Virginia & Astute SSN Batteries, Diesels & Snorkels

Virginia and Astute SSNs have 2 diesel generators, more than 100 tonnes of Lead-acid batteries and a snorkel for their diesels. (Diagram courtesy Stanford University, 2017)

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A less explored aspect of Virginia and Astute SSNs is that Lead-acid batteries and diesels are part of their electrical network. I’m not sure how batteries contribute to their constant, as against emergency, power needs? Three references: two online [1] [2] and my hardcopy Astute Manual [3], indicate the importance of batteries for nuclear submarines.

To date it seems all US nuclear subs (eg. Virginia's) and UK Astutes have been using standard Lead-acid batteries. Lead-acid batteries are comparatively safe, easy to manage, long life with a high number of recharge cycles, inexpensive and heavy enough to provide buoyancy "ballast" as they are placed along the base of a submarine’s hull.

While nuclear sub reactors are the ultimate propulsion and non-propulsion ‘hotel load” source of power, batteries provide (diesel rechargeable) backup in reactor shutdown emergencies, provide for silent running (maybe with occasional use thrusters?) and for other mission profiles.

US Virginia-class subs use 2? Caterpillar model 3512B V-12 diesel generators. In emergencies, at mast depth, these diesels can use the Virginia's snorkel to recharge the batteries and/or directly drive the propeller/pumpjet.

The UK Astutes each have 112 tonnes of Lead-acid batteries, use 2 MTU 396 or MTU 4000 diesel generators and a snorkel.

[1] The USN’s 2021 request for information on “Nickel-Zinc Submarine Main Storage Battery” https://www.navysbir.com/n21_1/N211-053.htm in part indicates “OBJECTIVE: Develop a Nickel-Zinc (NiZn) battery system that does not rely on Lithium Ion (Li-ion) technology and would replace lead-acid battery system with a more efficient, environmentally safe, maintenance free, and long life battery in the form of a large-format (1,000Ah+) NiZn battery with cycle life and capacity maximized within the design.”

DESCRIPTION: The U.S. Navy Submarine Fleet main storage battery currently employs Valve-Regulated Lead-Acid (VRLA) technology to meet platform energy and power requirements. However, with the increasing reliance of electronics on large platforms, future mission needs will require additional battery capacity beyond what current lead-acid battery technology is able to provide...[but] in the same volume. The development of a large-format NiZn battery will offer the needed battery capacity increase on submarines while offering a safer alternative to Li-ion batteries, which, though energy dense, come with a high risk of failure...NiZn is an emerging battery technology optimized for high capacity and long life while also delivering high power in an environmental friendly and safe chemistry…The NiZn battery concept must achieve 75% of capacity through 200+ Navy Equivalent Charge/Discharge cycles…” See whole document.

[2] Also see the short life (due to low number of recharge cycles) for contemporary Nickel-zinc batteries - discussed in this 2019 Submarine Matters’ article http://gentleseas.blogspot.com/2019/10/nickel-zinc-main-batteries-unsuited-to.html

[3] My hardcopy “Astute Class Nuclear Submarine Owners' Workshop Manual: 2010 to date” (Haynes, 2018) https://www.amazon.com/Astute-Nuclear-Submarine-Owners-Workshop/dp/1785210718 . Pages 118 to 122 indicate in summary: if the Astute submarine needs to run silent its reactor system will be reduced to minimum power. Power is then drawn from the battery for the sub’s hotel load and propulsion needs. On battery only slow submarine speed is possible. An Astute does have a snorkel to run its two MTU 396 or MTU 4000 diesel generators at mast depth. An Astute has 112 tonnes of Lead-acid batteries.

Pete Comment: It is unclear how long US and UK nuclear subs will continue to use Lead-acid batteries before these are replaced by NiZn, Li-ion or other formula batteries.