Regulatory Guide 1.45
| ML003740113 | |
| Person / Time | |
|---|---|
| Issue date: | 05/30/1973 |
| From: | Office of Nuclear Regulatory Research |
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| References | |
| RG-1.45 | |
| Download: ML003740113 (4) | |
May 1973 U.S. ATOMIC ENERGY COMMISSION
REGULATORY
DIRECTORATE OF RL'JLATORY STANDARDS
GUIDE
REGULATORY GUIDE 1.45 REACTOR COOLANT PRESSURE BOUNDARY
LEAKAGE DETECTION SYSTEMS
A. INTRODUCTION
Leakage Separation General Design Criterion 30, "Quality of Reactor A limited amount of leakage is expected from the Coolant Pressure Boundary," of Appendix A to 10 RCPB and from auxiliary systems within the CFR Part 50, "General Design Criteria for Nuclear containment such as from valve stem packing glands, Power Plants," requires that means be provided for circulating pump shaft seals, and other equipment that detecting and, to the extent practical, identifying the cannot practically be made 100% leaktight. The reactor location of the source of reactor coolant leakage. This vessel closure seals and safety and relief valves should guide describes acceptable methods of implementing not leak significantly; however, if leakage occurs via this requirement with regard to the selection of leakage these paths or via pump and valve seals, it should be detection systems for the reactor coolant pressure detectable and collectable and, to the extent practical, boundary. This guide applies to light-water-cooled isolated from the containment atmosphere so as not to reactors. The Advisory Committee on Reactor mask any potentially serious leak should it occur.
Safeguards has been consulted concerning this guide These leakages are known as "identified leakage" and and has concurred in the regulatory position. should be piped to tanks or sumps so that the flow rate can be established and monitored during plant
B. DISCUSSION
operation.
The safety significance of leaks from the reactor Uncollected leakage to the containment coolant pressure boundary (RCPB) can vary widely atmosphere from sources such as valve stem packing depending on the source of the leak as well as the glands and other sources that are not collected leakage rate and duration. Therefore, the detection and increases the humidity of the containment. The monitoring of leakage of reactor coolant into the moisture removed from the atmosphere by air coolers containment area is necessary. In most cases, methods together with any associated liquid leakage to the for separating the leakage from an identified source containment is known as "unidentified leakage" and from the leakage from an unidentified source are should be collected in tanks or sumps where the flow necessary to provide prompt and quantitative rate can be established and monitored during plant information to the operators to permit them to take operation. A small amount of unidentified leakage may immediate corrective action should a leak be be impractical to eliminate, but it should be reduced detrimental to the safety of the facility. Identified to a small flow rate, preferably less than one gallon per leakage is: (1) leakage into closed systems, such as minute (gpm), to permit the leakage detection systems pump seal or valve packing leaks that are captured, to detect positively and rapidly a small increase in flow flow metered, and conducted to a sump or collecting rate. Thus a small unidentified leakage rate that is of tank, or (2) leakage into the containment atmosphere concern will not be masked by a larger acceptable from sources that are both specifically located and identified leakage rate.
known either not to interfere with the operation of unidentified leakage monitoring systems or not to be Substantial intersystem leakage from the RCPB to from a flaw in the RCPB. Unidentified leakage is all other systems across passive barriers or valves is not other leakage. expected. However, should such leakage occur, it may USAEC REGULATORY GUIDES Copies of published guides may be obtained by request indicating the divisions desired to the U.S. Atomic Energy Commission, Washington, D.C. 20545, Regulatory Guides are issued to describe and make available to the public Attention: Director of Regulatory Standards. Comments and suggestions for methods acceptable to the AEC Regulatory staff of implementing specific parts of improvements in these guides are encouraged and should be sent to the Secretary the Commission's regulations, to delineate techniques "used by the staff in of the Commission, U.S. Atomic Energy Commission, Washington, D.C. 20545, evaluating specific problems or postulated accidents, or to provide guidance to Attention: Chief, Public Proceedings Staff.
applicants. Regulatory Guides are not substitutes for regulations and compliance with them is not required. Methods and solutions different from those set out in The guides are issued in the following ten broad divisions:
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. 1. Power Reactors
6. Products
2. Research and Test Reactors
7. Transportation
3. Fuels and Materials Facilities 8. Occupational Health Published guides will be revised periodically, as appropriate, to accommodate 4. Environmental and Siting 9. Antitrust Review comments and to reflect new information or experience. 5. Materials and Plant Protection 1
0. General
not be detectable through the above-mentioned specific nuclear power plant. However, since the detection systems, and other alarm and detection methods differ in sensitivity and response time, prudent methods should be employed. For example, steam selection of detection methods should include sufficient generator leakage in pressurized water reactors (PWR's) systems to assure effective monitoring during periods should be monitored to detect tube or tube sheet leaks. when some detection systems may be ineffective or inoperable. Some of these systems should serve as early Acceptable Detection Methods alarm systems signaling the operators that closer examination of other detection systems is necessary to Although monitoring of both identified and determine the extent of any corrective action that may unidentified leakage is important, effective systems for be required.
detecting and locating unidentified leakage are also needed. The following paragraphs describe some Detector Sensitivity acceptable detection methods.
It is essential that leakage detection systems have In addition to monitoring flow rate changes to tanks the capability to detect significant RCPB degradation as and sumps for liquid collection, other methods should soon after occurrence as practical to minimize the be included to indicate when and where coolant is potential for a gross boundary failure. It is possible that released to the containment atmosphere. For example, some cracks might develop and penetrate the RCPB wall, these additional detection methods would indicate exhibit very slow growth, and afford ample time for a and/or monitor changes in: safe and orderly plant shutdown after a leak is detected.
a. airborne particulate radioactivity, On the other hand, leakage such as that resulting from b. airborne gaseous radioactivity, stress-assisted corrosion in stainless steel or from a flaw c. containment atmosphere humidity, at a high fatigue point in the RCPB would demand rapid d. containment atmosphere pressure and detection and probable plant shutdown. Therefore, an temperature, early warning signal is necessary to permit proper e. condensate flow rate from air coolers. evaluation of all unidentified leakage.
Since intersystem leakage does not release reactor Industry practice has shown that water flow rate coolant to the containment atmosphere, detection changes of from 0.5 to 1.0 gpm can readily be detected methods should include monitoring of water in containment sumps by monitoring changes in sump radioactivity in the connected systems where the water level, in flow rate, or in the operating frequency of systems flows through the containment boundary, and pumps. Sumps and tanks used to collect unidentified monitoring of airborne radioactivity where such systems leakage and air cooler condensate should be are vented outside the containment boundary. Another instrumented to alarm for increases of from 0.5 to 1.0
important method of obtaining indications of gpm in the normal flow rates. This sensitivity would uncontrolled or undesirable intersystem flow would be provide an acceptable performance for detecting the use of a water inventory balance, designed to provide increases in unidentified liquid leakage by this method.
appropriate information such as abnormal water levels in tanks and abnormal water flow rates. An increase in humidity of the containment atmosphere would indicate release of water vapor to the Potential discharges from closed safety and relief containment. Dew point temperature measurements can valves are usually piped to tanks or water pools and be used to monitor humidity levels of the containment considered part of identified leakage. Temperature atmosphere. A 10 increase in dew point is well within sensors in the discharge path of safety and relief valves the sensitivity range capability of available instruments.
or flow meters in the leak-off lines would provide an Since the humidity level is influenced by several factors, acceptable method of signaling small leakage from these a quantitative evaluation of an indicated leakage rate valves. may be questionable and should be compared to observed increases in liquid flow from sumps and While the above-mentioned leakage detection condensate flow from air coolers. Humidity level systems reflect the present state of technology, it is monitoring is considered most useful as an alarm or recognized that other detection methods may be indirect indicating device to alert the operator to a developed and used in order to obtain operating potential problem.
experience with them. Among such methods are sonic indicators and moisture sensitive tapes applied to RCPB Reactor coolant normally contains sources of component parts. Because of the potential importance radiation which, when released to the containment, can of early leak detection in the prevention of accidents, be detected by the monitoring systems. However, continued improvements in leakage detection and reactor coolant radioactivity should be low during initial locating techniques should be sought. reactor startup and for a few weeks thereafter until activated corrosion products have been formed and It is not necessary that all of the above-mentioned fission products become available from failed fuel leakage detection methods or systems be employed in a elements; during this period, radioactivity monitoring
1.45-2
instruments may be of limited value in providing an Signal Correlation and Calibration early warning of very small leaks in the RCPB.
Instrument sensitivities of 10-9 MCi/cc radioactivity for It is important to be able to associate a signal or air particulate monitoring and of 10-6 pCi/cc indication of a change in the normal operating radioactivity for radiogas monitoring are practical for conditions with a quantitative leakage flow rate. Except Sthese leakage detection systems. Radioactivity for flow rate or level change measurements from tanks, monitoring systems should be included for every plant sumps, or pumps, signals from other leakage detection (especially particulate activity monitoring) because of systems do not provide information readily convertible their sensitivity and rapid response to leaks from the to a common denominator. Approximate relationships RCPB. converting these signals to units of water flow should be formulated to assist the operator in interpreting signals.
Since operating conditions may influence some of the Air temperature and pressure monitoring methods conversion procedures, the procedures should be revised may also be used to infer RCPB leakage to the during such periods. To assure the continued reliability containment. Containment temperature and pressure of the leakage detection systems, the equipment should fluctuate slightly during plant operation, but a rise above comply with Paragraph 4.10 of IEEE Std. 279-1971, the normally indicated range of values may indicate RCPB leakage into the containment. The accuracy and "Criteria for Protection Systems for Nuclear Power relevance of temperature and pressure measurements is a Generating Stations," 1 for tests and calibration.
function of containment free volume and detector Seismic Qualification location. Alarm signals from these instruments can be valuable in recognizing rapid and sizable energy-eleases Since nuclear power plants may be operating at the to the containment.
time an earthquake occurs and may continue to operate after earthquakes, it is prudent to require the leakage While the concern about instrument sensitivity detection systems to function under the same applies to the lower range of service for which the conditions. If a seismic event comparable to a safe instruments are selected, the upper instrument range shutdown earthquake (SSE) occurs, it would be limits should be established to prevent exceeding the important for the operator to assess the condition within saturation limits of instruments, thus making them the containment quickly. The proper functioning of at useless as indicators of containment conditions. least one leakage detection system would assist in evaluating the seriousness of the condition within the containment in the event leakage has developed in the Detector Response Time RCPB. The airborne particulate radioactivity monitoring equipment has the desirable sensitivity to indicate RCPB
The need to evaluate the severity of an alarm or leakage, and it should be included for all plants.
indication is important to the operators, and the ability Components for the airborne particulate radioactivity to compare with indications from other systems is equipment should be qualified to function through the necessary. The system response time should therefore be SSE.
included in the functional requirements for leakage detection systems. Except for the limitations during the
C. REGULATORY POSITION
initial few weeks of plant operation as discussed previously, all detector systems should respond to a one The source of reactor coolant leakage should be gpm, or its equivalent, leakage increase in one hour or identifiable to the extent practical. Reactor coolant less. Multiple instrument locations in monitored areas pressure boundary leakage detection and collection should be utilized if necessary to assure that the systems should be selected and designed to include the transport delay time of the leakage effluent from its following:
source to the detector or instrument location will yield an acceptable overall response time. A useful technique 1. Leakage to the primary reactor containment from in identifying the general location of a leakage area is the identified sources should be collected or otherwise placing of several sensors within the containment area isolated so that:
and observing differences in response from the sensors, a. the flow rates are monitored separately from and this technique should be used to satisfy this unidentified leakage, and requirement of General Design Criterion 30. b. the total flow rate can be established and monitored.
In analyzing the sensitivity of leak detection systems using airborne particulate or gaseous 2. Leakage to the primary reactor containment from radioactivity, a realistic primary coolant radioactivity unidentified sources should be collected and the flow concentration assumption should be used. The expected 'Copies may be obtained from the Institute of Electrical
"values used in the plant environmental report would be and Electronics Engineers, United Engineering Center, 345 East acceptable. 47th Street, New York, N.Y. 10017.
1.45-3
rate monitored with an accuracy of one gallon per employed for unidentified leakage should be adequate to minute (gpm) or better. detect a leakage rate, or its equivalent, of one gpm in less than one hour.
3. At least three separate detection methods should be employed and two of these methods should be (1) sump 6. The leakage detection systems should be capable of level and flow monitoring and (2) airborne particulate performing their functions following seismic events that radioactivity monitoring. The third 'method may be do not require plant shutdown. The airborne particulate selected from the following: radioactivity monitoring system should remain a. monitoring of condensate flow rate from air functional when subjected to the SSE.
coolers, b. monitoring of airborne gaseous radioactivity. 7. Indicators and alarms for each leakage detection Humidity, temperature, or pressure monitoring of system should be provided in the main control room.
the containment atmosphere should be considered as Procedures for converting various indications to a alarms or indirect indication of leakage to the common leakage equivalent should be available to the containment. operators. The calibration of the indicators should account for needed independent variables.
4. Provisions should be made to monitor systems
8. The leakage detection systems should be equipped connected to the RCPB for signs of intersystem leakage.
with provisions to readily permit testing for operability Methods should include radioactivity monitoring and and calibration during plant operation.
indicators to show abnormal water levels or flow in the affected area.
9. The technical specifications should include the limiting conditions for identified and unidentified
5. The sensitivity and response time of each leakage leakage and address the availability of various types of detection system in regulatory position 3. above instruments to assure adequate coverage at all times.
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