Canadian SSN requirement 1987-89

[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. But 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 ...