Regulatory Guide 1.95

Protection of Nuclear Power Plant Control Room Operators Against an Accidental Chlorine Release

ML12298A134
Person / Time
Issue date:	01/31/1977
From:	Office of Nuclear Regulatory Research, NRC/OSD
To:
References
RG-1.095, Rev 1
Download: ML12298A134 (7)

U.S. NUCLEAR REGULATORY COMMISSIONREGULATORYGUIDEOFFICE OF STANDARDS DEVELOPMENTREGULATORY GUIDE 1.95PROTECTION OF NUCLEAR POWER PLANT CONTROL ROOMOPERATORS AGAINST AN ACCIDENTAL CHLORINE RELEASERevision 1January 1977A. INTRODUCTIONCriterion 4, "Environmental and missile designbases," of Appendix A, "General Design Criteria forNuclear Power Plants," to 10 CFR Part 50, "Licens-ing of Production and Utilization Facilities," re-quires, in part, that structures, systems, and compo-nents important to safety be designed to accom-modate the effects of and to be compatible with theenvironmental conditions associated with operation,maintenance, testing, and postulated accidents.Criterion 19, "Control room," requires that a controlroom be provided from which actions can be taken tooperate the nuclear power unit safely under normalconditions and to maintain it in a safe condition un-der accident conditions.The release of chlorine could potentially result inthe control room operators becoming incapacitated.This guide describes design features and proceduresthat are acceptable to the NRC staff for the protec-tion of nuclear plant control room operators againstan accidental chlorine release. The Advisory Com-mittee on Reactor Safeguards has been consultedconcerning this guide and has concurred in theregulatory position.B. DISCUSSIONMany nuclear power plants use chlorine for watertreatment in the circulating water system and in otherauxiliary systems. Chlorine is normally stored on thesite as liquified gas in one-ton tanks or large railroadcars (typically 16 to 55 tons).* Lines indicate substantive changes from previous issue.Regulatory Guide 1.78, "Assumptions forEvaluating the Habitability of a Nuclear Power PlantControl Room During a Postulated HazardousChemical Release," identifies chlorine as a hazardouschemical which, if present in the control room at-mosphere in sufficient quantity, could result in thecontrol room becoming uninhabitable. It is the pur-pose of this guide to describe specific design featuresand procedures that are acceptable to mitigatehazards to control room operators from an acciden-tal chlorine release. Although this guide wasdeveloped to provide protection from an onsitechlorine release, the protection provisions describedhere are also expected to be sufficient for an offsitechlorine release. The positions stated in this guide arebased on the specific physical properties andphysiological effects of chlorine.Two basic accident types can be postulated: a long-term, low-leakage-rate release and a short-term puffrelease. The majority of chlorine releases experiencedto date have been of the first type, involving leakagefrom valves or fittings and resulting in a long-termrelease with a leakage rate from near zero to less thanone pound of chlorine per second. Given warning,only breathing apparatus is necessary to protect thecontrol room operator from this kind of release.However, because such a release might continue un-abated for many hours, self-contained breathing ap-paratus, a t sourc a.. :i.. mafo- outlets, orequivalent protection capable of operation for an ex-tended period of time should be available.A less probable but more severe accident would bethe failure of a manhole cover on the chlorine con-tainer or the outright failure of the container itself.USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. NuclearRegulatory Guides are issued to describe and make available to the public Regulatory Commission. Washington, DC. 20555, Attention: Docketing andmethods acceptable to the NRC staff of implementing specific parts of the Service Section.Commission's regulations, to delineate techniques used by the staff in evalu- The guides are issued in the following ten broad divisions:ating specific problems or postulated accidents, or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance 1. Power Reactors 6. Productswith them is not required. Maethods and solutions different from those set out in 2. Research and Test Reactors 7. Transportationthe guides will be acceptable if they provide a basis for the findings requisite to 3. Fuels and Materials Facilities 8. Occupational Healththe issuance or continuance of a permit or license by the Commission. 4. Environmental and Siting 9. Antitrust ReviewComments and suggestions for improvements in these guides are encouraged 5. Materials and Plant Protection 10. Generalat all times, and guides will be revised, as appropriate, to accommodate com-ments and to reflect new information or experience. This guide was revised as a Copies of published guides may be obtained by written request indicating theresult of substantive comments received from the public and additional staff divisions desired to the U.S. Nuclear Regulatory Commission, Washington, D.C.review. 20555, Attention: Director. Office of Standards Developmen Such failure could occur during the transportation ofa container as a result of a handling mishap or couldbe due to naturally or accidently produced environ-ments such as earthquakes, flooding, fire, explosiveoverpressure, or missiles. A failure of this type couldresult in a puff release of about 25% of the chlorine.The balance of the chlorine would be vaporized andreleased over an extended period of time. As a resultof the cloud formed by the release from such an acci-dent, the chlorine concentration inside the controlroom might increase rapidly. In the absence of specialdesign measures to limit the buildup within the con-trol room, the operators might be incapacitatedbefore they are able to don breathing apparatus.Adequate protection of the control room operatorsagainst the types of accidental chlorine release discus-sed above will be achieved if features are included inthe plant design to (1) automatically isolate the con-trol room if there is a release, (2) make the controlroom sufficiently leak tight, and (3) provide equip-ment and procedures for ensuring the use ofbreathing apparatus by the control room operators.Protection provisions adequate for the large instan-taneous release will also provide protection againstthe low-leakage-rate release. Staff analysis of controlroom designs and the degree of protection affordedby each design has resulted in criteria for acceptance,as will be discussed in the next section. These criteriaare based on the limitation (given in RegulatoryGuide 1.78) that the chlorine concentration withinthe control room should not exceed 15 ppm byvolume (45 mg/m3) within two minutes after theoperators are made aware of the presence ofchlorine.' This concentration, the toxicity limit, is themaximum concentration that can be tolerated for twominutes without physical incapacitation of anaverage human (i.e., severe coughing, eye burn, orsevere skin irritation).Table 1 gives the maximum allowable weight of asingle container of chlorine as a function of distancefrom the control room for various control roomtypes. It is based on an instantaneous release of 25%of the contents of the chlorine container and an al-lowable chlorine concentration in the control roomof 45 mg/m3, the toxicity limit, for two minutes. Theinitial cloud dimensions assume expansion of thechlorine gas into a spherical cloud having. a Gaussianconcentration gradient. Dispersion of the cloud wascalculated using the instantaneous release diffusionmodel appearing in Appendix B of Regulatory Guide1.78. For those cases where the control room waslocated a short distance from the release point andthe amount of chlorine release was small, the modelwas adjusted to allow for additional dispersion in thevertical direction by assuming uniform mixingbetween the ground and the elevation of the fresh airTwo minutes is considered sufficient time for a trained operatorto put a self-contained breathing apparatus into operation, ifthese are to be used.inlet (a 15-meter elevation from ground level wasused). The maximum allowable chlorine weights weredetermined by using worst case conditions forcalculating the control room concentrations (signifi-cant parameters being wind speed, cloud dimensions,normal air exchange rate, time to isolate, and isolatedair exchange rate). For certain control roomcharacteristics and high wind speed, the maximumoperator exposure occurs before isolation. For othercases with other control room characteristics and lowwind speed, the maximum operator exposure occurstwo minutes after isolation and is primarily due to in-filtration. The six control room types listed in thetable span the expected range of protections requiredfor most plants. Other combinations of the signifi-cant parameters are possible, but those listed in thetable should provide sufficient guidance for mostcases.This guide does not address the protection of in-dividuals either outside the control room or withinthe control room but not directly involved in reactoroperations. Breathing apparatus should be providedand be readily accessible throughout the plant inorder to eliminate the need for personnel to seekshelter in the control room during a chlorine release.The features and procedures described in this guideapply to plants having conventional ventilationsystems. Any different methods of protectionproposed will be evaluated on a case-by-case basis.C. REGULATORY POSITIONControl room operators should be protectedagainst the effects of an accidental chlorine release asdescribed below.1. Liquified chlorine should not be stored within100 meters of a control room2 or its fresh air inlets.(Small quantities for laboratory use, 20 lbs or less, areexempt.)2. If a chlorine container having an inventory of150 lbs or less is stored more than 100 meters fromthe control room or its fresh air inlets, the capabilityfor manual isolation of the control room should beprovided.3. For single container quantities exceeding 150 lb,the maximum allowable chlorine inventory in a singlecontainer stored at specified distances from the con-trol room or its fresh air inlet is given in Table 1 forcontrol room Types I through VI (described below).For each control room type, the maximum allowablechlorine inventory in a single container is given as afunction of distance from the control room. If thereare several chlorine containers, only the failure of thelargest container is normally considered unless the2 Control room is defined to include all zones serviced by theemergency ventilation system.1I1.95-2

,low wTABLE 1MAXIMUM ALLOWABLE CHLORINE INVENTORY IN A SINGLE CONTAINERControlRoomTypeControl Room CharacteristicsIsolation Air ExchangeLocal Remote Time Rate -NormalDetectors Detectors (sec) (hrIAir ExchangeRate -Isolated(hr4)0.06Maximum Weight (1000 Ib) ofChlorine as a Function of Distancefrom Control Rooma100 m 200 m 300 m 500 m 2000 m(330 ft) (660 ft) (980 ft) (1640 ft) (6560 ft)10 1200IIIIIIVVVIYesYesYesYesYesYesNoNoNoNoYesbYesb10410410.30.30.060.060.0150.060.01512687010.55 12 40 34006 14 36 270020 60 230 3200020 50 120 50002410c10c1180 3801300 60000aTo determine allowable chlorine inventories for distances between those given in this table, log-log interpolation is acceptable.bsee Regulatory Position 3.e for an alternative to remote detectors.cThe isolation time of 10 seconds refers to detection by local detectors. If detection is by remote detectors, isolation time is effectively zero since detection and isolation will beaccomplished before the chlorine reaches the control room isolation damper containers are interconnected in such a manner thatfailure of a single container could cause a chlorinerelease from several containers.a. Type I control rooms should include the follow-ing protective features:(1) Quick-response chlorine detectors located inthe fresh air inlets. Within 10 seconds3 after arrival ofthe chlorine, detection should initiate completeclosure of isolation dampers to the control room.(2) A normal fresh air makeup rate of less thanone air change per hour. The fresh air inlet should beat least 15 meters above grade.(3) Low-leakage construction with an equivalentair exchange rate of less than 0.06 hr-I when allpenetrations are exposed to a 1/8-inch water gagepressure differential. Construction details should beprovided to show that this limit is met.(4) Low-leakage dampers or valves installed onthe upstream side of recirculation fans or other loca-tions where negative systems pressure exists andwhere inleakage from chlorine-contaminated outsideair is possible.b. Type II control rooms should include theprotective features of paragraph a except that theisolation time should be 4 seconds or less rather than10 seconds or less.c. Type III control rooms should include theprotective features of paragraph a except that thenormal fresh air makeup rate should be limited to 0.3air change per hour or less.d. Type IV control rooms should include theprotective features of paragraph a except that theisolation time and the normal air exchange rateshould be equal to or less than 4 seconds and 0.3 airchange per hour, respectively. In addition, the con-trol room isolated air exchange rate should bereduced to 0.015 air change per hour or less (seedescription of required leak rate verification test inRegulatory Position 5).e. Type V control rooms should include theprotec-tive features of paragraph a with the addition ofremote chlorine -detectors located at the chlorinestorage and unloading location. These additionaldetectors should be placed and the detector trippoints adjusted so as to ensure detection of either aleak or a container rupture. A detector trip signalshould accomplish automatic isolation of the controlThis is the time interval between the time the chlorineconcentration exceeds 5 ppm at the isolation dampers and thetime the dampers are completely closed. Note that if the chlorinedetectors are upstream from the isolation dampers, credit will beallowed for the travel time between the detectors and thedampers.room before chlorine arrives at the isolationdampers. The detector trip signal should also set offan alarm and provide a readout in the control room.An alternative to the installation of remote detectorswould be to provide an isolation system using localdetectors but having an isolation time of effectivelyzero. This can be accomplished by ensuring that thetime required for chlorine to travel from the chlorinedetector to the isolation damper, within the inletducting, is equal to or greater than the time requiredto detect the chlorine and close the isolation damper.f. Type VI control rooms should include theprotective features in paragraph e except that thecontrol room isolated air exchange rate should bereduced to 0.015 air change per hour or less. Forisolated exchange rates between 0.0 15 hr- ' and 0.06hr-' , linear interpolation of the weights given forcontrol room Types V and VI in Table 1 can be made.Verification testing is required within this range ofexchange rates (see Regulatory Position 5).4. The following should be applied to all controlroom types (I through VI):a. Immediately after control room isolation, theemergency recirculating charcoal filter or equivalentequipment designed to remove or otherwise limit theaccumulation of chlorine within the control roomshould be started up and operated.b. Steps should be taken to ensure that the isolatedexchange rate is not inadvertently increased by designor operating error. For instance, the following shouldbe considered:(1) An administrative procedure should requirethat all doors leading to the control room be keptclosed when not in use.(2) Ventilation equipment for the control roomand for the adjacent zones should be reviewed to en-sure that enhanced air exchange between the isolatedcontrol room and the outside will not occur (e.g., ifthere is a chlorine release, exhaust fans should bestopped and/or isolated from the control room ven-tilation zone by low-leakage dampers or valves).(3) A control room exit leading directly to theoutside of the building should have two low-leakagedoors in series.c. The use of full-face self-contained pressure-demand-type breathing apparatus (or the equivalent)and the use of protective clothing should be con-sidered in the development of a chlorine releaseemergency plan. Because calculations indicate thatchlorine concentrations may increase rapidly,emergency plan provisions and rehearsal of theseprovisions are necessary to ensure donning ofbreathing apparatus on detection of high chlorineI41.95-4 concentrations. Storage provisions for breathing ap-paratus and procedures for their use should be suchthat operators can begin using the apparatus withintwo minutes after an alarm. Adequate air capacity forthe breathing apparatus (at least six hours) should bereadily available onsite to ensure that sufficient timeis available to transport additional bottled air fromoffsite locations. This offsite supply should becapable of delivering several hundred hours of bot-tled air to members of the emergency crew. Aminimum emergency crew should consist of thosepersonnel required to maintain the plant in a safecondition, including orderly shutdown or scram ofthe reactor. As a guideline, a minimum of five unitsof breathing apparatus should be provided for theemergency crew.d. The air supply apparatus should meet the singlefailure criterion and be designated Seismic CategoryI. (In the case of self-contained breathing apparatus,the single failure criterion may be met by supplyingone extra unit for every three units required.)The isolation system components should be of aquality that ensures high reliability and availability.One method to meet these goals is to provide asystem that meets the requirements of IEEE-279,"Criteria for Protection Systems for Nuclear PowerGenerating Stations." In all cases, the isolationsystem, recirculating filter system, and air condition-ing system should meet IEEE-279 since they are re-quired to maintain a habitable environment in thecontrol room during design basis radiological events.Specific acceptance criteria for the chlorine detec-tion system and allied actuating electronics are as fol-lows:(1) Chlorine Concentration Level. Detectorsshould be able to detect and signal a chlorine con-centration of 5 ppm.(2) System Response Time. The system responsetime, which incorporates the detector response time,the valve closure time, and associated instrumentdelays, should be less than or equal to the requiredisolation time.(3) Single Failure Criteria. The chlorine detectionsystem should be redundant and physically separateto accomplish decoupling of the effects of unsafe en-vironmental factors, electric transients, physical acci-dents, and component failure.Local detectors should consist of two physicallyseparate channels for each fresh air inlet. Each chan-nel should consist of a separate power supply, detec-tor, actuating electronics, and interconnecting ca-bling. Remote detectors should also consist of twoseparate channels having detectors located at thechlorine unloading facility.(4) Seismic Qualification. The chlorine detectionsystem should be designated as Seismic Category Iand be qualified as such.(5) Environmental Qualification. The detectionsystem should be qualified for all expected environ-ments and for severe environments that could clearlylead to or be a result of a chlorine release. The instal-lation of the detectors should ensure that they areprotected from adverse temperature effects.(6) Maintenance, Testing, and Calibration. Themanufacturer's maintenance recommendations areacceptable provided they follow sound engineeringpractice and are compatible with the proposed ap-plication. A routine operational check should be con-ducted at one-week intervals.Verification testing and calibration of thechlorine detectors and verification testing of thesystem response time should be conducted at six-month intervals.5. The gross leakage characteristic of the controlroom should be determined by pressurizing the con-trol room to 1/8-inch water gage and determining thepressurization flow rate. (The use of a higher pressuredifferential is acceptable provided the flow rate isconservatively adjusted to correspond to 1/8-inchwater gage.) For air exchange rates of less than 0.06hr -', periodic verification testing should be per-formed. An acceptable method for periodic testingwould be the use of a permanently installedcalibrated pressurization fan. The system would havea known pressure-versus-flow characteristic so thatthe leak rate could be determined by measuring thecontrol room pressure differential. Testing should beconducted at least every six months and after any ma-jor alteration that may affect the control roomleakage.6. Emergency procedures to be initiated in theevent of a chlorine release should be provided.Methods of detecting the event by station personnel,both during normal workday operation and duringminimum staffing periods (late night and weekendshift staffing), should be discussed. Instrumentationthat has been provided for the detection of chlorineshould be described including sensitivity; action in-itiated by detecting instrument and level at which thisaction is initiated; technical specification limitationson instrument availability; and instructions formaintenance, calibration, and testing. Criteria shouldbe defined for the isolation of the control room, forthe use of protective breathing apparatus and otherprotective measures, and for maintenance of theplant in a safe condition including the capability fororderly shutdown or scram of the reactor. Criteriaand procedures for evacuating nonessential personnelfrom the station should also be defined.1.95-5 D. IMPLEMENTATIONThe purpose of this section is to provide informa-tion to applicants regarding the NRC staff's plans forusing this regulatory guide.This guide reflects current NRC staff practice.Therefore, except in those cases in which the appli-cant proposes an acceptable alternative method forcomplying with specified portions of the Commis-sion's regulations, the method described herein is be-ing and will continue to be used in the evaluation ofsubmittals for construction permit applications untilthis guide is revised as a result of suggestions from thepublic or additional staff review.I*11.95-6 UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, 0. C. 20555OFFICIAL BUSINESSPENALTY FOR PRIVATE USE, $300POSTAGE AND FEES PAIDU.S. NUCLEAR REGULATORYCOMMISSION4194Z.60020012 -SN..: 0:177U S NRCOFFICE OF INSPECTION .&"'.ENFORCER J BORES531 PARK AVENUEKING OF 'PRUSSIA- PA '19406