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Scrapping Nuclear Submarines
Trafalgar class submarine HMS Tireless at sea, 2012 |
BY MATTHEW GUNTHER
The UK is facing a £7.5 billion bill to dismantle its
20 defunct vessels
The UK defence department has not scrapped any
of its 20 defunct nuclear submarines in more than three decades, according to
a recent public
spending report.
Storing the vessels has already cost the
government around £500 million.
But why has the UK left these submarines in
dockyards for so long – and how difficult is it to dismantle them?
What is a nuclear submarine?
A ‘nuclear’ submarine can refer to a submarine that carries
nuclear warheads, one that is powered using nuclear energy, or both.
In the UK, the Vanguard, Astute and Trafalgar class submarines
are all powered using a nuclear reactor, but only the four Vanguard class
submarines carry nuclear warheads – Astute and Trafalgar submarines are ‘The
UK’s current fleet relies on a reactor typically seen in power stations across
the world – the pressurised water reactor (PWR).
These compact power plants produce vast amounts of heat through
the splitting of uranium-235 (235U).
This fissile isotope exists in very small quantities (less than
1%) in natural uranium, which mainly consists of uranium-238 (238U).
To use it as fuel, the 235U is
increased relative to the 238U in a process known as
enrichment.
In the PWR, waste fission products are made,
such as caesium, xenon and krypton, as neutrons split the 235U
fuel, with 238U also absorbing neutrons to form plutonium.
These fission products can damage the ceramic
fuel and reduce the reactor’s efficiency.
The vessel that contains this whole process is
also bombarded with high levels of radiation over its operational life.
What
happens to a nuclear submarine once it is removed from service?
Once a nuclear-powered submarine is
decommissioned, it is placed into long-term storage.
HMS Spartan, a Swiftsure-class submarine, pictured leaving Faslane Naval Base in Scotland. Spartan was decomissioned in 2006. |
Since 1980, the UK Ministry of Defence has
taken 20 nuclear-powered submarines out of service.
Of these 20 subs, the UK has not fully
disposed any of them and nine still contain highly radioactive nuclear fuel.
The vessels have languished at dockyards in Plymouth
and Rosyth.
This is not a sustainable solution, but it is
in stark contrast with other countries’ past policies.
During the Cold War, the Soviet Union dumped
19 ships containing nuclear waste in the Kara Sea, as well as 14 reactors and
the K-27 nuclear submarine.
With such vessels continuing to rust on the
seabed, there are concerns these sites could harbour a potential environmental
crisis.
However, the subs stored in the UK are
constantly monitored in a controlled environment.
Although a far cry from the Arctic submarine
graveyards, the UK fleet still lies exposed to salty water, with the vessels
rusting in the dockyards.
Why
are the submarines still in storage?
It is an incredibly complex situation, but the
government stopped defueling its disbanded fleet back in 2004.
Astute class submarine HMS Ambush during sea trials near Scotland |
Mired in delays and inflating budgets, the
defueling may not restart until 2023 – the original start date was 2012.
Even when the subs are ready for their next
voyage through the disposal process, it is a journey fraught with complexity.
What
is the plan for the nuclear waste?
Once defueling starts, the sub will be moved
to a ‘reactor access house’ on rails.
In this facility, engineers will remove the
spent nuclear fuel from the sub, which contains various actinides and
radionuclides.
The fuel is highly radioactive and generates
heat, so needs to be cooled in water before any further work can begin.
Nuclear submarine HMS Vanguard arrives back at HM Naval Base Clyde, Faslane, Scotland following a patrol. |
To cool the fuel rods, the waste is sent to a
specialised plant at Sellafield, where it is stored in vast water ponds.
The water acts as both an efficient coolant
and radiation barrier. Historically, this spent fuel would have then been
recycled to form new nuclear fuel.
During reprocessing, the fissile uranium and
plutonium is separated through solvent extraction, before converting the
remaining liquid waste into a glass for long-term storage.
However, it is now unclear whether this will
still happen. It is more likely that the spent nuclear fuel will be stored
indefinitely after cooling.
The current UK strategy is to bury this waste
in a highly-engineered geological disposal facility, which would see more than
650,000m3 of waste stored in an underground cavern, according
to recent government estimates.
But plans are still ongoing and a facility is
yet to be built.
What
happens to the submarine after defueling?
After defueling, the sub will return to the
‘wet’ dock for another period of storage and monitoring.
Following this, the submarine is dismantled.
Components such as pipes and pumps exposed to radiation are taken away and the
reactor vessel removed.
However, engineers do not simply remove the
reactor.
In many countries, the reactor is lifted out
with the two empty compartments either side of it and then sealed off to
minimise the risk of exposure.
After removing this ‘three-compartment unit’,
the submarine is cast off for its final voyage to a commercial shipyard for
recycling.
But it will be a costly endeavour. The UK may
face costs of up to £7.5bn if it wants to take the entire fleet through this
voyage of defueling and disposal.
It remains unclear whether the plans will stay
on course, but the defence department has committed to dismantling the fleet
‘as soon as reasonably practicable’.
Matthew Gunther
During my PhD in Manchester,
which focused on the UK’s nuclear waste inventory, I developed a strong passion
for communicating science to the wider public. Armed only with a solitary
microphone, my friends and I set up a podcast and blog tackling the top nuclear
issues of the day, the Hitchhiker’s Guide to Nuclear. I even decided to go
one step further and dabble in scientific stand-up comedy with Bright Club
Manchester. Following my PhD, I decided to pursue a career in science writing
and was a science correspondent for Chemistry World until the end of
2016.
https://www.chemistryworld.com/news/how-do-you-scrap-a-nuclear-submarine/3010405.article
Vangard class submarine HMS Victorious on transit to the Clyde Submarine Base Faslane, 2003 |
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