Ultrasonic Cleaning and Re-use of HEPA Filters in Nuclear Fuel Manufacturing Facility

Abstract

In the nuclear industry, High Efficiency Particulate Air (HEPA) filters are used as an important engineering safeguard to prevent the potential release of airborne radioactive particulates into the environment during the plant operations. These filters have high efficiency (99.97%) in removing particulate matters in the sub-micron range and are widely used in the entire fuel cycle from the stage of mining/milling to nuclear waste management operations. Nuclear Fuel Complex (NFC) at Hyderabad manufactures nuclear fuel for all the commercial nuclear power reactors in the country.The fuel is in the form of high density Uranium dioxide (UO2) pellets clad in Zircalloy- 4 tubes. Many chemical and metallurgical processes are employed for the production of UO2 pellets starting from the raw material magnesium diuranate (MDU). HEPA filters are used for final filtration of off-gases from these processes as well as the working areas/plants. Each fully loaded HEPA filter contains around 3-5 kgs of uranium bearing fine powder, which needs to be recovered as it is a costly material. Normally, HEPA filters are used once-through, as suitable technique for nondestructive decontamination has not been developed. This has resulted in a large accumulation of loaded HEPA filters at NFC, which is a cause for concern. The reuse of the HEPA filt-ers depends on the extent of decontamination achieved. As the conventional cleaning techniques are found to be ineffective, the decontamination of HEPA filters presents a challenging problem. Therefore, development work was taken up at NFC to evolve a suitable decontamination technique for HEPA filters. A state-of-the-art ultrasonic decontamination technique using commercial acetone has been developed at NFC. The technique offers a suitable nondestructive method to ensure removal of uranium fines from the filter media completely and thereby rendering the HEPA filter suitable for reuse. The observations and results of this development work are presented in this paper.