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:
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.
"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."