BY DR. JOEY PALU-AY DACUDAO
IN THIS article, we emphasize important points found in the previous two.
In the issue of safety, the most important factor to consider in the Philippines is earthquakes.
The safest nuclear reactors in the world, based on their essential physics, are fourth generation nuclear plants. The laws of physics dictate that they cannot suffer from a loss of coolant meltdown or explosion (an advantage in the Philippines’ reoccurring scenarios of mighty earthquakes). They do not even use water as coolant.
At present, only Russia and China are building them for commercial purposes. Russia is concentrating on lead-cooled and sodium-cooled nuclear plants. Russia has functioning commercial sodium-cooled reactors that can theoretically even consume nuclear wastes. China at present has a functioning pebble-bed reactor providing commercial electricity to a power grid, and is also building a molten salt reactor prototype.
The pebble-bed reactor (PBR) has its nuclear fuel (uranium or thorium oxide or carbide) encased in graphite (elemental carbon) and silicon carbide pebbles. Commercial PBRs were first built in Germany in the 1980s. Historically, an issue with them is the rare occurrence of cracks from the pebbles, and leaks of radioactive dust. If catastrophically breached in a strong earthquake, theoretically they may release large amounts of radioactive carbon dust, or even burn. Nevertheless, they are generally safe. The functioning ones in China (the Chinese have bought patents for them from Germany) as of now have not experienced major safety issues.
USA successfully built and operated (for four years) an experimental molten salt reactor (MSR). The MSR is powered by uranium or thorium fluoride fuel dissolved in a mixture of molten lithium fluoride and beryllium fluoride salt. It can theoretically function as a fast breeder reactor, meaning it can consume as fuel the dangerous long-lived radioactive actinides, the main problematic nuclear waste. While operating, its safety in the US has been confirmed. Theoretically, if breached in an earthquake, the molten salt will just crystalize into solid salt under atmospheric temperature and pressure. Historically, the MSR’s main problem is the corrosiveness of fluoride salts, and their tendency to form gases when stored in the long term. Thus there were problems in decommissioning and nuclear waste management, as seen from the US experience. China at present is building an MSR and thus far has had no major problems.
Russia is concentrating on liquid metal reactors, sodium-cooled and lead-cooled. These are fast breeder reactors. As mentioned above, fast reactors (named after the fast moving neutrons they produce which fission nuclear fuel) can consume as fuel the dangerous long-lived radioactive actinides, the main problematic nuclear waste.
Sodium-cooled reactors have an inherent disadvantage in that elemental sodium may react explosively with water and oxygen. This has already happened in an experimental sodium-cooled reactor in Japan. In case of an earthquake-induced breach, this can turn into a disaster.
Probably the safest of the fourth generation nuclear plants is the lead-cooled nuclear reactor, based on physical laws. In case of an earthquake-induced major breach, the molten lead just dribbles out and immediately solidifies under atmospheric temperature and pressure, thus containing the dangerous radionuclides. Moreover, unlike sodium, lead is highly resistant to oxidation (chemically preferring to bind with sulfur). You never hear of lead fires or lead explosions. Lead-cooled reactors won’t explode if breached.
Among the third generation nuclear plants, the one most suited to the Philippines is the modular floating nuclear reactor. Russia developed it from its nuclear powered icebreaker ships used to clearing Arctic ice. Since Russia has been building these ships for half a century, it has had the experience in its manufacture and maintenance. At present one modular floating nuclear reactor is powering an Arctic town. (To be continued)/PN
