4.9 Monitoring of Operational Variables
Instruments and Controls shall meet the requirements of ASME AG-i, Section IA.
4.10 Adsorbent Cooling
Where heat of radioactive decay or heat of oxidation or both may be significant, means shall be provided to remove this heat from the adsorbent beds to limit temperatures to values below 300°F (149°C) to prevent significant iodine desorption.
For this purpose, a minimum circulatory air flow shall be available for all operational modes of the air-cleaning unit and shall be based on the maximum possible radioactivity loading on the adsorbent beds. Water deluge systems are not acceptable for this purpose.
4.11 Fire Protection
4.11.1 General. Nuclear air-treatment systems shall be designed, fabricated, and installed so as to minimize the use of combustibles.
Filter media, sealants, gaskets, and insulation shall meet the requirements in ASME AG-i.
4.11.2 Fire Detection. When adsorbers are provided, a fire detection system shall be installed downstream of each carbon adsorber bank to detect either abnormally elevated temperature or products of combustion. The fire detection system shall be designed to be responsive to the unique features of the installation and application (e.g., low air velocity, stratification). A two-stage alarm shall be provided. The fire detection system shall operate an alarm (first stage) upon detection of temperature above a prearranged setpoint and automatically trip fan(s) and isolate the air-cleaning unit. The second stage shall operate an alarm when a fire is detected. Documentation shall be provided to the owner which shows that the fire detection system is designed to be responsive to a fire within the carbon adsorber bed.
4.11.3 Fire Hazard Procedures. Plant fire protection procedures should include requirements that upon firststage, high-temperature alarm, the plant fire brigade is dispatched to the area to take appropriate action.
4.11.4 Fire Hazard Analysis. A fire hazard analysis shall be performed for all air-cleaning units and components in accordance with 10 CFR 50 Appendix R and NFPA 803, except that for adsorbers consideration shall be given to the type of carbon (or other media) utilized in adsorbers and the potential for fire.
4.11.5 Fire Protection Systems. Fire protection systems, when provided, may use water deluge, inert gases (e.g., halon, C02) or other extinguishing agents as appropriate for the hazard and designed in accordance with all applicable NFPA standards:
4.11.6 Water Deluge Systems. Deluge nozzles should
be permanently mounted within the housing and located to ensure that both deep-seated or surface fires can be extinguished. Nozzles shall be piped to an accessible location outside the housing and provided with redundant leak-tight isolation valves and a connection suitable for manual attachment to the plant’s fire protection system. Permanently connected fire protection systems are not recommended, but may be used in lieu of manual hose connections.
4.11.7 Actuation of Fire Protection Systems. If the result of the fire hazard analysis requires that a fire protection system be provided for an air-cleaning unit, the fire protection system should be manually actuated. Automatic actuating water deluge systems are not recommended because spurious actuation of detection! automatic protection systems will significantly degrade adsorber capability and damage the adsorber.
4.11.8 Permanently Connected Fire Protection System. If permanently connected fire protection systems are installed, provision shall be made to activate an alarm upon initiation of flow of extinguishing agent (e.g., water, halon, C02).
4.11.9 Returning Air-Cleaning Unit to Service. If carbon does become wet, the wet carbon shall be removed from the adsorber as soon as practical to prevent structural damage to the adsorber due to chemical interaction. Before placing the air-cleaning unit back in service, the adsorber shall be thoroughly dried, visually inspected for corrosion damage, dried carbon shall be laboratory tested per ASME AG-i, Section FF and adsorber leak testing shall be performed per ASME AG-i, Section TA.