Arpit Kanodia at 7/31/2026 6:41 PM made some very interesting comments regarding problematic non-PWR novel reactors:
"Reply to Shawn C [Pete will also reply to Shawn in a future article] from previous post: The marine reactor South Korea (SK) is trying is an MSR (Molten Salt Reactor). [Pete AI confirmation is HERE] I don't know what their goals are or what they are trying to achieve, but not a single land-based commercial reactor based on an MSR exists; they are all test reactors. And the (SKs) want this for marine ships and submarines? This is nothing but hubris." [Pete comment - Very true Arpit]
[Pete's has used Google AI, yielding ]
"Neither the US nor the Soviet Union ever used Molten Salt Reactors (MSRs) in operational submarines. However, both nations experimented with liquid-metal cooled reactors during the Cold War, which are sometimes confused with molten salt systems.
"Neither the US nor the Soviet Union ever used Molten Salt Reactors (MSRs) in operational submarines. However, both nations experimented with liquid-metal cooled reactors during the Cold War, which are sometimes confused with molten salt systems.
Soviet Liquid-Metal Submarines Project 645 (K-27): The Soviet Navy built one experimental submarine powered by twin lead-bismuth eutectic (liquid metal) cooled VT-1 reactors. It suffered severe reactor problems and a core partial meltdown in 1968.
Alfa Class (Project 705 "Lira"): The Soviets later built a series of high-speed attack submarines powered by lead-bismuth liquid-metal reactors (OK-550 and BM-40A). While fast and deep-diving, their coolant systems had to be kept externally heated at all times in port to prevent the metal alloy from solidifying. [Pete: The Alfas docked in very cold Arctic ports.]
See 's comments 6 years ago:
"Those reactors are something else. The coolant is a molten lead alloy. Once the reactor is running, it has to keep running all the time. If it ever stopped, and the alloy cooled, the entire cooling system seizes up and can’t be started again. Maintenance had to be done in port, with the coolant rerouted through an external furnace to keep it molten."
US Liquid-Metal Submarine [a very early "Seawolf" SSN-575 - nothing to do with the 1990 onwards seawolf class]: The US Navy tested a liquid sodium-cooled reactor on this single-hull attack boat. Sodium proved hazardous and difficult to manage due to its violent reaction with water, so the Navy decommissioned the plant and rebuilt the submarine with a standard PWR." [AI portion ends]
The US Atomic Energy Commission (AEC) historians' [according to Wikipedia] account of the sodium-cooled reactor experience was:
"Although makeshift repairs permitted the Seawolf to complete her initial sea trials on reduced power in February 1957, RICKOVER had already decided to abandon the sodium-cooled reactor. Early in November 1956, he informed the AEC that he would take steps toward replacing the reactor in Seawolf with a water-cooled plant similar to that in the Nautilus.
The leaks in the Seawolf steam plant were an important factor in the decision but even more persuasive were the inherent limitations in sodium-cooled systems. In Rickover's words they were "expensive to build, complex to operate, susceptible to prolonged shutdown as a result of even minor malfunctions, and difficult and time-consuming to repair."[6]
The S2G reactor was replaced with a pressurized water reactor similar to Nautilus and designated S2Wa, the replacement process lasting from 12 December 1958 to 30 September 1960.[7]"
[Arpit continues]
"This was the same thing tried by India in the 1980s. In 1980, DRDO proposed a [pressurised HEAVY water reactor] PHWR reactor for submarines, which [Indian] Naval Headquarters refused to sanction, and rightly so, it was madness."
SubMatts will resume with Arpit's very interesting comments on the dangers and complexities (adding up to extreme costs) of refuelling submarine reactors later in August.
7 comments:
One thing I'd like to add, which some people seem to be brushing under the carpet, is that the single most important component of a nuclear submarine is still the nuclear reactor.
Technologies like integrated electric propulsion (IEP) or a pump-jet are relatively low-hanging fruit. Yes, the sensor package is also a critical technology, especially if a navy wants to move toward conformal sonar arrays for SSNs. However, an SSN can still operate effectively with a conventional cylindrical sonar array—but it cannot function without a nuclear reactor.
The Suffren-class SSN was laid down in 2007 and did not complete its sea trials until 2020. It took France 13 years to verify and validate the K15 nuclear reactor. France is one of the world's leading nuclear powers, yet it still required 13 years to bring the reactor to operational maturity.
https://www.armscontrol.org/act/2026-07/news/south-korea-announces-plans-nuclear-powered-submarines
But here, they want an SSN by 2035. That's just nine years, despite not even having selected a reactor design. They also lack the necessary nuclear infrastructure, training pipeline, and human resources. They have not even begun developing the specialized workforce required to build, operate, and maintain a nuclear submarine, which demands an entirely different set of skills from those needed for conventional submarines or operating a civilian reactor.
I just want to say that they are completely delusional.
Hi Arpit at 8/04/2026 4:50 PM
I think most agree SK and/or the US developing novel reactors for SK-SSNs is a non-starter. I further suspect its a decoy from a long term SK program to develop PWR for submarine for decades.
This PWR may have been developed with US knowledge - just like the US knew of Israel's program from the 1940s to cooperate with France to build nuclear weapons for Israel AND France.
Unhelpfully I have no proof of a SK PWR for submarine program but given NK's steady, predictable nuclear weapon advances the US would give SK considerable latitude to develop PWR for submarine especially if its just LEU (so far).
Similarly I think US intel had extensive knowledge of India's H bomb program and Soviet assisted PWR reactor programs. It being in US interests to permit India to balance China's early 1960's lead in A and H bombs and Pakistan's 1998 H bomb advances.
Basically much is observed under the surface by great/super powers - and they allow things to go on if its in great/super power national interests eg on balance allowing Israel to have the "never again" bomb to limit Soviet retaliation and support for Soviet proxies in the 1950s-70s Middle East. Also Israeli nuclear weapons balancing conventional/numerical Arab and Iranian superiority over Israel from 1948 until now.
Cheers Pete
I think that's giving the U.S. far more credit than the historical record supports.
The one major exception was in the 1950s and 1960s under the Atoms for Peace framework, when Canada supplied the CIRUS reactor (with U.S.-supplied heavy water) and later CANDU-derived technology was made available for India's civilian nuclear program. Ironically, the plutonium produced in CIRUS was used for the 1974 Smiling Buddha test. But after the 1972 Nixon-Mao rapprochement and India's 1974 nuclear test, Washington's policy shifted dramatically. The U.S. backed the creation of the Nuclear Suppliers Group, tightened export controls, and spent the next three decades trying to restrict India's access to nuclear technology.
It's also worth remembering the strategic situation India faced. By the early 1980s, there were credible reports that Pakistan had cold-tested a nuclear device, and by the late 1980s its nuclear weapons program was widely understood to be nearing completion. At the same time, China had already been a nuclear power for two decades. India was facing the prospect of two nuclear-armed adversaries.
PM Rajiv Gandhi is often remembered for the IPKF debacle, but one of the most consequential decisions of his tenure was pushing forward the weaponisation effort and preserving India's nuclear option. That laid much of the groundwork for what followed.
The 1990s were an especially difficult period. India was dealing with insurgencies in Kashmir and the Northeast, militancy in Punjab in the preceding years, a severe balance-of-payments crisis, and sustained U.S. pressure under the Clinton administration to cap or roll back its nuclear program and sign the CTBT. Despite all that, Prime Minister P. V. Narasimha Rao kept the program alive while simultaneously liberalising the economy and restoring India's strategic position. Many also credit him with authorising preparations for nuclear testing in 1995, which were reportedly deferred after U.S. satellites detected activity.
It's entirely possible that U.S. intelligence knew a great deal about India's nuclear program—that's what intelligence agencies do. But knowing about it is very different from permitting or supporting it. With the exception of the early civilian nuclear cooperation that unintentionally benefited India's program, the historical record after the 1970s is overwhelmingly one of technology denial, sanctions, and diplomatic pressure rather than quiet approval.
As for Pakistan, the case for quiet tolerance is far more plausible—anyone who has studied A.Q. Khan's procurement network can't help but wonder how such an extensive operation was allowed to function for so long during the Cold War.
News story on SK nuclear submarine program. It discusses the size of the proposed submarine and the use of LEU but does not specify reactor technology.
https://www.upi.com/Top_News/World-News/2026/08/04/nuclear-powered-submarine/2991785890196/
Thanks Bill your 8/06/2026 6:29 PM
From the Virginia sized KSS-N (or K-SSBN?) discussed at https://www.upi.com/Top_News/World-News/2026/08/04/nuclear-powered-submarine/2991785890196/ I wonder whether SK is taking a shortcut to a Virginia Block V SSGN outer hull with an LEU reactor.
Cheers Pete
French Ano
Concerning the delay in the Suffren class it has more to do with funding in particular at the Cadarache N facilite
The séminal model ,the ultra compact K 48 (LEU plate .,steam generator above in the same hull,automated handling.) was in operation as of 1982
The Rubis for instance was retired after 39 years (14 years in immersion… and10 year maintenance /upgrade with an availability (2 lternate crews) well above 60/65%
French Ano
The Fr Defense budget was neatrly halved beetween 2000 and 2015
No urgency...remember France was selling weapons to Russia incl navy ships (Mistral class)up to 2015…!
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