International Atomic Energy Agency

Fukushima nuclear power plant situation explained

I’ll try to explain this without having to go talk about Nuclear plant design. For non-science majors, I wrote “Fukushima nuclear power plant meltdown explained simply” on Blog Watch. This article is going to be a little more technical, but it still won’t be Physics major-level. Pardon its simplistic explanation.

The 2011 Sendai Earthquake was without a doubt the most powerful earthquake to hit Japan, as we have recorded it. People didn’t start keeping record until 1900, so you can imagine that there is vast amount of information that we do not know about. Fukushima started producing electricity in 1971. In February 2011, Japanese nuclear energy regulators gave it another 10 years to operate. Fukushima nuclear power plant was designed to take on an 8.2 earthquake. And the beauty of Japanese Engineering showed through how Fukushima successfully withstood a 9.0 Earthquake, and a 7 meter high tsunami.

Nuclear power plants are designed in such a way that there are cascading backups. And Fukushima had redundancy written all over it. Fukushima suffered what experts call, “Level 4 Nuclear Event Scale. In English, it means an accident has occured but without significant off-site risk. The accident involves a significant damage to the core such as a partial core meltdown, or an overexposure of one or more workers that may lead to death. It also means an off-site release of radiation dose, measured in millisieverts.

There are seven levels of Nuclear Event Scale. The highest is Level 7, which is a Chernobyl-level type of accident where a major level of radioactive material is released causing widespread health and environment problems.

What the Japanese are now doing at Fukushima is preventing a core meltdown. One Unit 1 of the reactor, they have already flooded it with SeaWater mixed with boron. This forces the Core from cooling down.

So what’s the status now? According to Brave New Climate:

“Unit 1: Seawater injection continues and it is thought the reactor core is now sufficiently cool. Safety regulators consider reactor pressure of 353 kPa an indication of a stable condition.

Unit 2: The normal reactor core isolation cooling system is in use. Fuel rods are covered by about 3.8 metres of water.

Unit 3: Operations to relieve pressure in the containment of Fukushima Daiichi 3 have taken place after the failure of a core coolant system. Seawater is being injected to make certain of core cooling. Malfunctions have hampered efforts but there are strong indications of stability.

What of the explosions? Here’s a bit technical explanation of the explosion:

“Gas pressure in steel reactor pressure vessel rises when coolant systems are not active and is vented to reactor building by engineers. {In my view there is not yet plausible evidence that the temperature of the PV water was sufficiently high to spontaneously split water}

j. The hydrogen in the reactor building is ignited in an explosion which blows out the walls but is not likely to have damaged Steel pressure vessel or concrete containment.

{this is true of both scenarios –but the source of the hydrogen is also external to the PV and containment in my explanation, overcoming the problem of why there was not a hydrogen explosion within the containment and outside the PV!}”

The problem really is that there are mixed-signals being given. World Nuclear News reports:
“The Japan Atomic Industry Forum (JAIF) reported back from a press conference given by the Nuclear and Industrial Safety Agency (NISA) at 11.30pm. The trade body said that a malfunctioning guage means that water levels cannot be confirmed. The gauge in question reads that water levels are around two metres below the top of the nuclear fuel assemblies, which would represent a very serious situation with the risk of fuel damage.

“It is unknown whether [the reading] is real or not,” said JAIF. Other readings from the reactor system do not indicate that the reading – and the associated potential damage to fuel – are the true situation. Pressure levels stand at around 250 kPa, compared to reference levels of 400 kPa – and a high of 840 kPa recorded at unit 1 yesterday. Radiation levels have dropped during the seawater injection, said NISA.”

The situation is serious, but manageable.

FAQ on the Japan Nuclear power plant situation.