PWR3

The Rolls-Royce pressurised water reactor (PWR) series has powered the UK's Royal Navy nuclear submarines since the , commissioned in 1966. The first British nuclear submarine, , was powered by a Westinghouse S5W reactor.

Nuclear reactor designs, operating methods and performance standards are highly classified. Details of this type regarding the reactors are not available.

PWR1

The first British naval reactor, the PWR1, utilising a core and reactor assembly of purely British design, went critical in 1965, four years later than planned. Technology transfers under the 1958 US-UK Mutual Defence Agreement eventually made Rolls-Royce entirely self-sufficient in reactor design in exchange for a "considerable amount" of information regarding submarine design and quietening techniques being passed on to the United States.

The reactor fuel is highly enriched uranium (HEU) enriched to between 93% and 97%. Each nuclear core has a life of about 10 years, so has to be refueled about two times during the lifetime of a submarine.

Rolls-Royce Marine Power Operations at Derby is the centre for design and manufacture of the UK's submarine reactors. The Ministry of Defence's Vulcan Nuclear Reactor Testing Establishment (NRTE), at Dounreay, tested each reactor core design prior to its installation in nuclear submarines.

Submarines

*Prototype
** Vulcan Naval Reactor Test Establishment, Dounreay
*Core A
** ''Valiant''-class SSN
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** ''Resolution''-class SSBN
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*Core B
** ''Churchill''-class SSN
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*Core Z
** ''Swiftsure''-class SSN
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** ''Trafalgar''-class SSN
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PWR2

The PWR2 was developed for the Trident missile submarines and is a development of the PWR1. The first PWR2 reactor was completed in 1985 with testing beginning in August 1987 at the Vulcan Naval Reactor Test Establishment.

The reactor fuel is highly enriched uranium (HEU) enriched to between 93% and 97%. The latest PWR2 reactor core design is "Core H", which has a life of about 30 years removing the need for refueling, allowing a submarine to avoid two reactor refits in its service life. HMS ''Vanguard'' will be fitted with the new core during its refit, followed by her three sister boats. The s have this full-life core installed. As they were developed for SSBNs, the reactors are considerably larger than those of current British fleet submarines. The diameter of ''Astute''-class hulls has therefore been increased to accommodate the PWR2.

A safety assessment of the PWR2 design by the Defence Nuclear Safety Regulator in November 2009 was released under a Freedom of Information request in March 2011. The regulator identified two major areas where UK practice fell significantly short of comparable good practice: loss-of-coolant accident and control of submarine depth following emergency reactor shutdown. The regulator concluded that PWR2 was "potentially vulnerable to a structural failure of the primary circuit", which was a failure mode with significant safety hazards to crew and the public.

In January 2012 radiation was detected in the PWR2 test reactor's coolant water, caused by a microscopic breach in fuel cladding. This discovery led to being scheduled to be refueled early and contingency measures being applied to other ''Vanguard'' and ''Astute''-class submarines, at a cost of £270 million. This was not revealed to the public until 2014.

In February 2013, the Ministry of Defence (MoD) awarded Rolls-Royce a ten year "foundation" contract to "deliver and maintain" the reactors of the ''Astute''-class and the ''Vanguard''-class replacement the Successor. In February 2019, the MoD awarded Rolls-Royce a three year contract for Nuclear Propulsion Lifetime Management for the ''Trafalgar'', ''Vanguard'' and ''Astute'' classes.

Submarines

*Core H
** ''Vanguard''-class SSBN
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** ''Astute''-class SSN
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PWR3

Three propulsion options were considered for the replacement of the ''Vanguard''-class, the Successor: PWR2, PWR2b (derivative with improved performance) and PWR3. PWR3 was a new system "based on a US design but using UK reactor technology". The Royal Institution of Naval Architects reported that it was likely that the UK was given access to the US Navy S9G reactor design used in their ''Virginia''-class submarines. The PWR3 was a simpler and safer design with a longer life and lower maintenance requirements than the PWR2 variants and cost roughly the same as the PWR2b. The PWR3 has 30% fewer parts compared to the PWR2.

In March 2011, Defence Secretary Liam Fox said the PWR3 was the preferred option "because those reactors give us a better safety outlook". In May 2011, the Ministry of Defence announced that PWR3 had been selected for the Successor (later named the ''Dreadnought''-class in 2016). The PWR3 cost about more per boat to purchase and operate compared to PWR2 designs. This is offset by the PWR3's longer life over the 25-year life PWR2 designs. The PWR3 does not require reactor core prototype tests; instead computational modelling is used. Consequently, the Vulcan Nuclear Reactor Testing Establishment operated by Rolls-Royce closed in 2015.

In June 2012, the MoD awarded Rolls-Royce a contract to produce reactors for the ''Dreadnought''-class and also for the final boat of the ''Astute''-class HMS ''Agincourt''. The MoD also awarded Rolls-Royce to refurbish their Rolls-Royce Marine Power Operations reactor core manufacturing plant at Derby to manufacture the PWR3 and to extend the plant's operational life to 2056. In January 2020, the National Audit Office reported that the construction of the plant was five years behind schedule and was now forecast to be in service in 2026.

Submarines

* ''Dreadnought''-class SSBN
**HMS ''Dreadnought'' (under construction)
**HMS ''Valiant'' (under construction)
**HMS ''Warspite'' (on order)
**HMS ''King George VI'' (on order)
* ''SSN(R)''-class SSN
**First design contract awarded

See also

*AUKUS
* List of commercial nuclear reactors
* List of United States Naval reactors
* Nuclear marine propulsion
*Soviet naval reactors
*United States naval reactors

References

Further reading

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External links

Rolls-Royce Marine Products - Nuclear Plant

{{DEFAULTSORT:Rolls-Royce Pwr
Nuclear reactors
PWR
Naval reactors
Trident (UK nuclear programme)
Nuclear technology in the United Kingdom