As I'm sure everyone knows, there has been a catastrophic earthquake centered off the northeast coast of Japan measured at 9.0 on the Richter scale. This is one of the strongest quakes in history, eclipsing the devastating 1906 San Francisco earthquake which registered 7.9. Since the Richter scale is a base-10 logarithmic, the Japanese quake was more than100 times more powerful the famous Frisco quake.
The Earthquake: This earthquake created a 20-30 foot tsunami that created even more damage than the quake, since the Japanese have designed their buildings to withstand earthquakes. The purpose of this post is to provide some accurate information on this event that seems to be lacking in our news media. Some of this information is based on Alert Bulletins from Stratfor.com, an accepted reliable source.
First, a few words about plate tectonics. The crust of the Earth is made up of several huge tectonic plates that move, probably due in part to cooling and to rotation dynamics. The plates tend to move in an east-west direction. The largest of these plates is the Pacific plate that covers most of the Pacific Ocean. It extends from the coast of the United States to nearly Japan and Indonesia. This plate is moving in a westerly direction, butting up against a leg of the North American plate off the northeast coast of Japan. These plates are pushing against each other, which causes one plate to slide under the other, pushing it up. When stresses build and sudden relative movement occurs, the result is an earthquake.
This movement results in extremely sudden lifting or sinking of the crust. When it occurs under water, this displacement creates a huge swell that expands from the epicenter at incredible speeds, as much as 500 mph. In the open ocean, this swell may be only a few feet high, but when it encounters land, the water underneath is slowed by friction and lifted, resulting in a towering wave--a tsunami--causing massive destruction. Water traveling at high speed is like steel, irresistible.
NOTE: Since the U.S. west coast (California, etc.), is at an angle, the plate movement is sliding. Thus, California quakes are the result of slippage, not one plate pushing under the other (subsidence) as in the Pacific Rim. In South America, the plate movement is pulling apart.
Sadly, the Japanese were well-prepaered to deal with large earthquakes, even one as monstrous as this one. Many buildings held up only to be toppled by the speeding wall of water. The great loss of life and incredible damage was due mainly to the towering tsunami, for which there was no protection.
Nuclear Power Plants: This is a bit mysterious because one would expect the Japanese to have designed carefully to protect against damage from earthquakes and consequent tsunamis. Yet, at least three nuclear power plants are in trouble and one, the Fukishima Daiichi plant in Okuma, is in dire straits. Although there are conflicting and confusing reports coming from Japan, and altogether too much uninformed media reporting and speculation, it appears that the Fukushima plant withstood the earthquake but not the massive tsumani for which it was not designed. In my opinion, this was shortsighted as the two often go hand-in-hand. First, though, let's review nuclear power plant design and operation.
Reactor Design: The reactor core (or pile) consists of nuclear fissionable material, usually a radioactive isotope (variant) of uranium (U235), inside a heavy confining vessel called a containment structure or dome. In the Japanese design, this dome is made of 6-inch thick steel. A byproduct of the fission process is plutonium (Pu239), also a radioactive isotope.
Graphite control rods are inserted into holes or spaces in the pile to absorb nuclear radiation (neutrons). The rods are raised and lowered to maintain the chain reaction in equilibrium. Circulating water (raised to its boiling point or beyond) cools the pile and provides the heat energy to drive turbine generators. The cooling water also functions to moderate the nuclear reaction by absorbing neutrons.
There are two major types of nuclear power reactors. One is the pressurized water reactor (PWR) where the cooling water is highly pressurized, raising its boiling point. In this design, the water used to cool the pile does not boil and create steam. Steam is created in a separate steam generator outside the containment vessel and used to power turbine electric generators. The cooling water also is employed to control the nuclear pile by absorbing neutrons, but is not the primary control mechanism. (See my blog post "Oil and Nukes", August 4, 2008, for a more detailed description of the PWR reactor design.) This is an important distinction. Most U.S. nuclear power reactors are the PWR design.
Pressurized Water Reactor (PWR) Diagram
The Japanese reactors, on the other hand, are boiling water reactors (BWR), where the cooling water is allowed to boil, creating steam voids. This accomplishes two purposes. It eliminates the necessity of a separate steam generator and it increases the range of nuclear pile control possible with the cooling water alone. (Steam voids absorb little radiation. The more steam the hotter the nuclear reaction.) In fact, cooling water/steam is the primary method of control in a BWR, while control rods perform this function in a PWR. The BWR design also employs control rods, but they are used more to fine tune the pile activity.
A salient and unanswered question in anything I have read is why the Japanese reactors at Fukushima Daiichi--there are six reactors in the plant--were not immediately shut down--called "SCRAMMING"--when the earthquake hit. The control rods in these reactors are electrically activated, which system failed when power was lost due to the tsumani and backup power also failed. This also disabled the cooling water pumps, eliminating that method of control.
In modern reactor design (the Japanese reactors were built in the 1970's), power failure results in immediate, mechanically-actuated, full insertion of the control rods, SCRAMMING the reactor and shutting down the nuclear reaction. If this is not done immediately, loss of cooling water circulation due to pump failure may result in heat-induced distortions that jam the rods, preventing shutdown. This is apparently what happened in Japan, for reasons I find mystifying. I understand that all U.S. reactors employ automatic power failure SCRAMMING. (Due to operator error, the Three Mile Island reactor was allowed to overheat, jamming the control rods and resulting in a partial meltdown.)
Present Status: As previously stated, there are conflicting reports. The latest information I have indicates a dire situation that is getting worse. Despite frantic efforts by the Japanese to contain the situation at the Fukushima plant, it appears to be deteriorating. Several explosions have occurred in the plant, damaging at least two of the reactors. It is possible that the reactor No. 2 containment vessel was damaged, but that is presently not confirmed.
Steam pressure is rising to dangerous levels in at least three of the reactors, requiring venting radioactive steam into the atmosphere. While this is spectacular, it is not particularly dangerous as the radioactivity level of the steam is low and it dissipates rapidly. So long as the containment dome is not breached, the danger from radiation is minimal except in the immediate vicinity. However, there are credible reports that the containment vessel at reactor No. 2 may have been damaged. If this damage constitutes a breach--and this is not clear--substantial radiation exposure is likely.
There have been at least three explosions, but they do not involve radioactive material. The high temperatures and superheated steam inside the containment vessel result in accelerated electrolytic corrosion, breaking down the water molecules into oxygen and hydrogen--the well-known electrolysis process. The oxygen is absorbed in the corrosion process but the hydrogen accumulates. As it is vented along with the very hot steam, it strikes the oxygen-rich atmosphere and explodes. These explosions are outside the pile containment vessel and would normally cause only building structural damage.
There are reports of widening and increasingly elevated radiation levels downwind of the plant, causing widespread evacuations. So far, the levels are not lethal but are potentially harmful. Also, workers are being evacuated from the Fukushima plant. This suggests at least a partial breach which is not good news. Should efforts to cool the pile or piles at the facility fail, the radioactive cores, having lost all cooling, will melt and create pools that could reach temperatures of 1000's of degrees. This is the classic meltdown which, if there is accompanying fire which is likely, could spread significant radioactive smoke over a wide area. This now would look more like Chernobyl than Three Mile Island.
That this potentially is a disaster of unprecedented magnitude is clear. The key is containment breach combined with fire. Despite hyperactive media speculation, we in the U.S. are not in danger of radioactive fallout. We are 7000 miles away from Japan, and any radioactive smoke will have long dissipated on its way across the Pacific, despite prevailing winds. In Japan, the potential is much more scary. If the worst happens with the Fukushima Daiichi plant--containment breach and fire--then Japan will be a long time recovering. They will need our prayers.
Finally, let me reiterate that all U.S. reactors incorporate fail-safe nuclear pile shutdown features that obviate anything like what is happening in Japan. I truly am surprised at the apparent short-sighted design of their plants. Our are designed and configured to withstand any conceivable terrorist attacks, which would serve well in the event of a natural disaster.