Mitigating Nuclear Hazards - Part 4, Fuel

I rejoined NRC in 1999 until 2005 and got involved with nuclear waste disposal, uranium mill tailings sites, relicensing nuclear power plants, the 9/11 response to terrorism and the incident response operations center (IROC). Supporting the IROC involved conducting exercise drills to simulate various threats and potential to actual emergency situations involving numerous federal and state agencies. I provided maps using Geographical Information Systems (GIS) to show nuclear facilities, roads, population information and more. The center became an exciting place for observing how natural events like hurricanes could create storm surges hitting nuclear power plants which either kept operating or needed to shut down. One time while we were practicing a drill, we got a call from a facility that a truck driver transporting uranium hexafluoride (UF6) was missing. We launched into emergency mode for about an hour trying to obtain information on the transportation routes until the driver called into to the facility to say he had overslept on the side of the road!

So what is UF6 and how does processed uranium U3O8 “yellowcake” (as described in the previous blog) become fuel that is needed to operate nuclear reactors? Yellowcake is sent in 55-gallon drums to conversion plants to remove impurities and is converted to UF6 gas. The process is described by NRC and the World Nuclear Association with conversion plants located worldwide. The primary hazard is potential chemical exposure to inhaling the gas. Waste byproducts are produced and sites have contaminated groundwater, such as at the Sequoyah Fuels site in Oklahoma. NRC has reviewed and approved several license applications to construct new conversion plants that are on hold.

The UF6 canisters are then sent to a fuel enrichment facility where U-235 isotopes are concentrated from about 0.7% to up to 5%. The gas centrifuge process is currently the preferred method and only one plant operating in the U.S. is located in southeastern New Mexico.

A major byproduct of uranium enrichment is called “depleted uranium” (where the material contains about 0.3% U-235). According the the NRC, ”if an enrichment facility processes 1,000 kilograms (kg) of natural uranium to raise the U235 concentration from 0.7 percent to 5 percent, the facility would produce 85 kg of enriched uranium and 915 kg of depleted uranium.” Depleted uranium is used for military and aviation applications.

The 9/11 terrorist attack of crashing 747 airplanes into the World Trade Center, the Pentagon, and in Pennsylvania, horrified the world. From our office in Rockville, Maryland at the NRC — we could see the fire from the Pentagon. I was the acting technical assistant to the Nuclear Materials Safety and Safeguards (NMSS) office director and immediately became tasked to join a committee to review all protective measures, such as at nuclear power plants. I was not aware that depleted uranium could have be used as ballast in aircraft and felt more incredibly shocked when the EPA Administrator told first responders that it was safe to breath the air at ground zero!

Here is an interesting article on the IAEA website about the properties, uses and primary concerns of breathing depleted uranium. U-238 follows a decay chain of radioactive daughters including radium and radon that is hazardous to breath where it comes from natural or refined sources.

There is a tremendous amount of depleted uranium waste byproduct requiring disposal. Hundreds of thousands of metric tons are stored at Energy’s (shutdown) enrichment plants in Portsmouth, Ohio, and Paducah, Kentucky. GAO advocated for DOE to sell depleted uranium back to industry for use as a fuel which competes with uranium supply, causing downward pressure on prices, which is generally opposed by industry. Recently, DOE Secretary Perry agreed to limit supplies of domestic and Russian non-proliferation materials provided to the open market.

The enriched uranium is then sent to fuel fabrication plants to produce uranium dioxide powder that is compressed into pellets inserted into Zircoloy tubes for the fuel assembly.

Overall, there is significant processing and transportation required to produce nuclear fuel and most of the risks are chemical rather than radiological. The fuel rods do not become radioactively “hot” until they are used for starting the nuclear chain reaction at the reactor as will be described in the next blog.