The WIPP waste is also divided into 3 main wasteforms: Debris Waste, Homogeneous Waste (including solidified sludges and 'powdered' plutonium), and Soils & Gravels. Each of these is divided into various sub-categories. For instance, Debris Waste can be rags and booties or it can be a huge machine that is too large to ship to WIPP whole. It can also be 49% unsolidified powdered plutonium and still be called Debris Waste since each container is defined by what fills 51% of its volume.
In addition to being defined by their form, all the wastes are also divided into Waste Streams. Waste Streams are wastes that all came out of the same process using the same materials so that they should have the same chemicals, heavy metals and radionuclides in them. Waste Streams are important when the waste is characterized since characterization begins with documents describing the process which created each Waste Stream (These documents and other similar information are called Process Knowledge or Acceptable Knowledge--AK) Each Waste Stream stays together as it goes through the characterization process, is shipped to WIPP and is placed underground. In fact, the non-random emplacement of waste--that is, keeping each Waste Stream together as it's stacked in the disposal rooms--might create problems in certain breach scenarios. The regulations are written assuming that each kind of radionuclide or toxic waste is spread randomly throughout the repository so that if someone drills into the waste later they will bring only a certain amount up into the accessible environment. However, some waste streams contain significantly more plutonium than others; some contain more toxic chemicals. If these are drilled into the dose on the surface could be much higher.
Characterization is an essential part of the safety program at WIPP. It is necessary to know what is in the waste to see whether the waste is compatible with the repository and with the other waste. Unsuitable or incompatible waste can cause serious containment and safety problems in a disposal facility. For instance, the residues in the failed Los Alamos National Laboratory (LANL) container at the right are plutonium-bearing salts. These salts are both corrosive and reactive--waste characteristics that are prohibited by the WIPP Hazardous Waste Facility Permit in waste being buried at WIPP.
Transuranic waste is characterized at the generator sites before it is transported to WIPP. Characterization of the radioactive component of the waste is overseen by the EPA. Non-destructive methods are used to survey the waste containers and calculate what kinds of radioactive materials are in the waste. This information is then compared to whatever Acceptable Knowledge (AK) may exist for that Waste Stream.
Characterization of the hazardous component of the waste is overseen by the NMED and is more complicated. First, waste is characterized by reviewing its Acceptable Knowledge. Just as some waste is stored neatly and retrievably, and some waste has been allowed to corrode and degrade in storage, some AK is comprehensive while some is in poor condition. Newly generated waste can have excellent documentation on all the radioactive and hazardous materials in a drum. AK from older waste, however, may not be at all clear about what is in a container or the process from which it came.
After making a determination on whether the waste is mixed or not through AK, the AK is confirmed with various tests. All waste, even waste that is believed to be purely radioactive, undergoes the same characterization tests. Headspace gas is sampled and analyzed from all containers to calculate the amount of Volatile Organic Compounds (VOCs) in the drums. VOCs are hazardous, used solvents which can cause cancer, brain damage and other problems. Since all the drums are vented, these toxic gases are released into the mine while workers are emplacing the waste. These workers are breathing between 33 and 36 hours per year of these VOCs, so the amount of VOCs allowed into each room has to be kept below toxic levels. Analysis of the VOCs helps to determine what solvents are in the waste, as well. All containers are either Visually Examined (VE) or X-rayed using Real Time Radiography (RTR) to check for prohibited items like free liquids or sealed inner containers. (The radiograph above-left shows a plutonium package at Argonne National Laboratory East which has several inner containers surrounded by a plastic bag inside a 55 gallon drum.) Homogenous Solids and Soils & Gravels are sampled and analyzed for various chemicals and compounds. (The photo below-right shows samples being taken from solidified homogenous waste by coring.)
Characterization accounts for 50% of the costs of the whole WIPP project, so DOE is looking for various ways to reduce the amount of characterization they have to do. They also have major problems with the characterization of the RH-TRU waste. DOE wants to bring RH waste to WIPP soon but they do not have the infrastructure at most of their sites to characterize this type of waste. In addition, the high radioactivity of these wastes makes some analyses difficult or impossible to do. DOE would like to have the requirements to do these analyses waved for RH-TRU and simply characterize it on the basis of (un)Acceptable Knowledge alone. It is unclear whether they will get NMED to allow this.
There is a lot of flammable gas in the waste including hydrogen, methane and VOCs. The hydrogen and methane, are generated from waste corrosion and drum corrosion, microbial activity and radiolysis. The VOCs come from spent solvents. These gases could pressurize the contaminated brine and push it through natural, or created fractures out of the repository. Gas generation will also have an effect on the rate at which storage rooms close around the waste and the rate at which brine flows into and out of the rooms.
Many of these gases are flammable and pose a danger of fire or explosion in the waste rooms after they are closed and during transport. All the drums are vented to keep explosive hydrogen and methane gases from building up in the drums. Even so, after about 25 years DOE and NMED postulate that there could be a methane gas explosion in sealed rooms or panels at WIPP. This could occur even while people are still working underound at WIPP excavating the mine or emplacing waste.
In addition, because only small quantities of High Wattage Wastes can be shipped at a time DOE wants to get the hydrogen gas limit raised. ('High Wattage' wastes generate an extra large amount of hydrogen through radiolysis because they are so 'hot') DOE has called for studies to see how large an explosion or fire the O-rings in the TRUPACT-II could withstand during transport and to figure out how to receive and unload drums of waste full of flammable gas at WIPP. They have also applied for a revision to the Nuclear Regulatory Commission's requirements for the TRUpact-II which would 'solve' most of their problems with this waste.
There have already been at least 13 reported incidents of fire, explosion or over-pressurization in drums of waste like those to be shipped to WIPP. One blew up in the truck where it was sitting. At least one of these drums contained material that wasn't supposed to be in it. (EEG 48: An Assessment of the Flammability and Explosion Potential of Transuranic Waste)