Naval Nuclear Reactor Discussion

[Scott Kenny]

According to the old Forecast International document linked below, the Rubis-class SSNs offered to Canada would have actually been the somewhat upgraded Améthyste sub-class.

https://www.forecastinternational.com/archive/disp_old_pdf.cfm?ARC_ID=1737

Single steam loop?

Go F yourself, Mister DeGaulle! There's a reason everyone else keeps the primary loop inside the reactor compartment and lets it boil water in the secondary loop to spin the turbines.

 

[Grey Havoc]

To be fair, it was more likely a wheeze by ye old beancounters rather than de Gaulle.

 

[Scott Kenny]

To be fair, it was more likely a wheeze by ye old beancounters rather than de Gaulle.

Which is ironic, because it makes things lots more expensive.

two-loop reactor plants means that your steam turbines are all non-radioactive (unless you get a pinhole leak in the steam generators). single loop reactors means your turbines are contaminated and all maintenance needs to be done in bunny suits etc to keep the crew safe.

And then when you scrap the ship, that's all radioactive waste instead of stuff you can shovel directly into a steel furnace to recycle.

 

[TinWing]

Which is ironic, because it makes things lots more expensive.

two-loop reactor plants means that your steam turbines are all non-radioactive (unless you get a pinhole leak in the steam generators). single loop reactors means your turbines are contaminated and all maintenance needs to be done in bunny suits etc to keep the crew safe.

And then when you scrap the ship, that's all radioactive waste instead of stuff you can shovel directly into a steel furnace to recycle.

Consider for a moment that the Rubis class has a higher availability rate and gets more days at sea than UK and American SSNs. And this is despite the need for periodic reactor refuelings by way of a very cleverly designed hatch. I’d say that the design actually has superior serviceability, even with LEU and a single loop steam plant. Something that’s worthy of study if not outright emulation. As far as I can remember, quieting was the primary problem with early Rubis class and that was solved by the Amethyst rebuilds.

The reality is that the eventual scrap value of steam turbines or the entire machinery section of a nuclear submarineis of negligible concern. The reactor section gets buried in a trench. Why not throw in the machinery section as well?

Considering that the United States is struggling with current SSN construction, it might be time to think about a mobilization SSN design to go along with that new, cheaper mobilization torpedo that might supplement the Mk 48. A single loop steam plant is a good place to start with for a quicker and cheaper to build design. At some point, instead of arguing over 1 or 2 or 3 SSNs per year, we might need to build out a fleet of 100+ as quickly as possible.

 

[Scott Kenny]

Consider for a moment that the Rubis class has a higher availability rate and gets more days at sea than UK and American SSNs. And this is despite the need for periodic reactor refuelings by way of a very cleverly designed hatch. I’d say that the design actually has superior serviceability, even with LEU and a single loop steam plant. Something that’s worthy of study if not outright emulation. As far as I can remember, quieting was the primary problem with early Rubis class and that was solved by the Amethyst rebuilds.

The reality is that the eventual scrap value of steam turbines or the entire machinery section of a nuclear submarineis of negligible concern. The reactor section gets buried in a trench. Why not throw in the machinery section as well?

Considering that the United States is struggling with current SSN construction, it might be time to think about a mobilization SSN design to go along with that new, cheaper mobilization torpedo that might supplement the Mk 48. A single loop steam plant is a good place to start with for a quicker and cheaper to build design. At some point, instead of arguing over 1 or 2 or 3 SSNs per year, we might need to build out a fleet of 100+ as quickly as possible.

Steam lines like to rupture, if not very well maintained.

This kills everyone in the engineroom, of course, but if it's a dual loop reactor you don't contaminate the entire engineroom and ventilation system.

 

[Yellow Palace]

Which is ironic, because it makes things lots more expensive.

It makes the initial procurement cheaper, which can be preferable for a certain type of beancounter.

That said, I thought the early MAGNOX reactors that had unshielded steam generators were bad. Running primary steam through the turbines... that's a no from me.

 

[TinWing]

Steam lines like to rupture, if not very well maintained.

This kills everyone in the engineroom, of course, but if it's a dual loop reactor you don't contaminate the entire engineroom and ventilation system.

I’d say that the French must maintain their steam lines very well. All considered, you really don’t to permanently staff the machinery spaces, either.

Single loop designs have worked well enough in the past. There was a lot wrong with Russia’s HEN class submarines but the actual single loop steam plant seems to have been fine. K-11 was contaminated with radioactive steam from the reactor vessel itself. Similarly, the US Army operated the single loop “General Sturgis” floating power plant in Panama with reasonable safety.

 

[Archibald]

Eeerhm the French navy certainly maintain its Rubis submarines better than the Soviets - which is not a very high bar, incidentally.

 

[Scott Kenny]

Eeerhm the French navy certainly maintain its Rubis submarines better than the Soviets - which is not a very high bar, incidentally.

That bar is so low it's a trip hazard.

 

[Scott Kenny]

I’d say that the French must maintain their steam lines very well. All considered, you really don’t to permanently staff the machinery spaces, either.

The US does, there's around a dozen people on watch in the engineroom 24/7.

Wonder where France puts their reactor controls and instrumentation, if not in the same compartment as the steam turbines?

 

[RP1]

There seems to be some confusion as to what "single loop" means in this case, specifically confusing a boiling water reactor, in which steam is generated in the reactor vessel, seperated using a steam seperator and passed to the turbine. In a BWR the steam will be radioactive and so the turbines and steam lines must be shielded. The CAS-48 reactor is an integral Pressurised Water Reactor (PWR), in which the primary (active) circuit does not contain steam and instead steam is generated in a secondary circuit using heat exchangers (steam generators).

The term "single loop" refers to the fact that, unlike an American or British reactor (and the reactor used on the original French SSBNs), where there are two steam generators with their own secondary loop and turbine, the early French integral reactor had a single steam generator mounted over the reactor core, with a single secondary loop.

There is technically a contamination risk here, as with only one loop and one turbine, a fault in the heat exchanger could lead to contamination passing into the secondary circuit, although this exists with any PWR, the issue with a single loop is that you would have to accept it if you wanted to keep the reactor running, whereas in theory one could shut down one side of a two-loop plant.

Note that an integral reactor can have multiple loops if the steam generators are appropriately segregated and do not share a common steam header, the French chose not to for their first integral plant.

 

[TomS]

There seems to be some confusion as to what "single loop" means in this case, specifically confusing a boiling water reactor, in which steam is generated in the reactor vessel, seperated using a steam seperator and passed to the turbine. In a BWR the steam will be radioactive and so the turbines and steam lines must be shielded. The CAS-48 reactor is an integral Pressurised Water Reactor (PWR), in which the primary (active) circuit does not contain steam and instead steam is generated in a secondary circuit using heat exchangers (steam generators).

The term "single loop" refers to the fact that, unlike an American or British reactor (and the reactor used on the original French SSBNs), where there are two steam generators with their own secondary loop and turbine, the early French integral reactor had a single steam generator mounted over the reactor core, with a single secondary loop.

There is technically a contamination risk here, as with only one loop and one turbine, a fault in the heat exchanger could lead to contamination passing into the secondary circuit, although this exists with any PWR, the issue with a single loop is that you would have to accept it if you wanted to keep the reactor running, whereas in theory one could shut down one side of a two-loop plant.

Note that an integral reactor can have multiple loops if the steam generators are appropriately segregated and do not share a common steam header, the French chose not to for their first integral plant.

View attachment 725817

Thanks for the clear explanation. I suspected this was the case but I could not track down a detailed description of CAS-48 to explain it properly.

 

[Scott Kenny]

There seems to be some confusion as to what "single loop" means in this case, specifically confusing a boiling water reactor, in which steam is generated in the reactor vessel, seperated using a steam seperator and passed to the turbine. In a BWR the steam will be radioactive and so the turbines and steam lines must be shielded. The CAS-48 reactor is an integral Pressurised Water Reactor (PWR), in which the primary (active) circuit does not contain steam and instead steam is generated in a secondary circuit using heat exchangers (steam generators).

The term "single loop" refers to the fact that, unlike an American or British reactor (and the reactor used on the original French SSBNs), where there are two steam generators with their own secondary loop and turbine, the early French integral reactor had a single steam generator mounted over the reactor core, with a single secondary loop.

There is technically a contamination risk here, as with only one loop and one turbine, a fault in the heat exchanger could lead to contamination passing into the secondary circuit, although this exists with any PWR, the issue with a single loop is that you would have to accept it if you wanted to keep the reactor running, whereas in theory one could shut down one side of a two-loop plant.

Note that an integral reactor can have multiple loops if the steam generators are appropriately segregated and do not share a common steam header, the French chose not to for their first integral plant.

View attachment 725817

Okay, that's a lot better.

Single secondary loop is vastly safer than boiling water, and yes, only has half the "other stuff" (turbines, generators, etc) and if direct drive has much simpler reduction gearing than a twin secondary system. So that does make it cheaper on that side, and since the turbines etc aren't contaminated working on them or scrapping them is cheaper as well.

I am still not very fond of the LEU reactors needing refueling every ~7 years or so, because refueling is expensive and leaves the sub unavailable for a year or two.

But if you're selling the boats abroad LEU is essentially not a proliferation risk while a life-of-ship core is full of weapons-grade uranium.

 

[TomS]

I am still not very fond of the LEU reactors needing refueling every ~7 years or so, because refueling is expensive and leaves the sub unavailable for a year or two.

The Rubis design is a bit different than USN because they designed for this regular refueling. There's a built-in hull patch that can just be unbolted to swap out the core. A Rubis RCOH takes less than 15 months every 8 years, which is a good deal faster than a US ERO overhaul these days.

 

[Scott Kenny]

The Rubis design is a bit different than USN because they designed for this regular refueling. There's a built-in hull patch that can just be unbolted to swap out the core. A Rubis RCOH takes less than 15 months every 8 years, which is a good deal faster than a US ERO overhaul these days.

That's not entirely a fair comparison, US nuclear work has gotten so undermanned and way behind. In the 1980s the US was doing RCOHs in about 15 months or so.

 

[BROF]

It makes the initial procurement cheaper, which can be preferable for a certain type of beancounter.

That said, I thought the early MAGNOX reactors that had unshielded steam generators were bad. Running primary steam through the turbines... that's a no from me.

MAGNOX did not run the steam loop into the core. Heat was transfered to it by a CO2 loop.

 

[BROF]

Single steam loop?

Go F yourself, Mister DeGaulle! There's a reason everyone else keeps the primary loop inside the reactor compartment and lets it boil water in the secondary loop to spin the turbines.

This is really silly. Rubis reactor is a PWR with a primary loop in the upper, separate comprtment of reactor vessel and a secondary loop. What has de Gaulle to do here? And explain how anyone could design a direct cycle pressurised-water reactor? With a pressurised condenser, perhaps? How ridiculous.

BTW, mister "F yourself", what you do not know, obviously, is that your anglo-saxon pope of naval nuclear propulsion, Hyman Rickover, had as an initial idea, when he made the first R&D contracts for naval reactors at BuEng in April 1945, a BWR, where steam would be produced directly in the core, as a direct subsitute to fuel-fired boilers. Like the "excellent" US-designed GE BWR reactors at Fukushima Daichi, you remember? And of course the turbine, condenser, steam lines would suffer from (admitedly short-life) radioactive contamination, as is a case in a commercial BWR reactor nowadays (where staff do not enter the vicinity of the turbine during operation). It is only later in 1946, when it became clear that a BWR would produce very low-quality steam and need more volume and mass that Rickover switched to PWR.

This ridiculous reaction reminds me of the 1962 hearings in the US senate on the agreement for supply of HEU to France for the PAT reactor (the on-shore prototype for the first SNLE PWR reactor). Rickover, also a known francophobe, was expected to oppose it, but did not. When asked why, he said on record "because even with this HEU, "the French" will never be able to build a nuclear-powered submarine". The first SNLE reactor became critical in 1969. Up yours...
.

 

[BROF]

CANDU are PHWR, not PWR. The fundamental of nuclear physics are understood in every physics department around the world but what matter is the technical capability to produce a specific technology that Canada never developed. In Australia even opposition agrees on SSN on condition to never develop a civilian nuclear industry, demonstrating that the public opinion is maybe concerned with the size of the military spending, not so much with a specific set of equipment. Civilian regulations and authority are completely different from the military ones. So Canada sub program of the '80s would have needed basically the creation of a wholly new industrial sector, something that has not happened to the majority of the civilian nuclear power because their civil program born as a spin off of their military program.

Indeed, CANDU is, or rather was, a natural U / heavy reactor. Physics are very different from a LEU-fuelled LWR, pressurised or boiling water. It is not possible to create a CANDU type of reactor for naval propulsion, primarily because of low power density and very small reactivity margin, that would made repeated power transients difficult to manage. Low power density precludes a single, compact pressure vessel. CANDU have no pressure vessel; primary containment is achieved, theoretically, by each of the numerous pressure tubes, as in an RBMK. This was one of the reasons why Canada chose CANDU in 1954: Canadian industry did not have the capabilty to forge large pressure vessels (Official History of AECL / Histoire officielle d'ÉACLtée, Ottawa 1987).

 

[Scott Kenny]

This is really silly. Rubis reactor is a PWR with a primary loop in the upper, separate comprtment of reactor vessel and a secondary loop. What has de Gaulle to do here? And explain how anyone could design a direct cycle pressurised-water reactor? With a pressurised condenser, perhaps? How ridiculous.

BTW, mister "F yourself", what you do not know, obviously, is that your anglo-saxon pope of naval nuclear propulsion, Hyman Rickover, had as an initial idea, when he made the first R&D contracts for naval reactors at BuEng in April 1945, a BWR, where steam would be produced directly in the core, as a direct subsitute to fuel-fired boilers. Like the "excellent" US-designed GE BWR reactors at Fukushima Daichi, you remember? And of course the turbine, condenser, steam lines would suffer from (admitedly short-life) radioactive contamination, as is a case in a commercial BWR reactor nowadays (where staff do not enter the vicinity of the turbine during operation). It is only later in 1946, when it became clear that a BWR would produce very low-quality steam and need more volume and mass that Rickover switched to PWR.

This ridiculous reaction reminds me of the 1962 hearings in the US senate on the agreement for supply of HEU to France for the PAT reactor (the on-shore prototype for the first SNLE PWR reactor). Rickover, also a known francophobe, was expected to oppose it, but did not. When asked why, he said on record "because even with this HEU, "the French" will never be able to build a nuclear-powered submarine". The first SNLE reactor became critical in 1969. Up yours...
.

That was a misunderstanding on my part on the meaning of single loop. Because there's two ways to picture it. Normal primary/secondary/tertiary loops but only one of them, or a BWR that makes steam directly. And I absolutely despise BWRs due to their failure modes.

As to Rickover, the man was an ass. A bigger one than I am, which is saying something. But in terms of engineering, BWRs as a direct replacement for the oil fired boilers is simple. Just can't make enough high energy steam, so we go to PWRs like the high pressure/high temp boilers with steam superheaters.

======

I still don't like the French LEU reactors because it forces you to refuel every 7-8 years and costs you at least one deployment cycle in the process. Yes, there's a big hatch on the hull of the sub to access the reactor, but you have to make sure it seals perfectly. I cannot imagine the tension for the first dive after a refueling.

If you have the equipment to make HEU, that's massively better to refuel once every 20 years or to stretch it to 35-40 years without refueling at all. Takes some interesting engineering, though. Yes, you get piles of DU as waste, but that has other uses. Like ballast for aircraft or tank ammunition.

 

[Yellow Palace]

MAGNOX did not run the steam loop into the core. Heat was transfered to it by a CO2 loop.

Yep, but the heat exchangers that transferred the heat from the CO2 loop to the steam loop were outside the primary containment vessel, leading to gamma shine. Which is nowhere near as bad as putting primary steam through the turbines, though it doesn't look like anyone was daft enough to do that.

I still don't like the French LEU reactors because it forces you to refuel every 7-8 years and costs you at least one deployment cycle in the process. Yes, there's a big hatch on the hull of the sub to access the reactor, but you have to make sure it seals perfectly. I cannot imagine the tension for the first dive after a refueling.

If you have the equipment to make HEU, that's massively better to refuel once every 20 years or to stretch it to 35-40 years without refueling at all. Takes some interesting engineering, though. Yes, you get piles of DU as waste, but that has other uses. Like ballast for aircraft or tank ammunition.

Remember that the first USN reactors needed refuelling every few years, even with HEU. The idea of cores lasting half the life of the ship is comparatively recent, and even I'm young enough to remember whole-life cores becoming a technical possibility. I don't remember exactly why the French naval nuclear power programme chose to use LEU, but the French defence industry is very switched-on to economic considerations and won't have done it without good reason.

 

[Scott Kenny]

Remember that the first USN reactors needed refuelling every few years, even with HEU. The idea of cores lasting half the life of the ship is comparatively recent, and even I'm young enough to remember whole-life cores becoming a technical possibility. I don't remember exactly why the French naval nuclear power programme chose to use LEU, but the French defence industry is very switched-on to economic considerations and won't have done it without good reason.

I'm not sure that the "refuel every 5-8 years" reactors were HEU. (Wasn't something that came up when qualifying, but it makes me kinda wish I'd asked now.)

I mean, the whole reason for ~20yr refuelings (started with 688s and 726s, it looks like) was because they used HEU to still have fissionables left after a decade. The life of ship reactors had to get creative for how to burn away some neutron poisons in the control rods once they got past 20 years.

 

[TomS]

I'm not sure that the "refuel every 5-8 years" reactors were HEU. (Wasn't something that came up when qualifying, but it makes me kinda wish I'd asked now.)

I mean, the whole reason for ~20yr refuelings (started with 688s and 726s, it looks like) was because they used HEU to still have fissionables left after a decade. The life of ship reactors had to get creative for how to burn away some neutron poisons in the control rods once they got past 20 years.

US SSNs have always been HEU. But HEU covers a wide range, anything from 20% enrichment (apparently used in early US SSNs and still by some other navies) up to weapons grade (>93%) HEU in modern US subs.

US study of reactor and fuel types to enable naval reactors to shift from HEU fuel

Alan Kuperman, Frank von Hippel In February 2020, the US Department of Energy's office of Defense Nuclear Nonproliferation released its report, Initial Evaluation of Fuel-Reactor Concepts for Advanced LEU Fuel Development, a screening study for potential fuel and reactor types...

fissilematerials.org

https://sgs.princeton.edu/sites/default/files/2019-11/philippe-vonhippel-2016.pdf

 

[Scott Kenny]

US SSNs have always been HEU. But HEU covers a wide range, anything from 20% enrichment (apparently used in early US SSNs and still by some other navies) up to weapons grade (>93%) HEU in modern US subs.

Okay, yes, if you're defining 20% as highly enriched then the early USN reactors were HEU.

20% ain't weapons grade by modern standards, though. 20% HEU means 10,000lb nukes that burn maybe 2lbs of Uranium in detonation for 20kt booms.

The 20+ year cores are weapons grade by modern standards, 90something%.

US study of reactor and fuel types to enable naval reactors to shift from HEU fuel

Alan Kuperman, Frank von Hippel In February 2020, the US Department of Energy's office of Defense Nuclear Nonproliferation released its report, Initial Evaluation of Fuel-Reactor Concepts for Advanced LEU Fuel Development, a screening study for potential fuel and reactor types...

fissilematerials.org

I don't see liquid metal cooled reactors working in any situation where you need to start up and shut down a lot. For example, a ship. You'd have to keep the reactor hot enough to keep the metal molten one way or the other.

And sodium can stay the hell out of my steam generators, thank you very much!

 

[TomS]

Okay, yes, if you're defining 20% as highly enriched then the early USN reactors were HEU.

20% ain't weapons grade by modern standards, though. 20% HEU means 10,000lb nukes that burn maybe 2lbs of Uranium in detonation for 20kt booms.

True, but HEU is not a synonym for weapons grade. HEU is a technical term that refers to >20% enrichment. Most commercial reactors run on Low-Enriched Uranium (4-5%)

The reason HEU is considered a significant line is that once you've reached that purity, it becomes progressively easier to keep enriching the metal to get to weapons-usable material (>80%)

https://www.energy.gov/ne/nuclear-fuel-facts-uranium

 

[Apophenia]

Impressive! A full two dozen posts since anything directly related to Canadian SSN procurement has been mentioned ...

 

[Hood]

I've cleaned up the Canadian SSN thread, this new thread can serve for wider discussion about naval reactors and associated topics.

 

[Cordy]

Cost.

Nuclear reactors are not cheap, and training their operators is even more expensive. HEU is on the order of $250k per kg for fuel, for example. Reactors also need a lot more crew than GTs, which is even more expensive.

It's much easier to pack a bunch of gas turbines directly driving electrical generators into a hull, and spin the props via electric motors. Then you have lots of excess power generation since you're usually cruising at about half design HP or less.

The only thing I'd add to the IEP system is a cogeneration setup to boil water or ammonia using the turbine exhaust heat, and use that to spin another turbine generator. If you do it right, the exhaust gasses are whatever the ambient air temperatures are. Near zero thermal emissions!

Another additional cost of nuclear ships is the disposal of the highly irradiated radioactive plant, semi-remember a GAO report where they estimated CVN Enterprise disposal cost of several $billions, whereas the previous gen conventional powered aircraft carrier Ranger Navy sold off to shipbreakers for 1 cent.

 

[BROF]

Cost.

Nuclear reactors are not cheap, and training their operators is even more expensive. HEU is on the order of $250k per kg for fuel, for example. Reactors also need a lot more crew than GTs, which is even more expensive.

It's much easier to pack a bunch of gas turbines directly driving electrical generators into a hull, and spin the props via electric motors. Then you have lots of excess power generation since you're usually cruising at about half design HP or less.

The only thing I'd add to the IEP system is a cogeneration setup to boil water or ammonia using the turbine exhaust heat, and use that to spin another turbine generator. If you do it right, the exhaust gasses are whatever the ambient air temperatures are. Near zero thermal emissions!

HEU is not mandatory for naval propulsion applications. It is perfectly possible to design naval reactors using oxyde fuel enriched at commercial levels, with obvious cost and non-proliferation benefits, especially if requirements for refuelling are fully intergrated in both the ship design and its operationnal cycle.

 

[Yellow Palace]

HEU is not mandatory for naval propulsion applications. It is perfectly possible to design naval reactors using oxyde fuel enriched at commercial levels, with obvious cost and non-proliferation benefits, especially if requirements for refuelling are fully intergrated in both the ship design and its operationnal cycle.

For good or ill, the US Navy has hitched its wagon to HEU fuel for naval reactors.

 

[BlackBat242]

The French Navy has, contrarily, chosen LEU reactors for its submarines and aircraft carriers (at least for de Gaulle) on the grounds of lower purchase, operational, and disposal costs.

This comes with a frequent refueling schedule of every 10-12 years, but as the ships are designed for easy reactor core access, it only takes a few months, compared to 2-3 years for that portion of the RCOH (Refueling and Complex Overhaul) that USN carriers undergo at the 30-year mark (the new cores in the Ford-class reactors are 50-year cores).

 

[Cordy]

The French Navy has, contrarily, chosen LEU reactors for its submarines and aircraft carriers (at least for de Gaulle) on the grounds of lower purchase, operational, and disposal costs.

This comes with a frequent refueling schedule of every 10-12 years, but as the ships are designed for easy reactor core access, it only takes a few months, compared to 2-3 years for that portion of the RCOH (Refueling and Complex Overhaul) that USN carriers undergo at the 30-year mark (the new cores in the Ford-class reactors are 50-year cores).

Understood it was only the Columbia SSBN reactor, S1B, Submarine/1st gen core/Bechtel Corp, where it was explicitly stated as designed to operate for 40 years without refueling.

Whereas the more powerful Ford class carriers reactors, AIB, Aircraft Carrier/1st gen core/Bechtel Corp, have seen no mention that it was designed to operate for 40 years without refueling, so assumed still required mid-life refueling ?

 

[DesScorp]

Found this design from HII at SAS 2017 while browsing old naval expo reports. Named the "Future Surface Combatant", it is marketed as a replacement to the Ticos and to fulfill their BMD and fleet air defense role. It is fitted with the maximum size variant of the AN/SPY-6 with a 35 ft array along with 96 VLS cells for very long range interception. Based on the proven LPD-17 hull form, it has a large room for upgrades but is consequently much heavier and slower than the Ticos at an estimated 27000t with a top speed of 20+ knots.

Seems to me good for carrier protection with such an impressive radar and missile capacity, but speed may affect its ability to keep up with a CSG.

20 knots is not going to be enough to keep up with nuclear carriers when they're hustling, let alone other cruisers. There were times back when I was on the Enterprise that we'd get a directive to get someplace, fast, and when we moved, we would MOVE... the ole' gal would shake she was going so fast, and leave escorts in her wake.

I really like the idea of a modern version of the old Armed Merchantman concept for certain duties... commercial convoy escort, piracy patrol, etc ... but I really don't think these things would cut it in strike groups or carrier escorts.

 

[Firefinder]

The French Navy has, contrarily, chosen LEU reactors for its submarines and aircraft carriers (at least for de Gaulle) on the grounds of lower purchase, operational, and disposal costs.

This comes with a frequent refueling schedule of every 10-12 years, but as the ships are designed for easy reactor core access, it only takes a few months, compared to 2-3 years for that portion of the RCOH (Refueling and Complex Overhaul) that USN carriers undergo at the 30-year mark (the new cores in the Ford-class reactors are 50-year cores).

Thing is the USN ROCH is not just a refueling.

But a complete overhaul of the entire vessel where everything is replace from wear parts like bearings to the fancy shit like the computers.

With 25 30 years mark be right when you NEED to do that type of overhaul.

As is the Actual refueling is apparently takes up only 6 months of the ROCH with most of it weighting on the new fuel to arrive. The US Carrier cores ARE design for fairly easy access, there bolted on hatchs leading straight to them through all the decks.

The USN finds it more efficient to replace it once and only have the carrier down a few years in a major overhaul that you need to do anyways compare to needing to juggle doing all 10 in the same period.

And it shows with the Nimitz and the Fords, with the Enterprise and nuke cruisers before them, having a vastly higher up time then the french.

Those generally only needing a 2 month time in drydock for a cleaning every few years, which is a standard ship maintenance needs, for the whole 25-30 years either side of the ROCH.


Then you need to figure out were to put the waste.

One of the Naval Depots have all the cores the USN had used since the 1950s plus several from the other branchs.

Take up bout you average highschool football field with lots of room to spare.

Nuclear Waste doesn't take up much room, it just a pita shipping it to the location due to all the NIMBY issues.

People hear nuke on Loss their damn minds, and the US Gov cant tell them to shut it like the French can.

 

[Vepr157]

Understood it was only the Columbia SSBN reactor, S1B, Submarine/1st gen core/Bechtel Corp, where it was explicitly stated as designed to operate for 40 years without refueling.

Whereas the more powerful Ford class carriers reactors, AIB, Aircraft Carrier/1st gen core/Bechtel Corp, have seen no mention that it was designed to operate for 40 years without refueling, so assumed still required mid-life refueling ?

Starting with the Seawolf's S6W, all U.S. Navy submarine reactors have life-of-the-ship cores (I recall reading that the D2W core on the later 688s was also a life-of-the-ship core, but I'm not sure). Granted, these were nominally 30-year cores instead of 40-year cores.

A very pedantic note: the number in the reactor/core designation isn't the generation, but rather the model number for the type (S) and contractor (B), analogous to the way Navy aircraft were designated before the 1960s (e.g., F4F, F3H, A1D, etc.). If GE had still operated Knolls, I guess the S1B would be the S10G.

 

[Scott Kenny]

HEU is not mandatory for naval propulsion applications. It is perfectly possible to design naval reactors using oxyde fuel enriched at commercial levels, with obvious cost and non-proliferation benefits, especially if requirements for refuelling are fully intergrated in both the ship design and its operationnal cycle.

HEU means that you don't need to refuel the reactor at all, or you only need to refuel the ship once. Either one is a significant improvement over needing to stick the ship in drydock for 6-9 months every 8-12 years (not counting any other refit work that needs to happen)

 

[BlackBat242]

Then you need to figure out were to put the waste.

One of the Naval Depots have all the cores the USN had used since the 1950s plus several from the other branchs.

Take up bout you average highschool football field with lots of room to spare.

Nuclear Waste doesn't take up much room, it just a pita shipping it to the location due to all the NIMBY issues.

Here is the USN's storage site for all of the reactor compartments from all of the scrapped USN SSNs, SSBNs, and CGNs - at Hanford, Washington. Note that this is inland, east of the Cascade mountains... they are brought up the Columbia River to the closed Hanford nuclear material production facility, where they are stored in a large trench.




Hanford Main Area (there are several sites on the facility some distance away from this image):




Here is an older photo labeling which vessel the compartments came from - only sub compartments were there then, but the 9 decommissioned CGNs' cores are here now. :



And this is very recent. It appears that they will have to either enlarge the trench or dig a new one soon:

 

[Yellow Palace]

And that's probably significantly more materials than you'd actually need to deal with as high level waste.

Hanford is holding the entire submarine Reactor Compartment and looks like the entire primary containment for the surface ships. Not just the reactor vessels, the structure around the reactors.

You can look to the UK for what you actually need to deal with as HLW. Not having the space to entomb the entire reactor compartment, the UK is actually scrapping the whole boat, with only the reactor pressure vessel needing long term storage. SWIFTSURE has been in dock for that work for about a year.

The original 'plan', if you can call it that, was to dump the entire reactor compartment in deep water. That plan was only ever carried out for the original (sodium cooled) plant on SSN-575 SEAWOLF when the entire reactor compartment - fuel and all - was cut out and replaced with a PWR plant at its first refuelling.

That one object accounts for something like two thirds of the nuclear waste the US has disposed of at sea.

 

[Atomic Coyote]

To clarify a bit, the reactor compartments are stored in Hanford, but the actual fuel goes to Naval Reactors Facility on INL.



That long building at the top is the spent fuel pool, for "temporary" storage (until a long term site like Yucca mountain) opens they go into the purple building at top right. Years ago the old cores used to be dissolved and reprocessed a bit down the road, but Carter stopped that and then Clinton killed it for good.

Still, the point that USN spent fuel occupies a very small area stands. (Most of that facility in the pic is left over from when the site hosted the S1W/A1W/S5G prototype/training reactors.

 

[Atomic Coyote]

Speaking of spent fuel, from a USN standpoint the process is pretty optimized for dealing with HEU spent fuel. LEU stuff isn't necessarily worse, but it does have more transuranics and a bit different mix of fission products. Given civilians handle spent LEU it's not an intractable problem, but it would require money/time to switch over. Back in ~2015 when the USN switching to LEU was being bandied about for political reasons everyone I knew with program involvement was very opposed.

 

[Pirate Pete]

I uploaded this to another discussion about nuclear power on the board but think it’s more pertinent here…