ML20006F442
| ML20006F442 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 02/16/1990 |
| From: | Cockfield D PORTLAND GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20006F290 | List: |
| References | |
| NUDOCS 9002280034 | |
| Download: ML20006F442 (8) | |
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1 PORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND l
PACIFIC POWER & LIGHT COMPANY Opetating License NPF-1 Docket 50-344 I* cense Change Application 193 This License Change App 12.ation requests modifications to Operating License NPF-1 for the Trojan Nuclear Plant to modify the actions and surveillance requirement for Trojan Technical Specification 3/4.2.4,
- ' Quadrant Power Tilt Ratio".
PORTLAND GENERAL ELECTRIC COMPANY By ~
D. W. Cockfi' eld
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Vice President, Nuclear Division 1
Subscribed and sworn to before me this 16th day of February 1990.
Notary Public of Oregon 8
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9002280034 900216 PDR ADOCK 05000344 P
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e UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION ~
In the Matter of
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PORTLAND GENERAL ELECTRIC COMPANY,
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Docket 50-344 THE CITY OF EUGENE, OREGON, AND
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Operating License NPF-1 PACIFIC POWER & LIGHT COMPANY.
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-i (TROJAN NUCLEAR PLANT)
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CERTIFICATE OF SERVICE I hereby certify that copies of License Change Application 193 to the Operating License for Trojan Nuclear Plant, dated February 16, 1990, have been served on the following by hand delivery or by deposit in the United States mail, first' class, this 16th day of February 1990:
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State of Oregon
. Department of Energy 625 Marion St NE Salem OR 97310 Mr. Michael J. Sykes Chairman of County Commissioners Columbia County Courthouse St. Helens OR 97051-.
Ma. A S. A. Bauer, Manager Muclear Regulation Branch Nuclear Safety & Regulation Subscribed and sworn to before me this 16th day of February 1990.
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LCA 193 U
Attachment A Page 1 of 6 Description of changes Four changes are proposed for Trojan Technical Specification (TTS) 3/4.2.4,
" Quadrant Power Tilt Ratio (QPTR)".
These changes are consistent with the guidance of NUREG-0452, Rev.
4,." Standard Technical Specifications for Westinghouse Pressurized Water Reactors".
The first ' change modifies the actions in.each instance the QPTR excoeds 1.02 to require the calculation cf the QPTR at least once per hour until either tho'QPTR is reduced to within its limit, or thermal power is reduced to'less than 50 percent of rated thermal power..
The second change-requires that when the QPTR is between 1.02 and 1.09, or in excess of 1.09 due to rod misalignment, thermal power be reduced at least 3 percent from rated thermal power.
.The third change requires, for subsequent power operations abovo 50 per-cent, the QPTR be verified within its limits at least once per hour for 12 houry,.
The fourth change revises the surveillance requirement regarding operation above 75 percent rated thermal power when one power range channel is inoperable to require the movable incore detectors be used to confirm the normalized symmetric power. distribution obtained from the four pairs of symmetric thimble locations is consistent with the indicated OFTR.
One' change is made to the bases for TTS 3/4.2.4 by' adding a sentence allowing the Nuclear Instrumentation System (NIS) alarm setpoints to be set at 1.03 since historical data has shown that the true tilt ratio will be less than 1.02.
Reason for Changes The proposed changes to the TTS will:
1.
Provide clarification that surveillance requirements on QPTR are not required to be met at or below 50 percent of full power. -This clarification also responds to a concern raised during an audit by NRC staff (see Inspection Repcrt 50-344/87-37, open Item 87-37-01).
l 2.
provide improved Plant performance by requiring power reduction from f
rated power (3,411 MWt) as opposed to the power level-at which the Plant is operating, since power reduction from rated power is the goal of the action statement.
3.
Provide a-defined time period, 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, during which the QPTR is verified to be within its limit as opposed to the present open-ended requirement.
This change will ensure a minimum of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of surveillance.
fj-LCA 193 -
l Attachment A l
Page 2 of 6 i
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Provide a more timely evaluation of an indicated QPTR by permitting l
-core mapping using four pairs of symmetric thimble locations. This-b
.will reduce the time required to conduct a surveillance an'd reduce the data.
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The change to the bases to allow a 1.03 alarm setpoint is made to avoid intermittent spurious alarms of a 2 percent core power tilt when there li are none. The spurious alarm is suspected to be caused by the combined L
effect of small (<1/2 percent) core power tilts and nominal operating excore signal variations which, when compared with the reduced excore 7
channel signals present in a low-leakage loading pattern, results in'the p
tilt alarm. The cycle beginning-of-life channel currents have decreased-by about 25 percent (500pa to 330pa).
Consequently, a smaller excore L
detector current change can produce the indication of a 2 percent core tilt.
Incore detector core-flux maps, which are our most accurate l
measurement technique, have shown a true core quadrant power tilt of H
typically less than 1/2 percent when the NIS comparator circuit was showing nearly 2 percent tilt. The root NIS calibration is performed in Periodic Engineering Test (PET)-2, "Incore/Excore Calibration", at the start of the reload cycle.
1
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Factors considered in changing the alarm setpoint are the following:
1.
TTS 3.2.4 sets the QPTR limit at 1.02.
Although TTS 1.18 defines QPTR in terms.of "excore detector calibrated output" it is clear from the bases to TTS 3/4.2.4 that the QPTR limits are intended to H
assure the reactor core power distributions and hot channel factors are maintained. The. bases statement that the limit of 1.02 was selected to. provide an allowance for the uncertainty associated with
'I il the_ indicated power tilt may provide for handling.the uncertainty associated with the concept of monitoring incore conditions from an excore vantage, but it does not allow for NIS hardware equipment limitations when operating with reduced core fast neutron radial ~
leakage, such as we now have.
2; Westinghouse's " Precautions, Limitations, an6 Setpoints" (PLS)
Nuclear Power Range Channel deviation alarms show the use of a-i2 percent of full-power setpoint with a Note (3) qualifier.
Note (3) says that the alarm setpoints are expected to be adjusted during startup and subsequent operation such that they are just beyond the range of normal operating variation'.
Our alarm setpoint, primarily on one channel (N42 lower), is often on the borderline of f;
normal operation, especially early in the reload cycle when NIS currents are lowest.
Trojan uses a low-leakage loading pattern.
3.
Westinghouse letter (83PO*-G-028, July 11, 1983) to PGE discussing startup quadrant tilt problems points out in Attachment 1 under quadrant power tilt definition that the purpose of the 1.02 limit is to detect gross changes in core power distribution.
The Trojan Plant does not have the gross core power change, but nevertheless has the "inntrumentation tilt" due to limitations of the equipment itself.
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LCA 193' Attachment A g
Page 3 of 6:
l 4
t 4.. The Westinghouse Control and Protection manual has a QPIR calibration procedure that contains the use of a table that correlates comparator Evoltages with equivalent power tilt percentages. The Plant now cali-;
brates the comparator in accordance with the Westinghouse procedure using the-2 percent trip voltages. A variable resistor is provided in the circuits to allow setting the trip and reset to various values.
Significant Hazards Determination In accordance with the requirements of Part 50.92 of Title 10 of the Code of Federal Regulations (10 CFR 50.92), this license change is judged to-involve no significant hazards based upon the following considerations:
- 1.. Does the change involve a significant increase in the probability or consequences of an accident previously evaluated?
The purpose of the QPTR Technical Specification is to assure that core power tilts will be detected, monitored, and appropriate corrective action taken to ensure that the fuel is operating within acceptable limits.- The proposed changes to the Technical-Specification do not affect the limits at which action must be taken.
The change that the allowance of. quadrant tilt ratios for a given-power level be based on rated thermal power rather than the initial
. power level is consistent with the recognition that the core power distribution limits (Fq and FAH) are normalized for 100 percent power operation. Operation at lower power levels allows greater power variation, provided it'is within the full power limits.
A tilt observed at a lower power level may be bounded by the-full power limits, and thus, no power reduction is required. As long as the
. peak assembly is within allowable limits, there is no increase in the l
probability or consequences of previously evaluated accidents.
The change in this part of the Technical Specification eases an overly
' restrictive condition and does not increase the probability or L
consequences of'a previously evaluated accident.
The change to monitor the quadrant tilt for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is a more stringent requirement that will not increase the probability or-consequences of a previously evaluated accident, l
The change to the subsequent actions, namely that a full-core flux p?
map is not needed when a power range channel is inoperable, is reasonable, since the existence of a quadrant tilt is best evaluated by symmetric comparison of in-core flux measurements. A full core
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map only offers some improvement over specific measurements of the affected quadrant (s) because many full-core positions are either not symmetrical, or not in the affected quadrant, and thus do not contri-l bute to the determination of a flux tilt' An advantage of using
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LCA 193.
Attachment A j.
Page 4 of 6' eight symmetrical in-core measurements is that the quadrant tilt may be measured more quickly than from a full. core measurement. Because-a quadrant tilt is a perturbation that varies with time, the advan-tage of a prompt determination when one channel is out of service outweighs the increase in information provided by a full-core map.
It is concluded that this change does not significantly increase the probability or consequences of previously evaluated accidents.
j The change to the bases to allow adjustments to the alarm setpoint does not affect the requirements to take action upon exceeding a true power-tilt of 1.02 because the true core power tilting is substan-tially smaller for the given excore tilt. Adjustment of the alarm setpoints to just beyond the range of normal operating variations avoids spurious false alarms.
Thus, this change does not increase the probability or consequences of a previously evaluated accident.
2.
Does the change create _the possibility of a new or different kind of accident from any accident previously evaluated?
The types of accidents related to a quadrant tilt are power distri-bution events which may result from misloaded assemblies, dropped control rods, and reactivity anomalies. Misloaded' assemblies and dropped control rods are already examined in the Final Safety
. Analysis Report (FSAR) and new or different types of these events could not be created by the proposed. changes to the QPTR Technical Specification. The ability to detect adverse power distribution conditions is unchanged because the measurement instruments and L
operating limits are the same.
L Thus, the changes to the surveillance' requirements, the corrective L
actions, and the bases do not create the possibility of new or L
different accidents because they do not alter the underlying causes f
of a tilt nor significantly change the corrective actions to respond L
to a tilt.
L 3.
Is the margin of safety as defined in the basis for any Technical l
Specification reduced?
+
The basis for TTS 3/A.2.4 describes the reason for the Technical Specification and the allowance for instrument uncertainty and time to take corrective action or reduce power.
The changes made to this Technical Specification are in the areas of:
(1) surveillance time; l
.(2) alternate testing methods (eight in-core measurements vs full core); (3) the required power reduction for tilts; and (4) clarification of indicated versus actual quadrant power tilt alarm setpoints. The affect that these changes have on the margin of safety are in:
(1) instrument accuracy due to the alternate measurement with eight in-core measurements vs a full core; and (2) the power reduction for tilts in oxcess of two percent but less than nine percent. The change to the bases to clarify that the f.
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.3 O.S LCA 193.
Attachment A-R Page 5 of.6 alarm setpoints may be adjusted to 1.03 is not a change in the margin of' safety because the margin of safety is based on actual power, not
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' indicated valur..?
From historical data, we have shown that actual QPTR values are around 1.005 when spurious alarms are being received ton the excore detectors at 1.02.
The power reduction of three percent for each one percent of core-tilt (when tilt is between 1.02 and 1.09) is stated to provide
-adequate margin for the overall power peaking limit Fq.-
The Fq limit is based on full power operation, and this limiting'Fq should be allowed to increase as power is reduced because the Fq limit ~is based on power generation in order to limit fission gas release, initial fuel temperature, and clad mechanical properties that are l
input into the Loss of Coolant Accident (LOCA) analysis. The change l
continues to provide this margin by requiring power reductions from i
rated thermal power (100 percent) rather than from what has been interpreted as the initial thermal power at the time of the tilt alarm. 'The Fq limit is based on LOCA analyses that are performed j
at-(or in excess of)'102 percent of rated thermal p;wer. The margin of this Technical Specification is the reduction of power three per-cent for each one percent of tilt, and not-that an initial power level is significant.
Thus, the margin as defined in the Technical
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Specification bases is not reduced by this change.
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The overall, accuracy of in-core measurements is considered better
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than the excore detectors that are providing the quadrant tilt
-l alarm.
Given that symmetric detectors in the affected quadrant are most useful in confirming a tilt (the non-symmetric locations with inferred power help support the symmetric measurements) the reduction in measurement locations is not significant.
Given that a tilt may
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be a transient occurrence, the additional speed of symmetric thimble mapping in determining a tilt is preferable over tilts from a full i
core map. Adjustment of the alarm setpoints to reflect a-true power tilt in' excess of 1.02 ensures corrective actions and surveillance requirements are taken when warranted by the actual conditions. 'The 4
-margin-of safety as defined in the Technical Specifications is j
retained.
1 In the March 6, 1986 Federal Register, the NRC published a list of examples of amendments that are not likely to involve a significant j
hazards consideration.
Example (vii) from this list states:
"A change to conform a license to changes in the regulations, where the license change results in very minor changes to facility operations clearly in keeping with the regulations."
The proposed changes are similar to the above example in that they conform with guidance provided in NUREG 0452, Rev. 4.
y.
t LCA 193 Attachment A Page 6 of 6 Safety / Environmental Evaluation Safety and environmental evaluations were performed as required by i
10 CFR 50 and the TTS.
The review determined that the proposed changes do not create an unreviewed safety question, nor do they create an unreviewed environmental question.
Implementation Consideration-It is requested that the effective date of the amendment be thirty days after issuance by the NRC.
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