[Peace-discuss] Japanese warning

[C. G. Estabrook]

Not for some.


On 3/13/11 11:10 PM, Brussel Morton K. wrote:
> Another evaluation…  It will take some time to get a clearer picture of what 
> happened and its health consequences.
>
>
>     Perspectives of a nuclear engineer on the Japanese nuclear power plant
>     accidents
>
> by AJ Nosek <http://www.facebook.com/ajnosek> on Saturday, March 12, 2011 at 
> 2:49pm
>
> I am a nuclear engineer and I study radionuclide releases from severe 
> accidents where I work, including scenarios very close to this one.  This is 
> what I can understand from the news at this point in time, but first let me 
> explain what the issue is.
>
>
> After a reactor is shut down, it is still hot.  Think of it as a stove: after 
> you turn it off, you can still burn yourself.  The difference is that a 
> reactor still produces some residual power.  Therefore the goal in accident 
> mitigation is to shut down the reactor core and keep it cooled.  Keeping the 
> core covered with water (or even just a good fraction of the core), will avert 
> significant core damage.  Keeping the core covered requires power to run 
> valves, pumps, and sensors.
>
>
> The accident at the five reactors in question is classified as a “station 
> blackout” (SBO).  SBO is an event in which you lose all AC power, and is very 
> rare as it requires an initiating event that knocks out power from both 
> offsite power sources and both backup diesel generators.
>
>
> In such an event, Boiling Water Reactors (BWR) have a special pump that is 
> powered by steam instead of electricity, known as the Reactor Core Isolation 
> Cooling (RCIC) pump.  However, in order to properly run the pump, you still 
> need indicators and the ability to manipulate valves.  As a stop gap, this 
> power can be supplied with batteries for 8 hours, and potentially much longer 
> depending how fast operators can shed unnecessary loads, find other power 
> sources, or restore AC power.  A small generator with gas and should be able 
> to keep the batteries charged indefinitely.
>
>
> Many (if not all) the five reactors have been using this system.  The steam 
> from the reactor vessel goes through a safety relief valve and into the 
> suppression pool (inside containment), which has a high decontamination 
> factor.  At some point, however, if heat is not being removed from the 
> suppression pool/containment, containment pressure will increase and the steam 
> inside will have to be vented through an additional filtered system.  This 
> means a very small amount of radiation will be released, as this steam has 
> been through the reactor, but fuel has not been damaged, fission products will 
> not be released, and it itself is not a significant event.
>
>
> The Fukushima Daiichi Unit-1, a small Boiling Water Reactor (BWR) with a 
> Mark-I containment, is having problems maintaining the water level in the 
> reactor core.  The battle has centered on restoring power, and keeping the 
> core covered with water.  The reactor core has certainly had some amount of 
> damage, and this is confirmed by the hydrogen buildup.  Hydrogen is produced 
> from zirconium (a structural metal in the core) and steam at about 1700 
> degrees.  The hydrogen must have been released from the vessel and from the 
> containment, as the detonation occurred outside, in the reactor building.  
> This is consistent with the KyodoNews report that stated that (at one point) a 
> third of the active core had become uncovered, and also consistent with 
> reports of cesium which indicate there has been at least some level of core 
> damage.
>
>
> This has been a long, protracted accident.  The many hours that have past 
> since the reactor was operating, and that means the residual power has dropped 
> significantly.  Without decay heat, significantly smaller fraction radioactive 
> material will escape into the atmosphere.  More time also means more decay of 
> most radioactive material and evacuation.  Whatever the final outcome, this 
> accident is much less significant than Chernobyl.
>
>
> At this time, reports say the reactor has been covered with seawater and 
> radiation levels are dropping.  The doses from the plant are about 100 
> mrem/hr.   (A nuclear plant worker dose annual dose limit is 5000 mrem, so a 
> worker could stand there for 2 days before reaching his limit.)  This is a 
> good sign because this is not a significant amount of release from a severe 
> accident.
>
>
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