Transuranic refers to atoms of elements that are higher in atomic number than uranium (which is 92), almost all of which are synthetic. Atomic number equals the number of protons in the nucleus, while atomic mass means the total number of protons plus neutrons in the nucleus. An element is defined by its atomic number - i.e. 92 is always uranium - but can contain varying numbers of neutrons, referred to as isotopes. So uranium comes in different masses, like U-238 or U-235. The most common transuranic element is plutonium (94), which is found in most forms of transuranic waste.
It turns out that plutonium does occur naturally in very small
amounts in a type of uranium ore called pitchblende, which contains approximately one part per trillion of
natural plutonium. The uranium in pitchblende decays primarily by alpha-particle emission (2 protons and 2 neutrons), but there is also a process called "spontaneous fission" that occurs occasionally. In spontaneous fission the nucleus splits ("fissions")
and neutrons are released. These neutrons can then sometimes be absorbed (captured) by another
U-238 nucleus, triggering a process that produces Pu-239. In addition, trace quantities of Pu-244 were found in Precambrian Age phosphate from southern California in 1971. Because of its long
radioactive half-life scientists believe that this isotope has existed since the creation of Earth about 4.5 billion years ago. However, these isotopes exist in such small quantities that for all practical purposes, any element past uranium is considered anthropogenic (human-made). Transuranic radioactive waste consists of items like tools, rags, laboratory equipment and safety gear (suits etc.) that has been contaminated by contact with radioactive materials. It also includes organic and inorganic residues and even entire enclosed contaminated cases in which radioactive materials were handled. Transuranic (TRU) waste materials have been generated in the U.S. since the 1940's.
By its very nature, TRU has a mixture of properties. Some waste will emit high levels of penetrating radiation, while other waste will emit small particles that have little energy but can inhaled and cause significant damage to lung tissue (alpha emitters like radon gas) or ingested and cause organ damage. Most of the elements involved are long-lived, which means will stay radioactive for a long time.
There are 15 different isotopes of plutonium, each of which has a different half-life (the time it takes for half of the original atoms to decay into a new form, called a daughter product). The half-life of Pu-239 is 24,000 years and the half-life of Pu-241 is 14.4 years. Naturally occurring Pu-244 has a radioactive half-life of 80 million years. The plutonium isotope with the shortest half-life, 20 minutes, is Pu-233. Substances with shorter half-lives emit stronger radioactive energy, so they decay more quickly than those with longer half-lives but would also do more damage if you were exposed to them.
In 1970, the Atomic Energy Commission (predecessor to
the DOE - Department of Energy) decided that TRU waste should be stored for easy retrieval
to await disposal at a permanent repository. Federal facilities in Washington,
Idaho, California, Colorado, New Mexico, Nevada, Tennessee, South
Carolina, Ohio, and Illinois are currently storing TRU waste.  |
| The DOSCO Rotary Head Mining Machine Underground at the Waste Isolation Pilot Plant. |
WIPP began operations in 1999 when the first waste shipment, from Los Alamos National Laboratory, arrived. As of February 28, 20104, the plant had received and stored 11,872 shipments composed of 90,807 cubic meters of waste in 170,946 containers.
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| Emplacing Transuranic Waste in Room 6 of Panel 3 |
According to the DOE, at 11:30pm Friday, February 14th, "a continuous air monitor detected airborne radiation in the underground." There were no employees working underground at the time and employees on the surface sheltered in place as a precaution. Nobody knows exactly what happened, but the most likely scenario is that a huge chunk of salt fell from the ceiling and ruptured a drum or multiple drums of waste. The other suggestion is that a forklift (automated ?) punctured a canister. It could be weeks before they can get underground to find out what caused this.
On the 15th, the DOE reported that "Multiple perimeter monitors at the WIPP boundary have confirmed there is no danger to human health or the environment. No contamination has been found on any equipment, personnel, or facilities.
Any possible release is minimized by the highly protective filtration system that is designed to filter any air leaving the WIPP repository.
WIPP’s ventilation system automatically switched to Filtration Mode when airborne radiation was detected underground.
As a precautionary measure, employees on the surface were instructed to shelter in place.
At 5:00 PM MST, a determination was made to allow non-essential employees to leave the site.
These employees were cleared by radiological control technicians prior to departure. All non-essential employees were off-site by 5:30 PM MST."
Then, according to NPR, "two days later, independent monitoring stations operated by New Mexico State University detected radioactive americium and plutonium on the surface." The levels reported are extremely low, well below Environmental Protection Agency reporting limits, according to the head of the Carlsbad Environmental Monitoring and Research Center. The DOE reported on the 19th that trace amounts of americium and plutonium had been detected at one of the WIPP sampling stations located on an access road. They say this is expected because the HEPA filters remove 99.97% of contaminants from the air, so a minute amount can still pass through the system. WIPP officials reiterated their previous statements that residents of nearby communities are not at risk and the radiation levels detected were very low.
Then, around 5 a.m. on Wednesday (2/26/14) WIPP officials informed 13 workers that they had tested positive for radiation contamination. These workers were performing above-ground duties at the WIPP facility on Feb. 14, the day the radiation leak was detected. They have also identified additional employees who were on-site the morning of Feb. 15 and have requested biological samples from them to determine if they are have been affected.
WIPP officials said Thursday it's premature to say what effect the radiation will have on the workers' health and what course of treatment is necessary. Officials said these results are preliminary, and more tests need to be done.
There are about 300 employees on the physical property each day, according to the DOE. About 200 of them are classified as essential, and they have kept the plant running since the accident.
WIPP officials also said that an attempt will be made to get back into the mine for testing. They plan to send two probes down the salt-handling shaft to get airborne radiation readings and air quality readings. From there, officials will attempt to safely fix the leak and bring the facility back to full operation. Depending on what caused the accident, this could take months.
This accident is the first-known release of radiation since the site began accepting plutonium-contaminated waste from the nation's nuclear bomb building sites 15 years ago, in 1999.
This leak came just nine days after a truck hauling salt in the plant's deep mines caught fire, but officials say they are confident the incidents are unrelated.
No transuranic waste shipments were scheduled from February 14 though March 10 for planned annual maintenance, but as of now all shipments have been suspended.
Official announcements from the DOE are at http://www.wipp.energy.gov/
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| This is the image from the WIPP Environmental Sampling pdf |
