ASME N509 pdf free download

ASME N509 pdf free download NUCLEAR POWERPLANT AIR-CLEANING UNITS AND COMPONENTS
4.7 Nuclear Air-Treatment System Configuration and Location Physical location and arrangement of the components of a nuclear air-treatment system influence the require- ments for leak tightness for the various parts of the pressure boundary. Air flow should be from potentially less contaminated areas to potentially more contami- nated areas. Whenever possible, routing of contami- nated air through clean spaces or interspaces should be avoided. If this can not be done, the general guidance in this Section should be followed. Figures B-1410-1, B-1410-2, and B-1410-3 ofASME AG- 1, Section SA schematically depict examples of possible combinations and location of fan and air-cleaning unit to minimize impact of system contaminated outleakage on surrounding clean spaces and interspaces as well as contaminated inleakage into a cleaner system com- ponent.
4.7.1 Effluent Nuclear Air-Treatment System (Once- Through) (a) Maintain ducts conveying contaminated air through clean spaces or clean interspaces at a negative pressure with respect to the surrounding areas. (b) With air-cleaning unit located in a clean interspace, locate exhaust fan downstream of air-clean- ingunitinorder to keep air-cleaningunitunder negative pressure. Any leakage through fan shaft will be from clean interspace. (c) When air-cleaning units are located in contami- nated spaces or interspaces, the fan shall be located upstream of the air-cleaning unit in order to keep air- cleaning unit under positive pressure and to prevent infiltration of contaminated air through fan shaft, or into the filter housing downstream of filters, thereby bypassing filters. (d) The length of positive pressure discharge ducts from the air-cleaning unit routed through clean spaces or interspaces should be kept as short as practical to minimize outleakage from ductwork from impacting in- plant personnel exposure.
4.7.2 Habitability Systems (a) Outside air ducts routed through clean spaces or interspaces that may convey radioactive air following a release shall be under a negative pressure relative to the spaces. (b) Negative pressure recirculating air ducts that pass outside the habitable space should be avoided or addi- tional filtration provided. (c) The makeup air fan shall be located: (1) upstream of air-cleaning unit if air-cleaning unit is in a contaminated space; (2) downstream of air-cleaning unit if air-cleaning unit is in a clean space. (d) The length of positive pressure ducts outside of the habitable boundary should be keptas shortas practical to reduce effect of duct leakage on ability to pressur- ize habitable boundary. (e) Recirculating system housings should be kept at a positive pressure iflocated outside habitable boundary in a contaminated space or interspace. 4.7.3 Recirculating Nuclear Air-Treatment Systems (a) If an air-cleaning unit is located in a clean space or interspace outside of the space served, the fan should be located downstream of the air-cleaning unit. (b) Fansmaybe eitherupstreamordownstreamofaircleaning units if located totally within the space served. (c) The length of ductwork outside the space served should be kept as short as practical.
4.8 Maintainability Criteria 4.8.1 Access for Service, Testing, and Inspection. The air-cleaning unit shall be designed to keep radiation exposures during maintenance, testing, and inspection as low as reasonably achievable (ALARA). Some design features which contribute to keeping these exposures ALARA are the following. (a) Man-entry air-cleaning units should be located at floor level or should be equipped with a permanent service gallery at least 4 ft (1.23 m) wide with permanent stairs or fixed ladders. (b) Smaller air-cleaning units should be located at a height above the floor or work gallery level convenient for access, based on human factors and the design of the housing. (c) The area in which the air-cleaning unit is located shallbe served by a clearaisle wide enough to accommo- date servicing of internal components and equipment. (d) Sufficientlywide cleararea adjacentto the housing door or hatch shall be provided to allow servicing the air-cleaning unit; a space of at least 4 ft wide x 7 ft (1.23 m wide x 2.15 m) high is recommended. The clear work space may also serve as aisle space as long as it can be used while servicing the air-cleaning unit, or it may serve as the clear space for an adjacent air-cleaning unit. (e) Clearance of 18 in. (0.46 m) is recommended above the housing for installation and inspection. (f) Elevated work galleries shall be designed in accor- dance with Occupational Safety and Health Act (OSHA) requirements. (g) Ducts that are cleaned out periodically shall be equipped with low leakage access hatches at strategic points