ML20046C735
| ML20046C735 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 07/01/1993 |
| From: | Kenyon T Office of Nuclear Reactor Regulation |
| To: | Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| References | |
| NUDOCS 9308120027 | |
| Download: ML20046C735 (11) | |
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UNITED STATES
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8 July 1,1993
.....f Docket No.52-003 Mr. Nicholas J. Liparulo Nuclear Safety and Regulatory Activities Westinghouse Electric Corporation P.O. Box 355 Pittsburgh, Pennsylvania 15230
Dear Mr. Liparulo:
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION ON THE AP600 As a result of its review of the June 1992 application for design certifica-tion of the AP600, the staff has determined that it needs additional informa-tion in order to complete its review. The additional information is needed in the areas of containment systems, testing, and severe accident mitigation (Q480.6-Q480.37).
Enclosed are the staff's questions.
Please respond to this request within 90 days of the date of receipt of this letter.
You have requested that portions of the information submitted in the June 1992, application for design certification be exempt from mandatory public disclosure. While the staff has not completed its review of your request in accordance with the requirements of 10 CFR 2.790, that portion of the submitted information is being withheld from public disclosure pending the staff's final determination. The staff concludes that this request for additional information does not contain those portions of the information for which exemption is sought. However, the staff will withhold this letter from public disclosure for 30 calendar days from the date of this letter to allow Westinghouse the opportunity to verify the staff's conclusions.
If, after that time, you do not request that all or portions of the information in the enclosures be withheld from public disclosure in accordance with 10 CFR 2.790, this letter will be placed in the NRC's Public Document Room.
- The numbers in parentheses designate the tracking numbers assigned to the questions.
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i 9308120027 930701 PDR ADOCK 05200003 i:
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Mr. Nicholas J. Liparulo July 1, 1993 This request for additional information affects fewer nine or fewer respon-dents, and therefore is not subject to review by the Office of Management and Budget under P.L.96-511.
If you have any questions regarding this matter, you can contact me'at (301) 504-1120.
Sincerely, OdgIlidShn @ d Thomas J. Kenyon, Project Manager Standardization Project Directorate Associate Director for Advanced Reactors and License Renewal Office of Nuclear Reactor Regulation
Enclosure:
As stated cc w/ enclosure:
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DOCUMENT NAME: JUNE.RAI
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Mr. Nicholas J. Liparulo Westinghouse Electric Corporation Docket No.52-003 AP600 cc:
Mr. B. A. McIntyre Advanced Plant Safety & Licensing Westinghouse Electric Corporation Energy Systems Business Unit P.O. Box 355 Pittsburgh, Pennsylvania 15230 Mr. John C. Butler Advanced Plant Safety & Licensing Westinghouse Electric Corporation Energy Systems Business Unit Box 355 Pittsburgh, Pennsylvania 15230 Mr. M. D. Beaumont Nuclear and Advanced Technology Division Westinghouse Electric Corporation One Montrose Metro 11921 Rockville Pike Suite 350 Rockville, Maryland 20852 Mr. Sterling Franks U. S. Department of Energy NE-42 1
Washington, D.C.
20585 Mr. S. M. Modro EG&G Idaho Inc.
Post Office Box 1625 Idaho Falls, Idaho 83415 Mr. Steve Goldberg Budget Examiner 725 17th Street, N.W.
Room 8002 Washington, D.C.
20503 Mr. Frank A. Ross U.S. Department of Energy, NE-42 Office of LWR Safety and Technology 19901 Germantown Road Germantown, Maryland 20874
REQUEST FOR ADDITIONAL INFORMATION ON THE WESTINGHOUSE AP600 DESIGN CONTAINMENT SYSTEMS 480.6 Determination of Safety Relief Valve Pool Dynamic Loads and Temperature Limits Section 1.9 of the SSAR includes a list of all generic and unresolved safety issues, and a discussion of how each applicable GSI and USI is addressed, as required by 10 CFR 52. Under USI A-39, " Determination of Safety Relief Valve Pool Dynamic Loads and Temperature Limits for BWR Containments," Westinghouse indicates that this is a GE/BWR issue, and is not applicable to the AP600 design.
While it is true that the AP600 is not a BWR and does not have a suppression pool, per se, it nevertheless does have the in-containment refueling water storage tank (IRWST), which acts as the equivalent of a suppression pool when the automatic depressurization system (ADS) is actuated, and which will undergo many of the same kinds of loads as a suppression pool during ADS operation.
Furthermore, this pool is a key safety-related component, because it serves as the source of almost 90% of the emergency core coolant for the AP600.
Because there is a similarity in function of the IRWST and a BWR suppression pool, address USI A-39 (Section 6.2).
480.7 Environmental Qualification of Components Inside Containment in a Post-Accident Environment Because there are no safety-related containment spray system and fan coolers, severe and adverse environmental conditions are likely to persist inside the AP600 containment for a longer period of time than would be expected in the current generation of plants.
Identify how the AP600 design meets the requirements of 10 CFR 50.49.
Describe the steps Westinghouse is taking to ensure that key components will survive and function under postulated adverse conditions (both design basis accidents and severe accidents).
What additional testing will these components be subject to, both before (pre-operational / qualification testing) and after (technical specifications or other programmatic surveillances) installation?
For example, in the slides from the May 26-27th,1993, presentatien to the NRC, Westinghouse quoted operability qualification times of 3 days for the ADS valves. The maximum pressure, temperature and humidity were 45 psig, 370 *F, and 100%, respectively. Are there any tests that demonstrate the capability of the ADS valves and motor operators to survive under the postulated accident conditions in the SSAR (Section 6.2)?
ENCLOSURE
. TEST AND SCALING 480.8 Natural Circulation of Air in the Passive Containment Cooling System (PCCS)
Natural circulation of air is the only heat removal mechanism for the dry containment case (severe accident).
In addition, degradation of the performance of the PCCS is of concern for the case in which the containment is striped or partially wet (design basis accident).
Provide additional information or justification concerning (Chapter 14):
(a) not simulating the baffle in the large scale test facility, (b) the ability of the AP600 to sustain air cooling under natural circulation, (c) the potential that air circulation in the counter-current, two-annuli AP600 prototype could be affected by heat conduction through the baffle wall, and (d) the potential for flow reversal and instability of the air flow, which could lead to degradation of the PCCS performance, especially under dry operating conditions.
480.9 Heat Transfer to Internal Structures and Mixing in the Containment Provide additional rationale for (Chapter 14):
(a) the simulation of concrete structures in the scale test
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facility.
(b) the geometry of flow paths in the large scale test facility, including their scaling.
(c) how the relatively complex geometry below the operating deck of the AP600 was reduced and scaled to three simple volumes in the large scale test facility.
480.10 Jet Discharge:
Location /0rientation/ Scaling Provide the rationale for the choice of jet discharge location, orientation, and scaling in the large scale test facility.
Why is the chosen single release point representative of the family of release points that could exist in the actual AP6007 Include a discussion of multiple release points.
Under design basis accident conditions, what is the important equipment to protect? Given that, how does Westinghouse rationalize its selection of break location, orientation, and scaling (Chapter 14)?
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480.11 1/8-Scale Facility Instrumentation Provide information concerning the adequacy of the following for the 1/8-Scale Facility (Chapter 14):
(a) grab samples (both their number and frequency),
(b) water film thickness measurement instrumentation / observation for film flows on the exterior of the containment shell, (c) air flow instrumentation (anemometers) in the annular region, (d) instrumentation for measuring the temperature profile in the containment steel shell wall.
The concern here is 3D heat conduction (as opposed to simple ID radial heat conduction) in the steel shell wall could cause nonlinear temperature profiles in the steel shell wall.
(e) instrumentation in the large scale test facility.
Is it sufficient to understand the physics / phenomena inside the containment and permit adequate validation of the MG0THIC j
computer code? Compensating errors may be hidden in global measurements.
Also, provide information on the assessment of film thickness models I
on the inner surface of the containment shell.
480.12 1/8-Scale Facility Test Matrix Provide the rationale for the tests in the 1/8-Scale Facility Test Matrix.
Include discussion of test descriptions, conditions, and I
ranging of parameters as it relates to scaling analysis.
The document I
should clearly delineate the purposes of the test, and whether they are primarily to investigate design basis accidents or severe accidents.
It should also address the following concerns (Chapter 14):
j (a)
The tests are scheduled to be performed at pressures that are too high for long term simulation.
This may lead to more turbulence and better mass transfer than would have been seen at lower i
pressures.
(b) Helium-only tests (no steam) could be included in the matrix to help demonstrate the adequacy of the grab samples.
(c) Could a properly scaled test be added that would be useful in validating the capability of MG0THIC to predict the post'reflood pressure peak that occurs roughly 15-minutes following a loss of
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coolant accident?
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4-480.13 Westinghouse Scaling Approach Provide additional documentation and rationale beyond that in Chapter 7 of WCAP-13246 for the scaling approach.
In particular, provide information on how the large scale test parameters and characteristics scale to the AP600 design.
Provide additional justification for the use of MG0THIC to predict AP600 prototype behavior (Chapter 14).
480.14 Mechanistic Correlations in MGOTHIC Provide additional documentation and justification for the heat and mass transfer correlations used in MG0THIC, including information on the applicability and validation of:
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(a) the correlations used (such as McAdams vs. alternate correlations for downward facing surfaces) to simulate the internal thermal hydraulic behavior of the containment, (b) the Colburn correlation. This correlation is based on forced convection flow in a pipe (internal flow), and its use must therefore be further justified for use in other geometries (in particular for the case of heat and mass transfer when film evaporation takes place, driven by heat transfer from the wall).
(c) the heat and mass transfer analogies used in MG0THIC, and (d) the forced / mixed convection correlations used in the annular gap.
The MGOTHIC models assume a weak dependence on the scaling length.
Justify using the models in the free convection regime by presenting dimensionless plots of Nusselt number vs. the product of the Grashof and Prandt1 numbers (Chapter 14).
480.15 HGOTHIC Validation Using (Integral and Large Scale) Test Data Provide justification for the use of MG0THIC to predict AP600 i
prototype behavior based upon integral and large scale test data, discussion and analysis of the HG0THIC models, and a rigorous scaling analysis that shows that the range of test parameters (when properly scaled) are representative of conditions that would be expected in the AP600 prototype.
In addition, provide information on the modeling approach and model validation of:
(a) subcooling in MG0THIC, (b) condensation models for use inside the containment vessel, and (c) steam / air / hydrogen stratification.
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. Provide additional information and justification for the use of MG0THIC in a lumped-parameter mode to predict hydrogen stratification.
The staff believes that any lumped-parameter code will tend to underestimate the concentration of hydrogen in the containment dome and overestimate the amount of mixing. These effects are i
nonconservative. Therefore, justify the exclusive use of a lumped-i parameter approach (see Q480.32).
Alternatively, Westinghouse may provide finite-difference-based WG0THIC calculations to predict hydrogen stratification and a justification for why the finite-difference based calculations accurately predict hydrogen distributions (Chapter 14).
480.16 WG0THIC Numerics Provide additional information on WG0THIC numerics. There is no discussion in WCAP-13246 of any nodalization studies to demonstrate the robustness of the HG0THIC code and its sensitivity to the choice of grid size and the number of computational nodes.
There is also no discussion of time step size. How was it chosen and what is its relationship to the Courant condition?
In one of the small tests (Figure 22, page 109 of WCAP-13246),
velocity fluctuations near the vessel wall indicate the possibility of numerical instabilities (Chapter 14).
480.17 External Film Pattern / Water Distribution Tests Provide additional information on the external film / water distribution that is expected for the AP600. The Waltz Hill tests were done using a steel shell at ambient temperature. Will the film pattern be affected by heating of the shell?
Is there a difference in the film behavior in the large scale test facility in cases where the shell is not heated, versus cases where the shell is heated?
480.18 Degree of " Rain" in the AP600 Containment For the purpose of PRA/ dose calculations, Westinghouse appears to take credit for fission product removal by " rain out" in the containment.
However, during a meeting with Westinghouse, it was stated that the i
collection ducts in the interior of the large scale test facility (away from the walls) collected no " rain" during testing.
Provide clarification concerning the amount of " rain" expected in the AP600 (Chapter 14).
SEVERE ACCIDENTS 480.19 External Reactor Vessel Cooling - Reactor Vessel Insulation Provide a more thorough assessment of the ability of water to migrate to the reactor vessel through the insulation. What controls will be
used to ensure adequate sizing of the insulation spacing? What is to prevent maintenance personnel from achieving a " perfect" fit for the insulation? What criteria has Westinghouse used to test the AP600 design in this area (WCAP-13388)?
480.20 External Reactor Vessel Cooling - Existing Database Provide an evaluation of the scalability and applicability of the existing database (WCAP-13388).
480.21 External Reactor Vessel Cooling - Impact of the Use of Subcooled Water Discuss the impact of the use of subcooled water in the experiments on the downward heat flux and the conditions expected to be present in the AP600 (WCAP-13388).
480.22 High Pressure Melt Ejection Discuss the rationale for concluding that high-temperature hydrogen will not burn during a high pressure melt ejection (HPME) with high steam concentrations (WCAP-13388).
480.23 Steam Explosions How are energetic or explosive forces accounted for in calculation of ex-vessel steam explosions (WCAP-13388)?
480.24 Core-Concrete Interactions - Core Debris Equilibrium Height Provide the basis for assuming the core debris spreads to an equilibrium height, given the existence of the doorway through which it must travel (WCAP-13388).
480.25 Core-Concrete Interactions - Core Debris Coolability/ MACE Address the assumption of core debris coolability in light of failure of the MACE tests to demonstrate this (WCAP-13388).
480.26 Core-Concrete Interactions - Containment Integrity / Liner Penetration WCAP-13388 indicates that a threat to containment integrity exists if the basemat is penetrated.
Discuss why containment integrity is not breached once the liner is penetrated?
480.27 Core-Concrete Interactions - Deflagration / Detonation of Combustible Gases Discuss the potential for deflagration or detonation of combustible gases produced during core-concrete interactions and their impact on containment (WCAP-13388).
- 480.28 Core-Concrete Interactions - Hand Calculations Compare the results of the hand calculations with that predicted using analytical methods (WCAP-13388).
480.29 Core-Concrete Interactions - Long-term radial ablation How is the effect of long-term radial ablation accounted for (WCAP-13388)?
480.30 Core-Concrete Interactions - Heat Removal from Core Debris Although water is necessary for quenching to occur, provide the experimental data base that indicates that' sufficient heat can be extracted from the core debris to rapidly overcome the decay heat and chemical reaction heat (WCAP-13388).
480.31 Core-Concrete Interactions - Water Ingression into Solidified Debris Provide the basis for the assumption of water ingression into solidified debris, as opposed to the counter flow of steam out of the debris (WCAP-13388).
480.32 Hydrogen Control - Prediction of Hydrogen Distribution Provide a discussion of the methods used to predict the hydrogen distribution within the containment.
In particular, the SSAR appears to rely on the HG0THIC. code used in a lumped-parameter mode.
Lumped-parameter codes are notorious fnr overpredicting mixing, and underpredicting the stratification of hydrogen in the containment dome. This is non-conservative. Why is HGOTHIC (used in the lumped-parameter mode) any different? Have any other experiments or calculations been performed to confirm Westinghouse's ability to predict hydrogen distributions in the AP600 containment (WCAP-13388)?
(see Q480.15) i 1
480.33 Hydrogen Control - Passive Autocatalytic Recombiners What is Westinghouse's position on the use of Passive Autocatalytic Recombiners (WCAP-13388)?
480.34 Hydrogen Control - Rationale for Hydrogen Igniter Placement Provide the rationale for hydrogen igniter placement and the supporting data base (WCAP-13388).
480.35 Hydrogen Control - Localized Detonations, Alternate DDT Mechanisms, and Impulsive Loads from Subsonic Accelerated Flames Provide an evaluation of the potential impact of localized detonations, alternate DDT mechanisms, and impulsive loads from subsonic accelerated flames (WCAP-13388).
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.. 480.36 Hydrogen Control - Diffusion Flames Above IRWST Discuss the potential for and impact on the steel containment of diffusion flames above the in-containment refueling water storage tank (WCAP-13388).
480.37 Hydrogen Control - Mechanisms to Achieve Uniform Hydrogen Distributions Describe the nature and extent of the expected turbulence in the AP600 containment under severe accident conditions that will ensure uniform hydrogen mixing (WCAP-13388).
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