BY DR. JOSE PALU-AY DACUDAO
ELEMENTAL lead is also highly resistant to getting combusted explosively by oxygen in the air or water. So even if you shoot a bazooka into the reactor, the lead coolant will leak out peacefully and almost immediately solidify into solid lead under room temperature, thus trapping the radioactive materials in the reactor in solid form.
As mentioned above fast breeder reactors, such as lead cooled-reactors, are capable of burning long-lived actinides. You turn dangerous nuclear waste into fuel.
It seems that the ideal nuclear reactor for the Philippines (with our frequent earthquakes) is the molten lead reactor. Even if a huge quake splits the reactor open, the molten lead in its just solidifies when it leaks out.
Most nuclear plants in the world are second and third. These can be produced commercially. The top producer in the world is Russia. The main reason seems to be ease and economy of acquirement. In order to procure a Russian nuclear plant, you only have to deal with one company, the state-owned Rosatom.
This company constructs the reactor, provides the scientists, engineers, and technicians, provides the nuclear fuel, takes care of the nuclear wastes. In all other commercial nuclear plants, these functions are done by at least two institutions or companies. You have to deal with more people, organizations, countries, contracts, sources, and so on.
The main disadvantage to fourth gen nuclear plants is that they are relatively untested. However, their performances (few though they are) in Russian and China bespeak well of them thus far.
The second most important classifications system of nuclear plant reactors is by coolant. At present, most of commercial nuclear reactors in the world are water-cooled. There are two types, the pressurized water reactor (PWR) and the boiling water reactor (BWR). By far, the most common is the PWR.
Water acts as the primary coolant. Water under high pressure is pumped to the reactor core. In the reactor core, uranium is fissioned, thus releasing heat. The heat transfers to the water. The water coolant is pumped to a steam generator. The heat energy from the high-pressure primary water coolant is transferred to a secondary coolant, namely also water but under lower pressure. Steam is produced by the secondary water coolant. The steam drives turbines. The turbines spin an electric generator. Electricity is generated.
There should be a water source and outlet. Not a problem in the Philippines where there are lots of rivers and seas.
PWR and BWR both use ordinary water (there are reactors that use deuterium enriched âheavy waterâ such as the Canadian CANDU) as both coolant and neutron moderator.
US and French companies (and also the Russians) have had the most experience in building and maintaining PWRs.
There are other coolants. Canadian CANDU reactors use deuterium enriched heavy water. Its main advantage is that it can use unenriched uranium. (Natural uranium metal is made up of two isotopes, U-238, and the rarer U-235. It is U-235 that fissions in nuclear reactors. Thus light water-cooled reactors use uranium fuel enriched in U-235.)
However, you have to have a process of getting deuterium. Ordinary water mostly consists of an oxidized single proton, also called protium. It is chemically protium oxide. But heavy water is enriched in deuterium oxide.
Deuterium is a hydrogen isotope with one proton and one neutron. (Thus it is heavier than regular waterâs protium oxide.)
When deuterium absorbs a neutron in the reactor core, it transmutes into tritium, a radioactive hydrogen isotope with one proton and two neutrons. It has a half-life of about 12.5 years. You have to have another system of isolating radioactive tritium, storing it until it decays into stable helium-3, or selling it. (Tritium has its uses for the military. Itâs actually the hydrogen isotope used in fusion bombs.)
The third most important classifications system of nuclear plant reactors is by neutron moderator. Uranium fuel, specifically U-235 nuclide, fissions more easily if fast moving neutrons are slowed down. The term used is âmoderatedâ. As previously mentioned, pressurized water reactor (PWR) and boiling water reactor (BWR) both use ordinary water as neutron moderator.
There are other neutron moderators. Graphite (elemental carbon) is the next most commonly used. The first nuclear reactor during WW2, which the US used to develop the atomic fission bomb, used graphite. Chinaâs fourth gen pebble bed reactor uses graphite as moderator and helium as coolant. (To be continued)/PN
