SMR's, Ships, and History

January 2, 2020, 4:30PMANS Nuclear CafeWill Davis

As we start 2020 I find myself thinking about the slew of articles and posts that I'm seeing about SMR's - that is to say, Small Modular Reactors.  Many are written by knowledgeable people, many not so much - but in some places I've started to see some references to the pollution caused by heavy ocean shipping and whether or not we could use SMR's to stop that by converting ships to nuclear power.  Well, let's not rush into this - after all, all of the "consideration" phase was done once before and there was in fact ocean-going hardware.  So, keeping in mind that it's the holiday season, I'd like to just offer up a quick look at what was considered and what was surprisingly found out to be true in regards to nuclear cargo or passenger ships in the 1950's and 1960's.  I hope this is new for many of you!

The Beginning

Just like today, it was first thought in the 50's that the most economical process to apply nuclear power to commercial shipping was to take existing, in-production or reproducible designs for ships and "drop in" a nuclear plant.  That was relatively easier then than it is now because there were still a very large number of steam powered ships; using a reactor to produce steam was sort of a switchover from heavy oil to atoms.

Many studies were done - by firms you'd know, such as General Electric, and some you might not suspect.  For example, I have here in my files a complete report for a gas cooled reactor installation that was put out by the Cleveland Diesel Engine Division of General Motors (they actually subcontracted the report but intended to launch into construction at GM if it were approved - probably after buying the contractor, but that's just my guess.)  In all of these, the supposition was the same; nuclear conversion.  Even the NS SAVANNAH was designed starting with the US Maritime Administration's MARINER class cargo ships as a starting point with some modifications for the (larger and heavier than ideal) NSSS.

American Turbine Gas Cooled Maritime Nuclear Plant Closed Cycle 2

From a different study - American Turbine design for a "drop in" gas cooled plant operating on closed cycle. This never reached the hardware stage but is typical of the myriad of designs cooked up in the late 50's and very early 60's - compact, and somewhat scalable to fit various sizes of ships with varying power requirements. In some cases large ships would simply have used multiple reactors, gears and shafts.

The Realization

Two things began to make themselves apparent as studies for nuclear ships entered advanced phases in the 1960's and as the SAVANNAH entered operation.  First, the pay required for the nuclear operators on the ships was a very significant factor - higher than had been considered.  In fact, disputes over pay led to a halt in SAVANNAH's operation and a change of operating contractors.  Second, insurance for such ships would be very costly indeed if the ships were not government-owned.

A further issue was the massive size and weight of the NSSS's being considered in the light water range.  Gas cooled offered much lower theoretical weight but wasn't ready when the phone rang, so light water it was.  This meant that you could not simply stick the NSSS where the boilers had been on any given ship.  In many cases, you'd have had to use a smaller-than-optimal NSSS as a drop-in.

The use of nuclear power in existing blueprints thus handicapped the designers into sketching ships that would be uneconomic from the start.  There appeared to be two options available to move nuclear ships into economic reality:

1.  Make the ships very large.  A huge amount of bulk cargo, paid by the ton meaning large profit, which could be fairly rapidly unloaded (think oil or coal, not televisions or cars) would ensure the highest "at-sea" time, which would mean the highest revenue.  The size of the ship only increased the power required from the plant - four reactor operators on board, paid the same, would do as well for a 150 MW reactor as for a 5 MW reactor.  Thus pay was fixed by crew, not by ship, size.

2. If the ships were not very very large, then a cargo (or perhaps passenger) premium on high speed would be necessary.  Since nuclear offered a potentially much higher horsepower per pound of power plant, a very fast (but still decently large) ship could carry cargo or passengers who needed priority transit, and for which a high price could be charged.  Again, the cost of the plant operators was essentially fixed, so it constituted a center around which speed vs. capacity would be examined.

Of course, there were further concerns.  For extremely large ships, where would they pull in?  Would existing harbors accommodate them or would they have to be dredged and widened?  For extremely fast ships, would there be safety concerns?  Would there be a desire to militarize them in case of conflict (as the SS UNITED STATES was designed for)?  Regardless of these added concerns about design, there was also of course the huge diplomatic effort needed to get nations to allow nuclear ships to conduct trade in the first place - no small endeavor, and one which NS SAVANNAH undertook for years as a mobile statesman-showboat.


If we apply this thinking to today, we have some better elements and some worse ones.  On the one hand, ship size has increased beyond anything imagined in the 1950's and 1960's in both the passenger ship and the cargo (think 'supertanker') categories.  On the other hand, these ships are all today powered by gigantic diesel engines; the "straight over" convertability is pretty much gone.  A plus is the use of electric drives.

One thing that's "right" about today's thinking is the iPWR, or integral pressurized water reactor.  SAVANNAH proved that discrete component plants aren't good for space saving, and the next nuclear ship built in the West (OTTO HAHN) had an integral reactor.  Today's concepts are all along these lines more or less and we might say that they're "optimal" for use in ships.  They simply need to be connected to a different kind of power plant.

Whatever happens, it'd do us well to remember the lessons above.  There's no need to start with a clean sheet of paper totally, but trying to convert anything but the largest or fastest ships to nuclear power seems quite a bit down the profit scale (and thus, the "chances for success" scale.)  If we just take a moment to stand on the shoulders of those who came before and see what they saw, when we get back on the ground to run our own race we've a great chance of succeeding.  And I for one think this might be the decade that sees nuclear powered commercial ships return.  I'd hope so.

Will DavisWill Davis is a frequent contributor to the ANS Nuclear Cafe who probably spends too much time thinking about nuclear powered ships.  He wishes all of our readers and especially our American Nuclear Society members a Happy New Year, with continued health and happiness.  And yes, in this photo he's standing in the control room of NS SAVANNAH.