bush’s desire to test the new concepts on the Moon, a terrestrial 100 kwe plant was redesigned for use on both Mars and the Moon in the design project in the fall of 2004. As a result of these projects, the nuclear engineering department is gaining valuable experience in nuclear space applications.

Publications

Nuclear Space Applications (NSA) Program

Abstract	MIT-NSA-TR-001	V. Dostal, K. Gezelius, J. Horng, J. Koser, J.P. Iv, E. Shwageraus, P. Yarsky, and A.C. Kadak, "Mission to Mars: How to Get People There and Back with Nuclear Energy" (September 2004).
Abstract	MIT-NSA-TR-002	P. Yarsky, A.C. Kadak, and M.J. Driscoll, "Design of a Sodium-cooled Epithermal Long-term Exploration Nuclear Engine" (September 2004).
Abstract	MIT-NSA-TR-003	A. Bushman, D.M. Carpenter, T.S. Ellis, S.P. Gallagher, M.D. Hershcovitch, M.C. Hine, E.D. Johnson, S.C. Kane, M.R. Presley, A.H. Roach, S. Shaikh, M.P. Short, and M.A. Stawicki, "The Martian Surface Reactor: An Advanced Nuclear Power Station for Manned Extraterrestrial Exploration" (December 2004).

"Aplikasi IPTEK NUKLIR dalam Penjelajahan Angkasa Luar, Akan menjadi Power Utama"

~Arip~

Sources:

1.MIT Nuclear Space Research
2.SPACE POWER REACTORS
3.Nuclear Reactors for Space

Space Power Reactors

"Suatu hari nanti Umat manusia akan menyinggahi tempat-tempat asing dan Nuklir akan membawa mereka"

~Arip Nurahman~

This EOE article is adapted from an information paper published by the World Nuclear Association (WNA). WNA information papers are frequently updated, so for greater detail or more up to date numbers, please see the latest version on WNA website (link at end of article).

Introduction:

After a gap of several years, there is a revival of interest in the use of nuclear fission power for space missions. While Russia has used over 30 fission reactors in space, the USA has flown only one the SNAP-10A (System for Nuclear Auxiliary Power) in 1965.

The SNAP-10A reactor. (Source:NASA)

From 1959-73, there was a US nuclear rocket program—the Nuclear Engine for Rocket Vehicle Applications (NERVA)—focused on nuclear power replacing chemical rockets for the latter stages of launches. NERVA used graphite-core reactors, heating hydrogen and expelling it through a nozzle. Some 20 engines were tested in Nevada and yielded thrust up to more than half that of the space shuttle launchers. Since then, "nuclear rockets" have been about space propulsion, not launches. The successor to NERVA is today's nuclear thermal rocket (NTR). 

Another early idea was the US Project Orion, which would launch a substantial spacecraft from the Earth using a series of small nuclear explosions to propel it. The project commenced in 1958 and was aborted when the Atmospheric Test Ban Treaty of 1963 made it illegal, but radioactive fallout could have been a major problem. The Orion idea is still alive as other means of generating the propulsive pulses are considered.

* Radioisotope power sources have been an important source of energy in space since 1961.

* Fission power sources have been used mainly by Russia, but new and more powerful designs are under development in the USA.

After a gap of several years, there is a revival of interest in the use of nuclear fission power for space missions.

While Russia has used over 30 fission reactors in space, the USA has flown only one - the SNAP-10A (System for Nuclear Auxiliary Power) in 1965.

Early on, from 1959-73 there was a US nuclear rocket program - Nuclear Engine for Rocket Vehicle Applications (NERVA) which was focused on nuclear power replacing chemical rockets for the latter stages of launches. NERVA used graphite-core reactors heating hydrogen and expelling it through a nozzle. Some 20 engines were tested in Nevada and yielded thrust up to more than half that of the space shuttle launchers. Since then, "nuclear rockets" have been about space propulsion, not launches. The successor to NERVA is today's nuclear thermal rocket (NTR).

Another early idea was the US Project Orion, which would launch a substantial spacecraft - about 1000 tonnes - from the earth using a series of small nuclear explosions to propel it. The project was commenced in 1958 by General Atomics and was aborted in 1963 when the Atmospheric Test Ban Treaty made it illegal, but radioactive fallout could have been a major problem. The Orion idea is still alive, as other means of generating the propulsive pulses are considered.

Radioisotope Systems - RTGs

So far, radioisotope thermoelectric generators (RTGs) have been the main power source for US space work over nearly 50 years, since 1961. The high decay heat of Plutonium-238 (0.56 W/g) enables its use as an electricity source in the RTGs of spacecraft, satellites, navigation beacons, etc and its alpha decay process calls for minimal shielding. Heat from the oxide fuel is converted to electricity through static thermoelectric elements (solid-state thermocouples), with no moving parts. RTGs are safe, reliable and maintenance-free and can provide heat or electricity for decades under very harsh conditions, particularly where solar power is not feasible.

So far 45 RTGs have powered 25 US space vehicles including Apollo, Pioneer, Viking, Voyager, Galileo, Ulysses and New Horizons space missions as well as many civil and military satellites. The Cassini spacecraft carries three RTGs providing 870 watts of power as it explores Saturn. Voyager spacecraft which have sent back pictures of distant planets have already operated for over 20 years and are expected to send back signals powered by their RTGs for another 15-25 years. Galileo, launched in 1989, carried a 570 watt RTG. The Viking and Rover landers on Mars in 1975 depended on RTG power sources, as will the 900 kg Mars Science Laboratory Rover due to be launched in 2011 (the two Mars Rovers operating 2004-09 use solar panels and batteries).

The latest RTG is a 290 watt system known as the GPHS RTG. The thermal power for this system is from 18 General Purpose Heat Source (GPHS) units. Each GPHS contains four iridium-clad Pu-238 fuel pellets, stands 5 cm tall, 10 cm square and weighs 1.44 kg. The Multi-Mission RTG (MMRTG) will use 8 GPHS units producing 2 kW thermal which can be used to generate some 110 watts of electric power. It is a focus of current research and will be used in the Mars Science Laboratory, which will be a large mobile laboratory, the rover Curiosity, which is about five times the mass of previous Mars rovers.

The Stirling Radioisotope Generator (SRG) is based on a 55-watt electric converter powered by one GPHS unit. The hot end of the Stirling converter reaches 650°C and heated helium drives a free piston reciprocating in a linear alternator, heat being rejected at the cold end of the engine. The AC is then converted to 55 watts DC.

This Stirling engine produces about four times as much electric power from the plutonium fuel than an RTG. Thus each SRG will utilise two Stirling converter units with about 500 watts of thermal power supplied by two GPHS units and will deliver 100-140 watts of electric power from about 1 kg Pu-238. The SRG and Advanced SRG have been extensively tested but has not yet flown. NASA plans to use two ASRGs for its probe to Saturn's moon Titan (Titan Mare Explorer - TiME) or that to the comet Wirtanen.

Russia has developed RTGs using Po-210, two are still in orbit on 1965 Cosmos navigation satellites. But it concentrated on fission reactors for space power systems.

As well as RTGs, Radioactive Heater Units (RHUs) are used on satellites and spacecraft to keep instruments warm enough to function efficiently. Their output is only about one watt and they mostly use Pu-238 - typically about 2.7g of it. Dimensions are about 3 cm long and 2.5 cm diameter, weighing 40 grams. Some 240 have been used so far by USA and two are in shut-down Russian Lunar Rovers on the moon. Each of the US Mars Rovers which landed in 2004 uses eight of them to keep the batteries functional.

The Idaho National Laboratory's (INL) Centre for Space Nuclear Research (CSNR) in collaboration with NASA is developing an RTG-powered hopper vehicle for Mars exploration. When stationary the vehicle would study the area around it while slowly sucking up carbon dioxide from the atmosphere and freezing it, after compression by a Stirling engine.

Meanwhile a beryllium core would store heat energy required for the explosive vaporisation needed for the next hop. When ready for the next hop, nuclear heat would rapidly vaporise the carbon dioxide, creating a powerful jet to propel the craft up to 1000 metres into the 'air'.

A small hopper could cover 15 km at a time, repeating this every few days over a ten-year period. Hoppers could carry payloads of up to 200 kg and explore areas inaccessible to the Rovers. INL suggests that a few dozen hoppers could map the Martian surface in a few years, and possibly convey rock samples from all over the Martian surface to a craft that would bring them to Earth.

Both RTGs and RHUs are designed to survive major launch and re-entry accidents intact, as is the SRG.

Sources:

1. Poston, D.I. 2002, Nuclear design of SAFE-400 space fission reactor, Nuclear News, Dec 2001.
2. Poston, D.I. 2002, Nuclear design of HOMER-15 Mars surface fission reactor, Nuclear News, Dec 2001.
3. Vrillon et al, 1990, ERATO article, Nuclear Europe Worldscan 11-12, 1990.
4. US DOE web site- space applications.
5. Space.com 21/5/00, 16/6/00, 22/7/00, 17/1/03, 7/2/03.
6. www.nuclearspace.com
7. Delovy Mir 8/12/95.
8. G. Kulcinski, University of Wisconsin material on web.
9. Kleiner K. 2003, Fission Control, New Scientist 12/4/03.

10. OECD 1990, Emergency Preparedness for Nuclear-Powered Satellites.
11.  NASA web site