Japan Nuke Plants in a nutshell

First, sorry this took so long.  Work was pretty darn busy all last week and home life is by its nature insane so I just had no time to work on this.  So, let’s get down to business.

The earthquake triggered a shutdown of the plants, which initially went as planned.  The problem was that darned tsunami.  The first thing to note here is that the site was designed to handle a 6.5 meter tsunami.  The one that hit was 7 meters.  Yes, a lousy foot and a half of water is what caused all this mess.  In any case, the tsunami took out at least one of the emergency diesels directly and got the other one either by taking out some power lines or the fuel source.  I don’t have that much detail.  It was at this point that things began to get a little crazy.

Without the diesels , the coolant pumps continued to work off of batteries but after they went out (eight hours if I remember right), the pumps stopped and some important valves failed closed.  That is actually one of the odd things; why on earth would emergency cooling valves fail closed on a loss of power?  Perhaps there was a good reason or perhaps the layout of the plant prevents the establishment of any natural circulation anyway. 

In any case, from here, the water in the core just got hotter and hotter, boiling into steam and increasing pressure in the containment while also reducing the level of liquid in the core itself.  As we know, the pressure was dealt with by releasing the steam into the service floor enclosure.  This would have been fine except that the hydrogen and oxygen in the water had become separated, forming an explosive mixture that went boom.  Now, recall that this is a BWR, with the steam basically coming straight from the core itself.  It was these releases that are responsible for the food and land contamination that you have heard about.

As for the water in the core, the solution as we know has been to keep the core covered with seawater.  Unfortunately, this didn’t happen until the core had been up to ¾ uncovered.  That is very bad, at least for the plant.  Essentially there is no doubt that there was at least a partial core meltdown in at least two plants.  Put simply, they’ll never work again.

Since then, we know that there have controlled on uncontrolled releases of contaminated water into the ocean.  Fortunately, most of the contamination is due to iodine so it will decay quickly.  However, there was so much of it that at least some of the water was 100 Rem on contact (just found that out the other day).  That is HUGE!  You don’t want to be anywhere near that stuff.  It most likely won’t kill you, but it will make you very sick for a very long time.  And if you stay around it to long (say a few hours) it will kill you.  Or turn you into a superhero.  

As for the radiation in general, the area of the site only got up to an average of 12millisieverts or 1.2 Rem/hour with some areas peaking at 400mSv or 40R/hr.  The 40R/hr is bad, don’t walk, run out of that field if you can help it.  The 1.2R/hr general area dose rate is also a lot hotter than anything I have to deal with but it shouldn’t hurt you unless you spend all day in such a field, and even then, it should only make you sick. 

Concerning the way TEPCO has handled things, it would seem to me that for the most part they have done a good job, except in certain instances such as when they claimed that plutonium found on site was left over from old weapons testing.  Also, they apparently don’t play nice with WANO which is a global monitoring agency for nuke plants.  I’m willing to get that that will change or they’ll get out of the nuclear industry all together.  We’ll see. 

Finally, it would seem that they finally have their leak plugged so it should be all uphill from here.

One more thing.  I wanted to just say that the guys who stayed behind to restore emergency power to those plants are nothing short of amazing and should be recognized as the heroes they are.  I read some leaked emails and those guys were working for days even weeks without sleep or food, not knowing what happened to their families in the tsunami.  Please pray for them. 

One last thing.  If you want to see the plant for yourself, you can find it on Google Earth.  Just type in Fukushima, move to the eastern coast, zoom in and scroll south.  When you come to an obviously industrial site that has four primary rectangular buildings in a row, only three of the buildings aren’t so rectangular any more, you’re there.  The destruction that you will see is the result of the hydrogen explosions. 

Someone has done my work for me.

We got a powerpoint from Areva the other day at work.  Areva is one of the bigger and better contractors in the industry, so they have some good info on what happened.  Unfortunately, I can't post the powerpoint for some reason or another so I'll need a day or two to distill it.  I'll post the results afterwards.  After that, maybe I can get to some other things.

What is Contamination and Radiation?

Contamination is something that we have heard about a lot in the news lately.  However, as with most things in the news explanations have been sorely lacking.  So here is a brief primer on contamination and radiation.

Contamination is basically radioactive material in a place where it isn't suppossed to be.  It comes from a number of places such as byproducts of the fission process itself or from materials that have been "activated" by exposure to radiation.  That is, the energy from the fission process has actually rendered normally non-radioactive materials radioactive by adding energy to their atoms and making them unstable.  Contamination typically origniates in the reactor core, and is then carried around in the primary coolant.  Through various leaks in different systems and planned transfers to others the contaminated coolant makes its way to various areas of the plant.  The leaks of course present the biggest hazard for the spread of contamination.  Even when the water dries, it will leave the radioactive material behind to possibly be carried into the air or picked up on a boot or a tool.
Raidation is essentially the energy emitted from and unstable material.  It takes the form of gamma particles, beta particles (electrons), alpha particles (two protons and two neutrons, basically the nucleus of a helium atom), and neutrons.  The alpha particles are the most likely to cause damage as they have most mass and are the slowest moving and are therefore more likely to interact with the cells of your body, the can however, be stopped by a piece of paper.  Betas have less mass and are faster moving and so require more material to stop them, such as your clothes.  Gammas have little to no mass and move very fast and so will likely pass right through you without doing anything.  However, they are also the most plentiful form of radiation and so this is the kind to most wary of.  Basically, a handfull of pebbles won't hurt you much but a storm of them will.  Neutrons have mass but no electrical charge and so are unlikely to interact.  However, this also makes them harder to stop, like the gammas.  They also have a relatively large amount of mass making them dangerous when they do interact.  However, they are only present in appreciable quantities during the actual fission process. 
How dangerous a given piece of contamination is depends entirely on its makeup, that is, what sorts of fission products are present and how much?  Obviously, more material means more radiation which means more danger.  Also, if the contamination is largely something like nitrogen 16, it will not be dangerous for long as this has a half-life of minutes or hours.  Something like iodine has a half-life of days.  Potasium (like in your bannana) has a longer half-life.  The longer the half-life, the longer a bit of contamination will remain dangerous.

That's it for the primer.  Later this week, we'll start to get into exactly what the heck went on in Japan and how it will affect us here.

How Does Nuclear Power Work - Part 2

In the United States, we have two basic kinds of reactors.  These are Pressureized Water Reactors (PWR) and Boiling Water Reactors (BWR).  In a PWR, the reactor is cooled by water that is kept under high pressure to keep it from boiling.  The water is pumped to a steam generator, which is basically as very large heat exchanger.  The primary coolant flows through little tubes which are completely covered by what is typically called the feedwater.  This feed water then gets hot and turns to steam which then makes it way to the turbine.  The turbine blades spin a shaft that is connected to a generator at the other end, providing relative motion between a current carrying conductor and a magnetic field which generates the electricity that powers this laptop.  The steam goes from the turbine to a condenser and is then pumped back to the steam generator.  There are losses along the way which are replenished by water from a nearby water source, either a lake, a river or even a man-made pond.

BWRs differ primarily in the fact that the water boils in the core and the steam goes directly from there to the turbine.  Otherwise the process is the same. 

That one difference leads to others though, such as the fact that BWRs are potentially contaminated throughout the whole system with the entire plant being what is called a radiologically controlled area (RCA).  In a PWR then, there is an extra layer of separation between the fission products in the core and the rest of the world.  Naturally, this is something of an advantage is certain circumstances.  BWRs have the advantage of being cheaper and easier to run due to the fewer number of systems that need to be maintained.

Now, what I said about BWRs sounds bad from a radiation standpoint.  In our next installment we’ll take a quick

How Does Nuclear Power Work - Part 1

This is the first of a series of articles concerning the situation at the nuclear power plants in Japan.  I’m keeping it simple for two reasons.  The first is length; the second is the fact that most people don’t know much about it.  So going into detail would likely go over most people’s heads.  Still, if anyone wants more info, I’ll do my best to provide it.  I guess a third reason is that going into a lot of detail would also require me to do some review so as I don’t provide confusing information.  But again, I’m more that willing if anyone asks.  Here it goes.

First thing to keep in mind is that all non-renewable power  (coal, gas, oil, nukes) all amount to fancy ways to boil water.  The only difference is how the heat is being generated.  Nuclear of course generates an awful lot of energy for the mass involved. 

We start with a bunch of uranium.  There are numerous different versions of this element that are found in nature and still others that are produced through enrichment processes.  Most reactors need one kind of enriched uranium or another.  Some, such as the CANDU reactors used in Canada can pretty much process the raw ore and can even be refueled online.

But I’m getting ahead of myself.  Why uranium?  Uranium is a heavy element.  If you look at a periodic table, you will see that it is way down there with a big dang number.  The bigger the number, generally the more unstable the element is.  That is, it naturally decays into something else, emitting energy in the form of subatomic particles.  This is what makes it useful for nuclear power.  Get enough of it in one contained place, such as a nuclear reactor core and what happens is that the particles emitted through natural decay get absorbed by other uranium atoms, rendering them more unstable so that they decay faster, and so on until the energy is enough that that atoms split, releasing a ton of energy and leading to a self-sustaining reaction.  The reaction is controlled by a combination of controlling the temperature and pressure of the coolant, altering the amount of boron (which absorbs neutrons emitted by the fission reactions and helps slow the reaction) and control rod position (which are also loaded with neutron absorbing material).

Next, we'll  look at the difference between a PWR and a BWR reactor. 

The Japan Nukes

As some know, I work at a nuclear power plant.  Because of this, I am naturally interested in what is going on with the Japanese reactors following that horrible natural disaster.  I am also extremely annoyed with the way the media has been covering the situation.  First, let me just say that yes, the situation is bad.  But it is not "dire" and doesn't threaten the whole of Japan or anything like that.  Most of the reporting on levels of radiation in and around the plant are obviously not written by people who know anything about nuclear power.  I plan to work on a long post about the situation and make it somewhat educational to boot.  For now, I offer my prayers for the men who have stayed behind to get things under control.  I also offer a minor briefing we got on the first hours of the incident as a hold over.  As I said, it only covers the first few hours of the incident and thus is somewhat old news but here you go:

American Nuclear Society Backgrounder:
Japanese Earthquake/Tsunami; Problems with Nuclear Reactors
3/12/2011 5:22 PM EST
To begin, a sense of perspective is needed… right now, the Japanese earthquake/tsunami is clearly a
catastrophe; the situation at impacted nuclear reactors is, in the words of IAEA, an "Accident with
Local Consequences."
The Japanese earthquake and tsunami are natural catastrophes of historic proportions. The death toll is
likely to be in the thousands. While the information is still not complete at this time, the tragic loss of
life and destruction caused by the earthquake and tsunami will likely dwarf the damage caused by the
problems associated with the impacted Japanese nuclear plants.
What happened?
Recognizing that information is still not complete due to the destruction of the communication
infrastructure, producing reports that are conflicting, here is our best understanding of the sequence of
events at the Fukushima I‐1 power station.
 The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic
power system worked.
 All external power to the station was lost when the sea water swept away the power lines.
 Diesel generators started to provide backup electrical power to the plant’s backup cooling
system. The backup worked.
 The diesel generators ceased functioning after approximately one hour due to tsunami induced
damage, reportedly to their fuel supply.
 An Isolation condenser was used to remove the decay heat from the shutdown reactor.
 Apparently the plant then experienced a small loss of coolant from the reactor.
 Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were
used to replace reactor core water inventory, however, the battery‐supplied control valves lost
DC power after the prolonged use.
 DC power from batteries was consumed after approximately 8 hours.
 At that point, the plant experienced a complete blackout (no electric power at all).
 Hours passed as primary water inventory was lost and core degradation occurred (through some
combination of zirconium oxidation and clad failure).
 Portable diesel generators were delivered to the plant site.
 AC power was restored allowing for a different backup pumping system to replace inventory in
reactor pressure vessel (RPV).
 Pressure in the containment drywell rose as wetwell became hotter.
 The Drywell containment was vented to outside reactor building which surrounds the
containment.
 Hydrogen produced from zirconium oxidation was vented from the containment into the reactor
building.
 Hydrogen in reactor building exploded causing it to collapse around the containment.
 The containment around the reactor and RPV were reported to be intact.
 The decision was made to inject seawater into the RPV to continue to the cooling process,
another backup system that was designed into the plant from inception.
 Radioactivity releases from operator initiated venting appear to be decreasing.
Can it happen here in the US?
 While there are risks associated with operating nuclear plants and other industrial facilities, the
chances of an adverse event similar to what happened in Japan occurring in the US is small.
 Since September 11, 2001, additional safeguards and training have been put in place at US
nuclear reactors which allow plant operators to cool the reactor core during an extended power
outage and/or failure of backup generators – “blackout conditions.”
Is a nuclear reactor "meltdown" a catastrophic event?
 Not necessarily. Nuclear reactors are built with redundant safety systems. Even if the fuel in the
reactor melts, the reactor's containment systems are designed to prevent the spread of
radioactivity into the environment. Should an event like this occur, containing the radioactive
materials could actually be considered a "success" given the scale of this natural disaster that
had not been considered in the original design. The nuclear power industry will learn from this
event, and redesign our facilities as needed to make them safer in the future.
What is the ANS doing?
ANS has reached out to The Atomic Energy Society of Japan (AESJ) to offer technical assistance.
ANS has established an incident communications response team.
This team has compiling relevant news reports and other publicly available information on the ANS blog,
which can be found at ansnuclearcafe.org.
The team is also fielding media inquiries and providing reporters with background information and
technical perspective as the events unfold.
Finally, the ANS is collecting information from publicly available sources, our sources in government
agencies, and our sources on the ground in Japan, to better understand the extent and impact of the
incident.