Radionuclide clean-up at Fukushima Daiichi nuclear power plant
The use of sea water for cooling during the initial emergency response at the Fukushima Daiichi Nuclear Power Plant created a unique set of challenges not experienced with standard radionuclide cleanup at nuclear plants. Typical reactor coolant water consists of high purity water that is relatively simple to treat. The very high levels of sodium, chloride, magnesium, calcium and other competing impurities found in sea water, rapidly reduce the operating capacity of standard ion exchange or adsorptive media’s for the targeted radionuclides. New adsorptive media with higher selectivity for radionuclides in a high salt background had to be developed to meet this new challenge.
After several months of analysis, TEPCO established a strict remediation requirement of non-detect for all 62 radionuclides in the treated water. Technology companies interested in performing the cleanup of the contaminated seawater had to prove that their technology could achieve this specification This has never been achieved.
Computer modeling and laboratory screening using a surrogate water representative of the site conditions was initiated to provide data that would give an understanding of how ion exchange media behaved under the expected contaminated cooling water conditions at the plant site. Water analysis showed that the salt and hardness content was about 50,000 and 5,000 times (respectively) higher than that in high purity water, while the non-radioactive isotope of strontium p (from the emergency seawater) was over 200 times higher than the concentration of radioactive strontium generated by the reactor. In addition, the contaminated cooling water contained nickel and iron corrosion products as well as residues of oil, grease, dead animals and plant life.
Initial screening showed that chemical softening pretreatment of the water would be needed before the water made contact with the downstream CORE TECHNOLOGY medias. This would reduce the divalent cations such as calcium, magnesium and strontium that were competing for the radionuclides in the ion exchange process and allow the downstream medias comprising the CORE TECHNOLOGY to effectively reduce the radionuclides to non-detect levels. The softening process also simultaneously reduced the concentrations of nickel and iron corrosion products present in the water.Core Technology
It was determined that several of the radionuclide elements could exist as a complex variety of amphoteric species, some existing as cationic, some as anionic and some as non-ionic species, depending on the system pH. This meant that effective removal would require an approach targeting all species present to ensure the non-detect discharge target was met.
Removing all the species added a high level of complexity to the operation, resulting in a customized CORE TECHNOLOGY solution incorporating a variety of specially developed ion exchange resins and adsorbent media, with the necessity to include pH adjustment ahead of several of the selective media to adequately capture the range of species present.
Within this CORE TECHNOLOGY solution, media was customized to work in harmony with one another as each contaminant was selectively removed during the process steps. It was important to ensure that any foreseen changes in water chemistry could also be met.
Once the treatment regime was determined the evaluation work moved to a pilot operation located at the Fukushima Daiichi Nuclear plant site, using the actual cooling water to be treated. The process was optimized and validated to ensure that the non-detect discharge requirements were able to be met under a variety of conditions.
Non-detect on 62 radionuclides as specified by TEPCO.
This success was achieved after six months of intensive product development and on-site pilot testing in conjunction with our Japanese partner, resulting in a new generation of products tailored for efficient radionuclide clean-up meeting the non-detect levels specified by TEPCO.
In addition to meeting the goal of removing the radionuclides to non-detect limits, total waste volume was minimized by > 90% compared to the waste expected from a typical ion exchange system.
This was achieved by: