When someone sees the words Fort Calhoun and flooding in the same document, it gets attention. So we thought we’d provide some insight into a document — issued this week — with that very word combination.
The Fort Calhoun Station, located north of Omaha, Neb., and operated by the Omaha Public Power District (OPPD), recently restarted after a long hiatus. But months before that happened, in April 2012, OPPD asked permission to implement a license change involving actions to protect the plant at high and low river levels.
On Jan. 28, 2014, the NRC granted the request and issued a license amendment officially changing when the plant should be powered down during a flood scenario. Simply put, the change involves powering down at 1004 feet mean sea level versus the previously set level of 1009 feet. In addition to setting the river rising to a lower level, the NRC document also specifies that the plant must shutdown within six hours of river levels dropping below 976 feet 9 inches mean sea level.
This all started back in 2010 when NRC inspectors identified concerns with the plant’s flood protection strategy. So this is not a newly identified item and it does not change the plant’s design basis flood. It is an official change to the plant’s license during flood conditions and provides a more conservative level of action.
It is important to note that prior to restart, the licensee made modifications to the plant and had plans in place to protect the plant from rising river levels.
There is still ongoing and important work being done by OPPD, NRC and the U.S. Army Corps of Engineers to evaluate flood risks at the site in accordance with the post-Fukushima actions. The current target date for OPPD providing this information to the NRC is March 12, 2014. In the meantime, the plant is safe and has measures in place to respond to flooding events.
During construction of pipelines and fabrication of large metal structures, welding is used to join the parts. It is very important to know the welds are structurally sound and the whole piece will be strong enough for its job. For example, the pipes used to transport natural gas must be properly welded together so that the gas does not leak from the pipes.
And metal I-beams used in constructing a parking garage must be properly welded so that the structure can hold the weight of the vehicles in the garage. How can this be done? Often, workers perform “radiography” using sealed sources to inspect the weld to see if it is correct.
What is radiography? It is term used to describe using gamma rays or x-rays to inspect the structure of some large dense material. Although x-ray machines may be used for this, they are limited by their need for an electrical source, and because x-rays can only penetrate certain materials. A radiography device (sometimes referred to as a radiography camera) uses sealed sources that emit gamma radiation that can penetrate very dense materials such as metal. Radiography devices can be used without electricity and are portable, making them handy to use at work sites.
Because a radiography source, while small in size, emits gamma radiation that can penetrate several inches of metal, it must be stored in its shielded container. When a weld needs to be inspected, a long guide tube is connected to the device that allows the source to travel to the location that needs to be inspected. A long drive cable also is attached to the other end of the device. This allows the radiographer performing the inspection to stand far away from the radiation source during the inspection. Typically, the source is in the guide tube only a few seconds to a few minutes, depending on what is being inspected.
Radiography is used to inspect welds on pipes for oil rigs; large tanks that hold gasoline; airplane engines; and other large metal structures. So the next time you use natural gas, or park your car in a multi-story garage, you might remember the important role a radioactive source plays in keeping you safe.