ML20205D834
| ML20205D834 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/20/1987 |
| From: | Wilson R GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 5000-87-1198, 5211-87-2071, NUDOCS 8703300494 | |
| Download: ML20205D834 (4) | |
Text
I-2 GPU Nuclear i
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100 Interpace Parkway M -
Parsippany New Jersey 07054 201 263-6500 TELEX 136-482 Writer's Direct Dial Number:
March 20, 1987 5211-87-2071 5000-87-1198 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Operating License No. OPR-50 Docket No. 50-289 Asymmetric LOCA Loads Resolution By letter dated September 11, 1980 (TLL-386), GPUN identified that Babcock and Wilcox (B&W) report BAW-1621 (Effects of Asymmetric LOCA Loadings -
Phase II) was applicable to TMI-1. This report demonstrated the ability of TMI-l to withstand the effects of Asymetric LOCA Loads (ALL) and to maintain a coolable core geometry for all pipe breaks except a large hot leg line break. To enable TMI-l to survive a large hot leg break, it would be necessary to reduce the hot leg break opening area and so a modification to the hot leg restraint system was proposed. This letter indicated that the modifications would be made during the first refueling cycle following plant restart (i.e., Cycle 6R).
In a letter dated March 26, 1981 (Lil-078), GPUN changed the commitment so that either the modifications to the hot leg restraints would be installed or that a justification for the adequacy of the existing plant design would be provided to the NRC.
In subsequent letters to the NRC dated June 25, 1982 (5211-82-151), and June 15, 1984 (5211-84-2134), GPUN provided information which demonstrated that existing (i.e., unmodified) hot leg restraints would survive the dynamic effects of a large hot leg break. GPUN concluded that this would result in the limiting of the hot leg break opening arta, thus reducing the loads experienced by key plant structures
. 'to analyzed and acceptable values. The NRC accepted this finding and its implications in an August 17, 1984 letter to the licensee.
In revisiting
'Q the ALL issue in early 1986, GPUN recognized that the integrity of the
X unmodified hot leg restraints was not in itself an adequate resolution to
's' all the open issues concerning TMI-l generated by BAW-1621. The purpose of this letter is to inform you that GPUN plans to use analyses that demonstrate that the rupturing of PWR primary coolant loop piping at TMI-1 will not occur under design basis conditions without prior detectable Reactor Coolant System (RCS) leakage and, therefore, that the plant need not be modified to accommodate ALL.
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.i i GPUN has contracted with B&W for permission to use proprietary B&W Studies BAW-1847, Rev.1, and BAW-1889P. ThesegenericLeak-Before-Break (LBB) evaluations were endorsed by the NRC in~a letter dated December-12 -1985,'
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.from D. M. Crutchfield (NRC) to L. C..Oakes (B&W Owners Group).
GPUN has
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also contracted with B&W to perform a plant specific analysis.of the TMI-l RCS. The preliminary results of this plant specific analysis indicate that the ten. gallon per minute (10 gpm) leakage flaw' sizes for both the 28-inch and 36-inch straight RCS pipe sections meet or exceed-all three (3) safety factors recommended by NRC NUREG 1061, Volume 3, and used b the-B&W generic. studies. Specifically, the safety factor on applied; y moment exceeds the square root of two (2), the ratio of critical flaw size to the ten (10) gpm flaw size is greater than two (2), and the recomended safety factor for use in the Net Section Collapse. analysis (i.e., that the Eratio of-limit moment to applied moment be equal to three-(3)) is also exceeded. Finally..GPUN has performed an analysis of the RCS leakage detection capability. employed at TMI-1 and has compared it with the
. guidance of Regulatory Guide;1.45. This analysis appears as an attachment to this: letter. GPUN believes that the methodology and approach listed above is consistent with the intent of the revised language of General Design' Criteria (GDC) 4 of 10 CFR 50, Appendix A.
In_ summary, GPUN believes that with the.information provided above and in the attachment to this letter, the NRC has sufficient justification to conclude that TMI-l will not experience the dynamic effects associated with Asymetric LOCA Load and, therefore, does not need to modify the plant to accommodate these loads.
Siicer ly,
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. W lson Vice President.and Director Technical Functions RFW:JCA:jh 2141g-
. Attachments cc:
J. Thoma, USNRC J. Stolz, USNRC T. Murley, USNRC Region I R. Conte, USNRC TMI-l i'
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4 ATTACHMENT
-TMI-1 RCS LEAKAGE DETECTION CAPABILITY Regulatory Guide 1.45 recommends three (3) separate methods for the detection of RCS leakage. The sensitivity and response time of each method should be adequate to detect a leak rate of one (1) gpm in less than one (1) hour.~
TMI-1 utilizes the two (2) methods recommended in R.G. 1.45:. Reactor building sump level monitoring and containment airborne particulate radioactivity monitoring. The third method used at TMI-l is the mass balance method. This method is the principal means of quantifying RCS leakage. The subject of TMI-1 RCS leakage detection has been reviewed by the NRC.
RCS leak rate data has been reviewed by NRC inspectors and checked against the generic NRC code "RCSLK9". The inspectors have concluded that TMI-l leak rate
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determinations were in good agreement with those calculated by the NRC program
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(e.g., reference NRC' Inspection Reports 85-22, 86-17, 86-19).
The three (3) diverse methods, outlined below, provide the means to alert the operator to changing conditions which may indicate increasing RCS leakage. As NRC is aware, we currently are in the process of modifying the Technical Specification Bases to accurately reflect the methods of RCS leakage detection-employed at TMI-1.
Reactor Building (RB) Sump Level is monitored by two (2) safety grade instrument strings.
The readings are monitored by computer which alarms to alert the operators of abnormally high accumulation rates (i.e., greater than one (1) gpm).
In addition, the levels are checked and recorded once per shift. RB sump level provides a measure of leakage into containment provided the RB has not been purged (Losses due to purging could be significant enough
- up to 5 gpm - to invalidate sump results).
Since RB sump receives leakage from all systems inside containment, it is not specific to RCS leakage. Therefore, a greater than one (1).gpm accumulation rate is not necessarily indicative of increased RCS leakage.
However, an accumulation rate less than one (1) gpm does provide confidence that there are no serious defects in the reactor coolant pressure boundary inside containment. Operators are directed to check and record the sump level every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and take confirmatory actions if the accumulation rate indicated by the sump level monitor is greater than one (1) gpm.
Follow up actions include the application of the mass balance to quantify the leakage.
As noted above, the sump level is also monitored by the plant computer. A program is in place which calculates the rate of accumulation in the sump. An accumulation rate equal to or greater than one (1) gpm is printed out in the TMI-l Control Room.
The response time of the sump monitor to a step change in leakage cannot be accurately predicted since leakage from the RCS will flash upon release, and will have to condense elsewhere in the RB and then travel to the sump.
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ATTACHMENT (Continued)
Factors such as temperature, location of leakage, insulation, interfering structures, etc., will affect the time for leakage.to reach the RB sump.
However, a one (1) gpm leak will be detected within one (1) hour of entering the sump.
Containment Radiation Monitor - RM-A2 is a three (3) channel monitor consisting of a particulate channel, an iodine channel, and a gaseous channel. All three (3) channels are continuously monitored and read out in the TMI-1 Control Room.
In addition, all three (3) channels are alarmed to indicate an increase in containment activity.
Procedures require the operators to check and record the RM-A2 indicator readings once per shift.
Indications of increased activity (i.e., greater than 50% above the previous reading) require follow up actions to confirm the readings and, if confirmed, to perform a mass balance calculation to quantify the leakage.
Changes in containment activity should first be detected by the particulate channel, with the iodine and gaseous channels lagging.
Under conditions of no Reactor Building purge and assuming fuel defects of 0.03% and a baseline leak rate of 0.15 gpm, the containment particulate monitor will show a 50% increase in containment activity resulting from a one (1) gpm leakage increase in less than one (1) hour. Thus, the operator will easily note the increase during routine surveillance of the instrument.
Under these conditions, the audible alert setpoint of the particulate monitor would be reached within approximately four (4) hours providing confidence that leakage of this magnitude will be promptly detected.
The iodine and gaseous channels of the radiation monitor are not as responsive to leak rate changes as is the particulate monitor.
This is due to the longer half-life of the iodine and radio-gases being monitored. For this reason, both these channels are used to trend or confirm leakage and not as a means of quantification.
The mass balance calculation is the principal means used at TMI-l for quantitatively determining the RCS leak rate. This method involves observing the change in RCS inventory which occurs over a given time period.
System inventory is determined by observing levels in the make-up tank and pressurizer. Compensation is provided for changes in plant conditions which affect water densities. Unidentified leakage is determined by subtracting identified leakage and RCS losses from gross leakage.
RCS losses are determined by observing the inventory change which occurs in the reactor coolant drain tank.
Primary to secondary leakage is conservatively assumed to be zero.
When the RCS temperature is greater than 525 F, a mass balance calculation is required at least once per day, but is routinely performed once per shift. As noted earlier, both the radiation monitor and reactor building sump monitor can result in the application of the mass balance calculation if conditions warrant.
It should be further noted that one component of the mass balance calculation, the make-up tank level, is continuously monitored. An early indication of RCS leakage would be a decrease in the makeup tank level.
The makeup tank has a volume of 2 30 gallons per inch of level. A one (1) gpm leak would result in a decrease of two (2) inches (60 gallons) in one (1) hour. A change of this magnitude can be read off the strip chart recorder in the TMI-l Control Room.
A downward trend would be noted by the operators and would result in follow up actions to identify and quantify the leakrate through application of the mass balance technique.
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