back in April, workers were finally able to re-enter the underground storage facility and figure out what went wrong. The leading theories at the time were that a section of the salt ceiling had somehow gotten loose, fallen and broken one or more containers or that something else - like a forklift - had somehow compromised a container. In the course of several reconnaissance trips they confirmed that the accident occurred in Panel 7 and saw compromised MgO containers (magnesium oxide reacts with any carbon dioxide produced by the decay of organic carbon in the waste and waste emplacement materials to reduce air pressure in the facility and limits the amount of radioactive elements dissolved in WIPP brine), but still were unclear on the cause - though some new ideas were on the table.
|This photo was taken during the May 22 entry. It is a closeup of an unsealed waste container where the upper portion of the drum shows heat damage (the brown and black coloration.) You can see more photographs and some video footage here http://www.wipp.energy.gov/wipprecovery/photo_video.html|
By May the DOE had sorted out a cause and by late May now had photos for comfirmation. The official report is at http://www.wipp.energy.gov/Special/Waste_Container_Plan_5_30.pdf.
Quoting from the report (emphasis added) ...
On May 1, 2014, NWP declared a potentially inadequate safety analysis (PISA) based on the possibility that a container of inadequately remediated nitrate salt bearing waste had caused the release of radioactivity in the WIPP underground. Recent entries into underground Panel 7 have confirmed that at least one container from a nitrate salt bearing waste stream from Los Alamos National Laboratory is breached and is the most likely source of the release. Further investigation is underway to determine if other containers contributed to the release. ... Records for disposal in underground Panel 6 indicate that Rooms 1 and 2, which are the two rooms closest to the entry of the panel, also have containers of this waste. Panel 6 is full, but not closed and closure has been initiated.
But what does inadequately remediated nitrate salt bearing waste mean ? Well, first let's break down what nitrate salt bearing waste is.
Nitrate anions (NO₃−) are composed of a central nitrogen atom surrounded by three oxygen atoms. These ions will readily bond with cations (positively charged atoms or functional groups) to form 'salts' or ionically bonded molecules. Almost all inorganic nitrate salts are soluble in water under normal conditions.The other key property of nitrate salts is that thermal decomposition of the nitrate yields molecular nitrogen gas plus large amounts of chemical energy, due to the high energy content bond of molecular nitrogen - or in English, they are likely to go boom. You are probably already familiar with nitrates hazardous properties in the forms of nitroglycerin, gunpowder and ammonium nitrate (NH4NO3) explosions like the one at the West Fertilizer Company.
Large quantities of nitrate salt waste are generated by nuclear fuel processing - presumably due to the use of nitric acid for cleaning and decontamination. So basically, the resultant liquid waste involved here contains nitrates that are inherently unstable, in addition to being radioactive. You can't just fill drums with contaminated liquid, which means that they need to be stabilized somehow. So the inadequately remediated bit basically means that whatever was done to stabilize the waste for shipment and long term storage was the wrong thing - and this is where the kitty litter comes into it.
On May 20th, New Mexico Environment Department Secretary Ryan Flynn released the following statement (emphasis added):
Based on the May 15th visual inspection, the Department of Energy (DOE) has indicated that the radiological release in the Waste Isolation Pilot Plant (WIPP) underground did, in fact, originate from one of two transuranic (TRU) mixed waste containers. The containers in question contain nitrate salts, which DOE postulated may have been the source of the release. As soon as DOE suspected that a container with nitrate salt mixed with organic kitty litter may have been the source of the release, the Environment Department required DOE to take immediate action to isolate and secure all nitrate salt bearing waste containers at WIPP, LANL and WCS. Following the receipt of the most recent evidence from DOE, NMED issued an Administrative Order to DOE / Los Alamos National Security (LANS) yesterday to ensure implementation and documentation of all protective measures being taken to secure nitrate salt-bearing waste containers at LANL. NMED issued this second order today to WIPP to ensure that DOE / NWP submits an action plan to sufficiently secure nitrate saltbearing waste containers by expediting the closure of portions of the WIPP underground including Panel 6, which contains 313 nitrate salt-bearing waste containers and Panel 7, Room 7 which contains 55 nitrate salt-bearing waste containers.
Inorganic kitty litter is basically a mixture of geologic materials like clay minerals, diatomaceous earth, zeolites and/or bentonites and it has been used for decades, not only to stabilize radioactive liquids, but to clean up chemical spills and even to help remove oil stains from driveways. Urea and ammonia - prominent components in cat piddle - are chemical variants of the same kinds of nitrates that are being stabilized in the TRU waste barrels. Clay minerals have charged surfaces and 'all surface area' so that they can absorb and isolate ions.
The problem is that someone (who is probably gone into hiding at this point) decided to switch from traditional geological based inorganic kitty litter to organic “green” kitty litter, made from materials like wheat or corn. If you have ever used corn cob litter, you might have already noticed that it needs to be changed more often, doesn't seem to keep the smell down the same way and that there is often loose liquid in the litter box if you have fallen behind on cleaning the box. Organic litter simply doesn't isolate the waste products - either cat pee or TRU liquid containing nitrate salts - the same way.
So, instead of being properly isolated, the nitrates in the containers 'stabilized' with organic kitty litter dried out instead. When nitrates dry out they can ignite and if you mix them with plant organics you have just added cellulose to the system (that makes it worse - cellulose burns so this was like adding fuel). So basically it appears that in a couple of the TRU waste drums, the mix eventually achieved the right conditions and concentrations to achieve combustion. Any of the containers packed this way could slowly heat up and eventually blow out. It would be a slow motion kind of thing rather than a big, Mythbusters style explosion.
Authorities concluded last month that at least 368 drums of waste at the WIPP site – 313 in panel 6, which has already been filled and sealed, and 55 in panel 7 – could be susceptible to the chemical reaction suspected to have caused a drum to rupture in February.
Los Alamos National Laboratory apparently packed more than 500 barrels of nuclear waste with the wrong type of kitty litter and most of them are known to be at WIPP - 57 more are still at Los Alamos and more than 100 are at the Waste Control Specialists site in Andrews, Texas. I am unclear if other TRU producers also used organic litter to pack waste - I heard of at least one other site doing so but I can't seem to confirm it at the moment.
One thing that stands out to me right now is that the WIPP site performed the way it was supposed to, quickly isolating the release and protecting people, and the environment, from exposure. I don't see this accident as a reason to shut down the site - rather to the contrary it - performed well and demonstrated that it could function in an emergency. I am rather more worried about the other drums out there that were not placed in WIPP. Heat would speed up the dehydration of nitrates, so if you have TRU drums sitting around out there in the summer heat waiting for final disposal - well that worries me.