Date of Award
High Efficiency Particulate Arrestance (HEPA) filters serve an important role in safety of nuclear facilities and can be an important tool in safeguards verification of nuclear activities. This paper describes a new design for HEPA filter housing in nuclear facilities to reduce replacement time, improve safety, reduce worker dosage, and facilitate safeguards procedures post replacement. This design must meet the criteria of staying online during filter exchanges, assisting with International Atomic Energy Agency (IAEA) sampling practices, meeting the nuclear air and gas code specifications and relevant subsections, and adhering to the principles of ALARA (as low as reasonably achievable), for maintaining low radiation levels to maximize worker safety.
Our new design focuses on improved safety while achieving an online filter exchange. Not only will an online filter exchange reduce facility downtime and save facilities money, it has the potential to offer increased worker safety, and provide easy filter access for IAEA officials who wish to conduct sampling and inspection for safeguards. It would effectively eliminate the need for a facility to shut down for filters to be replaced. In our research, we did not find any current designs on the market that can perform an online HEPA filter exchange. We also conducted research on sealing techniques to support the online system design. We have established a project relationship with Radiation Protection Systems (RPS), Inc.: a contracting company based out of Groton, Connecticut, USA which specializes in mobile HEPA filter and carbon pre-filter housings for nuclear applications. The technical information exchange and partnership with RPS may result in an actual product that could be installed in future nuclear power plants if the design can be proven to work in concept and function. It may also be possible to retrofit existing HEPA installations in some cases.
The design includes a double door bag-in, bag-out design and operational procedure to maintain worker safety and allow for zero escape of radioactive volatiles or particulates into the air external to the facility enclosure. A combination of neoprene gasket, silicone gel, and brush sealing techniques are employed in the new design with continuity of airflow during the switch in mind. This innovative design improves safety as well as operational efficiency.
The design team is cognizant of safeguards considerations and aimed the design towards facilitating access. In particular, in our new design access to HEPA filter for sampling is much easier which can potentially improve the frequency and quality of sampling during IAEA inspections. Likewise, the lower level of effort (therefore cost) in switching filters will encourage changing filters more frequently. This will lower the risk of filter failures caused by clogged or possibly faulty filters. In fact, the IAEA reported that âAIJInvestigators from other national laboratories have suggested that aging effects could have contributed to over 80 percent of these failures. âAI The prototype design features a HEPA filter train (2 HEPA filters connected by a gel-seal interface) that slide seamlessly through the housing on rollers while the nuclear facility is online, the first (old) filter being dislodged into a sealed bagging unit, and the second (new) filter being clamped into place using a cam shaft clamping mechanism. There are two areas of design innovation here that are particularly exciting. The gel-seal interface that connects the filters will provide an air tight gap between two filters while they are exchanged. The clamping system features a brush seal interface on top and bottom, to maintain airflow and mobility of the filter while facilitating a switch.
Because extended radiation exposure may alter the properties of sealants and gaskets we are investigating the use of seals that can be replaced during these quick filter changes. The design prototype is a full-scale model, capable of housing a 12x24x12 inch HEPA filter. Currently, we have completed the design of the new housing unit, created a proof of concept build, as well as conducted the preliminary engineering analysis, cost analysis, and material selection of the final prototype. Manufacturing of the final housing is proceeding and upon completion will be validated with a set of rigorous testing procedures concerning sealing and safety of the system. These tests are standard industry practices and RPS will assist in performing the tests. Namely, ASME test FC-I- 3272, a test in which aerosol particles of 20 m, which are the most penetrating particle sizes (MPPS), are sent through the housing unit and penetration is monitored during an online switch. Further testing will include colored smoke being pumped through the unit to test sealing capabilities and to identify possible particulate buildup. Provided the tests show that the design is successful in maintaining air flow and safety during the filter exchange, methods of improvement for ease of use and the automation of the exchange process, improvements to continuity of knowledge, and radiation monitoring techniques will be investigated for a comprehensive final product design.
Bolt, Joshua; Carlson, Matthew; and Kehoe, David, "Online HEPA Filter Replacement" (2018). Mechanical Engineering Capstone Design Projects. Paper 32.