ENGINEER RELIES ON ALGOR'S NONLINEAR ANALYSIS SOFTWARE TO VERIFY DESIGN OF HIGH LEVEL NUCLEAR WASTE DISPOSAL CONTAINER

A West Valley Nuclear Services technician prepares to drop test a canister filled with non-radioactive vitrified glass. Testing confirmed the results of the Algor analysis of the design.

Innovative Technique from West Valley Nuclear Services Turns Liquid Waste Into Glass.

In 1976, the only commercial nuclear fuel reprocessing facility ever to operate in the United States, located near West Valley, New York, ceased operations. During its productive lifetime, from 1966 to 1972, the plant chemically reprocessed approximately 640 metric tons of spent nuclear fuel to recover useable uranium and plutonium.

When operations ceased, nearly 600,000 gallons of liquid high-level nuclear waste was left stored in an underground tank contained within a concrete vault.

In 1980, the President of the United States signed the West Valley Demonstration Project Act which directs the Department of Energy to solidify the waste into a durable, solid form suitable for shipment to a federal repository. The facility will then be cleaned and permanently closed.

Unique Method Developed

West Valley Nuclear Services Company (WVNS), a subsidiary of Westinghouse Electric Corporation, was selected as primary contractor for the project. The challenge was a big one. Over the years, the waste had separated into a layer of relatively clear liquid and a thick layer of sludge. After a lengthy and careful study, West Valley scientists and engineers came up with an innovative method for stabilizing the material: they decided to turn it into glass.

The project is actually being completed in two stages. In the first stage, the clear liquid is passed through a synthetic clay material which removes over 99.9 percent of the radioactivity. The resulting liquid is then concentrated, blended with cement, placed in 71- gallon steel drums and stored in an above- ground facility at the site. This part of the process has been underway for some time. To date, 80 percent of the radioactivity has been removed from the liquid portion of the waste and more than 11,000 drums of cemented waste have been produced.

The second stage of the project involves thoroughly washing and mixing the sludge layer and blending it with the clay material which contains the radioactivity from the liquid. This material will then be solidified into glass, through a process known as vitrification. This involves mixing the material with glass-making chemicals and heating it to 2,000 degrees Fahrenheit in a 52-ton ceramic melter. The molten glass will then be poured into 10-foot by 2-foot stainless steel containers to await shipment to a federal repository.

This line drawing shows the two-phase process which will be used to dispose of the two kinds of high-level nuclear waste at West Valley.

Container Design Critical

Obviously, the design of the container which will hold the now stable, but still highly radioactive, material is critical to the success of the project. Federal regulations require that the fully-loaded container must withstand a drop from seven meters onto a non- yielding surface (such as a cement floor) without breaching. This is not an easy requirement to meet, when one considers that a container filled with glass weighs almost 5,500 pounds.

The task of verifying the design of the critical container was given to Jean Dempster, Senior Engineer for Vitrification Process Development at West Valley Nuclear Services. In order to reduce the number of prototype containers that must be built and tested, Ms. Dempster decided to use Algor's Accupak high- accuracy nonlinear package to analytically verify the design to the stated government requirements. The result was a significant savings in time, money and effort.

Jean Dempster Senior Engineer for Vitrification Process Development at West Valley Nuclear Services, used Algor's nonlinear design and analysis software to verify the stainless steel canister design.

Series of Analyses and Loads

"An axisymmetric model was constructed using two-dimensional continuum elements," said Ms. Dempster, "Several investigative runs were done to determine the optimum mesh. It is important in the performance of dynamic analyses such as this, that the time step used not be larger than the period of the lowest natural frequency of the structure. Therefore, I began with a modal analysis to determine the size of the timesteps.

"The analysis was run with two different load curves," explained Ms. Dempster, "The first used a ramp function to apply the required force quickly, then hold it constant for the calculated pulse duration. The second load condition utilized a more constant ramping effect with the load increasing throughout the pulse duration, reaching the maximum load at the end of the pulse. The second loading represents a closer approximation of the actual conditions, however the first provides somewhat more conservative analysis results.

Here we see a light shaded view of the canister. The Copy, Rotate, Join commands were used to turn the original 2-D axisymmetric model into a 3-D representation for visualization purposes only.

Results Confirm Design

The Algor nonlinear analysis results confirmed that the WVNS canister design would withstand the government mandated drop test. "The canister bottom and a portion of the side wall yielded in both load cases," said Ms. Dempster, "This was an expected result for impact loading conditions. The criterion used to determine canister failure was the Algor analysis results compared to the allowable value. As the analysis value was much less, it can be concluded that the canister wall as presently designed does not breach upon impact from a seven meter vertical drop.

Prior to the completion of the analyses, a series of preliminary tests were conducted using prototype canisters filled with non- radioactive vitrified glass. These tests confirmed both the WVNS canister design and the accuracy of the Algor nonlinear analysis.

In July, Ms. Dempster presented a paper covering technical details of the canister design and analysis project at the American Society of Mechanical Engineers (ASME) Conference on Pressure Vessels. Many of the facts in this article were taken from the paper.

A small portion of the bottom of the 2-D axisymmetric model of the nuclear waste container shows deflection caused by the calculated forces of a drop from 7 meters onto a non-yielding surface.