ML19221B085
| ML19221B085 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-05.2.5, NUREG-75-87, NUREG-75-87-5.2.5, SRP-05.02.05, SRP-5.02.05, NUDOCS 7907120392 | |
| Download: ML19221B085 (8) | |
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STANDARD REVIEW PLAN
%.V OFFICE OF NUCLEAR REACTOR REGULATION Sectior 5.2.5 GEACTOR COOLANT FRESSURE COUNDARY LEAkACE DETECTION Ft V!E W PESPONSIBIL I T IES Primary - Reactor System' Branch (RSD)
Secondary - Electrical, Instrumentation and Control Systems Branch (EICSB)
Mechanical Engineering Branch (MEB)
I.
AREAS CF RIVIEW General Design Criterion 30 (Ref. 1) requires that means be provided for detecting and, to the extent practical, identifying the location of the source of reactor coalant leakage, ire areas of the SAR relating to the reactor coolant pressure boundary (RCFB) leakage detection systems are revieaed. The descriptive information and supporting figures, taoles, and graphs are reviewed to establish that sufficient infomation is provided to pemit a reasonable evaluation of the applicant's compliance with Regulatory Guide 1.45 (Ref. 2),
as follcws:
1.
Collection of Identified Leikage A limited amount of leakage is expected from components of the RCFB within the containment, such as valve sten packing glands, circulating purp thaft seals, and other equipcent that cannot practically t,e made completely leaktight. The reactor vessel closure seals and safety and relief valves should not leak significant!y; how-ever, leakage occurring via these paths or via pump and valve seals is detectable and Collectable and, to the extent prdCtical, should te isolated from the containment atmosphere 50 as not to mask any potentially serious leak should it occur. These leaks are known as " identified leakage" and are piped to tanks or sumps so that the flow rate can be established and monitored during plant operation. The provisions for collecting and monitoring leakage fron known leak sources are reviewed.
2.
Unidentified LeakaSe to Containrent Uncollected leakage to the containment atmosphere increases tne humidity of the centainment. The noisture removed from the atmosphere by air coolers together with any associated liquid leakage to the containment is kr.cwn as " unidentified leakage" and is collected in tanks or sumps where the flow rate can be established and monitored during plant operation. Unidentified leakage to the containment atmosphere should be kept to a minimum to permit the leakage detection systems to detect positively and rapidly a small increase in flow rate. Identified and unidentified USNRC STANDARD REVIEW PLAN
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leakages should be separated so that a small unidentified leakage that is of concern will not be masked by a larger acceptable identified leakage. Provisions for the detection and control of leakage to containment are reviewed.
3.
Leakage Detection Methods Continuous monitoring of both identified and unidentified leakage rates is important.
Effective systems for detecting and locating unidentified leakage are needed. The following describes some detection methods connonly used.
The primary nonitors determine flow rates and flow rate changes to tanks and sumps.
Methods to indicate when and where coolant is being released to the containment atmos;here include detection of changes in airborne particulate radioactivity, airborne gaseous radioactivity, containment atmosphere hunidity, pressure, and temperature, condensate flow rate from air coolers.
4.
Intersystem Leakage Substantial intersystem leakage f rom the RCPB to otner systems across passive barriers or valves is not expected. However, should such leakage occur, it should be detectable by the alarm and detection rethods which are employed. For exarple, steam generators in pressurized water r(. actors (PWR's) are monitored to detect tube sheet leaks.
Since intersystem laakage does not release reactor coolant to the containrent atnosphere, detection methods include monitoring of radioactivity in the connected systems where the flow is through the containment boundary, and nonitoring of airborne radioactivity where such systens are vented outside the containment boundary. Another important method of obtaining indications of uncontrolled or undesirable intersystem flow is the use of a water inventory balance, designed to provide appropriate information such as abnormal water levels in tanks and abnormal water flow rates.
5.
System Sensitivity and Response Tine Since leakage detection methods or systens differ in sensitivity and response tire, prudent selection of detection riethods should include a sufficient number of systers to ensure effective nonitoring during periods when some detection systems may be ineffective or inoperable. Some of these systems should serve as early alarn systers which signal the operators that closer examination of other detection syster s is necessary to determine the extent of any corrective action that may be required. It is essential that leakage detection systems have the capability to detect significant RCPB leakage as soon af ter occurrence as practical to minimize the potential for a gross boundary failure. Cracks that might develop and penetrate the RCFB wall are expected to exhibit very slow growth, and to affard ample time for a safe and orderly plant shutdown after a leak is detected. An early warning signal is necessary to perrit proper evaluation of all unidentified leakage.
147 087 5
6.
Seismic Capability of Systens Since nuclear power plants may be operating at the time an earthquake occurs and nay continue to operate af ter earthquakes, the leakage detection systems should be designed to continue functioning af ter seisnic events. If a seismic event comparable to a safe shutdown earthquace (SSE) occurs, it is important that the operator be able to assess the condition within the containment quickly. The proper functioning of at least one leakage detection system is essential in evaluating the seriousness of the condition within the containment in the event leakage has developed in the RCPB. The MEB reviews the seismic qualification of the electrical and instrunentation portion of the leak detection system in SRP 3.10 (Ref. 3).
7.
Quantitative Interpretation of Indicators and Alarns It is important to be able to associate a signal or indication of a departure from the normal operating conditions with a quantitative leakage flow rate. Except for flow rate or level change measurements from tanks, sumps, or pumps, signals from other leakage detection systems do not provide information readily convertible to a comnon denom'nator. Approximate relationships converting these signals to units of water flow are formulated to assist the operator in interpreting signals. The instrumentation associated with the leak detec; ion system is reviewed by FICSB in SRP 7.5 (Ref. 4).
Procedures for operator evaluation of leakage conditions are reviewed by RSB.
8.
Testability Provisions for testing the various systems during plant operation should be provided.
EICSB ensures that leakage detection equiprent is tested and calibrated in compliance 9
with IEEE Std. 279-1971 (Ref. 5).
9.
Technical Specifications RSB reviews the limiting conditions for operation that appear in the technical specifi-cations. Leakage limits for unidentified and total leakage, maximum time allowed to operate af ter a leak is discovered, ar.d action to take in the event of instrument malfunction are reviewed.
II.
ACCEPTANCE CRITERIA The acceptance criteria for the areas of review described in Section I of this plan are stated in Regulatory Guide 1.45 (Ref. 2). According to this guide the source of reactor coolant leakage should be identifiable to the extent practical. Reactor coolant pressure boundary leakage detection and collection systems are acceptable if they are in accordance with the following:
1.
Collection of Identified Leakage Leakage to the primary reactor containment from identified sources should be collected or otherwise isolated so that the flow rates are monitored separately from unidentified leakage, and the total flow rate can be established and monitored.
2.
Collection and Monitoring of Unidentified Leakage leakage to the primary reactor containment from unidentified sources should be collected and the flow rate monitored with an accuracy of one gallon per minute (gpm) or better.
10 088 5.2.5-3
3.
Leakage Detection Methods At least three separate detection methods should be erpioyed and two of these methods should be (1) su~p level and flow monitoring and (2) airborne particulate radicactivity monitoring. The third method may be selected from either the monitoring of condensate flow from air coo!ers, or nonitoring of airborne gaseous radioactivity.
Humidity, temperature, or pressure nonitoring of the containnent atmosphere are to be considered as alarms or indirect indications of leakage to the containrent.
4.
Intersys tem LeakaSe Provisions should be made to monitor systems connected to the RCPB for signs of intersystem leakage. Detection methods include radioactivity nonitoring and ind: ators to show abnormal water levels or flow in the potentially affected systems and unaccount-able increases in reactor coolant nake-up flow.
S.
System Sensitivity and Response Time The sensitivity and response time of each leakage detection system employed for nonitoring unidentified leakage to the containment should be adequate to detect an increase in leakage rate, or its equivalent, of one gpn in less than one hour.
6.
Seisnic Capability of Systens The leakage detection systens should be capable of performing their functions following seismic events that do not require plant shutdown and the airborne particulate radio-activity monitoring system should be capable of remaining functional when subjected to the safe shutdown earthquake (SSE).
7.
Indicators and Alanis Indicators and alar s for each leakage detection systen should be provided in the main control room and procedures for converting various indications to a common leakage equivalent should be available to the operators. The calibration of the indicators should account for the independent variables such as, in the case of an air particulate monitor, the isotope being monitored, plateout, and decay rate. Each systen should be set to alarm un an increase in leakage of 1 gpm above the h3ckground level deten,ined at the tire of calibration.
8.
Tes+ing The leakage detection systens should be equipped with provisions to permit calibration and operability tests during plant operation.
9.
Technical Specifications The technical specifications should include, in the limiting conditions for operation, the maximum permissible total and unidentified leakage, and address the availability of the leakage detection systens to ensure adequate coverage at all tires. The leakage limits are established on the basis of current practice for similar types of nuclear steam supply systems.
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III. REVIEW FROCEDURES The procedures below are used during the construction permit (CP) review to assure that the design criteria and bases and the preliminary design as set forth in the prelininary safety analysis report meet the acceptance criteria given in Section II of this plan.
For the operating license (OL) review, the procedures are utilized to verify that the initial design criteria and bases have been appropriately inplemented in the final design as set forth in the final safety analysis report. The OL review also includes the proposed tech-nical specifications, to assure that they are adequate in regard to limiting conditions of operation and allowable leakage rates.
The reviewer will select and emphasize material from the procedures described below, as nay be appropriate for a particular case, l.
Collection of Identified Leakage Information concerning the collection of identified leakage is reviewed for agreerent with Acceptance Criterion II.l.
The reviewer verifies that the SAR description of the reactor vessel flange leakage ronitoring, leakage ronitors f or other vessel flanges, and valve and pump seal leakage monitors is complete, and that this monitored leakage will Le collected in tanks or sumps where its rate of accumulatian will be surred to obtain an identified leak rate. The reviewer should establish that the identified leakage is not only collected and monitored but in such a fashion as to prevent identi-fied leakages from masking unidentified leaks.
2.
Collection and Monitoring of Unidentified Leakage Information concerning the collection and monitoring of unidentified leakage is reviewed for agreement with Acceptance Criterion II.2.
3.
Leakage Detection Methods The information describing the nurrber of systens and operating principles of each system, including scheratic diagrams, is reviewed to assure that suf ficient information is provided to comply with Acceptance Criterion II.3.
The review consists of a side-by-side corparison of the applicant's r"ethods and the acceptance criterion and a deter-mination that the number and type of rethods provided are acceptable.
4.
Intersystem Leakage Information describing the intersystem leakage detection system is reviewed for compliance with Acceptance Criterion II.4.
The reviewer determines that radiation monitoring systens have been provided for possible intersystem leakage paths, including all auxiliary cooling systems interfacing with the primary coolant, such as heat exchangers or steam generators in FWR plants. The reviewer determines that inter-system leakage monitors are sensitive to the radiation emitted by fission products such as I-131 and the radioactive isotopes of xenon and krypton. The reviewer assures that the monitoring systems and procedures to detect and control leakage are capable of keeping intersystem leakage within the limits assumed in accident analyses. For example, steam gener3 tor tube and tube sheet leaks should be detected and corrective action taken before the centaminatiori of the secondary coolant exceeds that assumed in evaluating the steam generator tube accident without offsite pcwer (see SRP 15.6.3).
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5.
System Sensitivity and Response Time The reviewer determines that all components for the detection of unidentified leakage called for by Acceptance Criterion II.3 meet the sensitivity and response time of Acceptance Criterion 11.5. Currently used systems that have been found acceptable measure leakage either directly in gpm, such as sump monitors and containment air cooler condensate monitors or indirectly in units of radiation, pCi/cc, in the containment atmosphere.
The two most-used radiation sensitive monitors are the air particulate monitor (APM) and the radiogas monitor (RGM). The threshhold sensitivity of the APM is 10 cci/cc of containment volume and the RGM can sense 10 tCi/cc. The APM is 1000 times more sensitive than the RGM, hence its selection in Requlatory Guide 1.45 as one of the two systems a plant should have without any alternate choice. Background activity levels corresponding to assumed nont,a1 conditions of primary coolant leanage and f ailed fuel fraction may ba used to evaluate the compliance to Acceptance Criterion 11.5.
6.
Seismic Capability of Systems The SAR should state that the leakage detection systems meet the seismic tapability recomendations of Acceptance Criterion II.6.
The reviewer verifies that the s kage detection systems will remain functional for all seismic events not requiring a shut-down. In addition, the reviewer verifies that the APM can function after the safe shutdown earthquake. The reviewer determines that the applicant has provided the capability to take grab samples of the coniainment atmosphere on a periodic basis and manually analyze these samples in his radiochemistry laboratory for particulate activity and to correlate the data to primary system leakage.
7.
Indicators and Alarms Inf ormation concerning the indicators and alarms is reviewed for compliance with Acceptance Cri terion 11.7.
The reviewer verifies that all of the leakage detection systems have readouts in the control room and are provided with alarms. Direct read-ing systems, such as sumps, will normally indicate in gpm. The indirect reading systens, such as the APM, will indicate in counts per minute. The reviewer determines that control roon operators will have a chart or graph that permits rapid conversion of count rate into gpa, that the conversion procedures take into account the isutope being monitored and the activity of the primary coolant, and that the plant will maintain a running record of background leakage, so that its effect may be subtracted from any sudden increases in leak indication, which may be " unidentified" leakage and require prompt action. If monitoring is computerized, backup procedures shoulr* be available to the operator.
8.
Testing Information concerning operability testing and system calibration during plant opera-tion is reviewed for corpliance with Acceptance Criterion 11.8.
The reviewer determines that the radiation monitoring systems have a radioactive source built into the system (the SAR refers to this feature as a " check source") to permit system test and cali-bration during operation. He also determines that the flow of " identified" leakage, which may amount to as little as 0.05 gpm or as much as 0.25 gpm, representing a total 5.2.5-6 147 C I
daily flow of between 72 and 360 gallons, will be used to provide an operability check during operation for the sump monitoring systems and the containment air cooler con-densate flow monitors. The directly measured quantity of flow thus obtained from the sump and air cooler monitors can be used to calibrate the radiaticn monitoring systems.
9.
Technical Specifications The technical specifications are reviewed for compliance with Acceptance Criterion 11.9.
The reviewer compares the proposed technical specification limits for unidentified and total allowable leakage to the design basis as determined in the review of items 1-5 and 7.
In addition, the reviewer determines that the availability of various components of the leakage detection system and the action to be taken if a component becomes inoperative are addressed in the technical specifications. The availatility of the leakage detection components has to be reviewed on a case-by-case basis due to the large numt,er of possible component combinations, multiplicity of systems, use or lack of redur.dancy, or the ability to use systems not specifically called out as
" leakage detection systems" but still able to perform this role as a secondary function to the primary design use of such system. An example would be containment vent radiation monitors. A suggested technical specification regarding availability is as follows:
"Both the sump monitoring and air particulate monitoring systems shall be operable during reac+or power operation. If either system becomes inoperable for any reason, reactor power operation is permissible only during the succeeding seven days unless the system is made operable sooner. If the above conditions cannot be ret, an orderly shutdown shall be initiated and the reactor shall be in a cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />."
10.
General Should the leakage detection system submittal contain additional data and analyses as a basis to support a system not discussed in Regulatory Guide 1.45, the reviewer should evaluate the applicant's data and analyses to determine if the proposed system has leakage detection capabilities comparable to those of the standard systems. The reviewer can also find guidance in review procedures III.l through 9, above, and in other SAR's where applicants may have proposed similar Mte nate systems.
IV.
EVALUATION FINDINGS The reviewer verifies that sufficient and adequate information has been provided in accordance with the requirements of this review plan, and that his evaluation provides the basis for conclusions of the following type, which should be included in the staff's safety evaluation report:
" Coolant leakage within the primary containment may be an indication of a small through-wall flaw developed in the reactor coolant pressure boundary (RCPB).
"The leakage detection system provided will include sufficiently diverse leak detection methods, with adequate sensi ivity to measure small leaks and to identify the leakage sources within practical lit s, with the aid of suitable control room alarms and read-outs. The major systems are the containment atmosphere particulate and radiogas moni-tors, and level indicators on t'e containment sumps. Indirect mdications of leakage are obtainable from the contaiament pressure, humity, and temperature indicators.
5.2.5-7
}
"The leakage detection systems provided to detect leakage from components of the re-actor coolant pressure boundary furnish reasonable assurance that structural degrada-tion, which may develop in pressure-retaining components of the RCPB and result in coolant leakage during service, will be detected on a timely basis, so that corrective actions can be made before such degradation could become sufficiently severe to jeop-ardize the safety of the system, or before the leakage could increase to a level beyond the capability of the makeup systems to replenish the coolant loss. The systems are in compliance with the recommendations of Regulatory duide 1.45 and satisfy the require-ments of General Design Criterion 30, Appendix A of 10 CFR Part 50."
V.
REFERENCES 1.
10 CFR Part 50, Appendix A, Criterion No. 30, " Quality of Reactor Coolant Pressure Boundary."
2.
Regulatory Guide 1.45, " Reactor Coolant Pressure Boundary Leakage Detection Systens."
3.
Standard Review Plan 3.10. " Seismic Qualification of Category I Instrumentation and Electrical Equipment."
4.
Standard Review Plan 7.5, " Safety-Related Display Instrumentation."
5.
IEEE Standard 279-1971, " Criteria f or Protection Systems for Nuclear Power Generating Stations."
9 5.2.5-8