Category: Japan

>What Really Happened at Fukushima?, Part II

~ Clarissa ~ 4 Comments

>In the boiling water reactors or BWR, the control rods as well as the fuel rods are contained in a metal jacket so GE made the fuel rods 14 feet high and the Boron control rods which were also in the primary containment were 14 feet long and had to be contracted so the total length was 28 feet plus.

The fuel rods have an uranium core and a zirconium cladding which cannot be exposed to air so you need another 16 feet of water above the reactor to lift the fuel rods vertically and drop them into the storage pool. Next you need a crane above the water with space above and below. Finally you need a roof. As you can see each design step leads to a higher structure. It’s also very rigid due the structural components and has a lot of mass at the top. This has a lot of inertia. You have just constructed the worst type of building for an earthquake zone – tall, rigid and high inertia which means that as the bottom moves laterally the top will tend to not move and tremendous strain develops in the structure. This is bad enough but it gets worse.  Over time the cumulative effects of damage caused by neutron irradiation to metal components include swelling (volume increase), irradiation hardening, and irradiation embrittlement (the influence of irradiation hardening on fracture toughness).  The Fukushima reactors were built in the seventies. This means the primary containment vessel which is made of metal is at risk of rupture even under normal pressure.  In this design the vessel is only removed on the decommissioning of the plant.

Unfortunately GE wanted to reduce the cost of construction in order to compete with its competitors so they made a pressure suppression design using a torus half filled with water. At higher pressure the water in the torus would condense the steam so lower pressures (1000 psi rather than 2000 psi) would exist in the primary containment. Lower pressure meant thinner metal containment and concrete secondary containment which in turn reduced the construction costs. 

People have made comparisons with Chernobyl.

Chernobyl had 200 tons of enriched uranium and Fukushima has 1800 tons if you include all of the reactors and storage pools. I find it ironic that 福島市, or Fukushima-shi means “good-fortune Island”. Dr. Gerhard Wotawa of the Austrian Institute said the iodine 131 released from Fukushima in the first three-four days was about 20 percent of that released from Chernobyl during a ten-day period based on measurements made at monitoring stations in Japan and the United States.


For Caesium-137, the figure could amount to some 50 percent of the amount released at Chernobyl. Pouring sea water onto the rods has several drawbacks. The cold water causes the zirconium cladding on the rods to crack if they are hot releasing radioactive uranium and fission products. The salt from the evaporating sea water coats the rods and acts as a thermal insulation increasing their temperature. The salt coating also reduces water flow through the reactor increasing the temperature. If the zirconium cladding gets too hot then it reacts with the water producing hydrogen which can explode and the zirconium can ignite with the oxygen to melt the uranium inside. 

Types of radioactive isotopes released from Chernobyl versus days 
P.S. A little later, I will publish a post on the social and cultural ramifications of nuclear exposure in Japan.

>What Really Happened at Fukushima?, Part I

~ Clarissa ~ 1 Comment

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My readers are the best. The moment I mentioned that the events surrounding the nuclear reactors at Fukushima were confusing and weren’t receiving a good coverage, reader Canukistani sent me the following insightful article on what happened. Even somebody so technologically challenged as I am can understand this clear explanation. I find this article to be very helpful and wanted to share it with you. Enjoy!

Fukushima Reactor Design

Poor reporting including the New York Times has been the norm on this subject. This has been legitimately criticized by MIT, GE and others. I decided to write this article after Fox News displayed a map of nuclear power plant locations in Japan where one of the sites is actually a rock and roll night club (Shibuyaeggman).
To understand the design we have to go back to the fifties when Admiral Rickover wanted build nuclear powered submarines for the US navy. There were two competitors, Westinghouse and General Electric. Westinghouse won and GE was left with a product which had a lot of R&D expenses and no customers. They decided to remarket it as a commercial electricity producing product.
According to Robert Cowan in an article entitled “Nuclear Powered Reactors, a technological lock-in”:

Recent theory has predicted that if competing technologies operate under dynamically increasing returns, one, possibly inferior, technology will dominate the market. The history of nuclear power technology is used to illustrate these results. Light water is considered inferior to other technologies, yet it dominates the market for power reactors. This is largely due to the early adoption and heavy development by the U.S. Navy of light water for submarine propulsion. When a market for civilian power emerged, light water had a large head start, and by the time other technologies were ready to enter the market, light water was entrenched.

Here is a chart of the various reactor types. The American government had a monopoly on the enrichment of uranium at the time so there were geopolitical reasons for pushing the light water reactor designs since any foreign purchaser would be on a short leash with respect to fuel.
Submarine nuclear reactors have to be squat in order to fit in the boat. They also have to separate coolant from the generator steam to protect the crew who are in close proximity.
In order to build a commercial version you have to deal with the problem of scaling. For higher heat generation in the rods which translates into more steam and ultimately more electricity, you need more uranium but this requires a different geometry. The volume of a sphere increases faster than the surface area which puts a restriction on the amount of uranium. They chose to alter the geometry by making the reactor taller. 


 

>Damage to Reactors 3 and 4 at Fukushima Daiicchi

~ Clarissa ~ Leave a comment

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Jay Lehr of the Heartland Institute on MSNBC just said that talking about the gravity of what’s happening in Japan is not a good idea because it will make people sick from stress. As I look at this picture of  the 3rd and the 4th reactors of the Fukushima Daiichi, I find it hard to believe that stress will be the main health risk here.