1、28.1CHAPTER 28NUCLEAR FACILITIESGENERAL DESIGN ISSUES . 28.1As Low as Reasonably Achievable (ALARA) . 28.1Design 28.1Normal or Power Design Basis 28.1Safety Design Basis 28.1Outdoor Conditions . 28.2Indoor Conditions 28.2Indoor Pressures 28.2Airborne Radioactivity. 28.2Tornado/Missile Protection 28.
2、2Fire Protection . 28.2Smoke Management . 28.3DEPARTMENT OF ENERGY FACILITIES . 28.4Confinement Systems . 28.4Ventilation 28.5COMMERCIAL FACILITIES . 28.6Operating Nuclear Power Plants . 28.6New Nuclear Power Plants. 28.7PLANT HVAC how-ever, careful and individual analysis of each facility is requir
3、ed forproper application.1.GENERAL DESIGN ISSUESCriticality, radiation fields, and regulation are three issues that aremore important in the design of nuclear-related HVAC systems thanin that of other special HVAC systems.Criticality. Criticality considerations are unique to nuclear facil-ities. Cri
4、ticality is the condition reached when the chain reaction offissionable material, which produces extreme radiation and heat,becomes self-sustaining. Unexpected or uncontrolled conditions ofcriticality must be prevented at all cost. In the United States, only alimited number of facilities, including
5、fuel-processing facilities,weapons facilities, naval shipboard reactors, and some nationallaboratories, handle special nuclear material subject to criticalityconcerns.Radiation Fields. All facilities using nuclear materials containradiation fields. They pose problems of material degradation andperso
6、nnel exposure. Although material degradation is usuallyaddressed by regulation, it must be considered in all designs. Thepersonnel exposure hazard is more difficult to measure than theamount of material degradation because a radiation field cannot bedetected without special instruments. It is the re
7、sponsibility of thedesigner and of the end user to monitor radiation fields and limit per-sonnel exposure. Regulation. In the United States, the Department of Energy(DOE) regulates weapons-related facilities and national laborato-ries, and the Nuclear Regulatory Commission (NRC) regulates com-mercia
8、l nuclear plants. Other local, state, and federal regulationsmay also be applicable. For example, meeting an NRC requirementdoes not relieve the designer or operator of the responsibility ofmeeting Occupational Safety and Health Administration (OSHA)requirements. The design of an HVAC system to be u
9、sed near radio-active materials must follow all guidelines set by these agencies andby the local, state, and federal governments.For facilities outside the United States, a combination of national,local, and possibly some U.S. regulations apply. In Canada, the Cana-dian National Safety Commission (C
10、NSC), formerly the AtomicEnergy Control Board (AECB), is responsible for nuclear regulation,whereas in the United Kingdom, the Nuclear Installations Inspector-ate (NII) and the Environment Agency (EA), are involved in issuingoperation licenses.1.1 AS LOW AS REASONABLY ACHIEVABLE (ALARA)ALARA means t
11、hat all aspects of a nuclear facility are designedto limit worker exposure and discharges to the environment to theminimum amount of radiation that is reasonably achievable. Thisrefers not to meeting legal requirements, but rather to attaining thelowest cost-effective below-legal levels.1.2 DESIGNHV
12、AC requirements for a facility using or associated with radio-active materials depend on the type of facility and the specific ser-vice required. The following are design considerations: Physical layout of the HVAC system that minimizes the accumu-lation of material within piping and ductworkControl
13、 of the system so that portions can be safely shut down formaintenance and testing or in the case of any event, accident, ornatural catastrophe that causes radioactivity to be releasedModular design for facilities that change operations regularlyPreservation of confinement integrity to limit the spr
14、ead of radio-active contamination in the physical plant and surrounding areas The design basis in existing nuclear facilities requires that safety-class systems and their components have active control for safe shut-down of the reactor, for mitigating a design basis accident (DBA)and for controlling
15、 radiation release to the environment as the resultof an accident. Advanced nuclear steam supply systems (NSSS) are being de-signed that incorporate more passive control to minimize dependenceon mechanical equipment to mitigate the consequences of a DBA.The preparation of this chapter is assigned to
16、 TC 9.2, Industrial AirConditioning.28.2 2015 ASHRAE HandbookHVAC Applications1.3 NORMAL OR POWER DESIGN BASISThe normal or power design basis for nuclear power plants cov-ers normal plant operation, including normal operation mode andnormal shutdown mode. This design basis imposes no require-ments
17、more stringent than those specified for standard indoor con-ditions. 1.4 SAFETY DESIGN BASISThe safety design basis establishes special requirements neces-sary for a safe work environment and public protection from expo-sure to radiation. Any system designated essential or safety relatedmust mitigat
18、e the effect of a design basis accident, or natural catas-trophe that may result in the release of radioactivity into the sur-roundings or the plant atmosphere. These safety systems must beoperable at all times unless allowed by a limited condition of oper-ation (LCO). The degree to which an HVAC sy
19、stem contributes tosafety determines which components must function during and aftera DBA or specific combinations of such events as a safe shutdownearthquake (SSE), a tornado, a loss of coolant accident (LOCA),fuel-handling accident (FHA), control rod drop accident (CRDA),main steam line break (MSL
20、B), and loss of off-site electrical power(LOSP). Non-safety-related systems are not credited in any designbasis accident and are designed not to adversely affect safety-relatedsystems.Previously, safety classification of structures, systems, and com-ponents (SSC) was based on a deterministic approac
21、h, but will bechanged to a risk-informed classification and classified as safety-significant (SS) or low safety-significant (LSS), and categorized infour groups. NRC Regulatory Guide 1.201 provides information onsafety classification of systems, structures and components.System Redundancy. Systems i
22、mportant to safety must beredundant and single-failure-proofed. Such a failure should notcause a failure in the back-up system. For additional redundancyrequirements, refer to the section on Commercial Facilities.Seismic Qualification. All safety-class components, includingequipment, pipe, duct, and
23、 conduit, must be seismically qualified bytesting or calculation to withstand and perform under the shock andvibration caused by an SSE or an operating-basis earthquake (OBE)(the largest earthquake postulated for the region). This qualificationalso covers any amplification by the building structure.
24、 In addition,any HVAC component that could, if it failed, jeopardize the essen-tial function of a safety-related component, must be seismicallyqualified or restrained to prevent such failure.Environmental Qualification. Safety-class components mustbe environmentally qualified; that is, the useful li
25、fe of the compo-nent in the environment in which it operates must be determinedthrough a program of accelerated aging. Environmental factors suchas temperature, humidity, pressure, and cumulative radiation dosemust be considered.Quality Assurance. All designs and components of safety-classsystems mu
26、st comply with the requirements of a quality assurance(QA) program for design control, inspection, documentation, andtraceability of material. For U.S. plant designs, refer to Appendix Bof Title 10 of the U.S. Code of Federal Regulations, Part 50(10CFR50) or ASME Standard NQA-1 for quality assurance
27、 pro-gram requirements.Canadian plant designs use two related series of quality assur-ance standards: CAN3-286.0 and its six daughter standards, plusfour standards in the Z299 series. Quality programs in the UnitedKingdom are based on ISO 9000. For other countries, refer to theapplicable national re
28、gulations.Emergency Power. All safety-class systems must have a backuppower source such as an emergency diesel generator.1.5 OUTDOOR CONDITIONSChapters 14 and 15 of the 2013 ASHRAE HandbookFunda-mentals, the U.S. National Oceanic and Atmospheric Administra-tion, national weather service of the site
29、country, or sitemeteorology can provide information on outdoor conditions, tem-perature, humidity, solar load, altitude, and wind.Nuclear facilities generally consist of heavy structures with highthermal inertia. Time and temperature lag should be considered indetermining heat loads. For some applic
30、ations, such as diesel gen-erator buildings or safety-related pumphouses in nuclear powerplants, the 24 h average temperature may be used as a steady-statevalue. For critical ventilation system design, site meteorologicaldata should be evaluated.1.6 INDOOR CONDITIONSIndoor temperatures are dictated
31、by occupancy, equipment orprocess requirements, and comfort requirements based on personnelactivities. HVAC system temperatures are dictated by the environ-mental qualification of the safety-class equipment located in thespace and by ambient conditions during the different operatingmodes of the equi
32、pment.1.7 INDOOR PRESSURESWhere control of airflow pattern is required, a specific buildingor area pressure relative to the outdoor atmosphere or to adjacentareas must be maintained. The effect of prevailing wind speed anddirection, based on site meteorological information, should be con-sidered. Fo
33、r process facilities with pressure zones, the pressure rela-tionships are specified in the section on Confinement Systems.In facilities where zoning is different from that in process facili-ties, and in cases where any airborne radioactivity must not spreadto rooms within the same zone, this airborn
34、e radioactivity must becontrolled by airflow.1.8 AIRBORNE RADIOACTIVITYThe level of airborne radioactivity within a facility and the amountreleased to the surroundings must be controlled to meet the require-ments of 10CFR20, 10CFR50, 10CFR61, 10CFR100, 10CFR835,and U.S. DOE Policy P 441.1, or equiva
35、lent national regulations ofthe site country.1.9 TORNADO/MISSILE PROTECTIONProtection from tornados and the objects or missiles launched bywind or other design basis events is normally required to prevent therelease of radioactive material to the atmosphere. A tornado passingover a facility causes a
36、 sharp drop in ambient pressure. If exposed tothis transient pressure, ducts and filter housings could collapsebecause the pressure inside the structure would still be that of theenvironment prior to the pressure drop. Protection is usually pro-vided by tornado dampers and missile barriers in all ap
37、propriateopenings to the outdoors. Tornado dampers are heavy-duty, low-leakage dampers designed for pressure differences in excess of3 psi. They are normally considered safety-class and are environ-mentally and seismically qualified.1.10 FIRE PROTECTIONFire protection for HVAC and filtration systems
38、 must complywith applicable requirements of RG 1.189, Appendix R of10CFR50, and NFPA, UL, and ANSI or equivalent standards of thesite country. Design criteria should be developed for all building fireprotection systems, including secondary sources, filter plenumprotection, fire dampers, and systems
39、for detection/suppression andNuclear Facilities 28.3smoke management. Fire protection systems may consist of a com-bination of building sprays, hoses and standpipes, and gaseous orfoam suppression. The type of fire postulated in the Fire HazardAnalysis (FHA) or equivalent determines which kind of sy
40、stem isused.A requirement specific to U.S. nuclear commercial facilities isprotection of carbon filter plenums and ventilation ductwork. Man-ually activated water sprays (window nozzles, fog nozzles, or stan-dard dry pipe/wet pipe system spray heads) are usually used for firesuppression in carbon fi
41、lter plenums.Heat detectors and fire suppression systems should be consid-ered for special equipment such as glove boxes. Application of thetwo systems in combination allows the shutdown of one system at atime for repairs, modifications, or maintenance.In a DOE facility, the exhaust system duct pene
42、trating a fire-ratedboundary does not need a fire damper for maintaining the integrityof the boundary if the duct is fire rated. The exhaust duct may berated at up to two hours by either wrapping, spraying, or enclosingthe duct in an approved material and qualifying it by an engineeringanalysis. Add
43、itional design guidance can be obtained from theNuclear Air Cleaning Handbook (DOE-HDBK-1169-2003).Smoke control criteria can be found in NFPA Standards 801,803, 804, and 901, or equivalent standards of the site country.1.11 SMOKE MANAGEMENTThe design objective for smoke management in a nuclear faci
44、lityis to protect the plant operators and equipment from internally andexternally generated smoke. Smoke management involves (1) use ofmaterials with low smoke-producing characteristics, (2) preventionof smoke movement to areas where operators may be overcome, (3)use of differential pressures to con
45、tain smoke to fire areas, (4) smokeventing to permit access to selected areas, and (5) purging to permitaccess to areas after a fire.Smoke control may be static, by prevention of smoke movement(NFPA 90A), or it may be dynamic, by controlling building pressureor air velocities (NFPA 92A). Ventilation
46、 systems in the affectedareas should be shut down to prevent smoke from migrating andovercoming occupants in other areas. Smoke management for aninternal fire source should allow the plant operator to shut down thereactor in a controlled manner and maintain shutdown condition.Smoke from an external
47、fire should be isolated and appropriatemeasures provided to prevent smoke from entering the main controlroom envelope. This envelope includes the main control room andother necessary areas such as restrooms, kitchens, and offices. Thelocation of the safe shutdown panels and the pathway to the safesh
48、utdown panel must be such that, in case of abandonment of themain control room because of fire and smoke, safe egress is ensured.Capabilities should be provided for purging smoke from fireareas to permit reentry into the areas after the fire is isolated andextinguished. Venting may be used to remove
49、 heat and smoke at thepoint of the fire to permit fire fighting and to control pressures gen-erated by fires.NFPA 90A, 204, and 92A and NUREG 800 SRP Branch Tech-nical Position CMEB 9.5-1 provide guidance for smoke manage-ment and discuss the discharge of smoke and corrosive gases.Control Room Habitability ZoneThe HVAC system in a control room is a safety-related systemthat must fulfill the following requirements during all normal andpostulated accident conditions:Maintain conditions comfortable to personnel, and ensure thatcontrol room equipment functions continuously and complieswith
