Published on March 14th,2011 at 8:52 AM
By >Ike

Fukushima Dai-Ichi: How a nuclear power plant works

Although we’re not nuclear scientists here, we felt this thead might be of help for al those who wish to keep a clear interpretation on what your local news broadcast is announcing. A major number of high end press agencies was already touting on about Japan’s Fukushima prefecture becoming a refurbished edition of Chernobyl.
Also if there are any mistakes or technical nonsense do not hesitate to contact us that we can make this post as accurate as possible, but don’t make an ass of yourself and try to keep it polite, we will not tolerate any wrong behavior today.

Japan being a major player in the constantly improved development in health and safety for it’s millions of inhabitants, clearly has more than one trick up it’s sleeve to make sure IF disaster hits the spot, that the people are as safe as possible. Unfortunately a tsunami + an 8.9 earthquake is just a bit to huge for even the most water tight evacuation plan out there. The Fukushima Dai-Ichi nuclear reactor buildings located closely to the epicenter of the quake are under constant monitorring and everything possible is done to make sure IF radioactive substances hit the air, the contaminated zone would be less than the 20km barrier currently used as a safety buffer. This is Fukushima Dai-Ichi, a state of the art reactor plant which won’t blow up like the current media headlines are stating.

What happened:
A) Due to the earthquake a wall got breached/cripped
B) The power went out due to the tsunami’s water reaching the building, rendering even the backup generators useless. Due to these events a hydrogen tank blew up.
C) 4 reactor cores are presently cooled with sea water (which is very corrosive and will most probably render the reactors useless after the emergency situation is moderate again.

Facts:
Reactor cores can go up to 2200 degrees Fahrenheit for the core still to be functioning, only when it heats up to about 4000 degrees Fahrenheit one can say they pose an imminent risk to melting since this is about the maximum temperature where the Uranium pellet start to melt. Only when the 4000 degrees barrier is breached, the potential exposure the radioactive substances is possible since the melting Uranium would corrode/eat it’s way through the reactor.

So how does a nuclear power plant work (explained very roughly in a few basic steps):

The process is called “Nuclear Fission”, it is a reaction between a free neutron that hits a Uranium atom. The Uranium absorbes this neutron, goes into an unstable state and bursts open (explodes). This process repeats itself over and over since every time the Uranium splits, new free neutrons are released and react with other Uranium atoms.

This “splicing” interaction produces energy, not enough in small quantities, but a a pound of highly enriched Uranium produces enough energy to power a full blown submarine. Equivalent to about a million gallons of gasoline/fuel. Thus a very interesting and clean source of power when controlled properly. Uranium reactions also produce an incredible amount of heat and gamma radiation.

Nuclear reactors are mainly divided into 3 ways of status-operiation. Critical mass, Subcritical mass and Supercritical mass. Roughly speaking it’s a form of control scientists use to determin how stable the temperature of the core will be depending on the Uranium atom’s form inside. In general nuclear power plants require a combination of critical and few supercritical mass to be able to rise and lower the temperature depending on the electricity required.

Operation inside the plant consists of the reactor which is a collection of long rods filled with Uranium bundled together. These bundles are put into a pressure vessel and submerged into something similar to a very deep swimming pool (water acts as a coolant). Uranium on it’s own would overheat almost instantly, thus control rods made of materials that can absorb these neutrons are placed inside and can be raised/lowered depending on the present reactions inside the core. Making sure the temperature can be controlled at all time.

The heat produced by the reactor’s core produces steam, this steam is used to drive a turbine where spinning electricity generators produce the power you can use in your home. Different ways to cool down nuclear reactors, some work on water, some on liquid metals, some are cooled by gas,… all depending on how productive you want the cores to become.

The steam produced that drives the generators is of course radioactive, so a concrete liner which absorbed the radiation is placed inside a steel vessel which contains all of the radioactivity released in the production process. To protect these crucial steel vessels a super thick concrete outer building is build in order to make sure none of the radiation escapes the compound when an accident should occur to the steel vessels. The outer buildings are strong enough to endure earthquakes up to crashing airplaned. Unfortunately the massive earthquake at the Fukushima Dai-Ichi premises made the wall of 1 reactor building crack, yet as long as the steel vessel(s) inside are not said to be severely damaged this doesn’t pose a risk to large scale radioactive steam releases.

We also would like you to take time to read, this VERY long but extremely interesting article on the Situation over at Fukushima : Why I am not worried about Japan’s nuclear reactors. It is very in-lighting as well!

Category Environment
              
Fukushima Dai-Ichi: How a nuclear power plant works
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Comments
 

  • Gafletcher

    Its a lot more complicated than that. A zircaloy/water reaction produced a lot of Hydrogen gas and this was vented int o SBGT system which probably failed to contain the H2 and vent up the stack. It is a testamate to the good engineering of the GE BWR,s

  • fh

    Some corrections/clarifications to the timeline:
    1) Earthquake triggered automatic shutdown of all reactors. Within a few seconds, control rods were inserted and the uranium reaction was stopped. What remained was the byproducts which continued to dissipate heat.
    2) When main power grid was cut, diesel generators provided power to cooling pumps temporarily. But when the tsunami hit, diesel generators were damaged.
    3) Batteries were then used supply power to the cooling pumps, while replacement diesel generators were flown in. It seems that there was an incompatibility with the replacement generators, however, which caused some delays in getting the cooling started.
    4) The reactors are built with multiple backup sources of cooling sources, but it is unclear at this time the reasons why they were not or could not be used.

    The two factors that had to be dealt with were pressure and heat. Regarding pressure:
    1) The venting of the steam from the reactor core contained radioactive elements, but as the main uranium reaction had already been long stopped, the radioactive elements were minor byproducts which have very short half-lifes and pose no serious health risk.
    2) Rather than venting the steam directly into the atmosphere, the operators must have decided to first vent it into the building containment in order to help contain the (harmless) radioactive elements locally. However, when releasing extreme pressure, hydrogen-oxygen bonds can quickly separate causing an explosive force. This is the presumed explanation for the explosion at reactor 1.
    3) The reactor core and venting mechanisms were designed to prevent hydrogen-oxygen explosion from occurring from within the reactor core (which is what happened at Chernobyl), so there was no significant risk of a catastrophic explosion and release of serious radioactive material.

    Regarding heat:
    1) The uranium pellets will stand up to 3000°C heat (not 4000).
    2) The pellets are housed in a Zircaloy containment (which makes up the fuel rod), itself capable of standing up to 2200°C.
    3) A small amount of Cesium was detected in the steam, so it is assumed that the Zircaloy rods may have partially melted.
    4) By the design of the outer containment vessel (to prevent any catastrophic explosion, as above), even if the fuel had melted and destroyed the reactor core, the melted elements would safely flow into the containment basin below the reactor, after which point operators would simply wait for the melted materials to cool and solidify, and then cleanup (at extreme expense, but no health risk).

    Misc points:
    1) Because of cooling the reactors with sea water, the reactor chambers will be contaminated with minerals (like salt) that would weaken the integrity of the structure. As a result, reactors 1 and 3 will almost certainly be decommissioned and dismantled (they are already at the end of their usable lifespan of 40 years).
    2) Inspection of the remaining reactors (including those at Onagawa and Tokai) may take at least 6 months to 3 years or more. Electricity will be at 15% below capacity, and the current implementation of rolling blackouts may continue for a significant length of time.

    For more detailed explanation, please see:
    http://bravenewclimate.com/2011/03/13/fukushima-simple-explanation/

    • Anonymous

      Thanks for the update!

  • Benjamindomingo

    As far as I know the steam produced by the reactor is not directly the steam used by the turbine.There is another circuit or heat exchanger not directly hooked up with this radioactive steam, In short there is another piping system with water being heated by the radioactive steam.

    • http://janette-lacoma.myopenid.com/ MixMasterFreshh

      Unfortunately, you are incorrect. This design uses the radioactive steam directly. You are probably thinking about CANDU reactors or similar.

  • http://www.facebook.com/people/Arizona-Jim/1629790835 Arizona Jim

    So this whole problem of plant overheating is the result of poorly thought out power backup and not by the nuke design itself? Amazing.

  • Twostupiddogs

    Thank you so much for the article. Though its not very good news but it still give a sense of hope that things might get back to normal soon. I really hope that is that case and pray to god.

  • Vasuki Naga

    One possible quick solution to cool the overheated fuel rods and reactors:
    Spray water on the reactors using powerful water cannons mounted on whaling ships.

    Japanese Whaling Ships are mounted with powerful water cannons to fight anti-whali­ng ships from a distance. Similarly, anti-whali­ng ships are also equipped powerful water cannons. Using water cannons mounted on ships, water can be sprayed on the overheated reactors round the clock, until the reactors cool down and the radiation level goes down.

    Please inform Japanese authorities, if it is a suitable solution. It can be quickly implemented, since Japan has lot of whaling ships.

    Demonstration of the powerful water cannons mounted on whaling ships:
    http://www­.allvoices­.com/news/­7804731-se­a-shepherd­-attacks-j­apanese-wh­aling-ship­s-in-antar­ctic-ocean­-video/ima­ge/6484029­5-the-sea-­shepherd-s­hip-steve-­irwin-l-ex­changes-wa­ter-cannon­-fire-with­-the-japan­ese-whalin­g

  • Ron Cournoyer

    As far as I know, & I’m 11, the cooling towers drive steam out of the generator, passing through the cleaner, and up. There’s an ocean near this one, so it doesn’t need a cooling resovwar, it pumps in through pipes sent to the reactor.

    Also, they put a nuclear power plant near an ocean in an earthquake and tsunami written country, and NO ONE SAW IT COMING!?

    • GRBE101

      Sorry, actual name is GRBE101 not r cournoyer

 

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