The size and configuration of boats like Soryu and Shortfin Barracuda are pretty much driven by Japan and Australia having blue water interests but no access to nuclear subs, so if 09V meets performance expectations and the new yard infrastructure can build them in numbers, large SSKs of this type will be rendered moot for China's purposes. Arguably *smaller* rather than even larger would then be the rational way forward for PLAN conventional subs, to take advantage of their inherent benefits in littoral waters (analogous to the Russian Pr. 677 class) - no reason to pantomime a SSN when you have the real thing.
09V/09VI (095/096) Nuclear Submarine Thread
- Thread starter Hendrik_2000
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Because lithium ion can be dangerous, they can catch fire or explode if not charged properly or if the battery has a defect. We have seen enough of that from the mobile and IT industry. Another is that they have short lives, they get significant charge degradation after so many recharge cycles. That is also common with mobile devices and notebooks. There is research going on to make Lithium Ion safer, have longer lives without losing their power density. The impetus for this is driven primarily for the mobile and EV industry, submarines will be a collateral benefit. Maybe the Japanese have figured out something.
Larger SSKs have more endurance than smaller SSKs; there is just no reason to have small SSKs when you can have an SSK the size of a Yuan. China also has good reasons to use SSKs over SSNs, not even merely because of cost differences, which are huge. The PLAN's current 09X/Yuan combo is a good balance between littoral and blue water capability.
... or the Boeing 787, for that matter. South Korea (also a leader in battery technology, of course) is considering Li-Ion technology for future SSKs too and it does look as though progress is being made regarding increased safety, but it's not a technology I'd be scrambling to be an early adopter of for submarine use. Maybe mounting the banks outside the pressure hull in the same way as the oxygen and hydrogen storage on the German Type 212 subs is a solution, but then why not use the established, safe fuel cell AIP in the first place?
Lithium Ion itself can be disrupted or enhanced by graphene battery technology, depending how you view it. Hydrogen and Oxygen storage and safe don't seem to belong on the same sentence but anyway Li batteries warp as they expand or contract under periods of high heat and cooling, and they may fail to restore their original shape. If the cells are tightly packed under pressure, the warp will create pressure among the packed cells themselves. So there has to be some cooling provided to the cells and some space to allow as margins for warping. Each battery will have an embedded circuit to monitor temperature and charge, with the ability to turn off the circuit to a failing battery, and access to remove and replace bad cells.
The Type 212 stores its hydrogen supply as metalhydride, so it is in a rather stable chemical state and storage tank pressure is very moderate. Actually, the bigger concern is the oxygen, but virtually all other AIP concepts (MESMA, closed-cycle diesel, Stirling) are in the same - wait for it! - boat
Since the alternatives share the same major concern you can't single out fuel cell AIP as especially dangerous, in fact by carrying both components outside the pressure hull (which I don't think other subs do) the Type 212 is arguably the safest implementation currently in service.The Type 212 stores its hydrogen supply as metalhydride, so it is in a rather stable chemical state and storage tank pressure is very moderate. Actually, the bigger concern is the oxygen, but virtually all other AIP concepts (MESMA, closed-cycle diesel, Stirling) are in the same - wait for it! - boat
But you still cannot store Li-Ion outside of the pressure hull as the batteries are pressure sensitive.
Mathematically, the failure rate of Li-Ion, even on mobile, is very low, like over a million to one, and for submarine, there is no reason to pack them in such a super thin way like batteries for mobile. As batteries are forced to get thinner as phones get thinner, there is this separator between the electrolytes that keep getting thinner with it, and things happen if the electrolytes breach this barrier. There might also be ways to make the batteries even more chemically safe and stable, and this seems to happen every year with the industry. Problems arise from QC defects, QC can be tightened up. The batteries can be safe and within the hull, along with putting a diagnostic, thermal measurement and management, and cutoff circuit within every single battery, with easy access for replacement. The biggest problem with Li-Ion might be public perception, and this itself isn't helped with every reporting of battery burn incident, and people suing.
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Having both SSNs and (small) SSKs is indeed a good thing, but SSNs pretty much obviate the requirement for big 4000 ton SSKs. Those are just poor man's SSNs, designed to do the same job but not quite able to - yes, cheaper, but you get what you pay for.
While sophisticated battery management systems help, in a critical application passive safety is always preferable - added complexity introduces new failure modes. Mounting the battery banks outside the pressure hull could be done in multiple small pressure-resistant containers, which is exactly what the hydrogen/oxygen tanks on a fuel cell AIP sub amount to, after all.
Alternatively, one of the more stable Li-Ion battery chemistries such as Lithium-Titanate might just be viable inside the pressure hull, but they typically *halve* the capacity advantage over conventional lead-acid that Lithium-Cobalt-Dioxide offers, such that NiMH becomes a credible contender. Either way, the energy storage efficiency still doesn't quite match the best AIPs while incurring similar design effort to render the best-performing chemistry safe, which brings us back to my initial question of why you'd bother.
Even 4,000t SSKs are not going to be used by the PLAN in blue waters since they have the SSNs for that. Having said that, 4,000t SSKs have far more endurance, carry more weapons and sensors, and are quieter (other things being equal), than smaller SSKs. Yuans are not just poor man's SSNs, they are potent littoral combatants. Not only that, you have to recognize that the PLAN doesn't have the same budget as the USN, so yes, cheaper SSKs will be bought and used, at least for now. Some day when the PLAN budget catches up with that of the USN, my hunch is that the PLAN will still be using large SSKs like the Yuan, mostly for the littorals where SSNs are unnecessarily overpriced. There are voices even in the USN that are advocating for a two-tier SSN/SSK sub fleet, making the exact same kinds of arguments.
With the revolutionary increase in energy storage capacity brought about by Lithium ion and similar battery technologies in existence, it is only a matter of time before Chinese SSKs switch from the clunky, heavy and large lead acid battery packs. Further along the line will be next gen battery tech-- batteries much superior to lithium ion, some of which have already been prototyped or demonstrated (but haven't replaced lithium ion because of lithium ion's enormous scale and associated cost advantages). All this can, however, be disrupted if China succeeds in the development of small, modular shipping container sized nuclear reactors.