[ RadSafe ] Article: A future for nuclear power

Thu Mar 30 10:40:20 CST 2006

>From "Physics World," April, 2006

http://physicsweb.org/articles/world/19/4/3

A future for nuclear power
Forum: April 2006

Two decades after the Chernobyl accident, Tony Goddard
believes that nuclear power must continue to be used
to generate electricity

Exactly 20 years ago this month, on 21 April 1986,
workers at the Chernobyl nuclear plant in the former
Soviet Union carried out an experiment at very low
power with one of the facility's two "RBMK" reactors.
They were, however, unaware that their actions would
make the reactor dangerously unstable. Its power
rapidly increased, leading to the destruction of the
core and a massive chemical explosion. The World
Health Organisation estimates that between 40 and 50
staff and emergency workers died as a result of
radiation released during the accident. It also
resulted in widespread contamination and radiation
exposure.

The Chernobyl disaster was a significant moment in the
development of nuclear power, particularly in terms of
the public's attitude to this form of energy. It also
highlighted how the Soviet nuclear industry was badly
regulated, suffered from lax operation and training,
and tolerated weak reactor designs. Surprisingly, one
power station in Lithuania and three in Russia are
still using RBMK reactors after design deficiencies
related to Chernobyl were corrected, although the
former is due to close in 2009 following appeals by
the European Union on safety grounds.

Now, however, it appears that the tide is turning back
in favour of nuclear power as countries contemplate
the problems of climate change, rising energy prices
and the fact that many nuclear plants are reaching the
end of their lives. In the UK, for example, five of
the nine "first-generation" Magnox power stations,
most of which were built in the 1960s, have already
closed after operating safely beyond their expected
lives. The rest of the country's 12 nuclear stations,
which use mainly "second-generation" advanced
gas-cooled reactors (AGRs), will all have closed by
2023. No new nuclear plants have opened since the UK's
single pressurized water reactor (PWR), Sizewell B,
came online in 1990 (see "The physics of nuclear
reactors").

Given that the UK's nuclear power stations together
generate 20% of the country's electricity's needs,
what will happen when these facilities shut? Can the
UK reduce its emissions of carbon dioxide and have a
diverse supply of electricity without nuclear power?
Is it a problem that the country will be importing
about 75% of its primary energy by 2020? To find
answers to these questions, the UK government has
recently launched a review of the country's energy
needs (see "Nuclear questions" Physics World January
2006 p14).

The review contains a consultation document entitled
"Our energy challenge" that sets out four goals: to
cut carbon-dioxide emissions; to ensure reliable
supplies of energy; to achieve sustainable economic
growth; and to ensure that every home is adequately
and affordably heated. The review is also examining
whether recent increases in energy prices have changed
the assessment in the government's energy White Paper
of 2003, which was that new nuclear power stations
might one day be needed to meet carbon-emission
targets but that "new build" should be a future option
only. The consultation ends on 14 April, with the
review team reporting to Tony Blair in the summer.

New designs

While the UK hesitates, several other countries are
already taking action. Finland has commissioned a new
European pressurised water (EPR) reactor at Olkiluoto,
which is currently being built by the French
state-owned firm Areva and Siemens of Germany. It is
set to open in 2009. Three companies in the US have
said they intend to apply for permits to build two
"advanced passive" AP-1000 power stations each, while
France, Taiwan and China are either planning or
building new stations.

One advantage of third-generation power stations like
the AP-1000 and the EPR is that they include more
"passive" safety features than first- and
second-generation plants - that is, systems relying
more on natural forces such as gravity, natural
circulation and compressed nitrogen gas rather than
relying on a multiplicity of pumps and valves. This
makes these plants also far simpler than a
conventional PWR.

In my view, the most likely candidates for new nuclear
power stations in the UK - assuming they are approved
- will be either Areva's EPR or the AP-1000, which is
designed by Westinghouse. Both are based on existing
PWR technology, with which UK regulators are familiar.
In terms of electrical output, the EPR generates 1.6
GW, while the AP-1000 generates 1.15 GW, which is
close to the output of Sizewell B. Another option is
the advanced CANDU reactor (ACR), which already
operates in Canada and several other countries, but it
is an unfamiliar system in Europe and is unlikely to
be chosen.

As part of a study of the regulatory health and safety
aspects of all future energy sources, the UK
government has asked the Health and Safety Executive
(HSE) - through the Nuclear Installations Inspectorate
- to consider the concept of "pre-licensing" designs,
as happens in the US. The HSE will report by June this
year. If pre-licensing is approved, the views of the
regulator might be available before an operator
decides which type of plant to build and a public
enquiry begins. This could make it more
straightforward for a firm wanting to build a nuclear
plant.

The next generation

Looking further into the future, the prospects are
even more exciting. In 2000 the US Department of
Energy launched an international initiative known as
Generation IV, which seeks to carry out research into
new nuclear power stations that could be ready to
build by 2030. The initiative now includes nine
countries - Argentina, Brazil, Canada, France, Japan,
North Korea, South Korea, South Africa and Switzerland
- plus the UK, which joined last year. (The European
Union's Euratom programme is also a member on behalf
of other European countries.)

The long-term focus of Generation IV research is to
build reactors that are economically competitive, safe
and environmentally sound. The aim is also to make the
reactors proliferation resistant, for example by
allowing both plutonium and long-lived waste to be
recycled together so that both can be destroyed
through further exposure in the reactors. However,
none of these targets are specific at this stage -
indeed, particular reactor concepts may have distinct
roles.

The Generation IV initiative has so far produced a
"technology roadmap" that identifies six reactor
concepts showing the most promise. Of these six, the
UK government and industry has decided to focus on
just three - the very high temperature reactor (VHTR)
led by France; the gas-cooled fast reactor (GFR) led
by the US; and the sodium-cooled fast reactor (SFR)
led by Japan. In the UK, the Department of Trade and
Industry will begin funding research on Generation IV
concepts from this month to the tune of £5m a year
over two years.

Each concept has its own advantages (see "Generation
IV: the UK's chosen designs"), but the most promising
at this stage appears to be the various forms of
high-temperature reactor cooled by helium and
containing a graphite core. Indeed, demonstration
plants based on this design are to be built in South
Africa and the US, while experimental reactors already
exist in Japan (HTTR) and China (HTR-10). Ironically,
the prototype for all these reactors was the "Dragon"
reactor experiment, which operated at Winfrith in the
UK between 1964 and 1973.

Causes for concern

But does the UK have the industrial strength to build
new nuclear power stations? It still runs a dozen
nuclear stations and builds nuclear-powered submarines
using PWRs, but it is more than 15 years since
Sizewell B opened. New stations would require the
country to use the expertise of overseas firms such as
Areva or Westinghouse, which BNFL sold to Toshiba
earlier this year. Some major components - such as the
steel pressure vessel, the large steam turbine and the
steam generators - would have to be built abroad.

Nevertheless, much of the construction would be civil
engineering, at which the UK excels. Indeed, the
Nuclear Industry Association (NIA) has estimated that
its member companies could build at least 50% of any
new nuclear power station. This proportion could rise
to about 80% if a series of power stations is
commissioned, because companies would then be more
likely to invest in greater industrial capacity.

Maintaining the UK skills base is crucial, which is
why the research councils' Keeping the Nuclear Option
Open (KNOO) programme is so essential. Led by Imperial
College, with support from the universities of
Bristol, Cardiff, Leeds, Manchester and Sheffield, it
funds research into new reactors and provides training
for postdocs and PhD students. The project includes
exciting research into Generation IV systems, as well
as research into advanced PWRs, materials and waste.

If new nuclear power stations are built, the UK
government's consultation document quite rightly
highlights waste management as an issue that must be
re-examined. The Nuclear Decommissioning Authority is
currently responsible for dealing with existing
radioactive waste from military and civil nuclear
programmes, while in 2003 the government appointed the
Committee on Radioactive Waste Management (CoRWM) to
consult on what to do with nuclear waste over the very
long term.

As the energy-review consultation document points out,
the CoRWM has confirmed that waste from new nuclear
reactors could be accommodated by the options for
waste repositories being considered. I agree with the
Royal Society, which earlier this year called on the
CoRWM to work more closely with scientists before it
makes a final recommendation to government in July on
what form of waste repositories should be built.

I hope that the UK's energy review will call for new
nuclear stations to be built. They are, I believe,
essential if we want a safe, secure and
environmentally friendly mix of electricity supply.
But nothing will happen unless the public supports new
stations and unless business can raise the capital
sums in what is a privatized and deregulated energy
market. Turning words into action will be far from
easy.

• See "The nuclear alternative" on pp42-43; print
version only 

The physics of nuclear reactors

Most existing nuclear power plants are pressurized
water reactors, in which water is used both to carry
heat away from the reactor core and as the "moderator"
to allow the chain reaction to take place. The water
is prevented from boiling by a pressurizer that
maintains the pressure somewhat above saturation so
that the water remains liquid. The core, enclosed in a
steel pressure vessel, consists of low-enrichment
uranium-oxide pellets made up into rods clad in
zirconium alloy, which in turn are grouped into fuel
assemblies.

Connected to the vessel are several "loops", each of
which takes the primary hot water to a generator, in
which steam is produced by boiling secondary water.
The loop then returns the primary water to the
pressure vessel. A reactor building, known as the
"nuclear island", encloses the vessel and its
surrounding pipe work and safety systems. Equipment
outside the island, such as steam turbine-generators,
is largely the same as for any fossil-fuelled station.

The above description is of a "thermal" reactor,
so-called because the moderator allows neutrons to
slow to thermal energies to cause fission. However, in
"fast" reactors, like the gas-cooled fast reactor
(GFR) and the sodium-cooled fast reactor (SFR), the
neutrons are not slowed and so could destroy
long-lived waste mixed in fuel through the process of
transmutation. Fast reactors also generate energy from
a larger proportion of the uranium than thermal
reactors.

Generation IV: the UK's chosen designs

Generation IV is an international research programme
into new forms of nuclear reactor that might come
on-line by 2030-2040. The UK is currently involved in
three of the six main designs that are being studied,
with the aim being to retain the country's skills in
nuclear-reactor design.

-- Led by France, the very high temperature thermal
reactor (VHTR) will be very safe and could produce
both electricity and high-temperature-process heat to
make hydrogen. The benefits for the UK are that it
already has extensive experience of the operation,
technology and licensing of gas-cooled
graphite-moderated systems. 

-- The gas-cooled fast reactor (GFR) is being led by
the US. The advantages of this design are that it can
recycle actinide waste and could provide a long-term
energy supply through extending the use of uranium
reserves. The UK already has extensive design and
development experience, including participation in
European research programmes in the field. 

-- The sodium-cooled fast reactor (SFR), led by Japan,
has three main benefits: the technical feasibility of
one variant has already been proved; the reactor could
recycle actinide waste; and it has potential as a
long-term energy supply. The UK has considerable
experience in this concept, through the prototype fast
reactor programme at Dounreay and the European fast
reactor programme.

About the author
Tony Goddard is professor of environmental safety in
the Department of Earth Science and Engineering,
Imperial College, London, UK, e-mail
a.goddard at imperial.ac.uk

+++++++++++++++++++
"We fear things in proportion to our ignorance of them."
Titus Livius
-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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