Regulatory Guide 1.95
| 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) | |
Revision 1 U.S. NUCLEAR REGULATORY COMMISSION January 1977 REGULATORYGUIDE
OFFICE OF STANDARDS DEVELOPMENT
REGULATORY GUIDE 1.95 PROTECTION OF NUCLEAR POWER PLANT CONTROL ROOM
OPERATORS AGAINST AN ACCIDENTAL CHLORINE RELEASE
A. INTRODUCTION
Regulatory Guide 1.78, "Assumptions for Evaluating the Habitability of a Nuclear Power Plant Criterion 4, "Environmental and missile design Control Room During a Postulated Hazardous bases," of Appendix A, "General Design Criteria for Chemical Release," identifies chlorine as a hazardous Nuclear Power Plants," to 10 CFR Part 50, "Licens- chemical which, if present in the control room at- ing of Production and Utilization Facilities," re- mosphere in sufficient quantity, could result in the quires, in part, that structures, systems, and compo- control room becoming uninhabitable. It is the pur- nents important to safety be designed to accom- pose of this guide to describe specific design features modate the effects of and to be compatible with the and procedures that are acceptable to mitigate environmental conditions associated with operation, hazards to control room operators from an acciden- maintenance, testing, and postulated accidents. tal chlorine release. Although this guide was Criterion 19, "Control room," requires that a control developed to provide protection from an onsite room be provided from which actions can be taken to chlorine release, the protection provisions described operate the nuclear power unit safely under normal here are also expected to be sufficient for an offsite conditions and to maintain it in a safe condition un- chlorine release. The positions stated in this guide are der accident conditions. based on the specific physical properties and physiological effects of chlorine.
The release of chlorine could potentially result in the control room operators becoming incapacitated. Two basic accident types can be postulated: a long- This guide describes design features and procedures term, low-leakage-rate release and a short-term puff that are acceptable to the NRC staff for the protec- release. The majority of chlorine releases experienced tion of nuclear plant control room operators against to date have been of the first type, involving leakage an accidental chlorine release. The Advisory Com- from valves or fittings and resulting in a long-term mittee on Reactor Safeguards has been consulted release with a leakage rate from near zero to less than concerning this guide and has concurred in the one pound of chlorine per second. Given warning, regulatory position. only breathing apparatus is necessary to protect the control room operator from this kind of release.
B. DISCUSSION
However, because such a release might continue un- abated for many hours, self-contained breathing ap- Many nuclear power plants use chlorine for water paratus, a t sourc a.. :i.. mafo- outlets, or treatment in the circulating water system and in other equivalent protection capable of operation for an ex- auxiliary systems. Chlorine is normally stored on the tended period of time should be available.
site as liquified gas in one-ton tanks or large railroad cars (typically 16 to 55 tons). A less probable but more severe accident would be the failure of a manhole cover on the chlorine con-
- Lines indicate substantive changes from previous issue. tainer or the outright failure of the container itself.
USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission. Washington, DC. 20555, Attention: Docketing and Regulatory Guides are issued to describe and make available to the public Service Section.
methods acceptable to the NRC staff of implementing specific parts of the 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 appli cants. Regulatory Guides are not substitutes for regulations, and compliance 1. Power Reactors 6. Products with them is not required. Maethods and solutions different from those set out in 2. Research and Test Reactors 7. Transportation the guides will be acceptable if they provide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission.
3.
4.
Fuels and Materials Facilities Environmental and Siting
8.
9.
Occupational Health Antitrust Review K
Comments and suggestions for improvements in these guides are encouraged 5. Materials and Plant Protection 10. General at 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 the result 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 Development.
Such failure could occur during the transportation of inlet (a 15-meter elevation from ground level was a container as a result of a handling mishap or could used). The maximum allowable chlorine weights were be due to naturally or accidently produced environ- determined by using worst case conditions for ments such as earthquakes, flooding, fire, explosive overpressure, or missiles. A failure of this type could calculating the control room concentrations (signifi- cant parameters being wind speed, cloud dimensions, 1 result in a puff release of about 25% of the chlorine. normal air exchange rate, time to isolate, and isolated The balance of the chlorine would be vaporized and air exchange rate). For certain control room released over an extended period of time. As a result characteristics and high wind speed, the maximum of the cloud formed by the release from such an acci- operator exposure occurs before isolation. For other dent, the chlorine concentration inside the control cases with other control room characteristics and low room might increase rapidly. In the absence of special wind speed, the maximum operator exposure occurs design measures to limit the buildup within the con- two minutes after isolation and is primarily due to in- trol room, the operators might be incapacitated filtration. The six control room types listed in the before they are able to don breathing apparatus. table span the expected range of protections required for most plants. Other combinations of the signifi- Adequate protection of the control room operators cant parameters are possible, but those listed in the against the types of accidental chlorine release discus- table should provide sufficient guidance for most sed above will be achieved if features are included in cases.
the plant design to (1) automatically isolate the con- trol room if there is a release, (2) make the control This guide does not address the protection of in- room sufficiently leak tight, and (3) provide equip- dividuals either outside the control room or within ment and procedures for ensuring the use of the control room but not directly involved in reactor breathing apparatus by the control room operators. operations. Breathing apparatus should be provided Protection provisions adequate for the large instan- and be readily accessible throughout the plant in taneous release will also provide protection against order to eliminate the need for personnel to seek the low-leakage-rate release. Staff analysis of control shelter in the control room during a chlorine release.
room designs and the degree of protection afforded by each design has resulted in criteria for acceptance, The features and procedures described in this guide as will be discussed in the next section. These criteria apply to plants having conventional ventilation are based on the limitation (given in Regulatory systems. Any different methods of protection Guide 1.78) that the chlorine concentration within proposed will be evaluated on a case-by-case basis.
the control room should not exceed 15 ppm by volume (45 mg/m 3) within two minutes after the operators are made aware of the presence of
C. REGULATORY POSITION
I
chlorine.' This concentration, the toxicity limit, is the Control room operators should be protected maximum concentration that can be tolerated for two against the effects of an accidental chlorine release as minutes without physical incapacitation of an described below.
average human (i.e., severe coughing, eye burn, or severe skin irritation). 1. Liquified chlorine should not be stored within
100 meters of a control room2 or its fresh air inlets.
Table 1 gives the maximum allowable weight of a (Small quantities for laboratory use, 20 lbs or less, are single container of chlorine as a function of distance exempt.)
from the control room for various control room types. It is based on an instantaneous release of 25% 2. If a chlorine container having an inventory of of the contents of the chlorine container and an al- 150 lbs or less is stored more than 100 meters from lowable chlorine concentration in the control room the control room or its fresh air inlets, the capability of 45 mg/m 3, the toxicity limit, for two minutes. The for manual isolation of the control room should be initial cloud dimensions assume expansion of the provided.
chlorine gas into a spherical cloud having. a Gaussian concentration gradient. Dispersion of the cloud was 3. For single container quantities exceeding 150 lb, calculated using the instantaneous release diffusion the maximum allowable chlorine inventory in a single model appearing in Appendix B of Regulatory Guide container stored at specified distances from the con-
1.78. For those cases where the control room was trol room or its fresh air inlet is given in Table 1 for located a short distance from the release point and control room Types I through VI (described below).
the amount of chlorine release was small, the model For each control room type, the maximum allowable was adjusted to allow for additional dispersion in the chlorine inventory in a single container is given as a vertical direction by assuming uniform mixing function of distance from the control room. If there between the ground and the elevation of the fresh air are several chlorine containers, only the failure of the largest container is normally considered unless the Two minutes is considered sufficient time for a trained operator to put a self-contained breathing apparatus into operation, if 2 Control room is defined to include all zones serviced by the these are to be used. emergency ventilation system.
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,lo w
w TABLE 1 MAXIMUM ALLOWABLE CHLORINE INVENTORY IN A SINGLE CONTAINER
Control Room Characteristics Maximum Weight (1000 Ib) of Control Isolation Air Exchange Air Exchange Chlorine as a Function of Distance Room Local Remote Time Rate - Normal Rate - Isolated from Control Rooma
4 Type Detectors Detectors (sec) (hrI (hr ) 100 m 200 m 300 m 500 m 2000 m )
(330 ft) (660 ft) (980 ft) (1640 ft) (6560 ft Yes No 10 1 0.06 0.5 2 4 10 1200
II Yes No 4 1 0.06 1 5 12 40 3400
- D
III Yes No 10 0.3 0.06 2 6 14 36 2700
IV Yes No 4 0.3 0.015 6 20 60 230 32000
V Yes Yesb 10c 0.06 8 20 50 120 5000
1 VI Yes Yesb 10c 0.015 70 180 380 1300 60000
aTo 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 be accomplished before the chlorine reaches the control room isolation dampers.
containers are interconnected in such a manner that room before chlorine arrives at the isolation failure of a single container could cause a chlorine dampers. The detector trip signal should also set off release from several containers. an alarm and provide a readout in the control room.
An alternative to the installation of remote detectors a. Type I control rooms should include the follow- ing protective features:
would be to provide an isolation system using local detectors but having an isolation time of effectively I
zero. This can be accomplished by ensuring that the
(1) Quick-response chlorine detectors located in time required for chlorine to travel from the chlorine the fresh air inlets. Within 10 seconds3 after arrival of detector to the isolation damper, within the inlet the chlorine, detection should initiate complete ducting, is equal to or greater than the time required closure of isolation dampers to the control room. to detect the chlorine and close the isolation damper.
(2) A normal fresh air makeup rate of less than f. Type VI control rooms should include the one air change per hour. The fresh air inlet should be protective features in paragraph e except that the at least 15 meters above grade. control room isolated air exchange rate should be reduced to 0.015 air change per hour or less. For
(3) Low-leakage construction with an equivalent isolated exchange rates between 0.0 15 hr- ' and 0.06 air exchange rate of less than 0.06 hr-I when all hr-' , linear interpolation of the weights given for penetrations are exposed to a 1/8-inch water gage control room Types V and VI in Table 1 can be made.
pressure differential. Construction details should be Verification testing is required within this range of provided to show that this limit is met. exchange rates (see Regulatory Position 5).
(4) Low-leakage dampers or valves installed on 4. The following should be applied to all control the upstream side of recirculation fans or other loca- room types (I through VI):
tions where negative systems pressure exists and where inleakage from chlorine-contaminated outside a. Immediately after control room isolation, the air is possible. emergency recirculating charcoal filter or equivalent equipment designed to remove or otherwise limit the b. Type II control rooms should include the accumulation of chlorine within the control room protective features of paragraph a except that the should be started up and operated.
isolation time should be 4 seconds or less rather than
10 seconds or less. b. Steps should be taken to ensure that the isolated exchange rate is not inadvertently increased by design c. Type III control rooms should include the protective features of paragraph a except that the or operating error. For instance, the following should be considered:
4 normal fresh air makeup rate should be limited to 0.3 air change per hour or less. (1) An administrative procedure should require that all doors leading to the control room be kept d. Type IV control rooms should include the closed when not in use.
protective features of paragraph a except that the isolation time and the normal air exchange rate (2) Ventilation equipment for the control room should be equal to or less than 4 seconds and 0.3 air and for the adjacent zones should be reviewed to en- change per hour, respectively. In addition, the con- sure that enhanced air exchange between the isolated trol room isolated air exchange rate should be control room and the outside will not occur (e.g., if reduced to 0.015 air change per hour or less (see there is a chlorine release, exhaust fans should be description of required leak rate verification test in stopped and/or isolated from the control room ven- Regulatory Position 5). tilation zone by low-leakage dampers or valves).
e. Type V control rooms should include theprotec- (3) A control room exit leading directly to the tive features of paragraph a with the addition of outside of the building should have two low-leakage remote chlorine -detectors located at the chlorine doors in series.
storage and unloading location. These additional detectors should be placed and the detector trip c. The use of full-face self-contained pressure- points adjusted so as to ensure detection of either a leak or a container rupture. A detector trip signal demand-type breathing apparatus (or the equivalent)
and the use of protective clothing should be con- should accomplish automatic isolation of the control sidered in the development of a chlorine release This is the time interval between the time the chlorine emergency plan. Because calculations indicate that concentration exceeds 5 ppm at the isolation dampers and the chlorine concentrations may increase rapidly, time the dampers are completely closed. Note that if the chlorine detectors are upstream from the isolation dampers, credit will be emergency plan provisions and rehearsal of these allowed for the travel time between the detectors and the provisions are necessary to ensure donning of dampers. breathing apparatus on detection of high chlorine
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concentrations. Storage provisions for breathing ap- (4) Seismic Qualification. The chlorine detection paratus and procedures for their use should be such system should be designated as Seismic Category I
that operators can begin using the apparatus within and be qualified as such.
two minutes after an alarm. Adequate air capacity for the breathing apparatus (at least six hours) should be (5) Environmental Qualification. The detection readily available onsite to ensure that sufficient time system should be qualified for all expected environ- is available to transport additional bottled air from ments and for severe environments that could clearly offsite locations. This offsite supply should be lead to or be a result of a chlorine release. The instal- capable of delivering several hundred hours of bot- lation of the detectors should ensure that they are tled air to members of the emergency crew. A protected from adverse temperature effects.
minimum emergency crew should consist of those personnel required to maintain the plant in a safe (6) Maintenance, Testing, and Calibration. The condition, including orderly shutdown or scram of manufacturer's maintenance recommendations are the reactor. As a guideline, a minimum of five units acceptable provided they follow sound engineering of breathing apparatus should be provided for the practice and are compatible with the proposed ap- emergency crew. plication. A routine operational check should be con- ducted at one-week intervals.
d. The air supply apparatus should meet the single failure criterion and be designated Seismic Category Verification testing and calibration of the I. (In the case of self-contained breathing apparatus, chlorine detectors and verification testing of the the single failure criterion may be met by supplying system response time should be conducted at six- one extra unit for every three units required.) month intervals.
The isolation system components should be of a quality that ensures high reliability and availability. 5. The gross leakage characteristic of the control One method to meet these goals is to provide a room should be determined by pressurizing the con- system that meets the requirements of IEEE-279, trol room to 1/8-inch water gage and determining the
"Criteria for Protection Systems for Nuclear Power pressurization flow rate. (The use of a higher pressure Generating Stations." In all cases, the isolation differential is acceptable provided the flow rate is system, recirculating filter system, and air condition- conservatively adjusted to correspond to 1/8-inch ing system should meet IEEE-279 since they are re- water gage.) For air exchange rates of less than 0.06 quired to maintain a habitable environment in the hr -', periodic verification testing should be per- control room during design basis radiological events. formed. An acceptable method for periodic testing would be the use of a permanently installed Specific acceptance criteria for the chlorine detec- calibrated pressurization fan. The system would have tion system and allied actuating electronics are as fol- a known pressure-versus-flow characteristic so that lows: the leak rate could be determined by measuring the control room pressure differentia
l. Testing should be
(1) Chlorine Concentration Level. Detectors conducted at least every six months and after any ma- should be able to detect and signal a chlorine con- jor alteration that may affect the control room centration of 5 ppm. leakage.
(2) System Response Time. The system response 6. Emergency procedures to be initiated in the time, which incorporates the detector response time, event of a chlorine release should be provided.
the valve closure time, and associated instrument Methods of detecting the event by station personnel, delays, should be less than or equal to the required both during normal workday operation and during isolation time. minimum staffing periods (late night and weekend shift staffing), should be discusse
d. Instrumentation
(3) Single Failure Criteria.The chlorine detection that has been provided for the detection of chlorine system should be redundant and physically separate should be described including sensitivity; action in- to accomplish decoupling of the effects of unsafe en- itiated by detecting instrument and level at which this vironmental factors, electric transients, physical acci- action is initiated; technical specification limitations dents, and component failure. on instrument availability; and instructions for maintenance, calibration, and testing. Criteria should Local detectors should consist of two physically be defined for the isolation of the control room, for separate channels for each fresh air inlet. Each chan- the use of protective breathing apparatus and other nel should consist of a separate power supply, detec- protective measures, and for maintenance of the tor, actuating electronics, and interconnecting ca- plant in a safe condition including the capability for bling. Remote detectors should also consist of two orderly shutdown or scram of the reactor. Criteria separate channels having detectors located at the and procedures for evacuating nonessential personnel chlorine unloading facility. from the station should also be defined.
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D. IMPLEMENTATION
cant proposes an acceptable alternative method for complying with specified portions of the Commis- The purpose of this section is to provide informa- sion's regulations, the method described herein is be- tion to applicants regarding the NRC staff's plans for ing and will continue to be used in the evaluation of using this regulatory guide.
This guide reflects current NRC staff practice.
submittals for construction permit applications until this guide is revised as a result of suggestions from the I
public or additional staff review.
Therefore, except in those cases in which the appli-
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