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g UNITED STATES NUCLEAR REGULATORY COMMISSION 5
I WASHINGTON, D.C. 20666 4 001
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EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FOR OPERABILITY ASSESSMENT OF INTERMEDIATE RANGE NEUTRON MONITORING INSTRUMENT ROC 9 ESTER GAS AND ELECTRIC CORPORATION R. E. GfNNA NUCLEAR POWER PLANT l
i 1.0 fACKGROUND On August 20,1996 the R. E. Ginna Nuclear Powar D! ant rear M' automatically tripped on low stearn generator level following closure of a feedwiter regulating valve due to a failure of a feedwater flow transmitter. Following the reactor trip, when the reactor power was decreasing, the intermediate range neutron monitoring (IRM) instruments N35 and N36 did not automatically energize the source range neutron monitoring (SRM) instruments as expected. The control room operators manually energized the SRM instrumentation channels.
The licensee determinew : hat IRM instrument N36 was undercompensated for proper detector voltage, allowing additional gamma radiation to be indicated, thereby preventing the N36 channel from reaching the setpoint for the P6-Permissive (SE-11 amps) until 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the trip. The N35 chsnnel reached the P6 setpoint in an expected duration ATTACHMENT l
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. after the trip, but since two-out-of two P6 permissives are required to energize the SRMs, the SRMs were not energized on decreasing reactor power. During the shutdown that followed, the licensee did not recalibrates the IRMs for voltage compensation, but instead postponed recalibration to a later date and performed a reactor startep. The licensee considered the IRMs operable because even with the undercompensated detector, the effects of gamma radiation on the high-level-trip setpoint (25% reactor power) is insignificant. In addition, since the SRMs were manually energized, the SRM's high-flux trip was also operable.
NRC inspectors performing an event followup reviewed the improved Technical Specifications (TS) for Ginna operability basis for the SRMs' high neutron flux trip function and the IRM permissive (P6) which energizes the SRM channels automatically on decreasing reactor power. The inspectors determined that TS Section 3.3.1 requires the SRM high flux trip to be operable with the plant in hot shutdown, during a reactor startup, and while at power. The safety basis for this was stated to be for protection against an inadvertent criticality (restart a.cident) or a rod ejection accident and to provide for an recurate neutron count rate when shutdown. Further, the inspector determined that permissive P-6 is required to be operable during a plant startup, and at power. As noted, the TS Bases (page B 3.3 32) for the P6 permissive states that the LCO requirement for the permissive ensures that the following function is performed: "... on decreasing power, the P-6 interlock automatically energizes the source range detectors and enables the
3-source renoa neutron flux reactor trip at SE-11 amps." It was not apparent to the inspectors that the TS requirement were adequately satisfied prior to the reactor startup.
In order to determine the licensee's compliance with the TS, the Region I staff requested assistance from NRR in evaluating operability of the Ginna IRM N35 and N36 channels.
2.0 PRINCIPLE OF OPERATION Neutron flux in a reactor-core is indicative of reactor power. The IRM system monitors neutron flux and generates signals for permissive-interlocks, alarms, control rod withdrawal inhibits, and reactor trips. It also indicates the rate of change of neutron flux during plant startup and shutdown periods. There are two IRM channels gnd the logic generating the signal for the P-6 permissive is based on a two-out-of two initiation configuration. Detectors for each IRM instrument contain two chambers, an outer chamber which generates a output current proportional to the total of neutron flux and gamma ray strength, and an inner chamber which generates an output current proportional only to gamma ray strength. At lower reactor power, the neutron population is low compared to gamma ray strength, but as the reactor power increases, the neutron population increases and at approximately a reactor power level equal to or above the setpoint of the IRM high neutron flux trip, gamma ray strength becomes insignificant compared to neutron population. Therefore, during low reactor power, to obtain an iRM output signal proportional only to neutron flux, the detector is compensated for gamma rays by subtracting the output current of the innerchamber from the output current of the L
outerchamber, thus nullifying the effects of gamma rays for the IRM output signal. The i
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. voltage source which drives this compensating current through the innerchamber is caXad the compensating voltage if the compensating voltage falls below its normal required value, the detector is undercompensated and the gamma ray component of the signal will not be nullified. Output current from the undercompensated instrument will not represent the wctual neutron flux, but will be the sum of currents due to neutron flux and gamma rays. Therefore, an undercompensated instrument will indicate a higher core power than is actually present.
3.0 EVALUATION The staff reviewed 1) the effects of undercompensated IRM instruments on plant k
operations (startup, power ascension and shutdown), 2) whether an undercompensated IRM instrument can be considered " OPERABLE" to satisfy the TS requirements for the SRM and IRM channels at Ginna, and 3) whether the licensee met TS requirements during the August 20,1996 event.
As stated above, at low power, an undercompencated IRM instrument will indicate a higher than actual reactor power. The deviation of the indicated power from its actual value will be in direct proportion to the degree of undercompensation. Since in the low power range the undercompensated IRM channel will always indicate higher than tim actual rsector power, the P-6 permissive channel will de-energize the SRM channels early
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during reactor power ascension, and will energize the SRM system late or not at all during reactor power descension. De-energizing the SRM channels early curing reactor power ascension or energizing the SRM channels late riuring decreasing reactor power, will cause the SRM high flux trip to be unavailable for a period of time.
IRM channel undercompensation has the following impact on plant operations. During pows descension, for the case with only one of the two IRM channels undercompensated, loss of the P-6 function of the undercompensated channel should normally be observed by I
t'ne operator (by comparing indications from the undercompensated instrument with that from the compensated instrument). Ths operator can then manually energize the SRM channels upon noting the IRM channel deviation and thereby make the SRM channel indication and SRM high-flux-trip available. During power ascension, although the bistable I
of the undercompensated P-6 permissive channel will trip early, the SRM channels will not
-i be de-energized until the bistable of the other (normal compensated) P-6 channel trips.
This is because the trip logic requires two-out of two P-6 channels to trip in order to de-energize the SRM channels automatically. Therefore, in this situation, under compenntion in one IRM channel will have no effect on the SRM doenergizing function of the P-6 interlock. Since the setpoint of the IRM channel high flux trip is not s, significantly affected by gamma rays, this trip will be availab!s and will meet the requirements of the TS.
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. 4.0 TS COMPLIANCE
- 1. The Ginna TS LCO requires two channels of the SRM high flux trip function to be
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" OPERABLE" during. reactor startup. In mode 2, when both IRM channels are < 5E-11 amps (below the P 6 setpoint), the SRM neutron hign flux trip function must be OPERABLE.
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During the August 20,1996 event at Ginna, because the operator manually energized l
l the SRM channels within the TS allowed time, the SRM neutron flux trip function was OPERABLE and available. The SRM channels were operable during shutdown and also during startup. Therefore, the above TS requirement was met.
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- 2. The TS LCO requires two channels of IRM neutron flux, P-6 permissive to be l
l OPERABLE in Mode 2 below the P-6 permissive setpoint. The TS basis (page B 3.3-32) for the P-6 permissive states that the LCO requirement for the permissive ensures that the following 'anction is performed: ".. on decreasing power, the P6 interlock automatically energizes the source range detectors and enables the cource range neutron flux reactor trip at SE-11 amps."
TC Section B 3.3.1, Page B 3.3-49, Actions S.1 and S.2 states, " condition S spplies to
'he P-6, P-7, P 8, P-9 and P-10 permissives. With one channel inoperable, the associated interlock must be verified to be in its required state for the existing plant j
condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or the associated RTS channel (s) must be declared inoperable.
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f These actions are conservative for the case where power levelis being raised.
Verifying the interlock status manually accomplishes the interlock's function. The completion time of ? hour is based on operating experience and the minimum amount of time allowed for manual operator actions."
During the August 20,1996 event at the Ginna plant, when one of the two P-6 I
permissives did not trip (due to the undercompensated detector) and the channel was inoperable, plant operators, consistent with the TS Action statement, energized the SRMs manually within 15 minutes of the reactor trip. Since manual verification of the interlock status is required manually energizing the SRM channels within the TS allowed time met the TS requirements for the P-6 permissive interlock.
- 3. The licensee restarted the plant without calibrating the undercompensated IRM neutron detector.
As ciscussed above, although the P 6 permissive of the undercompensated IRM instrument was degraded to the point of being inoperable, the IRM channels are operable, becausa the undercompensated IRM did not have significant effect on the IRM channel high-flux-trip setpoint. During power ascension, the undercompensated 1
instrument has a potential to generate the high flux-trip and rod withdrawal block signals ear!y. However, such an action is conasrvative and does not violate the plant
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-B-licensing basis, in addition, during startup, since the SRM channels were manually energized, the SRM range high flux trip was operable. The staff finds that although it was not desirable to restart the plant without recalibrating the undercompensated IRM instrument, the effect of such an action on plant safety was not significant.
LCO 3.0.4 states, "When an LCO is not met, entry into a MODE or other specified l
i condition in the Applicability shall not be made except when the associated ACTIONS l
to be entered permit continued operation in the MODE or other specified condition in i
the Applicability for en unlimited period of time. This Specification shall not prevent i
changes in MODES or other specified con fitions in the Applicability that are required to l
l comply with ACTIONS. Exceptions to this Specification are stated in the individual I
i Specifications."
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As per the above statement of LCO 3.0.4, the licensee did not violate the TS i
requirement by res' tarting the plant without calibrating the undercompensated IRM channel because, compliance with Required Actions (Actions S.1 and S.2, operable IRM high flux trip) permits continued operation of the plant for an unlimited period of j
time in a MODE or other specified condition and provides an acceptable level of safety for continued operation. The allowance for continued operation is without regard to the status of the plant before or after the MODE change, and therefore,in such cases, entry into a MODE ci other specified condition may be made in accordance with the I
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provisions of the Required Actions. Nevertheless, the staff believes that the licensee should exercise the good practice of restoring systems or components to fully operable status before entering a mode or other condition in which their operation is needed even if TS OPERABILITY is not specif!,d.
- 4. TS SR 3.3.1.8 requires a " Channel Operational Test" to be performed once every 92 days. Note 1. to this surveillance requirement states, "1. Not required for power range end intermediate range instrumentation until 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after reducing power < 6%
RTP." From this note it is obvious that the licensee was required to perform a channel operational test 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after the power level reached < 6% RTP. During the plant shutdown if the licensee performed this test, the test would have detected that the P-6' permissive was not operable, if ths !!censee did not conduct this test, then they are in violation of the TS
5.0 CONCLUSION
Based upon our review, the staff concludas thst the undercompensated IRM channel P-6 permissive interlock exhibited degraded performance but appropriate TS required actions were met. The staff believes that although restarting the plant without calibrating the undercompensated channel was riot a desirable action, the effect of the undereompensated IRM channel on the plant's safety was not significant and did not violate the planta licensing basis. The staff concludes that the licensee did not violate the l
l requirements of the TS unless the requirements of SR 3.3.1.8 were not met.
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September-16, 1997
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MEMORANDUM TO: Jon R. Johnson, Director Division of Reactor Projects Region 11 FROM:
Herbert N. Berkow, Director Project Directorate 11-2 Division of Reactor Projects - 1 Office of Nuclear Reactor Re lati
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SUBJECT:
TIA 97 07, VOGTLE REACTOR 'mlP SYSTEM AND ENGINEERED SAFETY FEATURES ACTUATION SYSTEM INSTRUMENTATION i
TRIP SETPOINTS -VOGTLE ELECTRIC GENERATING PLANT, l
UNITS 1 AND 2 (TAC NOS. M98528 AND M98529)
By memorandum dated March 28,1997, Region 11 requested NRR's position on Southem Nuclear Operating Company's (the licensee's) practice of establishing procedures for reactor trip system (RTS) and engineered safety features actuation system (ESFAG) instrument setpoints to be nominal values with tolerances beyond technical specification (TS) maximum and minimum
- allowed values." The concem resulted from an inspection conducted as a follow-up to an issue at Watts Bar and Sequoyah, which have similar RTS and ESFAS TS. The staff finds the licensee's practice acceptable because they have established intemal procedures to limit the resetting of trip setpoints consistent with the TS inequality value. However, at Vogtle and some other Westinghouse plants, discrepan:,ies between the TS Bases and the approved setpoint methodology have been identified and are being evaluated by NRR.for possible corrective actions. (For Vogtle, the approved setpoint methodology is specifed in Westinghouse Setpoint Methodology for Protection Systems, WCAP-11269.) A discussion of the staffs vows on this issue follows.
The TIA request noted that the licensee's procedures contain setpoint tolerance bands specifying setpoint ranges that the Region interprets as being able to result in the licensee setting setpoints outsioe the specifed TS limit. However, the inspection also showed that in no cose has the licensee taken advantage of procedure tolerances and set instrument trip setpoints beyond the TS ' allowed value." Further, the Repton stated that the licensee maintains that the TS Bases dorcument provides guidance that a measured setpoint, which does not exceed the 'allowsJ value,' is considered operable.
in response to 15e TIA, the staff reviewed Vogtle's RTS and ESFAS TS, TS Bases, and setpoint methodology documents. The Vogtle TS Bases state the following:
The Trip Setpoints are the nominal values at which the bistables are set. Any bistable l
i is considered to be property adjusted when the "as left" value is within the band for CHANNEL CALIBRATION accuracy. [ Emphasis added.)
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Based on the above TS Bases statement and our review of the associated licensing documents, the staff finds that the setpoint methodology and the TS Bases both agree that the TS trip setpoint is a nominal value. However, the staff notes Vogtle's RTS and ESFAS TS limits,.which are presented in the accompanying limiting conditions for operation (LCOs) as
" Trip Setpoint' and ' Allowable Value' table entries, specify trip setpoint minimum or maximum values (inequalities) for each function, rather than trip setpoint D9m1031 values. The Vogtle TS Bases also state the following about nominal trip setpoints:
The Trip Setpoints used in the bistables are based on the analytical limits stated in Reference 1. The selection of these Trip setpoints is such that adequate protection is provided when all sensor and processing time delays are taken into account. To allow for calibration tolerances, instrument uncertainties...the Trip Setpoints and Allowable Values specified in Table 3.3.1 1 in the accompanying LCO are conserva'imly adjusted with respect to the analytical limits.... The actual nominal Trip Setpoint entered into the bistable is more conservative than that specified by the Allouble Value to account for changes in random measurement errors detectable by a COT [ Channel Operational Test). (Brackets added.)
The requirements of 10 CFR 50.36(a) state that specifications require summary statements of the Bases or reasons for specifications, other than those covering administrative controls, but
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do not become part of the technical specifications. Thus, the Vogtle TS trip setpoint inequalities specified for RTS and ESFAS functions are TS limits, which cannot be aftered by the Bases discussion. For this reason, the staff interprets the Vogtle TS trip setpoints to represent the most limiting setting that is allowed for the trip setpoint.
Furthermore, from the Bases noted above, it is apparent that specifying Vogtle TS trip setpoints as inequalities represents a departure from the approved wtpoint methodology. In order to satisfy the TS setpoint inequality requirement, the licensee's practice has been to routinely set the trip setpoint value conservatively to the TS trip setpoint value inequality. The staff finds th acceptable provided the licensee's setting is bounded by the setpoint methodology calibratio tolerance and procedures (in the appropriate direction and magnitude). Therefore, it is the staffs position that TS compliance can be met by establishing appropriate controls to limit the resetting of the trip setpoint consistent with the TS inequality value.
The staff also compared Vogtle TS Bases, R TS, and ESFAS setpoint and allowable value TS limits to the setpoint methodology in response to the Region statement that the liconets maintains that the TS Bases document provides guidance that a measured setpoint that does not exceed the ' allowed value' is considered operable. The Vogtle TS Bases state the following:
Sa' points in accordance with the Allowable Value ensure that SLs are not violated during ADOr (and that L5e consequenas of DBAs will be acceptable, providing the unit is oportsd from within the LCOs at the onset of the ADO or DBA and the equipment functions as designed). Note that in the accompanying LCO 3.3.1, the Trip Setpe.ats of Table 3.1.1-1 are the LSSS.
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The staff concludes that the licensee's position is supported by the licensed setpoint methodology. However, the assignment of the Limiting Safety System Setting (LSSS) as the nominal trip setpoint in the Vogtle TS is inconsistent with the setpoint methodology for Vogtle (WCAP-11269), which recognizes the Allowable Value as the ! SSS. The Vogtle setpoint 1
methodo!ogy considers the trip setpoint value to be the " nominal safety system setting," which I
is considered the desired trip setpoint for the variable. By classifying the trip setpoint as the LSSS in the TS Bases, the trip setpoint, with inequality, becomes a defined operability limit pursuant to 10 CFR 50.36 (which requires incorporation of the LSSS in the TS). Because the trip setpoint is listed as the LSSS and is further defined by an inequality, exceeding the inequality by the calibration tolerance or finding the nominal trip setpoint greater than the Vople TS inequality resuits in TS noncomplianos and puts the licensee into the appiW.ete LCO remedial action. The first condition can occur when the nominal trip setpoint as-left value is set greater than the nominal trip setpoint inequality value but within the nominal trip setpoint calibration tolerance. In this case, the instrument setpoint is set within the assumption of the i
setpoint methodology (as-left) and is conservative to the Allowable Value, but the instrument could still be declared inoperable, in this regard, it is the stars position that the Vogtle TS Bases are inconsistent with the licensing basis topical report setpoint methodology for LSSS and the licensee should undertake an action to reconcile the Vogtle TS Bases with the epproved setpoint methodology.
In conclusion, the staff finds the licensee's practice acceptable provided the setting is bounded by the setpoint methodology calibration tolerance and procedures (in the appropriate direction and magnituds). It is the staffs position that TS compliance can be met by establishing appropriate controls to limit the resetting of the trip setpoint consistent with the TS inequality value, as the Vogtle licensee is currently doing.
Docket Nos. 50424 and 50-425 cc: C. W. Hehl, RI G. E. Grant, Rill T. P. Gwynn, RIV K. Perkins, RIV, WCFO 4
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