The International Steam Pages

Researching a nuclear-fuelled steam-turbine locomotive.

Harry Valentine, Transportation Researcher. writes (13th March 2001):

Harry adds (17th April 2001) "It appears that there is research underway in Brazil, which pertains to safer, small site nuclear energy conversion ...... a concept that can apparently be adapted to heat up a future steam locomotive."


Over the past 5-years, research has been undertaken by companies such as Eskom in South Africa, into the field of mini-nuclear reactors, known as the Pebblebed Modular Nuclear reactor. Such mini and micro reactors can operate without cooling ponds and emit next to no radiation. Experience with nuclear powered submarines has shown that the protective cladding surrounding the reactor can protect the onboard staff from the radiation effects. Within the next few years, it may become possible for a nuclear micro-reactor to enable successful operation of a steam locomotive.


The concept of minaturization has been adopted in many diverse industries, for a variety of purposes. In the USA, the Nucor company pioneered the concept of a mini-steel mill, a concept once thought to be unworkable and wholly uneconomical. In the field of hydro-electric power generation, efficient and cost-effective mini and micro-hydro dams have become common in several countries. Advances in thermodynamic technology has seen the development of small, single tube mini-boilers to convert water into steam and at efficiencies of 85%. Advances in electronics technology has seen computers shrink in size while becoming more versatile and less costly. Smaller batteries are now storing more energy, smaller solar panels are now delivering more electricity, and even capacitors have now been developed to start large engines or accelerate large commercial vehicles.

The concept of minaturization is resulting in development of various types of micro-machines. At the extreme end, a new technology called nanotechnology is evolving, where micro-machines can be constructed at the molecular level, for several purposes. In view of advancing trends in many fields of scientific and technological research and endeavour, the efforts toward developing mini and micro nuclear reactors ought to be seen as an inevitable outcome. Whereas nuclear power stations may generate 1, 000 to 10, 000 Megawatts (Mw), the nuclear power plant aboard a Soviet icebreaker is rated at 70-Mw. At present, the Eskom mini-reactors are proposed to operate in the 110-Mw to 120-Mw range and without the need for cooling ponds. A micro version of this technology at one tenth the rating, may become possible.

A Nuclear-fuelled (condensing) steam locomotive:

A heavy-haul steam locomotive rated at a maximum of 15, 000-Hp and using 4-turbines (1, 000-Hp;2, 000-Hp;4, 000-Hp and 8, 000-Hp) could offer 15-power settings at maximum efficiency. If a 500-Hp turbine is added (total 15, 500-Hp), 31-power settings would result, all at maximum efficiency. A micro-reactor capable of 12-Mw would be needed and would use helium as its working fluid to transfer heat from the micro-reactor into the superheater, boiler and heater/preheater. The helium would circulate in a sealed tube, including a coiled section inside the insulated boiler. The state of the art in nuclear power research indicates that mini and micro reactors using a gas like helium, instead of heavy water, could dispense with cooling pools. This could contribute to making mini and micro-nuclear power cost competitive present, a nuclear power installation is estimated at US$1-million/Mw. Future prices of micro-nuclear could drop, making nuclear powered heavy-haul locomotives cost competitive against other types, including them operating in extended duty cycles which exceed the capabilities of diesel powered or even future solid-oxide fuel cell (methanol fuel) locomotives costing US$2-million/Mw.

In intensive service, a nuclear powered locomotive's fuel reserve would enable it to continue pulling heavy trains, where diesel locomotives would require refueling, as would methanol (SOFC-types) or Methane-fueled types. It would require less attention pulling trains across long route across deserts, than competitive types. Modern research into condensing technology would enable continuous operation, ie; once a month to take on fuel pellets, top up on purified water, transfer spent fuel and undergo routine maintenance. Whereas diesel engines require periodic rebuilding and solid-oxide fuel cells need to be replaced (at US$2-million/Mw), a nuclear locomotive could have a hidden long-term cost benefit. The longevity and service life of its componentry could exceed that of other rail motive types. The mini and micro reactors are designed to require minimal attention, which would enable one-person locomotive operation (assisted by a computer) . Locomotives would not be the only users of mini and micro reactors ..... mini-power stations could also use them in remote areas. They could be used in the commercial marine industry, large industries could generate their own power. Urban electric public transport systems could generate their own electric power, as could some railway companies to energise stretches of high traffic-density electric lines. The same railway companies could use mobile reactors along long non-electrified stretches of rail-line, such as the long distance lines in the USA, across Australia, Canada and parts of China and the former USSR.

Nuclear fuels:

Uranium would be the basis of the locomotive fuel, however, not in the fuel rod bundle (the callandra) of main power stations. The Eskom mini-reactor is proposed to use fuel balls (about the size of a cricket ball or tennis ball), in which a small amount of uranium dioxide is encased in graphite or silicon-carbide. Alternatively, uranium carbide may also be used as fuel. In a locomotive using a micro-reactor, a fuel ball the size of a marble and containing tiny amounts of uranium, would be one option. The use of uranium carbide in a pyrolite coated graphite matrix is another proposed fuel possibility.

Dr. H. Takahashi of Brookhaven National Laboratory (USA) proposed using a thin foil, with tiny amounts of uranium dioxide fuel deposited on the thin foil. Helium gas
would flow directly over the foil to transfer heat for either propulsion, or to boil water. A solution reactor proposes to use uranium dioxide in a sulphur dioxide solution, a concept which could either eliminate or greatly reduce radiation, as well as eliminate the need for cooling pools.

Still yet another option is the fuel wafer, in a honeycomb shape, proposed to heat a gas to provide jet propulsion. A small version of this concept could be used inside a steam locomotive, where helium flows over the fuel wafer and carries the heat to a super heater (900-deg C), boiler and preheater. As research continues into the field of smaller nuclear reactors, other fuel concepts are likely to emerge.


Diesel locomotives have been identified as releasing some carcinogens from their exhausts. The exhaust emissions from a nuclear locomotive would contain less carbon dioxide or carbon monoxide from a solid-oxide fuel cell locomotive fuel by methanol. The radiation levels being emitted from a nuclear fueled locomotive should be less than the levels outside a nuclear submarine, when it is in port. Research into some types of mini and micro nuclear reactors, are suggesting that some variants may even be able to operate radiation free.

Due to the low levels of fuel being used, compared to a manned nuclear ice-breaker or manned nuclear submarine, the amount of spent fuel coming from a nuclear locomotive would reflect the small amount of fuel it would consume. The spent fuel pellets would go to the same locations to which nuclear power stations send their spent fuel rods. Nuclear fuels like uranium carbide may be quite unsuitable for use in weapons, weather in in the fuel pellet state ot whether in its spent state. Weapons grade fuel would have to originate from mega-powerstations, where high concentrations of the fuel are used. By comparison, a micro-reactor would process fuel in a very dilute state, that is, it is mixed into other elements like carbon, graphite, silicon-carbide or suphur-dioxide. The fuel used in the micro-reactor may be bonded to carbon, not oxygen, changing its fission characteristics.


A nuclear-fueled steam locomotive would be used where it will be cost competitive to do so. As future research further minaturizes the mini-reactor into a micro-reactor, its economics will become more attractive. Its main competitor along non-electrified long-distance railway lines, would be future solid-oxide fuel cell locomotives using methanol. The cost of solid oxide fuel cells (US$2-million/Mw) and their propensity to deteriorate when operating continuously at maximum efficiency, indicates a replacement cycle, at high cost.

Operating costs of diesel locomotives could increase drastically after 2010, given the projections of a decline on worldwide oil production. The SOFC locomotive will be an option, courtesy of government support. A nuclear locomotive is also a possible option. In countries like the USA, long distance railway electricification could run at US$5-million per mile and higher. Electrification will make sense along the high density freight lines, though along several other lines, another option could be more viable.

The Future:

A nuclear-fueled heavy haul steam-turbine locomotive is an option for the future: it is an option due to ongoing research in the nuclear industry, into mini-reactors. As a result of such research, a micro-reactor of a size suitable for locomotive use, is a possibility to be considered.

Harry Valentine, Transportation Researcher;

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Rob Dickinson