Diablo Canyon power plant guidelines for protection of carbon filters

There has been a long standing concern regarding the protection of carbon filters in the HVAC industry. Few quantitative guidelines have been provided concerning the significance of carbon exposure to smoke, chemicals or fumes, nor have limiting exposure quantities been determined. However, many nuclear plant license provisions require testing following painting, fire or chemical release within a zone communicating with the ventilation/filtration system. At Diablo Canyon Power Plant (DCPP) the authors have investigated the reasons behind the requirements for testing carbon filters after exposure. One known reason for testing is that the carbon is susceptible to hydrocarbon contamination, thereby saturating the adsorption sites on the carbon. Advances have been made to minimize exposure of carbon by initiation of constraints and precautions of surveillance testing, routine maintenance work and unexpected use of the filtration system. The utilization of pro-active plant personnel also provides for a better awareness and regard for the protection of these filters. DCPP has taken a progressive approach to quantify and identify threshold exposure limits which are based on engineering judgment, conversations with air filtration experts associated with the nuclear industry and also with representatives of the NRC