HMS Anson departs Barrow-in-Furness in 2023. Credit: UK MoD/Crown copyright

The UK Ministry of Defence has returned to French naval prime Naval Group for four additional Fresh Water Cooling Heat Exchanger (HEATEX) units, intended to be installed at a future date on the Astute-class nuclear-powered attack submarines (SSN) in service with the Royal Navy.

Used to provide cooling for SSN reactor and auxiliary systems, the HEATEX units have been sourced from France due to their “bespoke” design, according to a 3 January 2025 contract award notice posted by the UK government.

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The notice stated that Naval Group, as the original equipment manufacturer of the HEATEX units, was the only company with the necessary technical drawings and specialist tooling to supply the systems, which will be manufactured to an “improved specification”.

Valued at £12.5m ($15.5m), the contract follows an earlier deal in 2024 for the supply of two HEATEX systems.

The UK currently operates five Astute-class SSNs, with HMS Astute commissioned into service in 2010. This was followed by HMS Ambush (2013), HMS Artful (2016), HMS Audacious (2020), and HMS Anson (2022).

In addition, HMS Agamemnon is undergoing pre-sea trial testing at the BAE Systems Barrow-in-Furness facility, where the final Astute-class SSN, HMS Agincourt, is also under construction.

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In October 2024 a fire broke out at the BAE Systems Devonshire Dock Hall in Barrow-in-Furness, with local authorities issuing warning notices and calling on residents to stay inside their homes.

The cause of the fire was not determined at the time, nor any immediate impact to submarine manufacturing.

At the core of Astute propulsion

Central to the propulsion of the Astute class in the Rolls-Royce PWR 2 pressurised water reactor, which has a full life core, meaning it will not need to be refuelled throughout its time in service.

Other main machinery systems include two Alstom turbines and a single shaft with a Rolls-Royce pump-jet propulsor, which consists of moving rotor blades within a fixed duct.

Additionally, there are two diesel alternators, one emergency drive motor, and one auxiliary retractable propeller. The Astute-class submarines feature an MTU 600kW diesel generator.

CAE Electronics provided the digital, integrated controls and instrumentation system for steering, diving, depth control and platform management.

The PWR 2 second-generation nuclear reactor was developed for the Vanguard-class nuclear-powered ballistic missile submarines. Current generations of the PWR enable UK submarines to circumnavigate the world approximately 20 times, although developments could extend this to more than 40 times in future.

The major equipment components in the development of PWR 2 were the reactor pressure vessels from Babcock Energy, main coolant pumps from GEC and Weir, and protection and control instrumentation from Siemens Plessey and Thorn Automation.