Monthly Archives: April 2010


Chernobyl nuclear unit number four blew up 24 years ago today.  Officially the disaster killed about 31 people, but we all know that the death toll is much higher.  Today I'd like to briefly discuss the very basic premise of the accident, what actions the Soviets took, and what we can learn from this accident.
The accident occurred during a test that really should have already been preformed.  In the event of the plant losing external power it would take backup generators about a minute to get up to speed and start coolant circulating again.  This was dangerous and the engineers believed that they could use the inertia of the already spinning turbines to generate enough power to run the plant for about 45 seconds.  The details are well documented, but in the end the power spiked, control rods jammed, and the reactor went out of control.  
These RMBK reactors are inherently unstable at low power levels, and the operators did not understand reactor physics well enough to understand what the instrumentation was telling them.  The control rods only reached just over 2m into the reactor before they seized.  The reactor was 7m deep.  
There were two explosions, a steam explosion, followed closely by an explosion from nuclear excursion.  All of this is well explained elsewhere, but at the time the causes were unclear.  In fact, several of the operators thought a tank of hydrogen had exploded, even though they could see chunks of graphite on the ground outside.  
Almost immediately radioactive dust was showering from vents in the plant and many crew received lethal doses and a 'nuclear tan' very quickly.  They were simply replaced with workers from the other reactors.  Some were sent i to lower the control rods manually, only to find that none of that existed anymore.  They instead saw fire hoses dangling unmanned, the firefighters had already fallen after standing right above the core of the unit.   
The government lied in many cases to the workers and public.  One community was given masks and iodine but didn't distribute them to prevent a panic.  The supplies went to waste.  After that liquidation crews were brought in.  The robots were unreliable and failed quickly.  The government sent soldiers onto the reactor with little protection, they were called 'bio-robots'.  The human side of the story is excellently captured in the book Voices from Chernobyl: The Oral History of a Nuclear Disaster, available here.  The book is also available in many libraries and I highly recommend it, though some of the stories are graphic. Pictured above is the reactor after the explosion, it was enclosed in a hastily built sarcophagus, which is now unstable and must be rebuilt.  The condition of the tunnels dug under the plant by 'bio-robots' is also unknown.  The next picture is of a robot bulldozer being tested.  These were used to bury the cities, but failed to work well and were often replaced by humans.  Some photos from the zone also show spots, recording the massive radiation release.  
So what can be learned from this accident? The obvious results are more training, containment domes, and better reactor design.  The other lessons are about government and public education.  Let's focus on the less controversial public education issue.  Many people refused to leave the zone because nothing was wrong.  They couldn't understand the power of the atoms, the sky was blue, and there was a fire in the distance; why should it mean anything to them? This is why the public needs a basic science education, but now I fear the US has gone too far and induced a fear of the atom.  Nuclear power is a technology to be respected, not feared.  With proper construction, safety measures, and current technology there is no reason to fear an accident in the US.  Waste products are another issue entirely.  
In closing I encourage you to do some research and learn about this disaster.  Also remember all the brave 'bio-robots' that were sent to the station to die while attempting to contain the situation.  You can watch this short video for some photographs from the area.  A documentary about the accident is also available on youtube. 
(None of the photographs are mine, all sourced from Wikipedia)

Wisconsin Meteor - A Great Time to Play with Radar Data

As I'm sure you've heard by now last week, what is believed to be a meteor, passed into our atmosphere and exploded over Wisconsin.  The light was seen as far away at St.Louis, MO and was captured on a camera at the University of Wisconsin-Madison.  The video frames have been played on most news networks and are available everywhere online.
As you can imagine the 911 call center (actually 911 call centers over 6 states) was/were flooded with reports of the light, the sonic boom, and other observations.  The NWS also noticed a new trail appear on the radar.  I downloaded the level 2 data and plotted it up.  First we'll look at the reflection.

You can see the trail in the SW corner of Iowa county.  (KDVN radar)  Next is just a blow up of this image.  The meteor path was from west to east.  According to NASA scientists the meteorite was likely not from the current Gamma Virginids meteor shower, but a rock from the asteroid belt.
Next it would be interesting to look at this trail in 3D.  Using level II radar data this is possible.  The next images show this from several different angles.   The directions are labeled so it's easy to get bearings on which way you're looking.  If you notice the trail is sloping down slightly towards the SE.

The average hight for the event was right around 24,000-25,000 ft.  Looking at the plot you can see how small the plot was and how large the strongest reflector in the center is! A few back of the envelope calculations can be done using basic trig to determine some interesting things.  You can try this yourself.  I've posted a link to the radar data at the bottom and a link to a website where you can download a 21 day trail of GR2Analyst.  Just open the data and start slicing it!

Finally a sample of the meteorite has been recovered at is being examined currently.  There should be many other samples in the area also and hunters are already out looking for them.  With all this in mind you should remember it's not that uncommon for meteorites to enter the atmosphere.  Washing machine size chunks of rock are not abnormal and they burn up in the atmosphere.  If any material makes it to the ground it's probably never seen.  (Since most of the Earth is covered in water most probably hit there.)
Below: Scientists prepare a sample of the meteorite for a test

Gibson Ridge Software
Data for This Radar Scan

Highway to Hail

On the evening of April 6th, 2010 we had a nice little storm system move through central Oklahoma.  Short term models earlier in the day were breaking out a supercell around the OKC area about sunset and though those models had done exceptionally well with events in the previous days they missed the storm type here.

On the right is a radar image from that evening where the boundary is visible.  About this time the storm was moving over Norman producing moderately high winds, heavy rain, and small hail.

Above is an image I took right before the precipitation hit Norman, as the hail began to fall I noticed that it was a prime example of what we had already been discussing in cloud physics.

Hail grows around a hail embryo.  Commonly this is graupel or large drops, but sometimes insects have become entrained in the updraft and become the center of a hailstone!  Hail can undergo 'dry' and 'wet' growth implying things about where it is in the cloud at the time.  Without going into too much detail on this we can say that dry growth produces much less dense hail (more air and cloudy looking) while wet growth produces clear layers of almost solid ice.  Switching methods of growth produces the 'onion' like texture on the inside of a hailstone that so many falsely attribute to multiple trips through the updraft.  The trajectory of most hailstones (we think) is remarkably flat!  It is rare for them to recycle through the storm and when they do its not multiple trips.

The shape of the hailstone also tells us about its environment.  There are many excellent papers out on the topic.  After looking at the image above of some hailstones collected from this storm I encourage you to read more on the topic and next time it hails be sure to pick some up and think about the environment that could have formed it.  Could this stone have recycled? Could it have been warmer than it's environment (think latent heating)? Did it melt significantly on the way down?