Radioactive Waste 793 - Problems With Capsules Of Cesium And Strontium Stored At Hanford Nuclear Reservation - Part 3 of 5 Parts

Radioactive Waste 793 - Problems With Capsules Of Cesium And Strontium Stored At Hanford Nuclear Reservation - Part 3 of 5 Parts

Part 3 of 5 Parts (Please read Part 1 and 2 first)
      The cesium and strontium inside the capsules in the WESF at the Hanford Nuclear Reservation were once part of the mixture of toxic and radioactive materials in the one hundred and seventy-seven huge underground tanks. The heat generated by the radioactive isotopes of cesium and strontium decaying in the buried tanks was causing the high-level radioactive waste mixture in the tanks to start boiling. This forced the technicians to extract the cesium and strontium from the tanks and put them in capsules in the WESF for separate storage. This work was carried out between 1967 and 1985.
      At first, the DoE thought that the cesium and strontium could be used for a variety of purposes including thermoelectric power supplies, calibration of industrial instruments or to extend the shelf life of pork, wheat and spices. Unfortunately, consumers are generally concerned about the safety of irradiated foods. The DoE leased hundreds of the capsules to private U.S. companies for research.
      One of the companies that received Hanford cesium capsules was Radiation Sterilizers which utilized the cesium to sterilize mediate equipment at its facilities in Decatur, Georgia and Westerville, Ohio. In 1988, one of the DoE capsules being used in Decatur developed a tiny leak. Two one hundredths of one percent of the cesium escaped. This wound up taking the DoE four years to clean up and cost forty seven million dollars.
      Federal investigators discovered that when the capsules were moved in and out of cooling pools thousands of times, the temperature changes eventually damaged their steel. Radiation Sterilizers had removed temperature monitoring systems in its facilities. The company blamed the DoE, claiming that they were sent a damaged capsule. Whatever the truth was, the DoE immediately recalled all the capsules that it had distributed and returned them to the WESF.
      There are currently one thousand three hundred and thirty-five capsules of cesium chloride at the WESF. Most of the waste in those capsules consists of nonradioactive isotopes of cesium. Most of the radioactive isotopes are cesium-137 with a little cesium-135. Another six hundred and one capsules contain strontium fluoride with the main radioactive isotope being strontium-90.
      Cesium-137 has a half-life of thirty years and strontium-90 has a half-life of twenty-nine years. These are very short half-lives when compare to radioactive materials such as uranium and plutonium. However, the radioactivity in the capsules of strontium is so great that it will take over eight hundred years for the strontium capsules to decay enough to be classified as low-level waste. This was detailed in a 2003 report by the U.S. National Research Council. Although the radioactive isotope cesium-137 will fall to much lower levels in a few hundred years, the half-life of cesium-135 is two million three hundred thousand years. This means that that isotope will eventually become the dominant source of radioactivity in the cesium capsules.
      Workers at Hanford are continuing to monitor the condition of the capsules in the WESF. They periodically shake the capsules with a long metal gripping tool. If the result of the manipulation is a “clunk” sound, this means that the inner stainless-steel pipe is moving freely. This indicates that the capsule is still in good condition. If the inner pipe is damaged, rusty, or swollen, it will fail to move when the capsule is shaken. Around two dozen of these failed capsules have been sealed in a larger stainless-steel container and held apart from the other capsules. This is known as “overpacking.”
Please read Part 4 next