The world is ready for the floating nuclear power stations: Tom Blees responds to Tony Roulston’s comments on his article
I’d like to respond to the comments to clarify some points. To make it more readable I’ll include quotes from the Tony Roulston’s commentary and insert my response.

“Offshore molten salt reactors, which is a compounding of molten salt technology and its outside the physical boundary of a country…This would be a massive undertaking with the largest ships in the world with the largest reactors in the world installed. This concept might turn out to be economic but there is almost no evidence one way or another.”

Regarding the first point, the ships might be outside the physical boundary of a country but would certainly be within a country’s territorial waters. As to the size of the ships, the Thorcon company was founded by a former MIT marine engineering professor who designed and had built (in South Korean shipyards) the four largest double-hull oil tankers in the world. The power ships would be about 60% of their size (see graphic below), and the reactors are not nearly the largest reactors in the world. They are actually small modular reactors of 250 MWe each, with a single ship capable of having multiple such modules depending on the energy requirements of the area to be served. The standard design is for two modules to be operating at a time. The majority of the space would be taken up by the steam power generator system. That might well end up being a supercritical CO2 heat exchanger system soon after the first such ships are built, which would allow for the ship to be smaller.

As for the economics, Thorcon’s estimates are based on extensive ship design and building experience and on recent quotes from reputable shipyards and nuclear component manufacturers. In fact, a world-class shipyard, working off a highly automated panel line, parallelizing 3000-ton blocks which requires dimensional tolerances of +/- 5mm for a 30-meter cube, in a controlled environment with a dedicated work force, can build gigantic tankers—tankers bigger than the Thorcon power ships—for about 10 man-hours per steel ton, in about 10 months. This is an order of magnitude better than site-built productivity and the quality is far superior.

Note: This diagram shows a 1 GWe silo hall. Note that there are two reactor modules for each 250 MW, so that when one is being shut off for replacement the second would be fueled and operating to prevent downtime.

“Both our and MIT’s paper pointed to specific problems of physical security against terrorist attacks which perhaps not insurmountable would add complexity and cost.”

The Thorcon design takes into account events as serious as airliner strikes and tsunamis. As for terrorist attacks, one can always imagine a worse one than the worst that’s been yet contemplated. I addressed that in my article. Probably the most likely attack for a floating nuclear power plant is ramming it with a large ship that has had its bow reinforced and weight added. That will cost extra to defend against. Instead we are in shallow enough waters that we can use a breakwater – basically a pile of rocks. I believe your studies with MIT envisioned power plants floating offshore in open water, a very different scenario.

“The use of molten salt reactor technology bring new issues along with it new opportunities and benefits. Because it breeds new fissile material from widely available thorium it appear to have virtually limitless fuel…However, the technology is not at all proven though there are a number of design teams around the world proposing molten salt reactors.”

A thermal breeder that can be fed just thorium was the dream of Oak Ridge at a time when the world believed they would soon run out of Uranium235. Turns out we have enough U235. A breeder will indeed require substantial development—both technically and perhaps more challenging politically for the safeguards issues. Thorcon chose to prioritize getting to market faster and with a simpler power plant suitable for the developing world. So the MSRE of Oak Ridge does really serve as our prototype and we leave the technology development for a breeder for the future.

While these reactors can use thorium, it is not necessary. Uranium 235 would work just as well, or a combination of the two. I don’t understand your statement that the technology is not at all proven. As I pointed out in my article, this design is based on that reactor that ran for four years at Oak Ridge National Laboratory. By the time that project was shut down for political reasons, the engineers at Oak Ridge had already designed what was to be their next reactor like this, scaled up to 300 MWe. The Thorcon design is actually a bit smaller than that.

“Thorcon design is a breeding system using highly enriched uranium and thorium. The fissile share in the fuel would be high ~20% or more – occasioning proliferation problems. The fuel cycle being considered is new. Though there are technical theoretical arguments that the issues of mobile fission product and reactor wastes can be addressed there is little or no experimental evidence to back up these arguments.”

The preferred Thorcon design would use fuel enriched to slightly less than 20%, which is generally regarded internationally as acceptable from a proliferation prevention standpoint. It could use fuel enriched to as little as 5%. As for what to do with the spent fuel, there is every reason to believe (based on conversations with fuel experts at Idaho National Laboratory and Argonne National Laboratory) that a slight variant of the pyroprocessing technology proven effective for the Integral Fast Reactor project (the EBR-II reactor) could recycle the spent fuel from the Thorcon system. The salts are nearly identical. Even if that were not the case, it is not difficult to store the spent fuel for recycling later when another system could be developed. This may be a political issue, but it is certainly not a technical one, nor should it be considered a show stopper for a design that could utterly transform the world’s energy systems for the better.

“Before the technology could be commercialized there would need to be technology demonstrator built and it operated for a number of years to gain experience and confidence in the design. One would expect the technology to be first proven on land before being used on water. These necessary developmental steps make the possibility of a floating molten salt reactor before 2040 or perhaps 2050 is remote.”

As I said above, there was a prototype built and operated for four years. That was the Oak Ridge MSRE. Certainly the first module could be built and tested on land, but aside from licensing issues that’s virtually the same as having it on board a power barge either floating next to the shore or ballasted and sitting on the bottom. The plan is to build a demonstration plant, and thoroughly test it before starting production. Yes one can drag things out to take decades – but there is no reason to do so except to please the vendors of coal and gas.

I refuse to accept the notion that this technology can’t be built, tested, and deployed expeditiously. The government of Indonesia, for one, agrees. Looking at every other nuclear power design either built or in the pipeline, and looking at all the other supposed options for dealing effectively with climate change, I see nothing that comes close to this. Is it bold to project a rapid deployment of such reactor systems? National lab directors and executives at nuclear power companies who I’ve discussed this with at length agree that it is. But most importantly, they all believe that it can be done, and that it’s only the politics that can slow it down. So my question would be: Are you willing to buck the politics in order to bend the curve and respond effectively not only to the challenge of climate change but to the pressing need for abundant, inexpensive clean energy for the billions of people around the world who live in energy poverty today?


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May 2020