Tuesday, February 2, 2010

Would Thorium Powered Ships be better for the Navy?

The Navy is studying using alternative "green" fuels for powering Navy ships and would like to be climate conscientious while it defends the nation's shores. The Navy uses nuclear power for its largest ships but must use fuel oil for its smaller vessels. There is a style of nuclear energy that produces no green house gasses and is well adapted to mobile applications and safe operation under dangerous conditions as might exist in a sea battle.

The Navy could build substantially better nuclear power particularly appropriate for smaller Navy vessels based on alternative Thorium nuclear fuel in Molten Salt Reactors. Molten Salt Reactors have the highest energy density of any style of nuclear reactor (mostly because the molten coolant salt has the highest thermal transfer efficiency of any reactor coolant) and can safely change power levels and quickly respond to real time demands for varying power levels. Molten salt reactors tend to be physically smaller for a given power output and are not subject to core meltdowns or high pressure coolant accidents. When used in appropriate alternative reactors designed to burn it Thorium produces one hundredth the amount of nuclear waste [1].

In an effort to appear sensitive to the larger themes of the Obama Administration the Navy (and other services) appear to be making efforts to qualify their military systems to burn bio-fuels. I personally feel that down-grading range and performance of military systems to reduce carbon or import of foreign oil is perverse. It is better to chose technology that allows you to improve the performance of your military systems to levels that exceed anything your enemies can achieve.

The Navy would be better off with nuclear ships and would be a more effective integrated fighting force with both large and small ships able to operate at full speed for unlimited distances. A navy where only the largest ships are nuclear powered runs the risk of having to reduce speed and restrict range just to avoid outrunning smaller fossil fuel powered support vessels.

The power density and power to weight characteristics of Molten Salt Reactors is without peer among current Gen-4 nuclear designs (shielding must be provided for all reactors and shielding requirements can tend to swamp some of the advantages Molten Salt Reactors over other reactor concepts). The fact that salt coolant for Molten Salt Reactors operates at low pressure makes MSRs a safer and more suitable choice under battle conditions. If an enemy shell goes through the ship and damages the reactor plumbing or the reactor core of a MSR the fuel salt just drips into a flat collection tray pre-placed under the reactor and via this passively safe mechanism fission stops and the reactor stops operating. This beats core meltdown scenarios that other reactor concepts suffer when there is damage to coolant pumping in the primary coolant area. Physically small high power to weight reactors are important to get excellent high levels of performance out of small ships - MSRs can be successfully built in sizes as small as 2 MW and this permits use in even quite small Navy ships. MSRs do not require heavy forged steel reactor containment vessels to be safe – this is responsible for many performance advantages and high power to weight ratio when applied in naval applications in smaller ships.

Why not make plans for a future in which all Navy ships, not just the very largest, perform at high levels and exhibit extraordinary range and capability to stay on station as ordered without requirement for refueling?
Why compromise naval performance to be politically trendy when a better technology choice would eliminate production of GHG and preserve unmatched world class naval performance and safety?

[1] Le Brun, C., "Impact of the MSBR concept technology on long lived radio toxicity and proliferation resistance"



  1. Robert - though I agree with your statement about performance and biofuels, I am not sure how thorium reactors would be an improvement in power density over our current models. They are pretty amazing devices. We are now loading our submarine reactors with enough fuel to last their entire lifetime and it is in a dense matrix of corrosion resistant metal that retains fission products in a known location. Pumping molten salt around may be fine, but we have more than 50 years worth of experience with the systems that we have AND we have an existing infrastructure of equipment suppliers, quality assurance, maintenance facilities, training schools and qualification programs.

    Why start from scratch to build all that again? Why not just build smaller PWR's for the smaller ships? There is plenty of space and weight allowance available - just run the numbers to see how much fuel a diesel powered ship has to carry to be able to operate for even a few days without refueling.

  2. Admiral,

    With all due respect, you are being distracted into thinking there will be a significant alteration in sea ice and sea level as a consequence of "climate change". If the news of the past 3 months is any indication of where the debate is going, the Navy's carbon footprint is the least of your concerns. Nor should it ever have been.

    Though I have not been in military service, I support all branches of our military and urge you to focus on your first principles: defend our nation. We don't need additional attempts at social (or in this case, environmental) experiments within our uniformed services. Biofuels don't pass the smell test and, as Rod Adams has posted, perhaps LFTR/MSR don't either, in this application.

  3. I hope I can speak on a tangent. I find the direction to Thorium reactors & shipping to be a good possibility. While the navy may have good experience, what will we do for maritime logisitics in the future? The "heat" of thorium being so much under current typical nuclear fuels makes it a highly desirable fuel.

  4. 1. Why aren't commercial ships using nuclear power? One would think that a nuclear powered oil tanker would save the owners a lot money over the lifetime of the tanker.

    2. What about thorium in space ship designs where mass is real issue?

    1. 2. The recent and renewed interest in the Liquid Fluoride Thorium Reactor (LFTR) stems from work at NASA to find suitable energy production for terra-forming planet outposts. NASA's need for the frugal management of in-space resources...literally down to the molecule...was a key driver behind this approach.

  5. A MSR reactor looks like a good idea on land, but a very bad idea at see: If such a ship sinks, all the waste is dispersed to see, even if the reactor is not damaged - if not kept at temperature the fuel salt will likely get very corrosive like it did at the MSRE after shutdown.

    Since a reactor needs effective heavy shielding anyway - its not such a bad idea to have it inside a thick walled pressure vessel, even considerably thicker than in a civil ship. It's extra weight, but not much and it has dual benefits of mechanical protection and radiation shielding. As the reactor in a ship is relatively small - thickness will be still nothing unusually.

    The second point is, that nuclear powered warships are a bad idea per se: they are a type of dirty nuclear weapon - thus undermining the anti-proliferation treaty.

  6. To my recollection, Alwin Weinberg, the principal inventor behind both the PWR and the MSRE, argued for the PWR for submarine propulsion. It is my understanding he was a key influence behind ADM Rickover's decision to aggressively pursue the PWR for submarine propulsion. It is also my understanding that Weinberg argued against the scaling up of the LWR/PWR for civilian power generation, instead favoring the Liquid Fuel THERMAL BREEDER (due primarily to inherent safety benefits). He is famously quoted as saying the pursuit of the LWR/PWR for civilian power was a "Faustian bargain". Interestingly, Wigner and Teller also favored the THERMAL BREEDER for civilian power needs.

  7. There are a few companies developing Thorium reactors now. It makes good sense to me to use these on large commercial vessels... a large cargo ship can burn through over a hundred metric tons of fuel EVERY DAY. So Thorium reactors could save a lot of space on the ship for more cargo and save huge amounts of money - over a million dollars per trip ... it's a no-brainer so far as I can see. If anyone knows of a company looking into this please let me know as I'd like to buy in! ;-)