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RAI Responses to Round 7 RAI on ANP-10285PRockville, MDNovember 16, 2012Draf
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2NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Agenda Summary of outstanding issues and fuel design change Summary of preliminary results – loads on grids Grid strength definition, un-irradiated and irradiated – RAI 68 Impact of grid strength definition upon thermal-hydraulics,
non-LOCA, and LOCA Bundle deflection amplitude – RAI 64 Impact of grid deformation on loads – RAI 70 Impact of plant seismic reanalysis on fuel assembly closure
plan Summary and Next stepsDraf
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3NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Near Term Interactions Impact of fuel design change on thermal-hydraulics, non-
LOCA, and LOCA Irradiated fuel assembly damping
Draft
Summary of Outstanding Issues and Fuel Design ChangeBrett Matthews Draf
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5NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues To Be AddressedPrior to Modified Closure Plan
Presented on May 2, 2012
Forced vibration versus pluck test Empirical fuel assembly frequency response at high
amplitudes Fuel assembly characteristics in the irradiated condition Linear versus non-linear bundle modeling Definition of grid strength and testing protocol CASAC acceptability Modeling of grid post-buckling behavior Evaluation of coolability under grid buckling Evaluation of control rod insertion under grid buckling SSE plus AOO Criteria
Draft
6NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues To Be Addressed
Forced vibration versus pluck test Empirical fuel assembly frequency response at high
amplitudes Fuel assembly characteristics in the irradiated condition Linear versus non-linear bundle modeling Definition of grid strength and testing protocol CASAC acceptability Modeling of grid post-buckling behavior Evaluation of coolability under grid buckling Evaluation of control rod insertion under grid buckling SSE plus AOO Criteria
After Modifications
Draft
7NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Fuel Assembly Design Change Increased strip thickness
Two grids modified Located in the middle of the fuel assembly axially Grid loads are highest for these grids
Increased weld nugget size All grids impacted Strip thickness unchanged for other grids
Impact of change – mechanical Strength of all grids increased Strength of grids located in the middle of the fuel assembly axially
increased significantly Result is that all grids have margin to the grid strength definitionDraf
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8NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Design Change
Mechanical No significant impact on bundle characteristics
Lateral stiffness impact is minimal since the stronger grids are close to the middle of the bundle, where the rotation due to bending is minimal
Natural frequency impact is minimal as well, since stiffness does not change Mid-span stiffer grids could affect 2nd mode, but the participation factor for this mode is
zero for lateral acceleration loading. Updated spacer grid characteristics for grids 4 & 5
Lateral analysis accounts for new through-grid stiffness and damping for grids 4 & 5 Thermal-Mechanics
Evaluate rod stress with new grids Non-LOCA
No impact Thermal-Hydraulics
Discussed later LOCA
Discussed later
Draft
9NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues Remaining:Forced Vibration versus Pluck Test
UNCHANGED FROM MAY 2 PUBLIC MEETING:AREVA will perform comparative testing on a 14 ft HTP bundle representative of the U.S. EPR fuel design
Bundle will be in a simulated irradiated condition Both forced vibration (up to ~0.3 inches) and pluck test (up to ~1.0 inches)
will be performed
Objective is to demonstrate equivalency in the two approachesThereby validate the existing test basis for the U.S. EPR which is largely based on forced vibration testingDraf
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10NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues Remaining:Frequency Response at High AmplitudesUNCHANGED FROM MAY 2 PUBLIC MEETING:AREVA will perform testing on a 14 ft HTP bundle representative of the U.S. EPR fuel design
Bundle will be in a simulated irradiated condition Pluck test (up to ~1.0 inches) will be performed
This empirical information can be used to validate and reassess the range used for the frequency sweep
Draft
11NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues Remaining:FA Characteristics in Irradiated Condition
UPDATED FROM MAY 2 PUBLIC MEETING:Irradiated Bundle Frequency
AREVA will perform testing on a 14 ft bundle representative of the U.S. EPR fuel design Bundle will be in a simulated irradiated condition Pluck test (up to ~1.0 inches) will be performed
This empirical information can be used to validate and reassess the range used for the frequency sweep
Irradiated Condition Damping The primary fuel assembly damping mechanism is independent of the lateral
stiffness of the bundle, hence, it is the same at Un-irradiated and Irradiated UPDATE: This will be discussed in greater detail later in the presentation
Draft
12NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues Remaining:Linear versus Non-linear Bundle Modeling
UPDATED FROM MAY 2 PUBLIC MEETING:AREVA has provided information to show that the linear modeling (frequency versus amplitude) of the U.S. EPR is appropriateSensitivity to non-linear effects is reduced in absence of grid buckling
For grid impacts below buckling, the second order non-linear effects of the bundle stiffness vs. amplitude become even less significant.
With stable grid operation, the ability to capture the overall strain energy stored in the fuel assembly in a displaced configuration is the primary focus.
Importance of axial load re-distribution between grids lessens with stable grid operation.
Margin to buckling load further reduces the importance of secondorder effects (non-linear frequency versus amplitude)UPDATE: August 2012 RAI 64 response was been updated with new information and results, but no change to conclusion
Draft
13NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues Remaining:HTP Grid Strength and Testing Protocol
UPDATED FROM MAY 2 PUBLIC MEETING:August 2012 Responses to RAI 68 and 70 address this issue
Response to RAI 68 defines a protocol for simulating the irradiated condition in grid strength testing Based on simulating effects of in-reactor operation known to have a primary influence
- Irradiation Hardening of the Material- Irradiation Induced Relaxation of Spacer Grid Springs
Protocol and strength definition are consistent with regulatory and industry framework Grid strength definition must give consideration to the amount of permanent deformation
inherent at the allowable load level Unique definitions of grid strength are given for both Un-irradiated and the irradiated
condition- Both definitions fit within the regulatory and industry framework
August 2012 Response to RAI 70 adds discussion of the acceptability of the grid model as part of the core row models Allowable crushing load inherently includes a finite amount of permanent deformation The use of a linear visco-elastic element accurately predicts peak impact loads and rebound
velocities after impact Gap sensitivity studies show that the small deformations inherent in the allowable crushing
load do not significantly alter the fuel bundle response or predicted loads
Draft
14NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Key Issues Remaining:CASAC Acceptability
UNCHANGED FROM MAY 2 PUBLIC MEETING:Information previously provided:
CASAC code has been verified with sample problems with known answers, including problems that are directly representative of fuel assembly modeling
CASAC code and underlying modeling technique has been validated through full-scale testing with a row of six fuel assemblies for both in-air and in-water conditions.
Comparison of CASAC-generated load vs. deflection curves with actual test data is presented Draf
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Summary of Preliminary ResultsBrett Matthews Draf
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16NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Fuel Assembly Design Change
HTP Grid
HTP Grid
HTP Grid
HTP Grid
Max Loads at HTP 4 and 5 Draf
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17NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact AnalysisModifications to the Analysis
Spacer grid modeling changes [ ] strip HTP grids at locations 4 and 5
Increase in strength Increase in through-grid stiffness Increase in through-grid damping
[ ] strip HTP grids with [ ] WNS at locations 1, 2, 3, 6, 7, & 8
Increase in strength only
Modify bundle damping parameters Damping strength is maintained the same at all frequencies
Previous analyses used reduced damping at Irradiated conditions
Updated time histories Update model for reactor coolant system to include rotation of building in
determining the translational displacements of the core plates Ongoing updates from Nuclear Island civil/structural groups to account for
NRC requests in modeling of soil structure interaction, etc.
Draft
18NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact AnalysisSpacer Grid Testing
Draft
19NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact AnalysisSpacer Grid Testing
Draft
20NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact AnalysisPost Processing of Results
A total of 720 seismic cases have been analyzed 8 soil cases 2 directions (X and Z) 5 rows (7, 11, 13, 15, and 17) 9 frequencies [ ]
An additional 180 LOCA cases have been analyzed for the two most limiting LOCA events (HELB-0 and HELB-100)
Each case evaluates grid impacts at each grid elevation at everyinterface across the core for every time step in the run.
There are millions of data points. Data is processed to highlight limiting margins and general trends.
Draft
21NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Max Loads in Un-irradiated Condition
Grid Location HTP 4&5 HTP 3&6
Grid Description
Un-irradiated Grid Strength (lbs)
Un-irradiated Max Load - (lbs)
% Margin on Load
Peripheral Bundles
Interior Bundles
Grid
Max Load
Irrad. Strength
Margin
Frequency sweep cases from [ ] constitute the “Un-irradiated” condition
Draft
22NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact AnalysisMax Loads in Irradiated Condition
Frequency sweep cases from [ ] constitute the “Irradiated” condition
Grid Location HTP 4&5 HTP 3&6
Grid Description
Irradiated Grid Strength (lbs)
Irradiated Max Load - (lbs)
% Margin on Load
Peripheral Bundles
Interior Bundles
Grid
Max Load
Irrad. Strength
Margin
Draft
23NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Load Distribution Across Row, Un-irradiated
7 row (shortest) HTP 4 & 5 only Plotted loads
may come from different points in time
Draft
24NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Load Distribution Across Row, Un-irradiated
17 row (longest) HTP 4 & 5 only Plotted loads
may come from different points in time
Draft
25NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Load Distribution Across Row, Un-irradiated
Un-irradiated [ ]
11 row (limiting) HTP 4 & 5 only Plotted loads
may come from different points in time
Only case where 0.2% grid envelop deformation is exceeded
Draft
26NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Load Distribution Across Row, Irradiated
7 row (shortest) HTP 4 & 5 only Plotted loads
may come from different points in time
Draft
27NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Load Distribution Across Row, Irradiated
17 row (longest) HTP 4 & 5 only Plotted loads
may come from different points in time
Draft
28NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Load Distribution Across Row, Irradiated
Irradiated [ ]
11 row (limiting) HTP 4 & 5 only Plotted loads
may come from different points in timeDraf
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29NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Impact History
Un-irradiated [ ]
11 row (limiting) HTP 4 only Only case where
0.2% grid envelope deformation is exceededDraf
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30NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Observations
For Un-irradiated cases, comfortable margin exists to [ ] deformation on all cases
Positive margin can be shown for a more conservative criterion of 0.2% deformation on all cases, except one.
Un-irradiated loads tend to be higher than loads in the irradiated condition
LOCA loads contribute very little to the combined SSE/LOCA load
Overall peak loads and limiting margins occur on the periphery of the core Peak loads for specific soil and row cases generally occur on the
periphery of the core
Limiting loads do not result from row with largest available gapDraf
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31NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Conservatisms
Alignment of assemblies at constant frequency maximizes impact loads Maximizes assembly response when input motions approach resonance
Effect is further maximized with frequency sweep approach Non-linear effects disperse frequency response across the row and with
respect to time
0.2% deformation on grid bounds all interior bundles and nearly all periphery bundles for Un-irradiated condition Comfortable margin to [ ] limit exists for all locations Strength definition at [ ] leaves additional margin to actual
grid buckling
2-D row model neglects losses and interference from neighboring rows Unobstructed and frictionless impacts across a row is unrealistic, but
conservative
Draft
32NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Conservatisms
Maximum loads occur on the periphery of the core Ultimate requirements of coolability and control rod insertability are less
challenged on the periphery
Control rod insertability is conservatively validated during grid testing with a rigid, oversized control rod assembly gauge
CASAC uses a lumped mass fuel assembly model Concentrated masses at grid nodes results in higher impact loads than
what would be experienced for the real case with distributed mass
Seismic time histories are based on enveloping ground motion spectra and a broad range of soil conditions that are intended to bound all current potential applicants for the U.S. EPR Site specific analyses would yield additional margin
Draft
33NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Conservatisms
The fuel seismic analysis is downstream and relies on the output of civil/structural and NSSS evaluations All upstream conservatisms provide additional margin to the fuel
evaluation
Analysis extends beyond the guidance of SRP 4.2 to explicitly addresses the effects of irradiation on both bundle and grid characteristics (NRC Information Notice 2012-09)
The Un-irradiated condition is not representative of typical operating conditions. Fuel bundles are more accurately characterized by the irradiated condition over the majority of their operation.
Cases run at “+” frequencies in the frequency sweep are unrealistic because they could only occur with small deflection amplitudes. The fuel bundle does not maintain a high frequency response as it deflects from its nominal position.
Draft
34NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Lateral Impact Analysis Conservatisms
“Irradiated” grid strength testing is conservatively performed with hollow fuel rod cladding. The irradiated condition is moreaccurately represented with a solid rod to simulate the pellet-cladding contact. Testing with solid pins increases grid strength by approximately 10 to
30%, depending on the grid design
Draft
Grid Strength DefinitionUn-irradiated and Irradiated-RAI 68
Victor Hatman Draft
36NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition - Overview
Spacer Grid Impact Strength Definition – Regulatory Background NRC Guidance Documents Review Previously Approved Definitions and Test Methods for P(crit) Conclusions of the NRC Guidance and Industry Practices Review
Spacer Grid Strength – Effects of In-Reactor Operation Effects of In-Reactor Operation on Zirconium Alloys Effects of In-Reactor Operation on Spacer Grid Strength Summary of In-Reactor Operation Effects on Grid Strength
Proposed Spacer Grid Strength Definition and Test Protocol for the U.S.EPR Fuel General Requirements Proposed Un-Irradiated Allowable Crushing Load Definition for the U.S.EPR Proposed Irradiated Allowable Crushing Load Definition for the U.S.EPR
Draft
37NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition - Regulatory Guidance
SRP 4.2 – Appendix AThe consequences of grid deformation are small. Gross deformation of grids in many PWR assemblies would be needed to interfere with control rod insertion during an SSE (i.e., buckling of a few isolated grids could not displace guide tubes significantly from their proper location), …
In a LOCA, gross deformation of the hot channel in either a PWR or a BWR would result in only small increases in peak cladding temperature.
Therefore, average values are appropriate, and the allowable crushing load P(crit) should be the 95% confidence level on the true mean as taken from the distribution of measurements on un-irradiated production grids at (or corrected to) operating temperature. While P(crit) will increase with irradiation, ductility will be reduced. The extra margin in P(crit) for irradiated grids is thus assumed to offset the unknown deformation behavior of irradiated grids beyond P(crit).
Draft
38NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition - Regulatory Guidance Observations on SRP 4.2 P(crit) Definition
SRP 4.2 derives P(crit) from the average value of the test sample. This shows that the original design basis intent was to ensure that grid deformation
stays low for most grids, with some grids being allowed to buckle, and perfectly elastic operation of the grids was not required.
Provision made to account for the in-reactor temperature. By testing hot, or by testing cold, and correcting for operating temperature. The actual
correction procedure is not specified. The effects of irradiation are assumed to counteract the deformation behavior
the un-irradiated strength is the controlling design parameter. The focus of SRP 4.2 Appendix A is primarily on:
the statistical definition of P(crit) from the grid sample data, on the condition of the test grid specimens, and on the test environment,
SRP 4.2 does not specify an individual grid test failure criterion (maximum indicated load vs. limitations on total deformation).
Draft
39NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition - Regulatory Guidance NUREG/CR-1018
Discusses the actual grid failure criterion, and defines two spacer grid operation scenarios, the “no permanent deformation” and the “permanent deformation” case:
If spacer grid loading caused no permanent deformation of the spacer grid then rod to rod spacing and coolant channel flow area is undisturbed and a coolable geometry would be maintained. A small amount of permanent deformation is almost always present after spacer grid loading. Settling of the connecting strip joints and local deformation due to high local stresses are just two of the possible causes of permanent deformation. Obviously, a condition of no permanent deformation must be defined.
A sufficient condition to demonstrate that no permanent deformation has occurred appears to be that the spacer grid remain within manufacturing tolerances. This condition should be sufficient although possibly not necessary because the only meaningful definition of departure from a no-deformed condition would be that deformation which causes a measurable perturbation in the ECCS peak cladding temperature calculation. A manufacturing tolerance criteria should fall within this deformation definition. The quantity to be used for comparison with the calculated results could be defined as that load at which initial departure from the no deformation condition is obtained.
Draft
40NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition - Regulatory GuidanceObservations The items of interest when assessing whether a grid has “no permanent
deformation” are the rod-to-rod pitch and the flow channel area. These two parameters control the grid performance and its ability to perform the coolability
function. Since this is the “no permanent deformation” scenario, Control Rod insertability is not the primary concern.
The physical dimension of the overall envelope of the grid is not a concern. This dimension only affects the grid gaps, which NUREG/CR-1018 deems to be of second
order importance (Table I in Section II, sub-section 4.2.1). It is recognized that a small amount of permanent deformation will always be
present The condition of “no permanent deformation” cannot be taken literally, and needs to be
defined. The “no permanent deformation” condition is defined in terms of a finite but
acceptably small deformation which does not interfere with the coolabilityrequirement.
Essentially, the “no deformation” condition is taken to mean the deformation threshold beyond which, the coolability would begin to be measurably impacted.
Limiting the grid deformation to the manufacturing tolerances would constitute a sufficient but not strictly necessary criterion for the “no deformation” condition.
Draft
41NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Previously Approved Methodologies
AREVA BAW-10133PA Addendum 1
The grid strength definition is based on successive impact tests of grids at hot operating temperature of increasing kinetic energy content. The allowable grid impact load is defined as the lower bound of the 95% confidence interval on true mean of the instability load of the grids in the test sample.
Approved uses of the methodology: BAW-10172PA, BAW-10229PA, BAW-10239PA, BAW-10179PA, BAW-10186PA
EMF-93-074(P)(A) The grid strength was defined as the lower bound of the 95% confidence interval on true mean of the grid cold
condition buckling limit adjusted to operating temperature by scaling with the elastic modulus ratio
Combustion Engineering – CENPD-178 The defining criterion for grid “failure” is the channel closure. The maximum load at which there is no
significant deviation of channel dimensions from the original tolerances is deemed as the individual grid strength. The 95% confidence on true mean for the grid sample is defined as the general grid strength.
The most recently approved use of this methodology: WCAP-16500-NP-A, 2007
Westinghouse Electric Company – WCAP-8236(P) & WCAP-8288(NP)
The grid strength definition is based on successive impact tests of grids at hot operating temperature (or room temperature – corrected to hot) of increasing kinetic energy content. P(crit) is defined as the lower bound of the 95% confidence interval on true mean of the instability load of the grids in the test sample.
The most recently approved use of this methodology: AP-1000 Design Control Document, 2011
Draft
42NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Conclusions of Guidance and Industry Practices Review
The grid strength allowable is a statistical value set at the lower bound of the 95% confidence interval on the true mean of a grid sample.
Setting the allowable strength at a certain confidence level on the true mean, signifies that the original design basis intent was to ensure that most grids do not buckle, but a few isolated ones may experience buckling without compromising the coolability and control rod insertability, as explicitly stated in NUREG/CR-1018.
The individual grid allowable strength or failure point can be treated under two scenarios: the “no permanent deformation”, and the “permanent deformation”scenario.
The “no permanent deformation” scenario does not imply the complete absence of permanent deformation, but the presence of a finite but acceptably small level of permanent deformation.
The true individual grid failure criterion for the “no permanent deformation” case is the deformation threshold beyond which, the flow channel departure begins to impact grid thermal performance in a measurable way. A sufficient criterion limiting the permanent deformation within the grid manufacturing tolerances can be substituted for the flow channel departure.
Draft
43NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
SRP 4.2 – Normal Operation Main concern is with ductility degradation, oxidation, and crud Effects of In-Reactor Operation on Zirconium Alloys Hydrogen Pickup Irradiation Hardening Irradiation Stress Relaxation Irradiation Induced Loss of Ductility Oxidation Effects of In-Reactor Operation on Grid Strength Identify the Main Drivers on Spacer Grid Strength Discuss Oxidation Effects of In-Reactor Operation - Summary
Draft
44NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
Effects of In-Reactor Operation on Zirconium Alloys Hydrogen Pickup – second order effect
Ductility: In irradiated state, over the range of expected hydrogen uptake levels for M5®
structural components, the effect is completely negligible. The primary effect on ductility comes from irradiation
Yield Strength: hydrogen uptake has a minimal strength increasing effect
upper boundM5 structural components hydrogenuptake
representative Zr‐4 structural components hydrogenuptake
upper boundM5 structural components hydrogenuptake
representative Zr‐4 structural components hydrogenuptake
Ultimate Elongation and Yield Strength for Zirconium Alloy vs. Hydrogen Content
Draft
45NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
Effects of In-Reactor Operation on Zirconium Alloys Yield Strength Irradiation hardening is a first order
effect Strong increase in yield strength
[
]
Effect saturates at ~ 2.5e+25 n/m^2 Yield strength reaches the
asymptotic value after 1 year of full power operation
Draft
46NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects ofIn-Reactor Operation
Effects of In-Reactor Operation on Zirconium Alloys Ductility
Irradiation induced loss of ductility is a strong effect for Zirconium Alloys [
] Effect saturates at ~ 4.5e+25 n/m^2 Ductility loss reaches the asymptotic
value after ~2 years of full power operation Draf
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47NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
Effects of In-Reactor Operation on Zirconium Alloys Irradiation Stress Relaxation Irradiation stress relaxation is
first order effect – more details to follow
Effect saturates at ~ 3e+25 n/m^2
Ductility loss reaches the asymptotic value after ~1 year of full power operation
Asymptotic value is 100% the Irradiated grid cell insertion load is almost nil. Draf
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48NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation Zirconium Alloys Oxidation
M5® has reduced oxidation compared to Zr-4 For irradiated M5® grid strips, the oxide layer is [ ] Oxidation has a positive effect on grid strength – details to follow
M5® Cladding Oxidation vs. Burnup
Draft
49NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
Testing of AREVA Irradiated Grids 2003 submittal: Closure of Interim Report 02-002: Spacer Grid Crush
Strength – Effects of Irradiation Tests on full spacer grids operated in a reactor [
] Strength of irradiated grids was proven to be lower than that of fresh
production grids The irradiated grid failure mode is the same as for un-irradiated Inspection after crush test showed no signs of brittle fracture. The grid
material retained enough ductility Grid cell relaxation is the main factor contributing to the loss of grid
buckling strength Irradiated grid strength was shown to be strongly influenced by the grid
elevation in the fuel assembly – the center grids has the highest strengthDraf
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50NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
Irradiated Grid Failure Mode The irradiated grid failure mode
is the same as for un-irradiated Racking is concentrated in a few
rows Indicative of buckling failure Inspection after crush test
showed no signs of brittle fracture.
The grid material retained enough ductility even in irradiated condition Draf
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51NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects of In-Reactor Operation
Irradiated Grid Strength vs. Grid Cell Relaxation
The main driver of reduced grid strength in irradiated condition is the cell relaxation
Test Base: tested new, [ ] irradiated grids – plotted vs.
cladding insertion force (proxy for cell relaxation
Plot lot shows the grid buckling load vs. cladding insertion force
Strong correlation between grid buckling load and cell relaxation
Cell spring relaxation disrupts the fuel rod cladding straight line pattern, thus perturbing the load path through the cladding, and lowering the buckling strength
Draft
52NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects ofIn-Reactor Operation
Oxide Layer Effect on Grid Strength Irradiated grid strength was found to increase with grid elevation Oxide layer has a higher elastic modulus higher grid strip stiffness Strength increases by up to [ ] - not used in the U.S.EPR evaluation
Draft
53NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Effects ofIn-Reactor Operation
Effects of In-Reactor Operation - Summary Irradiation Induced Stress Relaxation
This is a first order effect. As shown on the irradiated grid tests, there is a very strong correlation between the grid buckling load and the average cell cladding insertion load. Cell spring relaxation reduces the stability of the fuel rod array, and reduces the buckling load.
Irradiation Induced Hardening This is a first order effect. The irradiated grid tests have indicated that the deformation to buckling of the
tested grids is less than for the new material grids. This indicates that the effective grid stiffness increases with increased material strength due to the fact that localized yielding of the grid strip material is reduced.
Oxidation The increased modulus of elasticity of the oxide layer contributes to the grid buckling capability.
Consequently, a grid strength evaluation without taking credit for oxidation is conservative. Irradiation Induced Loss of Ductility
This is a second order effect. Even if the loss of ductility is not negligible, the material retains enough ductility to prevent brittle fracture, as indicated by the irradiated condition grid tests
From a grid mechanical strength point of view, the irradiation induced loss of ductility is a second order effect. Hydrogen pick-up
This is a second order effect. The effects on ductility and strength are marginal when compared to the effects of irradiation.
Irradiated grid testing showed that the material retains sufficient ductility to avoid brittle fracture.Draf
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54NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition
P(crit) Definition – Overview Establish the General Requirements for P(crit) Definition
Stability of deformation on the loading curve Limited by either peak load or maximum allowable deformation Control rod insertability Deformation distributed uniformly between fuel rod rows negligible T/H impact
Formulate the Un-Irradiated P(crit) Definition Deformation controlled
Review the Test Basis for Un-Irradiated P(crit) Definition Loading curves / Control Rod Insertability
Formulate the Irradiated P(crit) Definition Load controlled
Formulate the Test Protocol for Irradiated Condition P(crit) Address material yield strength increase and stress relaxation
Review the Test Basis for Irradiated P(crit) Definition
Draft
55NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition
P(crit) Definition – General Requirements The Limit Point on the Stable Side of the Loading Curve
On the stable side of loading curve higher impacts are required to produce higher permanent deformation Contrast with the un-stable side, where decreasing impacts can produce increasing permanent deformation Consistent with the general philosophy of the ASME Code – use of load or stress limits to control deformation
Limit dictated by maximum allowable deformation (B) or buckling strength (A) NUREG/CR-1018 establishes that the real
P(crit) criterion is the threshold of deformationbeyond which there is a measurable impact on the thermal-hydraulic performance
In the case of more compliant grids, thedeformation limit is reached first
Draft
56NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition
P(crit) Definition – General Requirements (cont’d) Same grid design can exhibit different behaviors, and can trigger different limits in un-irradiated
and irradiated condition Irradiation induced material hardening makes the grid less compliant, which triggers the buckling load limit first Depending on the inherent grid stiffness, and the actual value of the deformation threshold, the allowable crushing
load at un-irradiated can be lower or higher than the Irradiated buckling strength. Control Rod insertability must be
ensured for the deformation limited scenario
For the U.S.EPR this is demonstrated througha prototypical gage insertion test
The deformed grid shape at the deformation limit must be approximately uniform
The uniformity of the deformed grid lattice isensured by visual inspection on grids tested only up to the deformation threshold
It is also confirmed by the coefficient of restitutionplots vs. impact kinetic energy – the coefficient of restitution is constant for the entire range of impactenergy up to buckling
Draft
57NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-Irradiated Case
U.S.EPR Grid Arrangement HMP Grids – at the top and bottom of the assembly
– these grids do not experience impacts. HTP [ ] – at the mid-elevation
locations. HTP [
] – at the remaining locations
Draft
58NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-Irradiated Case
HTP [ ] Strip – Un-irradiated Case The HTP [ ] grid allowable crushing load at un-irradiated is defined as the load
corresponding to a permanent deformation of [ ] on the standard loading curve – 95% confidence on true mean
[
] Test base:
[
] Observations:
[
]
Draft
59NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-irradiated Case
HTP [ ] – Uniform Deformation Distribution
Two grids stopped slightly above [ ] permanent deformation for the purpose of providing test evidence of the uniform character of grid deformation
The deformed shape of the grid is indistinguishable upon visual inspection
The grid cells maintain the regular array No concentration of the deformation in a
given area of the grid (as opposed to buckled grids, where the deformation is concentrated in a few rows)
These findings are consistent with the fact that the coefficient of restitution is constant over the entire stable side of the loading curve Draf
t
60NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-irradiated Case
HTP [ ] – Control Rod Insertability
All grids tested at [ ] permanent deformation using a prototypical control rod gage
Gage passed through all grids without any applied force
Sources of Conservatism: Gage pins were sized at [
]
Gage pins are rigid – test does not take advantage of the inherent flexibility of the control rods Draf
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61NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
HTP [ ] Strip – Un-irradiated Case The HTP [ ] grid allowable crushing load at un-irradiated is defined as the load
corresponding to a permanent deformation of [ ] on the standard loading curve – 95% confidence on true mean
[
] Test base:
[
] Observations:
[
]
Grid Strength Definition – Proposed P(crit) Definition – Un-irradiated Case
Draft
62NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-irradiated Case
HTP [ ] Strip – Control Rod Insertability and Uniform Deformation
All grids tested at [ ] permanent deformation using a prototypical control rod gage
Gage passed through all grids without any applied force
Gage pins were sized at [ ] OD –prototypical U.S.EPR control rod
Gage pins are rigid – test does not take advantage of the inherent flexibility of the control rods test is conservative
HTP [ ] Strip – Uniform Deformation
The uniform deformation proven for the [ ] grids,
which are stiffer and stronger These findings are consistent with the fact that
the coefficient of restitution is constant over the entire stable side of the loading curve
Draft
63NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-irradiated Case
U.S. EPR – P(crit) Definition - Un-irradiated Case - Summary Production grids tested at [ ] 95% confidence on true mean at [ ] permanent cumulative deformation
Draft
64NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Irradiated Case
Characteristics of the Irradiated Condition
Main drivers for grid strength [
] Hardening vs. relaxation
[
]
Test Protocol [
]
Draft
65NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Irradiated Case
[
][
]
[
]
Test Protocol for the Irradiated Condition
Draft
66NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Irradiated Case
Test Protocol for the Irradiated Condition – Test BasisTest performed in 2002 on Zr-4 AFA2G irradiated full grids
[
]Test Protocol
[
]Test Results
[
]
Draft
67NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Un-irradiated Case
U.S. EPR – P(crit) Definition - Irradiated Case - Summary [ ] 95% confidence on true mean of the buckling load Permanent Deformation is very low (less than ½ manufacturing tolerances)
Draft
68NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Conclusions
Comparison irradiated vs. un-irradiated – HTP [
] The un-irradiated strength at
[ ] permanent deformation is higher than the Irradiated strength
Permanent deformation in simulated Irradiated condition is very low – not a concern
Draft
69NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition - Conclusions
Comparison irradiated and un-irradiated – HTP [
] The un-irradiated strength at
[ ] permanent deformation is higher than the irradiated strength
Permanent deformation in simulated irradiated condition is very low – not a concern
Draft
70NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Conclusions
Conclusions The grid strength is defined based on the following considerations (per NUREG/CR-1018):
The objective criterion for establishing grid failure is the cumulative permanent deformation threshold beyond which the thermal-hydraulic performance of the grid would begin to be measurably impacted.
The load/deformation allowable point must be on the stable side of the loading curve. An HTP grid can be limited by either deformation, or buckling load, depending on the
irradiated condition. Control rod insertability must be proven at the limiting deformation. The deformed pattern of the grid lattice must be approximately uniform at the allowable
deformation level. The un-irradiated condition grid strength is defined as:
95% confidence on true mean load corresponding to a [ ] permanent deformation of the grid envelope, [
]Draft
71NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Grid Strength Definition – Proposed P(crit) Definition – Conclusions (continued)
Conclusions The irradiated condition grid strength is defined as:
95% confidence on true mean load at buckling. [
] Test protocol is based on [
]
Sources of conservatism: The un-irradiated [ ] deformation load limit is [ ] less than the actual grid
buckling capability. The [ ] deformation limit is conservative in terms of thermal-hydraulic acceptability. The irradiated grid test protocol ignores the potential benefit of oxidation for M5® grids
[ ]. The irradiated grid test protocol ignores the potential benefit of testing with solid fuel rod
pins (as opposed to hollow cladding segments). Potential benefits are in the same order of magnitude as oxidation.
Draft
Impact of Deformation Upon Thermal-Hydraulics, Non-LOCA and LOCARichard HarneLisa Gerken Draf
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73NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Deformation:T-H Considerations
Deformation Basis
All HTP grids reach a [ ] deformation
Uniformly distributed in one direction, leading to a slight loss of squareness, by [
]
Individual pin pitches could be reduced by [ ] in the direction of the deformation.
The lateral displacement of the fuel assembly would occur during the seismic event, however, the fuel assembly would shortly return to its nominal central position in its deformed state.
Draft
74NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Deformation:T-H Considerations
[ ] Deformation Impact on Subchannel Flow Areas
Draft
75NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Deformation:T-H Considerations
ACH-2 CHF Correlation Applicability in the Deformed State [
]
Conclusion The ACH-2 CHF correlation remains applicable for normal analyses and the post-
event state of a uniformly distributed [ ] deformation.Draft
76NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Deformation:T-H Considerations
DNBR Prediction Impact in the Deformed State DNBR predictions are performed with accommodations for uncertainties,
including an uncertainty for manufacturing variability.
The U.S. EPR DNB analyses were performed utilizing a [ ] uncertainty in the pin pitch for the limiting rod. Applied to the limiting subchannel
Produces a flow area differential with adjacent subchannels of nominal flow areas which conservatively accentuates the coolant flow expulsion from the limiting subchannel with the minimum DNBR prediction.
The ACH-2 CHF correlation is used to determine the DNBR worth of the manufacturing flexibility [ ]
Draft
77NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Deformation:T-H Considerations
DNBR Prediction Impact in the Deformed State Conclusion
The magnitude of the local pin pitch manufacturing flexibility, is greater than the local effect of the [ ] grid deformed state for subchannels in which the limiting hot rod is used to assess DNBR margin. Therefore, the ACH-2 CHF correlation remains applicable in the deformed state.
Verification will be made that the existing DNB impact of manufacturing flexibility is equal to or larger than the local deformed state DNB impact.
This conclusion is independent of core location or extent of deformation across the coreDraft
78NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Fuel Assembly Deformation:T-H Considerations
HTP Grid Hydraulic Resistance Impact in the Deformed State The [ ] reduction in the pin pitch, for interior cells, is within the
manufacturing variability observed in the pin pitch for HTP spacer grids.
Such variability would have been expected to be present within the pressure drop test fuel assembly due to HTP test grid fabrication.
Conclusion The uncertainty for manufacturing variability sufficiently accounts for the potential
impact of a [ ] deformed state within the spacer grid independent of core location or extent of deformation across the core.Draf
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79NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Modifications: Fuel Assembly Deformation
Non-LOCA impact for 1 mm deformation The grid deformation is [ ] uniformly distributed over the entire grid
With 17 fuel rods in a row, the fuel rod pitch would reduce by [ ] in lateral direction Assuming no change in longitudinal direction, the change in assembly and fuel rod flow areas is
less than [ ] Minimal impact on core pressure drop No impact on non-LOCA system response Thermal-Hydraullc impact has been assessed separately
Draft
80NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Impact of Modifications: Fuel Assembly Deformation
LOCA impact for 1 mm deformation The grid deformation is [ ] uniformly distributed over the entire grid
With 17 fuel rods in a row, the fuel rod pitch would reduce by [ ] in lateral direction Assuming no change in longitudinal direction, the change in assembly and fuel rod flow areas is
less than [ ] PCT occurs in between spacer grids
1 mm deformation has negligible impact on PCT [ ]Draf
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Bundle Deflection Amplitude-Revised RAI 64
Victor Hatman
Draft
82NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
RAI-64 Follow-up:Fuel Assembly Deflection Amplitude
Follow-up Question from November 2011 Audit This section is a follow-up to one of the questions raised during the November 2011 Audit
regarding the predicted in-core lateral displacements of the U.S.EPR fuel assembly comparedto previous designs
The following discussion must be considered as an addition to the RAI 64 response submitted in 2011
November 2011 Audit Summary RAI-64 questioned the applicability of the BAW-10133 linear bundle model to the U.S.EPR In the November 2011 audit, and the first draft of the RAI-64 response, AREVA presented
arguments based on the sources and strength of the non-linear effects in the U.S.EPR bundle, and concluded that these are weaker than in the case of previously approved designs
At the time of audit, the U.S.EPR design included weaker grids in the center two positions, which were predicted to exceed P(crit).
In May 2012, AREVA presented to the NRC a new closure plan which included a design change, consisting of stronger grids in the center two positions, which prevents grid buckling.
In view of the new U.S.EPR design change, the linearity of the bundle model becomes less critical.
A comparative table is shown on the next page
Draft
83NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Fuel Assembly Deflection Amplitude Comparison of “Stretched” Fuel Assembly Designs
12’ Assemblies 14’ Assemblies
Design AP-600 CE-14 AREVA
17x17
AP-1000 CE-16 U.S. EPRre-design
APWR
Lattice 17x17 14x14 17x17 17x17 16x16 17x17 17x17
Core Heightcold active fuel
144” 132” 144” 168” 156” 165.4” 168”
Stretch 12’ 14’
N/A N/A N/A 24” 24” 21.4” N/A
FA Model Linear Linear Linear Linear Linear Linear Non-linear
Grid Model Gap-Linear
Gap-Linear
Gap-Linear
Gap-Linear
Gap-Linear
Gap-Linear
Non-linear
Grid Loading <P(crit) <P(crit) <P(crit) <P(crit) <P(crit) <P(crit) >P(crit)
Topical Report WCAP-8288
CENPD-178
BAW-10133
WCAP-8288
CENPD-178
BAW-10133
MUAP-08007
Last Topical Revision
1973 1981 2000 1973 1981 2000 Under review
Draft
84NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
RAI-64 Follow-up:Fuel Assembly Deflection Amplitude
November 2011 Audit Remaining Question Request for a comparison of predicted FA amplitudes for the U.S.EPR and previous designs Table 64-1 in the ANP-10285Q10P document was revised to include transient deflections for the
U.S.EPR, for the Advanced Mk-BW and Mk-B-HTP Differences due to higher seismic excitation (0.3 g maximum ground acceleration for the U.S. EPR
versus 0.15 – 0.18 g for the other designs), and row length. A comparison of these designs, based on consistent seismic inputs, would yield deflections that are
more comparable than what is shown in Table 64-1. The total transient compression of the spacer grids is dominated by an elastically recoverable
component, which accounts for the additional deflection above the collapsed core gap space. Since the buckling limit of the grid is not exceeded, the ability of the core model to accurately predict
the bundle incoming kinetic energy, the peak impact force, and the rebound velocity, is maintained and is sufficient for the evaluation of fuel under external loads.
Draf
t
Impact of Grid Deformation on Loads-RAI 70Victor Hatman Draf
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86NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Spacer Grid Linear Model and Core Gap Sensitivity
Applicability of the current linear visco-elastic element to model grid impacts
RAI-70 questions the applicability of a linear visco-elastic model as a grid impact element
At the time RAI-70 was written, the maximum grid impact load exceeded the grid strength
Following the design change communicated during the May 2, 2012 Public Meeting, all grid impacts are below allowable
Grid deformation is acceptably small and bounded (peak impact on the stable side of the loading curve)
Focus shifts from accurately predicting the bundle deflection during post-buckling to accurately predicting the peak impact load and the rebound velocity.
The linear visco-elastic element captures the peak impact load and rebound velocity very accurately for permanent deformation levels above the imposed limit.
Only question remaining is the effect of the small grid deformation on subsequent impacts addressed via a core gap sensitivity study.
Draft
87NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Spacer Grid Linear Model and Core Gap Sensitivity
Core Gap Sensitivity Study based on the limiting time history and limiting row model 4 scenarios:
[
] Most representative scenario: FA-FA gaps nominal and FA-Baffle gaps increased In this case the sensitivity to gaps is less than [ ] Consistent with NUREG/CR-1018 assessment general conclusion that core gaps have a
second order effect on impact loads
Draft
Impact of Direct Method in Upstream Analyses on Fuel Closure PlanBrett Matthews Draf
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89NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Direct Method ImpactBackground
Core plate motion time histories used in fuel qualification result from upstream seismic analyses of Nuclear Island basematstructures (e.g., containment building) and the Reactor Coolant System
SASSI computer program is used to model the response of civil structures SASSI uses the “subtraction method” in accounting for soil structure
interaction between the building and its supporting soil Defense Nuclear Facilities Safety Board (DNFSB) issued a letter on April 8,
2011 highlighting issues related to the subtraction method NRC requested that AREVA justify the use of subtraction method
AREVA has decided to re-perform analyses using NRC-approved “direct method” in place of subtraction method
Draft
90NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Direct Method ImpactExpected Effects
AREVA’s preliminary evaluations from Nuclear Island civil/structural teams indicate: Change to direct method appears to affect soft soils more than firmer
cases Medium soil cases are limiting for fuel evaluation
Primary effects of the direct method appear to be in higher frequency content Low frequencies (i.e. below 10 Hz) are of primary concern for fuel evaluation
Based on preliminary evaluations, expectation is that the change to the direct method will not significantly alter resultsof the fuel evaluation Draf
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91NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Direct Method ImpactPlan for Reconciliation in Fuel Analysis
Expectation is that current analyses being performed will remain bounding
Work on Technical Report for fuel seismic evaluation will proceed based on current input core plate motions derived from the subtraction method
Technical Report will be submitted according to the schedule in the current closure plan using current core plate motions
Updated core plate motions, based on the direct method, will be made available for fuel evaluation in early 2013
Complete seismic evaluations of the fuel will be performed to confirm results presented in the Technical ReportDraf
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Summary and Next StepsJerry Holm
Draft
93NRC Meeting – RAI Responses to Round 7 RAI on ANP-10285P – November 16, 2012
Summary AREVA Seismic Methodology is Conservative Grid Strength Definition Consistent with NRC Historical
Guidance Grid Strength Definition has Negligible Impact on LOCA and
Thermal-Hydraulics Grid Deformation has Negligible Impact on Maximum Load Minimum Margin to Grid Strength is [ ]
Minimum Margin Occurs in Peripheral Fuel AssembliesDraft
Draft