Friday, October 29, 2010

Cleaning the Waste - Nuclear Waste

I'm a proponent of nuclear energy.  I believe that it has the potential to be one source of the solution to replace fossil fuels.  But, before that can happen, a few things need to occur:

  •  The general public needs to be educated on benefits and shortcomings of nuclear energy.
  • Politicians and policy makers also need to be educated.
  • Policy needs to be adjusted to current levels of understanding of nuclear processing, not the over constraining regulations made decades ago to safeguard the public from unknown technologies.
  • Finally, develop a way to better handle the waste.
An article back in the July issue of ASME's Mechanical Engineering Magazine has a great article about some new technologies being developed to deal with the waste.  Beyond that, reading deeper into the article and the you can see how much has changed in the processing of nuclear energy.

The Hanford Site
The Hanford Site in Washington State just ten (10) miles from the Columbia River has 149 aging radioactive waste tanks that need to be emptied and cleaned.  The U.S. Department of Energy wants these tanks cleared in 30 years.  It has been a decade, and only six (6) of the old tanks have been cleared of required amount of radioactive waste (99%).  Quick math:
10 years for 6 tanks = 1.667 years per tank * 149 tanks = 248 years >> 30  year requirement
Enter New Technology
Obviously, they need to speed up the job.  But, the problem isn't necessarily with cleaning up the tanks, but rather getting access to the sludge (the hard stuff known as heel).  The tanks are buried under ground.  They are made of single-shell construction with steel sides and floor and reinforced concrete roofs.  They leak, resulting in groundwater with excessive radioactivity (thus the reason for the cleanup).  Access to the contents of the tanks, built between 1940s - at the start of the Manhattan Project - through 1980s is via risers.  The risers vary in diameter to as little as 12 inches wide.  Not too much can go into a pipe diameter of 12 inches to clean out hard heel.

But before anyone latches on to the fact that groundwater is contaminated, remember that this is because these tanks and the storage process was developed at the same time we were just learning about nuclear energy.  Of course, in its infancy, there is bound to be some learning.  The fact that these things lasted 70 years is a testament to engineers who designed them with the working knowledge they had at the time.  What is quite intriguing is the fact that the 149 tanks are being replaced by 28 new, double-shell tanks.  Our understanding of nuclear waste as well as how we handle it has vastly improved since 1940.  There is no reason to maintain policies developed by such limited knowledge.  It is time to update them!

Going to MARS
Although some people would like to just toss our trash into someone else's backyard (not considering the opposition to nuclear powered spacecraft), I'm not referring to the planet.  MARS is the the Mobile Arm Retrieval System designed specifically to enter the old tanks, break up the heel, and vacuum out the waste material.  But MARS will not fit into a 12 inch pipe.  Therefore, engineers have devised a way to reinforce the ceiling of the old tanks and then cut a 54 inch diameter hole that MARS can fit into, while maintaining negative pressure in the tank so no contaminants can escape.  Using MARS will do in one (1) month what the old method took several. 

The Final Steps
Much work has to be done to prepare for MARS use, but the results may mean that the entire site will be cleaned by the deadline.  Of course, that means all 53,000,000 gallons of nuclear waste has to be processed and treated.  Permanent storage will be in a stable glass form - something that is safe and didn't exist in 1940.

For More Information
Washington River Protection Solutions
MARS [pdf]
The Hanford Site
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