00X/004 future nuclear CATOBAR carrier thread

[hkky]

I had no interest in naval reactor designs as it is classified, but this discussion on reactor design fuel enrichment piqued my interest. The US apparently is exploring using LEU to power future naval reactors,

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. Many of the questions asked may be answered.

According to the article, French reactor refuels every 7-10 years using LEU, and a new design has average enrichment less then 6% by increasing core volume (in other words, reduced power density). Since the 6% is average, they likely have different enrichments for different fuel assemblies to reduce power peaking (if local power is too high the coolant may boil, which violate PWR design criteria).

Given the average 6% enrichment and thus number of U-235 atoms available, the fuel could be metallic to pack more U-235 atoms in the same volume (commercial reactors use UO2). Some of the known types of metal fuel needs to operate at lower temperatures to avoid swelling from irradiation damage and fission products buildup. With this much U-235 in the core, they will need a lot of burnable neutron poison in addition to control rods.

The article mentions energy utilization of existing HEU reactor designs have to be budged to last the entire life of the sub. That means the reactor may be operating at low power much of the time and thus last many years compared to commercial reactors which operates at full power all the time (ideally) for the same U-235 loading.

 

[BoraTas]

I had no interest in naval reactor designs as it is classified, but this discussion on reactor design fuel enrichment piqued my interest. The US apparently is exploring using LEU to power future naval reactors,

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. Many of the questions asked may be answered.

According to the article, French reactor refuels every 7-10 years using LEU, and a new design has average enrichment less then 6% by increasing core volume (in other words, reduced power density). Since the 6% is average, they likely have different enrichments for different fuel assemblies to reduce power peaking (if local power is too high the coolant may boil, which violate PWR design criteria).

Given the average 6% enrichment and thus number of U-235 atoms available, the fuel could be metallic to pack more U-235 atoms in the same volume (commercial reactors use UO2). Some of the known types of metal fuel needs to operate at lower temperatures to avoid swelling from irradiation damage and fission products buildup. With this much U-235 in the core, they will need a lot of burnable neutron poison in addition to control rods.

The article mentions energy utilization of existing HEU reactor designs have to be budged to last the entire life of the sub. That means the reactor may be operating at low power much of the time and thus last many years compared to commercial reactors which operates at full power all the time (ideally) for the same U-235 loading.

You seem to be knowledgable on nuclear reactors. I have a question to ask. What would be the advantages of using LEU instead of HEU? The article mentions that it would be possible to obtain lifetime LEU cores (presumably at 19.75% enrichment) at 2-3 times the reactor core volume. I cannot imagine this being a big deal, considering how small the reactor cores themselves are.

 

[ACuriousPLAFan]

SOYO on Weibo mentioned that in the publicly-accessible illustrations (on the propulsion system's structural design) available so far, there has only been the setting with one reactor + one steam turbine + one steam turbine generator. Could it be that the 004 CVN adopting a 4-reactor architecture is a high-probability event?

 

[ACuriousPLAFan]

This is a very interesting post by 爱若丰狂SOYO历 on possible propulsion for 004. ACP100S. But I think the part about the electricity requirement from propulsion and weapon system is problem even more relevant.
He is saving >= 200 MW for electric propulsion and another 170MW for onboard systems. That's a lot of electric power.
using 4 reactors, we'd get 500MW of power generation and it would fit in the current 004 carrier.

View attachment 154804

Wondering how such setups compare to the A4W and A1B reactors of the Nimitz and Ford CVNs, especially when considering that the 004 CVN has largely the same (if not slightly larger) dimensions and full displacement as the Ford CVNs. Based on publicly-available information:

- Two A4W reactors per Nimitz generate 208MW of propulsion power for the 4x shafts plus ~100MW of electrical power = 308MW total.
- Two A1B reactors per Ford generate 520MW of propulsion power for the 4x shafts plus ~250MW of electrical power = 770MW total.

To be fair, are the figures for the A1B reactors actually legit? A 25% increase in thermal power output per reactor, but 2.5 times the combined propulsion + electrical power output over the Nimitzs?

 

[dingyibvs]

Wondering how such setups compare to the A4W and A1B reactors of the Nimitz and Ford CVNs, especially when considering that the 004 CVN has largely the same (if not slightly larger) dimensions and full displacement as the Ford CVNs. Based on publicly-available information:

- Two A4W reactors per Nimitz generate 208MW of propulsion power for the 4x shafts plus ~100MW of electrical power = 308MW total.
- Two A1B reactors per Ford generate 520MW of propulsion power for the 4x shafts plus ~250MW of electrical power = 770MW total.

To be fair, are the figures for the A1B reactors actually legit? A 25% increase in thermal power output per reactor, but 2.5 times the combined propulsion + electrical power output over the Nimitzs?

I wouldn't pay much attention to it. It's just a wiki entry, has zero citation on how that figure was arrived at from a ~700MWth reactor. There hasn't been any groundbreaking invention in energy conversion to justify such a massive increase in efficiency. Over 50% efficiency is just plain ludicrous.

 

[dingyibvs]

BTW the A4W entry is highly unlikely to be correct either. 208/550 = ~38% which is around the maximum efficiency achievable during its days, and not that much more these days. There's no way it can do that AND generate 100MW of electrical power. It's just thermodynamics, you need to either raise the reactor core coolant temperature or decrease the heatsink temperature to increase the efficiency of energy transfer. Neither of those things is feasible to any drastic extent with a PWR.

The heat sink temp is basically just the ocean water temp, so that's not gonna change with any reactor. The core coolant can be increased by using a different coolant like e.g. Sodium or Thorium salt, but as mentioned earlier they carry their own set of problems. Theoretically you can increase the pressure in the reactor core to raise the core coolant temp but there are no breakthroughs that will allow it to be done for any significant amount.

 

[charles18]

Could it be that the 004 CVN adopting a 4-reactor architecture is a high-probability event?

I mentioned the idea of a 4 reactor design previously on March 18

If this actually comes true then it's going to be an amazing prediction.

00X/004 future nuclear CATOBAR carrier thread

Gleaning from the following academic paper, and if the values presented in the paper are accurate to real life: 1. The propulsion-electrical system architecture on the 004 CVN will be similar to those on the Nimitz and Ford CVNs, namely featuring 4x steam turbines which drive 4x propulsion...

www.sinodefenceforum.com

 

[hkky]

You seem to be knowledgable on nuclear reactors. I have a question to ask. What would be the advantages of using LEU instead of HEU? The article mentions that it would be possible to obtain lifetime LEU cores (presumably at 19.75% enrichment) at 2-3 times the reactor core volume. I cannot imagine this being a big deal, considering how small the reactor cores themselves are.

I work in the commercial nuclear sector, mostly engaged in fuel safety and new fuel design research. I have no knowledge of naval reactors, only educated speculations since physics is the same.

Not entirely sure why they want to move away from HEU for naval reactors, but there is a push to replace HEU research reactor cores with LEU due to proliferation concerns. Maybe they got caught up in the movement.

From physics perspective, reactivity control would be slightly simpler with LEU and probably more efficient. It all goes back to holding back the power when you have excessive reactivity at beginning of life (i.e., more U-235 than you need to have chain reaction). When neutrons are absorbed by poisons they can't participate in chain reaction and thus lost efficiency. Normally some/extra neutrons are absorbed by U-238 and transmute to Pu-239 and limited amount of Pu-241 which can fission and generate energy just as U-235. This is like breed fuel as you go in fast reactors but at lower rate. In commercial reactors, most of the energy comes from Pu-239 and Pu-241 2nd half life of the fuel. To hold down the power for 20-30 years of operation, some serious combination of neutron absorbers are needed, i.e., neutron absorbers of different x-sections. Larger neutron capture x-section absorber don't last long since they burn out quickly. I do not know the balance of neutron absorption by absorbers between LEU and HEU fuel to know how significant it is from efficiency point of view. Obviously the more Pu-239/241 generated during operation, the less U-235 is needed at beginning of life.

Although the reactor core is small, but volume in a sub is limited and you'd want to make them as small as practical. Keep in mind economics/efficiency is not a primary concern.

 

[BoraTas]

BTW the A4W entry is highly unlikely to be correct either. 208/550 = ~38% which is around the maximum efficiency achievable during its days, and not that much more these days. There's no way it can do that AND generate 100MW of electrical power. It's just thermodynamics, you need to either raise the reactor core coolant temperature or decrease the heatsink temperature to increase the efficiency of energy transfer. Neither of those things is feasible to any drastic extent with a PWR.

The heat sink temp is basically just the ocean water temp, so that's not gonna change with any reactor. The core coolant can be increased by using a different coolant like e.g. Sodium or Thorium salt, but as mentioned earlier they carry their own set of problems. Theoretically you can increase the pressure in the reactor core to raise the core coolant temp but there are no breakthroughs that will allow it to be done for any significant amount.

38% efficiency claim on a naval PWR is ridiculous. It is just fanboyism the Wiki should shameful for echoing. The Nimitzes are known to have 8 turbogenerators each at 8 MW. That is 64 MW of electricity production. Early Nimitzses have 260,000 combined SHP. There is nothing in the public domain that suggests these were increased with the later Nimitzses. If an increase happened, I am sure it was small because the reactor is the same and it wasn't mentioned.

So the evidence suggests 194 MW of propulsion power combined with 64 MW of electricity generation capability. It means a 129 MW output per reactor which tracks with the usual 20-25% efficiency band we see with naval PWRs too.

The Ford is still a bit classified. According to DoE the increase in reactor energy is 25%. Though I am cautious as it may refer to the stored energy in the reactor. We know better about the electricity generation. It is 225% higher than the Nimitz according to this govt resource (reference 2, page 15). So it is 104 MW per reactor. There is no mention of an increase in shaft power anywhere. I would say most of the increased thermal capacity went to the electricity generation.

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[Tomboy]

Is there any actual advantages of having 4 reactors? It'll definitely take up much more space than twin reactors, and modern reactor failure is basically unheard off. The Nimitz class never had any major issues with their reactors on mission for over 40 odd years despite using 1970s technology. I doubt the extra redundancy arguement actually makes much sense considering all the downsides like extra space taken, extra complexity, extra manpower requires, much more expensive and maintaince heavy.

Ford could do just fine with two reactors and since Type 004 is larger than the Ford they could fit larger reactors in it even if they wanted more power and propulsion. IMO, theres just too many downsides for 4 reactors compared to just having 2. I'm hoping that Type 004 will be a pure electric ship using IEP(Hence why each reactor is hooked up to a single turbine), it's the most logical solution. It allows future proofing for laser weapons while also improving efficiency.