Yesterday there was a massive earthquake off the coast of Japan, registering 8.9. This seems to have caused a serious problem at the nearby Fukusima 1 nuclear plant. This plant is right on the coast. Google Earth indicates it is maybe 20-60 ft above sea level. The tsunami from the earthquake is reported as being 25ft above sea level, so some parts of the plant might have been inundated.
When a nuclear reactor is shutdown the heat production does not immediately switch off. It is essential that cooling systems continue to run, or else the reactor core will rise in temperature until it melts. The nuclear industry has spent a great deal of time and money to ensure that core cooling is never lost, under any circumstances. All reactors have multiple back-up systems to keep the core cool.
The news is now reporting that Unit 1 at Fukusima 1 has indeed lost core cooling. Unit 1 switched on in 1971, which makes it one of the oldest nuclear reactors currently operating. What is going on isn't clear, but I am reminded of what happened immediately after the Deepwater Horizon exploded and sank. Initial reports pointed to only a small oil leak, or maybe none at all. It took days for the full scale of the problem to become clear.
I going to speculate from here on. Loss of cooling in a nuclear plant implies multiple systems failures. This is not a case of a single generator failing. There are probably three separate systems, any one of which could keep the core cool. All must fail for cooling to be lost. That tends to imply severe damage to the plant. That could be consistent with inundation by a tsunami. Seawater isn't good for electrics, and tsunami waves could break piping and control cables. The plant would be trashed, with very many failed systems.
Pressure in the reactor is reported to be 50% above normal. That may be enough to open emergency pressure relief valves, which will vent moderately radioactive steam into the containment. This happens in order to keep pressure below the level which would burst the reactor pressure vessel. Radiation levels in the control room are reported to be far above normal, which could be due to steam venting plus failure of the ventilation systems. Steam venting means that the reactor is losing coolant, which raises the chance of a melt down.
In fact, a melt down might already be underway. If the damage includes failed instrumentation, and a control room which is becoming unusable, then plant operators might not have a clear picture of what is going on inside the reactor. That of course is speculation on my part, but the loss of cooling indicates that many, many things have gone wrong with this plant.
This kind of mess is why Japanese reactors, unlike Russian ones, are surrounded by containment buildings. At Three Mile Island, the containment building successfully contained the accident, and very little radiation was released. It seems quite likely that the containment building will be needed at Fukusima 1.
Latest reports indicate that four other reactors have also lost cooling. It looks like the situation is getting worse rather than better. If this follows the same course as Deepwater Horizon, then next few days are going to bring more bad news. There are at least 10 reactors along this stretch of coast, at least 3 of which were shut down for maintenance at the time of the quake. Out of the seven that were operating, at least five appear to be in trouble.