ML20045D084
| ML20045D084 | |
| Person / Time | |
|---|---|
| Issue date: | 10/12/1992 |
| From: | Catton I, Wilkins J Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2849, NUDOCS 9306250312 | |
| Download: ML20045D084 (40) | |
Text
a CERTIFIFD BY:
DATE ISSUED: 10/1/92
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m J..E. Wilkins - 10/12/92 I, Catton - 10/11/92 k[$'cM
[88 [h/!f'8 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS JOINT T/H PHENOMENA / CORE PERFORMANCE SUBCOMMITTEE MEETING MINUTES:
BWR CORE POWER STABILITY SEPTEMBER 17, 1992 BETHESDA, MARYLAND PURPOSE:
l The purpose of the meeting was for the Joint Subcommittee to continue its review of the issues pertaining to boiling water reactor (BWR) core power stability.
l ATTENDEES:
l l
Principal meeting attendees included:
l l
ACRS HEC I.
Catton, Co-Chairman L.
Phillips, NRR E. Wilkins, Co-Chairman J.
March-Leuba, ORNL T.
Kress, Member W.
Lindblad, Member GE D. Ward, Member H. Pfefferlin C.
Wylie, Member K. Garrett l
P.
Davis, Consultant M. Anderson l
"V.J." Dhir, Consultant l
W.
Kerr, Consultant Commonwealth Edison J.
Lee, Consultant T.
Raush W.
Lipinski, Consultant MEETING HIGHLIGHTS. AGREEMENTS. AND REOUESTS:
The meeting convened at 8:30 am, pursuant to Notice in the Federal Register.
Chairman's Onenina Remarks Dr. Catton noted the following points:
- In June,1989, the Committee initially reviewed the issue of BWR core power instability.
At that time, the BWR Owners Group (OG) instituted a set of (short-term) instructions to the BWR licensees to avoid operation in the portion of the power / flow map (exclusion region) known to be prone to instabilities.
The Committee opined that instability given i
operation of the RPS was not a significant risk.
Instability combined with an ATWS was thought to be risk significant.
l e At the April, 1990 Subcommittee meeting on this matter, the BWROG detailed three potential fixes for the case of insta-bilities with scram, termed long-term solution options.
The Subcommittee found these fixes acceptable and so reported to l
the Committee.
Resolution of the issue of ATWS with instabilities was confirmed as a
problem that needed attention.
DESIGNATED ORIGINAL x U(
9306250312 921012 N
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Joint Sub. Mtg. Minutes 2
September 17, 1992 e The current long-term solution options for the case of instabilities with scram available appear acceptable.
e For the case of ATWS with instabilities, the code calculations have significant uncertainties.
Even so, some fuel damage is predicted by the GE code (TRACG).
In this context, the Subcommittee needs to advise as to whether the bases of the ATWS Rule should be revisited, in light of the above analysis results.
Noting that the NRC staff conducted an audit of the capability of TRACG to model ATWS-related instabilities, the Subcommittee should also consider whether it should review TRACG as well.
The comments of the staff relative to both its audit of TRACG and its review of the GE ATWS/ instability Topical Report are disturbing.
The Subcommittee should consider the following questions:
e
- Is the long-term solutions program acceptable?
- Is the NRC staff approach to the issue of ATWS w/ oscillations reasonable?
- Should the ATWS Rule be revisited?
- What should we say about the GE TRACG code?
- What should NRC do about the capability of its own calculational tools?
BWROG Presentation Mr.
T.
Raush (Commonwealth Edison) spoke on behalf of the BWROG.
He updated the Subcommittee on the status of both the long-term solutions (LTS) program and the ATWS/ instability issue.
Referring to the above remarks by Dr. Catton, Mr. Raush noted that the OG has not seen the NRC staf f's (draft) reports dealing with resolution of the above two issues.
Regarding the LTS program, there are currently three option solutions under active development: Option I - Regional Exclusion, Option II - Quadrant-based APRM system, and Option III - an LPRM-based (oscillation) detection system.
All Options will feature automatic protection (scram) should an oscillation event occur.
Figure 1 summarizes these Options.
For Option I, two variations are offered (I-A and I-D).
Option I-D was recently developed and applies to a few plants that possess small cores with tight (fuel) inlet orifices.
Mr. Raush indicated that use of Option I-D is subject to demonstration that use of the APRM system in these plants will detect a regional oscillation event prior to exceeding critical power ratio (CPR) limits.
Details of the Option III trip algorithm concept were noted.
In response to Dr. Dhir, Dr. March-Leuba noted that GE will use three separate algorithms based on periodicity, growth rate and absolute
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i Joint Sub. Mtg. Minutes 3
September 17, 1992 magnitude in order to distinguish the onset of an oscillation event from random noise.
The overall status of the LTS program was noted (Figures 3-5).
Installation / testing of the LTS systems in lead plants is expected to begin in the second quarter of 1994.
Mr. Raush discussed the recent instability event that occurred at the WNP-2 plant.
Post-event evaluation showed that the main causes of the event were selection of a high radial peaking factor (~ 25%
higher than normal for the operating conditions existing at that time), and the fact that the a mixed load of (Siemens) 8X8 and 9X9 fuel resided in the core.
A team from the BWROG is being sent to the plant to evaluate the event.
Additional generic guidance will be issued as appropriate.
The OG believes that the Option 1-A methodology will bound this instability event and that the Option III detection algorithm would have initiated the suppression function early in the event.
In response to Dr. Catton, Mr. Raush indicated that the analytical tools can be relied on to predict oscillation events, as a post-event calculation showed that WNP-2 had a core decay ratio > 1.0.
Dr. Lee asked if use of Option I is clouded by the fact that the event occurred when power / flow was (just) outside the exclusion region.
Mr. Raush indicated that use of Option III may be more attractive, despite the additional hardware costs.
In response to another question, Mr.
Raush said that WNP-2 had an on-line stability monitor but it was not being used; (it was not required to be operational at the power / flow conditions existing at the time of the event).
If the monitor had been operational, it would have given advanced warning of the event.
In response to Dr. Kerr, Mr. Raush indicated that the OG has not performed any probabilistic analysis for the ATWS/ instability event, largely because it was not useful in resolution of this matter.
Lona-Term Solution Methodoloov Details of the methodology supporting the LTS was provided by Mr.
M. Anderson (GE).
He overviewed the LTS Options noted above.
Dr.
Lee requested additional information from GE on the methods supporting the establishment of the APRM flow-biased trip setpoints used in conjunction with Option I-D.
For development of the regional exclusion methodology (Option I),
GE uses a frequency domain code in conjunction with conservative criterion developed for determination of stable operating regimes (Figure 6).
The degree of conservatism associated with these calculations is estimated by comparisons with realistic input
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Joint Sub. Mtg. Minutes 4
September 17, 1992 parameters.
Figure 7 shows the resulting exclusion region on the i
power / flow operating map.
The Option III detect and suppress methodology is designed to continuously monitor the core and determine: power variation at a given core location, the relative power distribution during an oscillation event, oscillation-induced MCPR versus trip setpoints for same, and, the change in CPR with oscillation amplitude.
Figure 8 shows a schematic of the methodology components.
The trip detection algorithm is, as noted above, comprised of three diverse detection algorithm components: period-based, amplitude-based and growth-based.
Figures 9-12 provide some details.
Dr.
Lipinski asked why GE is not making use of autocorrelation for the signal processing.
Mr. Raush indicated that the method chosen for this function allows use of simplified software which is advantageous vis-a-vis its qualification for use in a safety-grade system (i.e. the RPS).
ATWS-Related Stability Issue Mr. Raush introduced the topic of ATWS combined with instability.
He noted that the OG has presented a two-part closure plan to the NRC staff: address the issue of the impact of ATWS/ instability on the ATWS rule bases, and ensure that steps are taken-to address this matter (i.e. develop mitigative strategies for use by plant operators).
As a result of a question from Dr. Dhir, Dr. Catton explained that in 1982 GE did not properly analyze the impact of the entire RCS as an instability driver, thus missing the potential for large damaging oscillations given an ATWS event.
Results of the OG's analysis show that the possibility of some fuel damage during an ATWS/ instability event cannot be precluded.
The amount of fuel involved ia predicted to be small (~ 0.5% of core volume), and thus the OG believes that there is no need to reopen ATWS rulemaking.
In response to questions from Dr. Catton, Mr.
Raush indicated that the OG believes that the probability of an ATWS is exceedingly low; however, given the existence of the ATWS Rule, it is not possible to resolve this matter via PRA.
In response to Mr. Davis, Mr. Raush said that injection of boron does not preclude fuel damage due to the time needed to effect shutdown
(~5-6 minutes).
The OG believes that the-ATWS Rule bases are not violated for the case of ATWS with instabilities because: the radiological limits of Part 100 are not exceeded; the integrity of the RCS and containment is maintained; and, core cooling is not impeded.
Two mitigative actions to address this event have been judged as the most potentially effective canaidates, immediate injection of boron given an ATWS and operator actions to lower the vessel water
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l September 17, 1992 level (feedwater runback) which reduces the oscillation amplitude.
Dr.
Catton asked if this event could be modeled via the IPE process.
Mr. Raush indicated that it is too late, as most of the licensees have concluded their IPEs.
ATWS With Core Power Instability K. Garrett (GE) discussed the details of the BWROG ATWS/ instability evaluations.
The following points were of note:
e The evaluation bases for both the ATWS and ATWS with instabilities calculations were noted.
For the former, GE characterized the values of selected input parameters chosen to be " reasonably conservative"; for the latter, plant models were selected to give reasonably bounding stability characteristics relative to the BWR fleet, and events were chosen that were likely to result in large oscillations.
The TRACG code was used to perform these analyses.
Figure 13 shows the code model schematic used.
Dr. Catton requested documentation supporting the use of TRACG for these analyses.
GE indicated that they intend to submit a comprehensive TRACG documentation package to the staff for its review later this year.
Further discussion resulted in Dr. Catton recommending that the Subcommittee meet to review l
this code early next year, following receipt of the GE l
documentation package.
. Results of ATWS/ instability analyses were presented for the following cases:
- BWR/5 Recirculation Pump Trip (Initial Conditions of LaSalle Event)
- BWR/S Turbine Trip With Bypass (Worse-Case Transient -
Results in Oscillations With Magnitudes of -3300% of Rated and Some Fuel Damage) j
- BWR/6 Turbine Trip With Bypass, Core Wide Oscillations J
- BWR/6 Turbine Trip With Bypass, Regional Oscillations Figures 14-24 detail the results of these analyses.
l As a result of the discussion of the above analyses, it was agreed that the following topics should be discussed during a future Subccmmittee meeting dealing with the details of the TRACG code:
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Joint Sub. Mtg. Minutes 6
September 17, 1992
- The bases supporting the TRACG analysis that for the case of large power oscillations (2-3000% of nominal),
the core average power does not increase.
- The ability of the code to model the rewet phenomenon
- The ability of the code to model transition boiling.
- The use of steady-state correlations to model transient T/H phenomena (e.g., flow oscillations).
. Considering the above results, GE believes that while large damaging power oscillations are possible, the energy deposited in the fuel is less than that needed for mechanical dispersion of same.
While the ATWS Rule bases is not compromised by the above results, the OG believes that the EPGs should be evaluated to ensure appropriate actions to mitigate such events are available.
The mitigative actions to be specified include immediate e
boron injection and reduction in vessel water level.
In response to questions from Mr. Davis, Mr. Garrett said that five U.S. plants are configured for automatic boron injection (the rest have manual injection).
Regarding the lowering of the vessel water level, GE said that the level is to be maintained at ~31 inches above the TAF.
Noting that this level will expose the feedring to steam, Dr.
Lipinski asked if GE had evaluated the potential and consequences of water hammer.
As a result of additional discussion of this point, Mr. L. Phillips (NRR) said that NRR will look into this issue relative to its evaluation of the proposed EPG actions and report back to the Subcommittee.
NRR Presentation - Introductory Remarks In opening comments Mr.
L.
Phillips (NRR) noted the following points:
e The Subcommittee was provided three reports - two Technical Evaluation Reports (TERs) dealing with review of the LTS Program and the issue of ATWS/ instability.
The third report contained the results of a NRC audit of the TRACG code vis-a-vis its capabilities to model ATWS/ instabilities. NRR concurs with the LTS TER and the TRACG audit report.
For the ATWS TER, minor editing is needed.
Safety Evaluation Reports will i
be written as " covers" for the above TERs.
While GE/BWROG have not seen the TERs, there should not be any surprises in them.
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Joint Sub. Mtg. Minutes 7
September 17, 1992 e Regarding the capability of TRACG to model stabilities given an ATWS, NRR believes the code does well for the case of moderate oscillation events; there is a large uncertainty associated with the calculation of large oscillation events however.
New fuel designs will not be allowed to be driven toward instability; NRR has a requirement that any new fuel designs must possess stability parameters at least equal to those of previously approved designs.
e The bases of the ATWS Rule did not preclude fuel damage; core coolability and adherence to the. radiological limits of Part 100 must be maintained however.
NRR believes that the extent of fuel damage could range to 12%
of the core volume (versus the GE prediction of 0.5%).
The maximum stored energy may reach 250 cal /gr. which is close to the 280 cal /gr limit set-by NRC.
NRR believes that core coolability will still be maintained,-but the consequence of ATWS risks is increased.
Given this, the staff will require
. l the OG to take actions to mitigate the severity of this event.
NRR also concurs with the OG proposal to lower.the vessel water level as a mitigation action, but is reserving judgment i
on the final level chosen.
Regarding the WNP-2 event, NRR will issue.an Information Notice that will provide an event description, root cause r
evaluation and generic implications.:
For resolution of the stability issue, NRR intends to issue e
a Generic Letter: specifying regulatory positions relative to the BWROG LTS fixes, discussing expanded role of stability monitors, and, strengthening the OG interim solutions. A SECY Paper will be sent to the Commission at the end of October which will include the closure plans for both the LTS and ATWS issues and recommend denial of the-OCRE petition to reopen ATWS rulemaking.
ACRS comments are sought regarding the staff positions on e
the closure of this matter.
AIT Investication of WNP-2 Instability Event Dr.
J.
March-Leuba discussed the details of the August 15, 1992 WNP-2 instability event and results of the subsequent NRC AIT investigation.
He noted the following points:
- During a return to power, following a repair to end leakage from the containment drywell, core power was held at 34% for I
Joint Sub. Mtg. Minutes 8
September 17, 1992 testing.
Following test completion, a flow control valve was
]
closed in preparation for upshift of the recirculation pumps, Core power oscillations began as the FCV was closed.
The e
oscillation were in-phase (whole core) and saturated at ~25%
P-P as seen in all LPRM signals.
The plant was manually scrammed, ending the event.
- Root causes of the event were: use of extremely skewed radial and axial power distributions caused both by the control rod pattern selected and the core loading scheme that placed highly reactive (new) fuel in uncontrolled locations (around the control rods), and, use of a mixed (8X8 and 9X9) fuel load that was not fully compatible on a T/H basis, Analyses using the ORNL LAPUR code showed that the e
oscillations could have been out-of-phase as the locations on the power / flow map where the decay ratio (DR) is unity for both in-and out-of-phase oscillations nearly coincide with the startup path taken during this event (Figure 25).
e Use of a
more conservative rod pattern results in dramatically lower DRs (e.g., 0.3 vs 1.05 for the 8/15 event).
- WNP-2 licensee has undertaken a number of corrective actions (Figure 26).
Generic Implications include, (1) the fact that low-power e
control rod patterns may be inconsistent with BWROG power distribution analyses, and control over these patterns appear necessary; (2) the adequacy of interim exclusion boundaries is called into question, and caution must be exercised when maneuvering in and around these regions; and, (3) instability concerns are increased by use of mixed-core fuel and mixed fuel types.
e Regarding use of stability monitors, it was noted that such monitors can provide an on-line calculation of the core DR.
Mr. Phillips noted, in response to Subcommittee questions that NRR will probably require some plants to install such monitors.
Mr. Raush indicated that the OG may rethink the need for stability monitors for licensees electing the "I-A" 4
Option.
NRR Reculatory Positions The proposed regulatory posit. ions for the issue of core power stability were reviewed by L. Phillips.
For the matter of the LTS program, NRR has approved use of Options 1-A, II, and III-III-A, subject to a number of conditions (Figutes %7 28).
Use of Option I-D will pend further review; however, if this Option is approved,
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1 Joint Sub. Mtg. Minutes 9
i September 17, 1992 use of a stability monitor will be required.
In fact, stability monitors will be required for any Options that are highly dependent '
on use of stability calculations to map exclusion regions.
As noted above, a Generic Letter will be drafted to close out the-review of the LTS program.
In; response to Dr. Catton, Mr. Phillips said he cannot promise that.a draft of this GL will-be available for the Committee's perusal, prior to the October ACRS Meeting.
Dr. Catton expressed concern that the Committee.could sign off on this matter, absent its review of the SERs.
l The result of the NRC audit Team's evaluation of the fidelity of' TRACG to model the ATWS/ instability phenomenon was briefly. reviewed l
by Dr. March-Leuba.
Essentially, the Team concluded that use of-TRACG. for evaluation 'of consequences of ATWS events with instabilities is acceptable providing recommended enhancements are emnloyed.
For the issue of ATWS with instabilities, NRR's. regulatory positions are:
I e Use of TRACG for these analyses is, as noted above,.
acceptable.
Adoption of the EPG actions to lower vessel. Water level o
given an ATWS with oscillations and to immediately begin boron injection will be required.
Specifics associated with'the vessel level action will be determined following review'of a yet-to-be-submitted OG report on this matter.
The staff concurs with the BWROG position-that no change to the ATWS Rule is required.
Additional information is pending from-the OG concerning the risks associated with tripping one of the two RCPs as a potential ~ mitigative measure.
There was discussion on the issue of potential fuel damage resulting from a " worse-case" ATWS/ instability event.. The focus of the discussion was on the degree of conservatism associated with the GE analysis of this event.
Messrs. Phillips and March-Leuba i
indicated that they believe the analysis. is.'sufficiently l
conservative and can be defended as such.
1 Mr. Phillips noted that two reports are to be submitted. by the BWROG/GE for NRR's review prior to issuance of a SER that is to close out the ATWS issue: a Supplement to the GE ATWS Topical Report that documents the ATWS calculations discussed above as well as the NRC request for additional information pertaining to the RCP trip issue noted above, and a report that evaluates the mitigative actions to be taken given an ATWS/ oscillation event.
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Coint Sub. Mtg. Minutes 10 September 17, 1992 In closing remarks, Mr. Raush said the OG is in basic agreement with the staff's resolution approach for both the LTS program and for ATWS/ instabilities.
He also is in agreement with.NRR's conclusion that any fuel damage seen during an ATWS will be self-limiting.
Mr. Raush also indicated that the OG does not favor use of predictive (versus noise-based) stability monitors due to the heavy operational burden that would accompany their use.
Subcommittee Caucus The subcommittee caucused regarding the issue of bringing this matter to the full Committee.
Concern was expressed over two matters
- 1 e The staff has not completed its review of either the LTS l
program or ATWS/ instabilities.
No SER would be available for the Committee's perusal if this matter is reviewed during its October Meeting.
There has not been any PRA-type analysis performed for the e
issue of ATWS with core power instability.
It was suggested by Drs. Kerr and Catton that analyses should be performed of the CDF associated with an ATWS event and the CDF associated with an ATWS accompanied with instabilities.
Thus one could evaluate the " delta-CDF" between the two.
This information would be useful in addressing the OCRE petition as well as help evaluate where these transients fall in the spectrum of CDF events.
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Given the above, the Subcommittee agreed to postpone ACRS review of this matter.
Dr. Catton will report to the Committee during its October Meeting.
Full Committee review will be tentati ily scheduled for the November Meeting, pending timely receipt of '
s i
SERs.
Dr. Catton will also propose that the Committee f e' ly request that the PRA-type analyses noted above be perfor-nd provided to the Committee for its consideration prior to it review of the stability issue.
The meeting was adjourned at 6:10 pm.
FUTURE SUBCOMMITTEE ACTIONS ON THIS MATTER AND ITEMS FOR FOLLOW-UP Euture Subcommittee Actions:
No further Subcommittee action on this issue is planned at this time, pending timely receipt of NRR's SERs that close out the stability issue and the requested PRA ATWS analyses.
Joint Sub. Mtg. Minutes 11 i
September 17, 1992 i
Follow-up Items:
- 1. Dr. Lee requested additional information from GE on the methods supporting the establishment of the APRM flow-biased trip setpoints used in conjunction with Option I-D.
- 2. Dr. Catton recommended that the Subcommittee meet to review this code early next year, following receipt of the GE documentation package.
It was agreed that the following topics should be
-l discussed during a future Subcommittee meeting' dealing with the details of the TRACG code:
- The bases supporting the TRACG analysis.that for the case of large power oscillations (2-3000% of nominal),
the core average power does not' increase.
- The ability of the code to model the rewet phenomenon
- The ability of the code to model, transition boiling.
- The fidelity of the post-dryout heat transfer coefficient used in the code.
- The use of steady-state correlations to model transient i
T/H phenomena (e.g., flow oscillations).
- 3. Mr. L. Phillips.(NRR) said that NRR will look into the issue of the potential for waterhammer in the vessel feedring associated with the' reduction in core water. level given an ATWS with oscillations, relative to NRR's evaluation of the proposed EPG actions, and report back to the Subcommittee.-
HACKGROUND MATERIAL PROVIDED THE SUBCOMMITTEE FOR THIS MEETING' 1.
ACRS Letter, dated June 14, 1989, " Boiling Water Reactor Core Power Stability"
- 2. Excerpt from Minutes of 361st ACRS Meeting, May,1990, report of j
April 27,1990 T/H Phenomena Subcommittee Meeting on BWR core power stability.
3.
Technical Evaluation Report, ORNL/NRC/:LTR-92/15, " Licensing Basis for Long-Term Solutions to BWR Stability Proposed by the BWR Owners' Group", dated August, 1992.
- 4. Technical Evaluation Report, ORNL/NRC/LTR-92/21, " Review of ATWS Rule Issues Relative to BWR.Thermohydraulic Stability", dated August, 1992 (Internal Use Only).
4 Joint Sub. Mtg. Minutes 12 l
September 17, 1992 5.
- Memo, P.
Boehnert to I.
Catton and J.E.
- Wilkins, "NRC PNO Report: Update / Final Report on the.WNP-2 Stability Event", dated-September 1, 1992.
- 6. GE Nuclear Energy Topical Report, NEDO-32047, "ATWS Rule Issues t
Relative to BWR Core Thermal-Hydraulic Stability", dated February, 1992.
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- 7. Memo, dated May 31, 1991, to attention of A. Thadani, NRR, from G. Beck, Chairman, BWR Owners Group, transmitting report "Long-Term
{
Solutions Licensing Methodology".
- 8. GE Nuclear Energy Topical Report, NEDO-31960, Supplement l',
"BWR Owners' Group Long-Term Stability Solutions Licensing Methodology (Supplement 1)",
dated March, 1992.
i Note:
Additional meeting details can be obtained from a transcript of this meeting available in the NRC Public Document Room, 2120 L St., NW, Washington DC 20006, (202) 634-3273, or can be purchased from Ann Riley and Associ-ates,_Ltd., 1612 K St.,
NW, Suite 300, Washington, DC 20006, (202) 293-3950.
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SCRAM OR SRI AT HIGH POWER / LOW FLOW POTENTIAL FOR SCRAM ON FW OR RECIRC PUMP TRIPS AND FLOW RUNBACKS I-D VERMONT YANKEE, MONTICELLO, DUANE ARNOLD, & FITZPATRICK SMALL CORE / TIGHT ORIFICE W/ ANALYSIS EXCLUSION REGION TO PREVENT OSCILLATIONS Il-ANALYSIS TO DEMONSTRATE REGIONAL OSCILLATIONS NOT
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'I GENERATE SCRAM IF DETECT OSCILLATIONS LOW MAINTENANCE AND OPERATIONAL IMPACT
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INTRODUCTION OPTION III TRIP ALGORITHM CONCEPT 0
CHARACTERISTICS OF OSCILLATIONS WELL KNOWN FREQUENCY (BETWEEN 0.3 AND 0.7 Hz)
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SHAPE (HIGH-LOW-HIGHER) 0 EXPECTED PLANT EVOLUTIONS CAN CAUSE TEMPORARY LPRM SIGNAL VARIATIONS i
PUMP STARTS / FLOW CHANGES CONTROL R0D MOTION PRESSURIZATION 0
TRIP LOGIC DETECTS OSCILLATIONS WITH HIGH CONFIDENCE M
YET DISCRIMINATES FROM OTHER SIGNALS THREE SEPARATE TRIP FEATURES USE OF PLANT DATA TO IDENTIFY SIGNATURES KNOWLEDGE OF OSCILLATIONS USED TO PREVENT SPURIOUS ACTUATIONS 0
ALARM PROVIDED IN ADVANCE OF TRIP o
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t INTRODUCTION LTS PROGRAM STATUS 0
METHODOLOGY / SOLUTION CONCEPT LTR SUBMITTED TO NRC (5/31/91)
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SUPPLEMENT 1 TO LTR ADDRESSING NEW DETECTION /
SUPPRESSION ALGORITHH AND LTR QUESTIONS SUBMITTED TO NRC (3/16/92)
O METHODOLOGY SUFFICIENTLY COMPLETE TO SUPPORT OWNER
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OPTION SELECTION
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i JC APPROXIMATE SETP0INTS/ IMPACTS IDENTIFIED yf' WORK REMAINS TO FINALIZE METHODOLOGY:
o INITIAL APPLICATION DEMONSTRATION o
RELOAD PROCEDURES 0
HW/SW BID SPECS FOR DETECTION / SUPPRESSION ISSUED; BID EVALUATION PROCESS UNDERWAY 0
LARGE HARDWARE DESIGN EFFORT IN PROGRESS S~ }cm AE SELECTED TO ASSIST BWROG DESIGN AND BID SPECIFICATIONS FOR DETECTION AND SUPPRESSION APPROACHES PREPARED AND ISSUED b
DIGITAL SYSTEM DESIGN AND LICENSING APPROACH DISCUSSED WITH NRC BID EVALUATION NEARLY COMPLETE HCP8/091092 3
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4 INTRODUCTION LTS PROGRAM STATUS (CONTINUED) 0 OPTION SELECTION EXPECTED IN OCT 1992 TIME FRAME FORMAL NRC APPROVAL OF OPTION CONCEPTS AND BASIC METHODOLOGY REQUIRED ALL UTILITIES PREPARING TO SELECT AN OPTION 0
INTERIM CORRECTIVE ACTIONS /BWROG GUIDANCE DEFINE 7)(
APPROPRIATE ACTIONS UNTIL LTS ARE IN PLACE HCP8/091092
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INTRODUCTION OPTION SELECTION PROCESS AND-CURRENT PLANS! SCHEDULE FOR LTS RESOLUTION 8/92 HW & PROCUREMENT. GROUPS RECOMMEND SUPPLIER (S) AND DISCUSS WITH EOC 9/92 TECHNICAL EVALUATION TEAM' AND PROCURMENT GROUP MEETING WITH CONTENDING BIDDER (S)
Discuss technical details of supplier (s) approach / options Resolve commercial considerations 9 or 10/92 NRC APPROVAL OF LTR &-SOLUTION CONCEPTS (Needed for subsequent tasks to proceed as scheduled) 10/92 ISSUE REPORT TO OWNERS Proposal evaluation results
& recommendation (s) w/ cost information 10/92 FULL COMMITTEE MEETING Can involve recommended supplier (s) 10 or 11/92 ESTABLISH OWNER / AGENT ROLE AND TERMS 10 or 11/92 OWNERS VOTE /RE-VOTE ON OPTION (S) 10 or 11/92 NRC ISSUES DRAFT GENERIC LETTER 11/92 FORMAL OPTION SELECTION / ALLOCATE FUNDS Possible I-A comm position to pursue until NRC decision 1 to 3/93 PREPARE DESIGN REQUIREMENTS / INITIATE DESIGNS 4 or 5/93 FINAL NRC GENERIC COMMUNICATION REQUIRING OWNERS TO COMMIT (TO OPTION OR SCHEDULE) 5/93 SUBMIT LTR SUPPL 2 (Methodology applic/RR proc's) 1993 SELECT LEAD PLANTS 1993/94 BEGIN HW FABRICATION (DATE DEPENDS ON OPTION) 1993/94 NRC INVOLVEMENT IN HW/SW DESIGN PROCESS TOPICAL REPORT SUBMITTED FOR EACH OPTION; 20/94 l A LEAD PLANT INSTALLATION / TESTING
- 40/94 lil-A LEAD PLANT INSTALLATION / TESTING 10/95 Ill LEAD PLANT INSTALLATION / TESTING 1996 OPTIONS READY FOR ALL PLANT INSTALLATION
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- Power must Exceed a Set-Point based on the Previous Peak to Cause Trip Algorithm has been Tested Against a Range of I Actualand HypotheticalInstabilities as wellas Operational Transients GE Nuclear Energv 9/17/92 13/2
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WNP-2 8/15 STAATUP CONDIT IONS 25 LAPUA,estima'ted Iihe of j
constantoutf-of-phaseDA=1 4
70
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25 20 20 25 30 35 40 45 50 55 60 FLOW (90 Figure 4.3 Best-estimate lines of constant decay ratio =1.0 for actual conditions of 8/15 event, assuming constant power distribution f)b-
~
Corrective Actions e WNP-2 will pre-analyze control rod patterns for stability h
pump up. Startup rod sequence and patterns for
-shift can not be changed by the operator without analyses and review.
s,e Analyzed conditions prior to FCV closure must-T result in a decay ratio less than 0.5.
je During startup, the following conditions must be met:
i Measured corewide decay ratio (using the h
ANNA system) must be less than 0.6 at all times.
Minimum CPR must be > 2.2 (1.9 on 8/15)
Maximum nodal peaking factor < 3.4 (3.86 on 8/15)
Expected core-average axial peaking < 1.45 (1.9 on 8/15)
Power < 33% prior to pump upshift.
~
i l.
~
i-l- :
Regulatory Position:. Solution Types 4
i l
y
- Solution I-A is acceptable for any BWR line.
y provided:
s 5
Full scram or SRI with delayed scram when i
k entering solution region.
1 1
j Administrative controls on power maneuvering assure conservatism of exclusion boundary.
]
1 i
Stability monitor required for low-flow power j
i k maneuvers in FCV plants.
May.be required on l
plant specific reviews of other plants.
j i
l Specific reload confirmation procedures must j
be developed.
l-Exclusion region scram setpoints should have l
sufficient conservatism built in to avoid j.
frequent cycle-to-cycle setpoint changes.
i j
e Solution I-B and 1-C not approved due to lack of
{
interest / development or demonstrated need.
1
- Solution I-D: If accepted, a stability monitor with I
h administratively controlled decay ratio limits-will be required.
i i
l; Regulatory Position: Solution Types i
e Solution 11 is acceptable for BWR/2s.
Oyster Creek has already submitted application.
- Solutions Ill and ill-A are acceptable for any BWR g provided:
A minimum of three diverse detection aQs mustM I
i Validity of scram setpoints must be i
demonstrated by analyses that include failed sensors.
Proposed LPRM groupings to detect expected j
I T
oscillation modes for Solutions Ill (OPRM) and N-Ill-A (octant based) are acceptable.
g Plants using SRI as the automatic protection j
q action must have a delayed scram backup.
i e Proposed solutions and implementation schedules pI for individual plants will be reviewed in a plant-by-plant basis, f
I ACRS-LTS 9/17/92 4
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