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Sunday, May 21, 2017

Nearby Radiological Emergency

This past week there was a radiological emergency at the Hanford Reservation.  The event caused a site-wide alert to shelter-in-place.  Very exciting.

The Hanford Reservation is a well-known environmental mess.  Here's Wikipedia:
In 2007, the Hanford site represented two-thirds of the nation's high-level radioactive waste by volume.[8] Hanford is currently the most contaminated nuclear site in the United States[9][10] and is the focus of the nation's largest environmental cleanup.[2]
The the environmental section of the Wiki article basically states that the place is a rad waste nightmare.  There are several large underground storage tanks that are leaking corrosive and highly radioactive goop into the aquifer.  The goop is mainly waste from the separation process of Plutonium during the cold war era.

In particular, the saga of underground storage tank SY-101 showed the precariousness of the operation.  This one tank would intermittently "burp" and fill itself with vast volumes of hydrogen gas, creating an explosive mixture.

Below, in the 1990's, a camera was lowered into tank SY-101 to image the surface.

The gunk in the above image is a wicked blend of spent nuclear fuel, plus acids and organic chemicals (like trichloroethylene) that were used to separate Plutonium from slugs of reactor fuel after irradiation.  The unwanted part of the fuel slug would be the remaining 99% that was not Plutonium - fission products, the remaining uranium fuel, and the aluminum cladding. So... all of the acids required to dissolve the fuel element, the organic chemicals needed to strip the Plutonium out of solution, and the other 99% (probably more like 99.99%) of the dissolved fuel element wound up inside these tanks.  For a primer on how Plutonium Production is accomplished, see here.

Turns out this willy-nilly blend of toxic chemicals and radioactivity produces some interesting effects - like causing a tank to burp massive hydrogen bubbles every once in a while!  The organic chemicals reacted together and formed a semi-solid surface crust.  Meanwhile, underneath, the hard radiation from the fission products would break apart water and dissolved chemicals radiolytically into hydrogen gas.  The gas would accumulate under the crust until the pressure built up high enough to break through, and then a huge hydrogen gas bubble would burst forth.

Needless to say, everyone was very alarmed that a tank full of high-level rad waste might detonate and scatter nasty juice all over the place - they'd probably prefer that everyone would just forget about the stuff.   SY-101 was eventually pumped down and the contents were segregated to a certain extent, then placed in a ventilated double-wall storage tank.  This is good, because of the 177 underground tanks, about a third have leaked, and have contaminated the aquifer.  This radioactivity is expected to reach the Columbia River in the next 12-50 years.  Get your non-radioactive salmon while you can...

That's just one example of the type of thinking that brought us to the point where we are: The laser-like focus on nothing but the fast and efficient production of large quantities of Plutonium 239.  The environment was barely a consideration, and the long-term effects weren't a consideration at all.  I can't even imagine the number of prison sentences that would be meted out, had such a mess been created without government involvement.

It shouldn't come as a huge surprise to see a cavalier attitude about other radioactive waste at the site.  Over the decades of Plutonium production at Hanford, nine reactors were built at various locations.  Each reactor continuously created highly radioactive fuel elements that each contained a minute amount of Plutonium-239.  These fuel elements were given a few weeks for the shorter-lived radioactivity to fade.  Next, they were loaded on a rail car and transferred using a remote-controlled locomotive to the PUREX facility, where the separation was performed.

When Plutonium production at the Hanford Reservation came to a close, several badly contaminated rail cars and locomotives remained.  From what I understand the contamination isn't immediately lethal.  Standing nearby would get a trained radiation worker (occupational limit) one year's worth of exposure in about an hour - so 5 Roentgen (or REM) per hour.  The general public exposure limits due to industrial exposure are far lower, at 0.1 REM/year.  Theoretically the public should never be exposed to industrial radiation of course!

Back to our contaminated train.  Even at Hanford, they seem to know better than to leave something like that outside to rust (or maybe the clean-up crews who followed behind the military contractors have better sense).  The wind-swept desert would blow sand and tumbleweeds, scouring the radioactive contamination off the rail cars.  Instead, they built a long above-ground tunnel over part of the rail line and then remotely drove the train inside.  They also put a bunch of other miscellaneous contaminated stuff in there.  There are two of these tunnels - one with concrete lining and the other supported by creosote-treated timber (like railroad ties).

A section of the wood-supported tunnel collapsed, allowing a portion of the tunnel's contents to be exposed.  It's possible that some of that surface contamination was disturbed by the infall of dirt and timber and becamet airborne.  This would be the reason that the "Shelter in Place" emergency notification was given for the Hanford site.  I wouldn't consider this to be a very big deal, because this was low-level stuff, most of it was attached to the rail cars, and there wasn't a lot of it to begin with.

Below, the PUREX building.  The two above-ground tunnels housing the locomotives and rail cars are at the bottom right. The red arrow is where it appears the tunnel collapse occurred, where the two tunnels converge.

Below, the collapsed section of tunnel.

Contrast that with a storage tank full of fission products exploding across the desert!  (Or leaking into the water table and thence into the Columbia River).  The stuff in those tanks would give you a fatal exposure within minutes.

The press of course reported that there was never any danger for anyone offsite.  I give the press no credibility whatsoever regarding radiological emergencies.  In the past they have always minimized any danger, and simply parroted whatever authorities have told them.  Every time.

So it was almost a good feeling when I was able to finally break out my digital Geiger Counter and take readings for myself.  The readings were normal background readings - about 20-28 counts per minute (CPM).  This is about what one would expect from a minor release about 150 miles upwind, on a non-windy week.  By the time the wind picked back up, they had buried the collapsed section with more dirt.

All good.  For now.  Get a radiation detector, folks.

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