Re: Nuclear Power: Unsafe, Uneconomical, Unsustainable

On 4 Feb, 18:49, dave.walt...@xxxxxxxxxxx wrote:
And, of course, you wouldn't want it tested, right? Heaven forbid that
the gods would be angry if it turned out the PBMR would prove to be
everything the designers said it would, right?

They could build these suckers on the West
Side of Manhatten and it would be perfectly safe.


The Pebble Bed Modular Reactor
Peter Bunyard disposes of the argument for nuclear power: it is highly
uneconomical, and the saving on greenhouse gas emissions negligible,
if any, compared to a gas-fired electricity generating plant
(extracts)
--------------
Case Studies:-
"The South African state-owned electric utility Eskom is currently
designing a PBRM in a consortium that includes the Industrial
Development Corporation of South Africa, and British Nuclear Fuels.
The US electric utility Exelon was a member but dropped out; its
involvement at an earlier stage is helpful, because it meant that many
Americans, including members of the US Nuclear Regulatory Commission,
have studied the proposals carefully and raised important issues. A
detailed and well-documented analysis has been done by Jim Harding,
the Director of Power Planning and Forecasting for Seattle City Light.
"
" The Eskom design is based on two German reactors. The first, the
small 15 MW AVR, began operating in 1967 and lasted 21 years. On the
whole, it performed well. The other, the 300 MW THTR-300, took 14
years to build, cost DM 4 billion against an original estimate of only
DM 650 million, and was shut down after four years. During its
operation, there was an incident in which radioactivity was released
into the environment. There was also a nuclear plant at Fort St. Vrain
(Colorado, USA) that used high temperature helium as a coolant, as the
PBMRs will, but this experienced many technical problems. After about
ten years, the reactor was decommissioned and the plant now runs on
natural gas. "
-------------------------
Safety Issues:-

Fuel The core of just one PBMR contains 5 billion microspheres. These
have to be made to high quality because it is the coatings that
prevent the release of fission products from the fuel during normal
operation. When the US Nuclear Regulatory Commission (NRC) considered
an application to build a PBMR in the USA, they noted that if the fuel
kernel is not perfectly centred in the microsphere it will migrate out
of the particle, so the fabrication must be accurate enough to prevent
that happening.
Another question is the packing of the pebbles in the core. It is hard
either to predict or to control how they will arrange themselves as
they move down, and this can lead to significant local variations from
the mean operating temperature. While the German AVR reactor had a
predicted maximum fuel temperature of 1 150 C, it turned out to have
many hot spots exceeding 1 280 C. That is important because the
coatings on the fuel pellets begin to degrade at 1 250 C. The current
design provides for neither in-core instrumentation nor emergency
cooling systems.
Fire The PBMR core contains a large amount of graphite, and this is an
obvious hazard because graphite can oxidise at 400 C and the reaction
becomes self-sustaining at 550 C, both well below the operating
temperature. There could also be dangerous reactions if water vapour
were allowed to enter. Using helium at high pressure clearly reduces
the chance that either air or water can reach the graphite, but it
remains to be seen by how much. For example, it has been shown that if
a pipe were to break and the helium system lose pressure, air inflow
could occur [9]. A fire in a PBMR would be especially serious, because
there is to be no containment building and the reactors are meant to
be built near the towns they serve.
Reliability of key components The PBMR has a number of components that
are the first of their kind, and how well they perform in practice has
obvious implications for both safety and cost.
External threats However well they are designed and built, nuclear
reactors are subject to threats such as earthquakes, plane crashes,
floods and terrorism. Articles on PWRs often point out that their
strong containment structures offer resistance to such threats.
Similar articles on PBMRs, which do not have the same protection, do
not mention external threats. Instead they are so blandly reassuring
that they become misleading
------------------
Disposal of Waste
Whether we use PWRs, PBMRs or any other form of reactor, we still have
to dispose of highly dangerous radioactive waste. There seems broad
agreement in principle that it should be possible to store the waste
safely in geologic repositories, but identifying actual sites is
turning out to be very difficult. The USA has been concentrating on
one particular location, Yucca Mountain in Nevada, but this has still
not been commissioned after 15 years. Moreover, it is estimated that
if there were a thousand 1 GW light water reactors in the world, a new
repository equivalent to Yucca Mountain would be required every three
or four years.

http://www.i-sis.org.uk/SNGNP.php

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