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Robert, the problem is decay heat. A lot of that 3 months is spent waiting for decay heat generation to decline to levels where it is safe to depressurise the plant and begin fuel handling. This is why refuels tend to be included as part of a general overhaul period for the ship. The maintenance crew won't be sitting on their hands for those three months. They will be maintaining other areas of the ship.
It is possible to refuel at high decay heat, but risky. Heat removal will be heavily reliant on pumped flow using systems like ECCS. Any loss of power for pumped flow or loss of heat sink and the water covering the fuel will start to boil off. The higher the decay heat, the less grace time you have for water makeup. The safety case ends up being difficult and the more redundancy you need for things like power supply, the more expensive the operation becomes. This risk is probably why the Russians do what they do at sea. I am not familiar with their operations. But you may find they also have to wait for decay heat levels to decline, especially if they are removing fuel from water to some sort of dry storage. The refuel itself may take only 3 days, but the cooldown period preceding it will probably be measured in months.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The other option to consider is avoiding refuel altogether. This means building a whole-life reactor core. Design the core to last for the intended operational life of the ship and then scrap the whole ship when the core is depleted. At least one nuclear navy does this already. It means that maintenance periods are shorter and easier. When time comes to scrap the ship, there is no problem just laying up in a basin for a decade, letting decay heat decline to low levels before removing the fuel.
There are pros and cons to this arrangement. It is tricky to do. The problems with this approach are: (1) It tends to necessitate high burnup, which can cause fuel swelling or even bowing of fuel elements. This is less of a problem if using oxide fuels. (2) To avoid excessive burnup of the central core, it is necessary to zone fuel enrichment and include burnable poisons, so that power generation is flat across the core. That makes the core more expensive. (3) Core chemistry control is more important. The coolant will carry more soluble neutron absorbers to counteract the reactivity introduced by more heavily enriched fuel. The fuel cladding will be exposed to neutron flux and oxidative attack from radiolytic oxygen for much longer. So tight control of dissolved oxygen is necessary. (4) A whole life core is safer in some ways as there are fewer intrusive operations that can potentially disrupt decay heat removal. But the core also carries a greater liad of fission products making the consequences of an accident worse.
On balance, this is probably the best approach for your ice breakers. Their mode of operation exposes the hull to a lot of flexural and shearing stresses. So replacing the boat every 20 years with a new one isn't a bad idea. It allows your navy to avoud the costs of refuelling and reduces the need for heavy maintenance periods. Although 20 year lifespan means higher capital costs, a more regular build schedule achieves economies of scale and better quality control.
There are a number of ways that the Canadian Navy could do this. Canada never invested in enrichment capability, because the CANDU can burn natural uranium. A CANDU is a less desirable option for a ship because core volume is large and online refuelling would be difficult at sea. The uranium market is well established now, so Canada could simply buy enriched U from the US, Russia or Europe. Or it can develop its own enrichment capability. Not a huge problem, its just time and money. The other option would be to reprocess spent CANDU fuel and make MOX for your ship reactors. That would cost a bit more, but it also reduces the spent fuel stockpile and puts in place a technology that could support wider Canadian nuclear industry. If Canada has reprocessing, it is a service that US nuclear operators will probably be interested in buying. Especially if they start building things like the natrium fast neutron reactor. Nuclear engineering is an area where there could be a lot of cross border trade.
Last edited by Calliban (Today 06:19:12)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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RobertDyck,
If Canada is serious about operating aircraft carriers while remaining within its limited military budget, then it should operate conventionally powered carriers that don't require spending any precious defense dollars on all the support activities required to operate naval nuclear reactors. There's no clear military justification for nuclear power on surface warships, unless all the ships in the battle group are nuclear powered, because an aircraft carrier would never leave its escorts behind. Nuclear power is an extravagance that most nations cannot afford. Since all the other ships in the battle group and the aircraft themselves are still conventionally powered, adding nuclear reactors to the carrier doesn't economize on very many underway refueling events.
The high fuel burn rates associated with historical conventionally powered American aircraft carriers were due to the poor thermal efficiency of WWII era steam boilers, which was about 16.5% according to empirical data collected for speeds of 20 knots and 30 knots from the Kitty Hawk class, which were the last class of conventionally powered American aircraft carriers. Modern gas turbines, such as the latest versions of the LM2500, when run at max output / max thermodynamic efficiency, fall between 36% and 39%. Supercritical CO2 gas turbines would be 50% thermally efficient.
Kitty Hawk class cruising range / operating hours at 20 knots / 23mph, by propulsion plant technology:
Foster-Wheeler or Babcock and Wilcox Marine Boilers: 13,800 statute miles (600 hours)
LM2500s: 30,109 statute miles (1,309 hours)
Supercritical CO2 gas turbines: 41,818 statute miles (1,818 hours)
Kitty Hawk's longest operational deployment covered 62,000 statute miles. That means you'd need to refuel the ship once per 6 month deployment, or perhaps never if you only deploy your carriers for 3 months.
If Canada operated navalized variants of Textron AirLand's Scorpion, equipped with the latest sensors and weapons, they'd have more real combat power than most other navies. These fighters would be drastically cheaper to operate than all the heavy fighters operated by other western navies, so several squadrons could be purchased and deployed. Their simplicity, economy of operation, and range matters a lot more than how fast they are. The Scorpion is a twin-engine subsonic ISR / attack jet with 2 crew members and an internal weapons bay. Naval fighters benefit greatly from the ability to loiter at significant distances from their carrier. Modern heavy fighters cannot loiter for any significant period of time because they require so much power to remain aloft.
Numbers of combat jets matter far more than theoretical capabilities. In real life you launch with 2 primary weapons to perform your mission, because that's what you can land with. If you can launch with a pair of 2,000 pound class munitions and 2 to 4 defensive missiles, that's as heavy a loadout as you need. Anything more than that rapidly becomes impractical nonsense.
Let's say you field 2 air wings with 48 Scorpions per air wing, and deploy with half of the air wing at any given time on 3 month deployments, so you deploy twice per year. Let's assert that 18 of the 24 jets can fly each day on a single 4 hour mission.
18 jets * 4 flight hours per day * 130 flight ops days per year * $3,000 per flight hour = $28.08M per half air wing per year
Each crew receives approximately 390 hours of operational flying from the carrier per year (similar to the number of hours our squadron's air crews were accumulating during Operation Enduring Freedom), plus maybe 50 to 70 hours of flying back at a naval air station for recurrent training / work-ups. That makes them highly proficient aviators in at least one mission area, with enough spare flight hours for a secondary specialty, because they're getting a lot more hours than virtually any other western flight crews receive during peace time. All of this is possible because Canada selected a fighter with modest CPFH, so the money saved on airframe maintenance can instead be devoted to far more training hours with high quality sensors / weapons.
$56.16M per air wing per year, or $113.32M total cost to maintain 2 carrier mobile air wings. That's the purchase price for 1X F-35C, but instead of spending that amount of money merely to purchase stealthy heavy fighters, you're fielding 2 complete air wings embarked aboard 4 CATOBAR aircraft carriers deployed over non-consecutive 3 month deployment periods per year to increase sailor retention and to reduce the toll exacted on the equipment that would otherwise be associated with 6+ month deployments. There should also be fewer problems with complacency killing people. Around the 3 to 4 month mark, the younger American sailors seem to become complacent to the danger they're in on the flight deck. Maybe Canadian sailors are different, but I doubt it. This is mostly a "young man" problem.
Since the carriers are conventionally powered, one ship can have a skeleton crew aboard while in-port undergoing repairs / refurbishment while the other carrier is at sea. That provides 24/7/365 at-sea defense of the Atlantic and Pacific Canadian coastlines, in order to get between any potential aggressor and the Canadian homeland. If Canada has something equivalent to a Defense Logistics Agency, those are the people who would be refurbishing the carrier in port, so that most of your sailors can fully crew the operational carrier.
One of the key features of conventionally powered carriers is that you truly can "walk away" from them if you need to. If one of the four carriers requires complex overhaul, that ship doesn't need her crew present to babysit the reactor. There is no such thing as walking away from a nuclear powered ship. You're married to her.
If you're smart about how you design the electronics suite and defensive weapons, the possibility exists for anything classified to be entirely removed from the ship and stored separately, such that even fewer crew members need to remain aboard, perhaps limited to a handful of engineering officers overseeing the repair activities. At that point, it's functionally no different from a civilian ship. If the officers and a yard crew need to take her out for a shakedown, they can do that with minimal fuss.
Minimal complexity that doesn't sacrifice real combat capability is the name of the game here. You get 2 limited capability carrier battle groups that have the most important features of an American blue water carrier battle group, at a fraction of what America pays for the pointless techno-gadgets that may have some theoretical advantage in some specific scenario, but aren't doing much for anyone at all other times.
AIM-174 - Fleet air defense against sea-skimming and ballistic missile threats
AIM-120 - General purpose air superiority
AIM-9 - Defensive missiles
JDAM-ER - Precision all-weather stand-off bombing with data-link
Harpoon / SLAM - All-weather stand-off anti-ship or land attack cruise missiles
AARGM-ER - Stand-off anti-radiation missile for SEAD
Bay-mounted ISAR Pod - Organic mini-AWACS capability
Bay-mounted Camera Pod - Organic photo-recon / bomb damage assessment capability
I think that provides a good mix of capabilities that cover most missions an air wing attached to a limited capability carrier battle group could realistically be tasked to perform. The weapons selected are adequate for their intended use cases. No specialty weapons such as Hellfire or APKWS or SDB or bunker busters were included because they're inappropriate for a blue water naval force primarily focused on interdicting enemy bombers, tactical fighters, and ships, with the odd land-based target of opportunity that may appear. You can still clobber the snot out of any tank with a JDAM. It's cheaper than a Hellfire, can potentially fly much farther, and there won't be much left after it hits. It will require off-board data link guidance to hit a moving target, but it works.
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