Stored High Level Waste example essay topic

NUCLEAR ENERGY HOW DO THEY WORK? To build a nuclear reactor, what you need is some mildly enriched uranium. Typically, the uranium is formed into pellets with approximately the same diameter as a dime and a length of an inch or so. The pellets are arranged into long rods, and the rods are collected together into bundles.

The bundles are then typically submerged in water inside a pressure vessel. The water acts as a coolant. In order for the reactor to work, the bundle, submerged in water, must be slightly supercritical. That would mean that, left to its own devices, the uranium would eventually overheat and melt. To prevent this, control rods made of a material that absorbs neutrons are inserted into the bundle using a mechanism that can raise or lower the control rods. Raising and lowering the control rods allow operators to control the rate of the nuclear reaction.

When an operator wants the uranium core to produce more heat, the rods are raised out of the uranium bundle. To create less heat, the rods are lowered into the uranium bundle. The rods can also be lowered completely into the uranium bundle to shut the reactor down in the case of an accident or to change the fuel. The uranium bundle acts as an extremely high-energy source of heat.

It heats the water and turns it to steam. The steam drives a steam turbine, which spins a generator to produce power. In some reactors, the steam from the reactor goes through a secondary, intermediate heat exchanger to convert another loop of water to steam, which drives the turbine. The advantage to this design is that the radioactive water / steam never contacts the turbine.

Also, in some reactors, the coolant fluid in contact with the reactor core is gas (carbon dioxide) or liquid metal (sodium, potassium); these types of reactors allow the core to be operated at higher temperatures. Once you get past the reactor itself, there is very little difference between a nuclear power plant and a coal-fired or oil-fired power plant except for the source of the heat used to create steam. The reactor's pressure vessel is typically housed inside a concrete liner that acts as a radiation shield. That liner is housed within a much larger steel containment vessel.

This vessel contains the reactor core as well the hardware (cranes, etc.) that allows workers at the plant to refuel and maintain the reactor. The steel containment vessel is intended to prevent leakage of any radioactive gases or fluids from the plant. Finally, the containment vessel is protected by an outer concrete building that is strong enough to survive such things as crashing jet airliners. These secondary containment structures are necessary to prevent the escape of radiation / radioactive steam in the event of an accident such as that at Three Mile Island.

The absence of secondary containment structures in Russian nuclear power plants allowed radioactive material to escape in an accident at Chernobyl. Uranium-235 is not the only possible fuel for a power plant. Another fissionable material is plutonium-239. Plutonium-239 can be created easily by bombarding U-238 with neutrons -- something that happens all the time in a nuclear reactor. NUCLEAR ACCIDENTS There have been two major accidents in the history of civil nuclear power generation; Three Mile Island (USA 1979) where the reactor was severely damaged but radiation was contained and there were no adverse health or environmental consequences.

Chernobyl (Ukraine 1986) where the destruction of the reactor by explosion and fire killed 31 people and had significant health and environmental consequences. These two significant accidents occurred during more than 10,000 reactor-years of civil operation. Only the Chernobyl accident resulted in loss of life or radiation doses to the public greater than those resulting from the exposure to natural sources. Other incidents (and one 'accident') have been completely confined to the plant. (There have also been a number of accidents in experimental reactors and in one military plutonium-producing pile - at Wind scale, UK, in 1957, but none of these resulted in loss of life outside the actual plant, or long-term environmental contamination.) WHERE IS WASTE STORED? Waste is generally stored pending shipment, treatment, or disposal.

"Short term" storage is provided at many facilities for up to 90 days before the wastes are shipped off-site for treatment or disposal. Some wastes must be stored for longer periods in anticipation of better treatment processes or while awaiting the availability of treatment facilities. In other cases, radioactive wastes may be placed in long-term storage to allow the level of radioactivity in the waste to decay. Many DOE sites and installations store waste temporarily until disposal sites are available and can accept the waste. Waste storage methods are dependent on the chemical and physical characteristics of the waste, as well as the type and concentration of radionuclides. Most solid DOE wastes are first put into appropriate storage containers, such as drums and concrete vaults.

These containers are generally stored in DOE storage facilities that are engineered to protect people and the environment from contamination. These DOE storage facilities are subject to regular monitoring by Federal and state regulators who conduct inspections to evaluate compliance with all regulatory health and safety requirements. DOE stores its high-level waste (primarily liquid wastes resulting from nuclear fuel reprocessing) in tanks at the West Valley, New York; Savannah River, South Carolina; and Hanford, Washington sites. At the Hanford Site, some of the original single-shell tanks that have begun to leak have been replaced by double-shell, carbon-steel tanks.

These range in volume from 500,000 to approximately one-million gallons each. The double-wall is actually a tank within a tank. Highly sensitive monitoring equipment is installed in the space between the tank walls to detect any leaks that might occur. At the Savannah River Site, high-level liquid waste is being removed from the tanks and converted to a solid-waste form suitable for permanent disposal. DOE reduces the volume of high-level waste that it vitrifies by p retreating the stored high-level waste to separate many of the nonradioactive substances from the radioactive ones. The remaining less radioactive waste will be mixed with cement and fly ash and solidified as grout or "saltstone" as a final form for disposal.

When DOE solidifies high-level waste into glass logs through vitrification, granular calcine, or concrete-like saltstone, the waste still needs to be stored awaiting final disposal.