ML20115B265
| ML20115B265 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 10/05/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20115B261 | List: |
| References | |
| NUDOCS 9210150372 | |
| Download: ML20115B265 (4) | |
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NUCLEAR REGULATORY COMMISSION
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SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMElOMENT NO.137 TO FACILITY OPERATING LICENSE NO. NPF-6 FNTERGY OPERATIONS. INC..
ARKANSAS NUCLEAR ONE. uni, NO. 2 QOCKET NO. 50-368
1.0 INTRODUCTION
By letter dated J:ily 9, 1992, Entergy Operations, Inc. (the licensee) submitted a request for changes to the Arkansas Nuclear One, Unit No. 2 (ANO-2) Technical Specifications (TSs). The requested changes would revise TS Table 2.2-1 Reactor Protective Instrumentation Trip Setpoint Limits and TS Table 3.3-4 Engineered Safety Feature Actuation System (ESFAS) Insi.rumentation 1
Trip Values, to allow for the replacement of the existing narrow range containment building pressure transmitters (pts) of the 0-70 psia range with new pts of the 0-27 psia range.
The Sept. ember 14, 1992, letter provided clarifying information that did not change the initial proposed no signifi
't hazards consideration.
2.0 B.ACKGROUND Containment building pressure at the !E0-2 is monitored using four narrow range pts which send signals to the R w tor Protecticn System (RPS) and ESFAS.
Upon sensing a high pressure in the containment building, the PT loops generate the following trip and actuations:
(1) High containment pressure trip of the RPS, (2) Actuation of the safety injection (SI) function of the ESFAS, (3) Actuation of the containment isolation function of the ESFAS, (4) Actuation of the cor.twnent cooling function of the ESFAS, and (5) Actuation of the containment spray function of the ESFAS.
The existing pts must bi replaced because of their approaching obsolescence, which leads to a lack of spare parts, and because they are approaching the end of their environmentally qualified life. The existing PT: are Rosemount 1153 series A, range code 6 type and have a calibr:ted range of 0-70 psia. The new pts will be Rosemont 1153 series D, range code 5 type and will have a smaller calibrated range of 0-27 psia. The licensee wanted to procure new F?; in tha 921015o372 921005 ADOCK03OOg8 DR
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same calibrated span of 0-70 psia, out due to a large increase in calculated errors of tM new PT loops, the licensee procured the pts with a smaller calibrated span.
In the past, the licensee calculated setpoints for existing PT loops using the methodology accepted at the time.
The past method of calculating setpoints did.not account for all possible.iources of errors and all possible environmental' effects on the setpoint.
The current methodology as prescribed by the Instrument Society of America (ISA) Standard 67.04, 1982 and endorsed by Regulatory Guide (RG) 1.105 Revision 2, " Instrument.Setpoints for Safety-Related Systems," is comprehensive and addresses more possible factors of errors.
Therefore, the present metbadology results in a total loop error larger than ti.e error resulting from the past methodoloay.
The larger span also results in larger Values of instrument errors, because the errors for most of the instruments are specified in proportion to the spans of these inctruments.
The licensee noted that, if the current methodology is applied to new pts having a span of 0-70 psia, which is also the span.of the existing pts, the sum of resulting uncertaintius would be larger than the existing allowable -
margin between the nominal setpoint and th TS limit.
Therefore, to reduce the total of the Pr loop uncertainties, the licensee se'.ected replacement pts of the 0-27 psia span, which is smaller than the 0-70 psia span of the existing pts. However, the sum of calculated loop errors even for the smaller span was slightly larger than the allowable margin between the nominal setpoint and TS limit of the process variable.
Therefore, the licensee needed to reduce the TS setpoints for the above-listed RPS trip and ESFAS actuations, by the difference between the margin and the new error total, so that the analytical limit of the rcntrolled variable could be maintained at its present value.
3.0 EVALUATION The NRC statf reviewed the setpoint calculation for the setpoints for the above-listed RPS trip and ESFAS actuations. The staff reviewed Engineering Calculation 91-EQ-2002-02, Revision G, " Loop Error, Setpoint, and Time Response Analysis for Narrow Range Containment Building Pressure ESFAS and RPS Trip Functions," provided by letter dated September 14,-1992.
The licensee performed this calculation to determine the uncertainties, setpoints, allowable values, and response times of the arrow range pressure loops of containment building pressure at ANO-2. TN licensee calculated the total of uncertainties in the loops for reference, abnormal, and accident conditions.
The statistical method of the square root of the sum of squares (SSRS) was used to determine the sum of random errors in individual components, and in the complete loop. Non random errors were combined algebraically with the sum of random errors tc establish total uncertainty of the PT loop. The licensee used a carrently accepted methodology for this calculation.
The staff found this practice accep!.able.
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The staff also reviewed the licensee's explanation (provided during telephone conversations and as documented in the September 14, 1992, letter) for the foilowing conditions in Section 3.0, " Assumptions and Given Conditions" of Engineering Calculation 91-EQ-2002-02:
(a) Accuracy of the measursment and test equipment (M&TE) used for e
calibration and testing devices of instrument loop was assumed to be twice as oood as the accuracy of the device or the loop being tested.
(b) Seismic and post seismic errors were not considered with any design basis events.
(c) The drift value for the signal converter device was assumed to be equal to the instrument's reference accuracy without specifying any time interval.
For item (a) above the licensee explained that it has implemented plant procedures that provide guidance for test technicians to verify the accuracy requirements of M&TE before starting any calibration or test activity.
The licensee stated that their technicians are adequately trained and plant procedures are implemented rigorously. The staff found this explanation acceptable.
For item (b), the licensee has implemented comprehensive procedures at the plant to assess the effects of seismic activity immediately after it occurs. The licensee stated that the plant operators are trained for these procedures. The staff found this explanation acceptable.
For item (c),
the licensee informed the staff that it had previously not been able to obtain values of instrument drift from the instrument vender.
Therefore, the licensee evaluated historical data from the past calibrations of these instruments.
Intervals of past calibrations were varied from 16 to 24 months.
The licensee found that the worst case difference noted between the as-found and as-lef t setpoints was nearly equal to the reference accuracy of the instrument.
Based oi an evalration of the historical calibration data, the licensee made an engiaeering judgement that assumed the drift value of the instrument would be equal to its reference accuracy.
The staff believes that taking the difference between the as-found and the as-left settings equal to drift is reasonable and conservative, although reason for such difference may s
not be just the drift, but rather a combinatica of drift added with changes in instrument characteristics due to environmental ef fects during interv'!s between successive calibrations.
The staff found the licer.see's expianation acceptable.
4.0
SUMMARY
Based upon our review as presented above, the NRC staff finds the licensee's proposed TS amendment acceptable.
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5.0 STATE LONSULTATION In accordance with the Commission's regulations, the Arkansas State official was notified of the proposed issuance lof the amendment. The State official had no commer.ts.
6.0 EUyIRONMENTAL CONSIDERATION The amendment changes a requirement with respect to installation or use of a facility component lochted within the restricted area as defined in 10 CFR Part 20.
The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (57 FR 34581). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR Sl.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment eaed be prepared in connection with the issuance of the amendment.
7.0 LONCLUS109 The Commissien has concluded, based on the considerations discussed above, that:
(1) there is reeronable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in ccmpliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common oefense aad security or to the health and safety of the public.
Principt.1 Cont,;butor:
S. Athavale, SICB Date' October 5, 1992 r
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