South Africa. Eskom’s proposed R14,5-billion pebble bed nuclear reactor, touted as "meltdown proof", cannot get certification in the United States in its current form because it does not meet Safety requirements there.
The PBMR demonstration reactor planned for Koeberg does not have a safety barrier – called a "secondary containment" – which is built into the design of all modern nuclear reactors to contain radiation in the event of an accident.
A German nuclear scientist, who has recently reinvestigated Safety problems of the nuclear plant that was the prototype of the South African pebble bed, said he considered it "irresponsible" to construct a nuclear plant without a secondary containment.
In simple terms, without this structure, there would be nothing to prevent a massive release of radioactivity into the environment if there were an accident.
Rainer Moormann, a nuclear scientist working for FZJ, a German research centre where the prototype pebble bed reactor was first developed, has published a paper about the "indisputable" facts relating to this reactor, called the AVR. It states that the old AVR plant was "heavily contaminated" with Strontium-90 and Caesium-137, which was the result of "inadmissible high core temperatures".
He said the problems with the AVR were not sufficiently understood, 20 years after its final shutdown.
Moormann said it was correct that the PBMR had some inherent safety features in specific areas where conventional nuclear reactors had safety problems, but this did not mean that one could conclude that the PBMR was "inherently safe".In fact, pebble beds had risks in areas where conventional reactors showed inherently safe features, he said.
"One example is reactor fire, which is possible in the PBMR because of the huge amount of burnable graphite in the core," Moormann said.
"This is not a hypothetical case. The two most severe accidents in reactors up to now (Chernobyl in 1986 and Windscale in 1957) were accompanied by graphite fires. These reactors also had graphite cores, although they were not PBMR-type reactors."
In 2001, Dana Power from the US Nuclear Regulatory Commission said a graphite fire was a "foreseeable accident scenario for the proposed PBMR".
Source: Cape Times
By: Melanie Gosling
Posted: 4 September 2008