A Study on Replacement of HEPA Filter In-place Leak Test Challenge Agent from DOP to PAO in NPP

Atmosphere cleanup system of nuclear power plants is a gas waste treatment system to minimize the leakage of radioactive materials produced during normal operation and accidents. The HEPA(High Efficiency Particulate Air) filter in this system has the major role to filter the particulate radioactive materials. The leak test method of HEPA filter conforms to the Reg. Guide 1.140 and Reg. Guide 1.52 of USNRC, which were both revised in 2001. The revisions include the permission of alternative challenging aerosol agents besides DOP (dioctyl phthalate) for HEPA filter in-place leak test. US DOE is demanding to stop using DOP since DOP was suspected as a carcinogen. Currently, industries other than nuclear power plants mostly use PAO (polyalpha olefin) as HEPA filter leak test challenge aerosol agent. Due to Reg. Guide 1.140(Rev.2) and 1.52(Rev.2), only DOP has been allowed to be used in nuclear power plants. As a result, nuclear power plant workers have been exposed to mental and physical risks whenever there is HEPA filter in-place leak test. In this paper, the leak test results using DOP and PAO are compared to verify that DOP can be replaced with non-carcinogenic PAO for HEPA filter leak test in nuclear power plants