Non-active in-situ Freon leak test for charcoal filter installations

A non-active in-situ leak test for modular charcoal filters using either Freon 11 or Freon 113 as the test agent, has been developed for use by the CEGB using halide detectors and generator. The non-active leak test, which has no deleterious effects on filter performance can be used as a precursor to an active test using methyl iodide - 131. The test provides information on seal integrity, a major problem when installing modular filters and also internal filter by-pass leakage flow. The time and expense of an abortive active test can thus be saved. A programme of development work has been carried out on a laboratory test facility to study the sensitivity of the method, the performance of the equipment and the limitations of the method over a range of air flowrates, temperatures and relative humidities. Modular filters containing charcoal impregnated with 1.5% potassium iodide (KI) and 5% triethylene diamine (TEDA) have been studied. Both Freon 11 and Freon 113 have been used and their likely poisoning effects were investigated. Several on site tests at CEGB Power Stations have been successfully carried out on modular filter installations and also on main blowdown iodine absorption beds. Details of experience gained and some results are given. (author)