Can Small Modular Reactors Revitalize Nuclear-Powered Surface Combatants?

[Flyboy]

Even on the civilian front, the reactor does make a lot of sense, at least for the big container freighters. They burn a lot of fuel oil per trip, and the cost of that over time is only going to go up. If you switch to nuclear, yeah, it's higher upfront costs, and refueling is expensive when it does happen, but you don't have to buy fuel for every leg of your journey, detours around geopolitical hotspots doesn't cost anything more than the lost time, you significantly reduce your emissions footprint, and if deployed properly and safely, it's a huge proof of the fact that modern nuclear power is indeed safe for widescale use and decarbonization of major emitters like the shipping industry. It'd be less about the speed, although you probably could go faster than a maritime diesel powered ship could, but I think that as the cost of fuel oil goes up, it'll become more economical to switch to nuclear. Might as well jump into at least development now so it's proven and mature by the time it's needed en masse.

As for the LCS... that's a whole 'nother can of worms. Concept is sound, execution is severely lacking.

 

[Vanadium 50]

I am not sure I would want my nuclear freighters flying under just any flag. Moldova? I'm not sure that shipowners want to fly under the US flag either, with the fees and regulations. So this would have to be a lot better, not just a little better.

 

[Vanadium 50]

Marine SMRs may be more practical/realistic - but what would that look like? What kind of power plant?

It's not clear to me how eVinci tuens heat into power to begin with. For various reasons, you probably want to go electric as soon as you can, and drive the screws with electricity, provided you can.

The power per unit volume of the eVinci is an order of magnitude higher than the D2G. So there is space. You want about 100 MW of power. You could do this with 20 eVincis. However, I doubt that is the right approach. I think you want a design like that, scaled up so you need perhaps 4. You want them small enough to get them in and out of the hull with minimum disruption, but you don't want the complexity of having to operate dozens per ship.

It seems to me that it is also not 100% crazy to consider this direction. A submarine gets out of trouble by driving its way out. Typically, it will have one reactor (with a handful of exceptions). The combination means that a reactor problem is a Very Very Bad Thing. Multiple, smaller reactors mitigates this risk.

 

[Astronuc]

It's not clear to me how eVinci tuens heat into power to begin with. For various reasons, you probably want to go electric as soon as you can, and drive the screws with electricity, provided you can.

https://www.westinghousenuclear.com/energy-systems/evinci-microreactor

eVinci is a microreactor, i.e., it is a small reactor 13 MWth converted to 5 MWe (implying 38.4% efficiency). Heat pipes move heat from the core to a heat exchanger, and the heat flows into a working fluid in a Rankine steam cycle, for example.

In the following, the presentation indicates an open air Brayton cycle (34% efficiency)
https://www.engineering.pitt.edu/co...fb89d9fa0ab9e3899/day1-pm3_thomas_tweedle.pdf

The reactor can provide process heat or district heating in remote areas. They do indicate possible use a mining locations, which might be remote from power lines, and an open air Brayton cycle might be practical in dry areas, or areas with restricted or nil water access.

Probably more details here (I haven't reviewed the files).
https://www.nrc.gov/reactors/new-re...vities/pre-application-activities/evinci.html

As gmax137 indicated, submarine reactors have excess reactivity to override Xe following shutdown.

 

[Astronuc]

I am not sure I would want my nuclear freighters flying under just any flag. Moldova?

UK? Austrlalia? I think we're mates.

 

[gmax137]

It isn't clear to me what exactly is meant by SMR in this thread. See the latest news in the thread on NuScale's SMR, https://www.physicsforums.com/threa...reactor-project-in-idaho.1057305/post-6983730

 

[Astronuc]

It isn't clear to me what exactly is meant by SMR in this thread. See the latest news in the thread on NuScale's SMR, https://www.physicsforums.com/threa...reactor-project-in-idaho.1057305/post-6983730

US NRC - "The NRC refers to light water reactor (LWR) designs generating 300 MWe or less as small modular reactors (SMRs)."
https://www.nrc.gov/reactors/new-reactors/smr.html

Typically a reactor would be coupled to its own power conversion system. I do not see a common power conversion system. A larger capacity unit might share containment with another unit, but there are issues with refueling then.

In the case of nuclear scale, the original idea was to have up to 12 reactors in a shared containment, with each reactor in a bay. They reactor module sits in a large pool of water in common to all 12 units. For refueling, the plan was/is to decouple the reactor from it's power conversion system, bring the reactor module to a refueling bay, open the reactor and refuel, then return to its operating bay, reconnect to the power conversion system, and voilà startup and run.

NuScale had in mind an inherently safe reactor design, so small plant footprint and emergency planning zone (EPZ), and economy of order couple of units, then a couple more, until the site is filled out to the desired number. They could have done 12, 8, or 6, or 4, which would be up to the utility. In small towns, maybe 1 or 2 would suffice.
For example - https://www.nrc.gov/reactors/new-re.../current-licensing-reviews/nuscale-us460.html (6 * 77 MWe = 462 MWe)

Different size concepts have very different ideas. So much for standardization.

 

[gmax137]

Thanks, @Astronuc !
But still, what is it about say NuScale's SMR that would make it a better marine reactor than the S9G or whatever the US navy is using in the current submarines?

 

[Astronuc]

Thanks, @Astronuc !
But still, what is it about say NuScale's SMR that would make it a better marine reactor than the S9G or whatever the US navy is using in the current submarines?

I don't think NuScale's design would be better than an S9G, or whatever the Navy uses. They are two different animals - different purposes - different operating environment.

Perhaps as a merchant marine propulsion reactor, it might work.

NuScale's design is a derivative of LWR (PWR) technology, which like the NS Savannah's reactor back in the day.
https://en.wikipedia.org/wiki/NS_Savannah#Reactor
I think mPower and a W design were closer in concept to the Savannah reactor - basically putting the steam generator on top of the core, or as close to it as possible. Still the main issue is neutron leakage and activation of the surrounding structures (the RPV and containment). Refueling is another issue.

 

[Vanadium 50]

Submarine reactors are very complicated things, and kind of tangential to this discussion. I'll just say that the S2G reactor design was....wow. Just wow.

It is also worth pointing out that submarines are dangerous beasts. The Bonefish fire, on a modern non-nuclear submarine, is an excellent example. The fact that only three lives were lost and not the entire boat was nothing short of miraculous.

As for shipping, most vessels are registered or "flagged" in countries other than their corporate base. Panama is the most popular, but also Liberia, the RMI, Mongolia, Bolivia, among others. Note that some of these countries are landlocked. The UK has about a fifth as many ships as Panama, the US 10% of the UK, and Australia 10% of that (14 ships).

 

[gmax137]

Submarine reactors are very complicated things, and kind of tangential to this discussion. I'll just say that the S2G reactor design was....wow. Just wow.

Yes, but at least back in the 1950s there was a willingness to try lots of new ideas.

 

[Vanadium 50]

Liquid sodium in an underwater vessel? What could possibly go wrong? (And the Alfa showed that people didn't learn)

Other stupid idea: Soviet Quebec ("Zippo") class - carrying liquid oxygen on board. What could go wrong there?
Hey, let's put radar on a submarine (USS Triton).
US Barbel class. Who needs nuclear power when you have diesels? And, for extra credit, lets put more torpedo tubes where the sonar goes. With enough ammo, you don't need to be able to find your target!

 

[gmax137]

I don't know much about the S2G reactor (other than the sodium). The Wikis on Seawolf, S2G, and S1G are interesting. How about this (https://en.wikipedia.org/wiki/USS_Seawolf_(SSN-575)):

On 18 April 1959, the Navy disposed of the radioactive S2G plant by sealing it in a 30-foot high stainless steel containment vessel, towing it out to sea on a barge, and then sinking the barge at a point about 120 miles due east of Maryland in 9,100 feet of water. Twenty-one years later, the Navy was unable to relocate the container, but said that the radioactive materials inside should decay before the containment vessel deteriorated.

As Lou Reed said, "those were different times..."

 

[Vanadium 50]

Probably better than grinding it up and disbursing the dust over an unfriendly nation.

 

[Astronuc]

IAEA has a publication on Small Modular Reactors for Marine-based Nuclear Power Plant

https://aris.iaea.org/Publications/2023 IAEA Marine Based SMR Booklet.pdf

 

[Astronuc]

I just happened to read a CNN article on SMRs.
https://www.cnn.com/2024/02/01/clim...russia-china-climate-solution-intl/index.html

This technology is also being used below sea level. Dozens of US submarines lurking in the depths of the world’s oceans are propelled by SMRs, as the compact reactors are known.

No, not really, or at least, not entirely accurate. Perhaps using a lose definition of 300 MWe or less, which the NRC uses for land-based reactors. Most references mention 'naval reactors'.
https://www.nrc.gov/reactors/new-reactors/smr.html

The NRC does not regulate naval reactors, which are under DOE/NNSA and DOD/Navy.
https://www.energy.gov/nnsa/powering-navy

the Naval Nuclear Propulsion Program, a joint Department of Navy and Department of Energy organization responsible for all aspects of the Navy’s nuclear propulsion, including research, design, construction, testing, operation, maintenance, and ultimate disposition of naval nuclear propulsion plants.

https://www.navy.mil/Press-Office/News-Stories/Article/3476093/naval-reactors-celebrates-75-years/

From the CNN article

At the COP28 climate talks in Dubai in December, the US led a pledge to triple the world’s nuclear energy capacity, which 25 nations have now signed onto. And the US government has earmarked $72 million to its international SMR program, known as FIRST, to provide countries with a whole suite of tools — from workshops to engineering and feasibility studies — to provide them with everything they need to buy an SMR fleet made in America.

But bigger money is coming in the form of loans from state financial institutions, like the US Export-Import Bank and its International Development Finance Corporation, which have offered up $3 billion and $1 billion, respectively. Those have gone to two SMRs in Poland designed by GE Hitachi Nuclear Energy, a US-Japanese partnership headquartered in North Carolina.