ASME N509:2002 pdf free download

ASME N509:2002 pdf free download NUCLEAR POWER PLANT UNITS AID CDMPONENTS AIR-CLEAMING
Physical location and arrangement of the componentsof a nuclear air-treatment system influence the require-ments for leak tightness for the various parts of thepressure boundary. Air flow should be from potentiallyless contaminated areas to potentially more contami-nated areas. Whenever possible, routing of contami-nated air through clean spaces or interspaces should beavoided. If this can not be done, the general guidancein this Section should be followed.
Figures B-1410-1,B-1410-2,and B-1410-3 of ASMEAG-1, Section SA schematically depict examples of possiblecombinations and location of fan and air-cleaning unitto minimize impact of system contaminated outleakageon surrounding clean spaces and interspaces as well ascontaminated inleakage into a cleaner system com-ponent.
4.7.1 Effluent Nuclear Air-Treatment System (once-Through)
(a) Maintain ducts conveying contaminated airthrough clean spaces or clean interspaces at a negativepressure with respect to the surrounding areas.
(b)With air-cleaning unit located in a cleaninterspace, locate exhaust fan downstream of air-clean-ing unit in order to keep air-cleaning unit under negativepressure. Any leakage through fan shaft will be fromclean interspace.
(c) When air-cleaning units are located in contami-nated spaces or interspaces,the fan shall be locatedupstream of the air-cleaning unit in order to keep air-cleaning unit under positive pressure and to preventinfiltration of contaminated air through fan shaft,orinto the filter housing downstream of filters,therebybypassing filters.
(d)The length of positive pressure discharge ductsfrom the air-cleaning unit routed through clean spacesor interspaces should be kept as short as practical tominimize outleakage from ductwork from impacting in-plant personnel exposure.
4.7.2 Habitability Systems
(a)Outside air ducts routed through clean spaces orinterspaces that may convey radioactive air following arelease shall be under a negative pressure relative to thespaces.
b)Negative pressure recirculating air ducts that passoutside 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 unitis in a contaminated space;
(2)downstream of air-cleaning unit if air-cleaningunit is in a clean space.
(d)The length of positive pressure ducts outside ofthe habitable boundary should be kept as short as practi-cal to reduce effect of duct leakage on ability to pressur-ize habitable boundary.
(e)Recirculating system housings should be kept ata positive pressure if located outside habitable boundaryin a contaminated space or interspace.
4.7.3 Recirculating Nuclear Air-Treatment Systems(a)If an air-cleaning unit is located in a clean spaceor interspace outside of the space served, the fan shouldbe located downstream of the air-cleaning unit.
b)Fans may be either upstream or downstream of air-cleaning units if located totally within the space served.(c)The length of ductwork outside the space servedshould be kept as short as practical.
4.8 Maintainability criteria
4.8.1 Access for Service,Testing, and Inspection. Theair-cleaning unit shall be designed to keep radiationexposures during maintenance, testing, and inspectionas low as reasonably achievable (ALARA). Some designfeatures which contribute to keeping these exposuresALARA are the following.
(a)Man-entry air-cleaning units should be located atfloor level or should be equipped with a permanentservice gallery at least 4 ft (1.23 m) wide with permanentstairs or fixed ladders.
(b)Smaller air-cleaning units should be located at aheight above the floor or work gallery level convenientfor access,based on human factors and the design ofthe housing.
(c)The area in which the air-cleaning unit is locatedshall be served by a clear aisle wide enough to accommo-date servicing of internal components and equipment.(d)Sufficiently wide clear area adjacent to the housingdoor or hatch shall be provided to allow servicing theair-cleaning unit; a space of at least 4 ft wide x 7 ft(1.23m wide x 2.15 m) high is recommended.The clear workspace may also serve as aisle space as long as it can beused while servicing the air-cleaning unit, or it mayserve as the clear space for an adjacent air-cleaning unit.(e) Clearance of 18 in. (0.46 m) is recommended abovethe housing for installation and inspection.
Elevated work galleries shall be designed in accor-dance with Occupational Safety and Health Act (OSHA)requirements.