n•. nuscale power- · 2015-06-02 · dynamic instabilities" dynamic instabilities require...

N•. NUSCALEPOWER- LO-0515-14243

Enclosure 1:

"NuScale Reactor Stability," PM-0515-14235-NP, Revision 0, nonproprietary version

NuScale Power, LLC1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928

www.nuscalepower.com

NuScale Nonproprietary

NuScale ReactorStability

Yousef Farawila, Ph.D.Nuclear Consultant

Maurice Ades, Ph.D., P.E.Principal Engineer, Nuclear Safety

Engineering

June 2, 2015

PM-0515-14235-NP

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* NUSCALEPOWER-Copyright 2015 by NuScale Power, LLC.

Outline1. Introduction

2. Review of stability mechanisms

3. Stability model description

4. Stability analysis sample applications

5. Observations and conclusions

6. Elements of stability protection methodology

7. Questions and discussions

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1. Introduction* Stability is a licensing requirement

- GDC 10, 12,13, 20, and 29

- GDC12 Suppression of reactor power oscillations. The reactor core andassociated coolant, control, and protection systems shall be designed to assurethat power oscillations which can result in conditions exceeding specifiedacceptable fuel design limits are not possible or can be reliably and readilydetected and suppressed.

* This pre-application presentation is a step towards demonstratingcompliance with all applicable regulations related to reactor stability

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1 Introduction0

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2. Review of Stability Mechanisms

• Survey and classification of instabilities

* Examine applicability to NuScale design

- not limited to past extensive BWR experience

- no a priori assumptions of trends

* Classification of instabilities

- static

- dynamic

- compound

Identify limiting instability mode(s) and analysis needs

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Static Instabilities" Static instabilities can be shown from steady-state

equations

" Dynamic instabilities require inertia effects

- Dynamic models can resolve static instabilities, but not vice versa

" Examples of static instabilities

- flow excursion or Ledinegg Instability

- boiling crisis

- flow pattern transition instability

- flashing instability

- geysering

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Static Instabilities* Flow excursion or Ledinegg instability

- present if the pressure drop along the flow path as function of mass flowrate is multi-valued (equivalently having a negative gradient)

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Static InstabilitiesBoiling crisis

- local heat flux exceeds critical value leading to departure fromnucleate boiling (CHF)

- unstable, possibly oscillating, vapor film

- covered in the literature, and mentioned here for completeness

- inverted-logic: boiling crisis is not a cause of instability but aplausible result of it. However, CHF is a protected SAFDL.

- no further consideration of this thermal instability mode

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Static Instabilities* Flow pattern transition instability

- for example, laminar-to-turbulent

- phenomena included in constructing the pressure drop around theloop as function of mass flow rate

- disposition implied as part of demonstrating Ledinegg stability


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Static Instabilities• Flashing instability

- relevant for heaters located under a tall riser

- hot (at or near saturation) liquid rises to lower pressure elevation

- evaporation at reduced pressure (flashing) drives flow disturbance

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Static Instabilities* Geysering

- somewhat similar to flashing instability, but where

- vapor is generated in the heater and expands in the riser

- possible liquid thermodynamic metastable state (superheated) dueto low flow and lack of nucleation sites

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Relevant phenomena in static instabilities are covered indynamic modeling, which is more general than static analysis

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Dynamic Instabilities" Dynamic instabilities require time-dependent models

- mechanical and thermal inertia effects

- dynamic models can resolve static instabilities, but not vice versa

- pure modes refer to simplest abstractions while more complex feedbackmechanisms and mixed phenomena are common in practice

" Feedback that is (a) negative, (b) delayed, and (c) strong, results inunstable (growing) oscillations

" Examples of pure dynamic instabilities

- pressure drop oscillations

- acoustic oscillations

- density waves

- xenon oscillation

- natural circulation instability

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Dynamic Instabilities* Pressure drop oscillations

- dynamic extension of flow excursion static instability

- multiple steady state points are possible

- plus a storage mechanism (e.g., pressurization of a volume in theflow circuit) to create time delay. Cyclical behavior replaces theone time static transition

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Dynamic Instabilities* Acoustic oscillations

- standing pressure waves (sound waves)

- energy feeding and sustaining the oscillation is thermal; forexample, compression collapses a vapor film and forces liquid-wallcontact and increases heat transfer, and vice versa

- may be applicable to systems under film boiling

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Dynamic InstabilitiesDensity waves

- extensively studied for boiling water reactors (BWR)

- pure mode in a vertical boiling channel under fixed pressure dropboundary condition and fixed heat source

- a perturbation in inlet flow rate creates traveling density wavesalong the heated channel

- delayed void fraction feedback creates density head response

- friction pressure drop response in 1- and 2-phase flow regions

- feedback is negative and tends to restore steady state, however

* time lag due to density wave traversing the channel allow oscillatoryresponse (oscillation period - bubble transit time)

* unstable oscillations if feedback is strong, e.g., high power-to-flow ratio

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Dynamic Instabilitiese Density waves in BWR make for a special case

- compound with reactivity feedback

- global and out-of-phase (regional) power oscillations

- destabilized for

° high power-to-flow ratio

" bottom-skewed axial power shape

° lower pressure

" high inlet flow subcooling

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Dynamic Instabilities

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Dynamic InstabilitiesXenon oscillation is a pure neutronic instability mode

- fission product 1135 decays into Xe 135 which is a strong neutronabsorber (poison)

- a perturbation increasing power is countered by negative feedbackdue to generation of the neutron absorber, but the feedback isdelayed, so it may result in oscillations

- main factor for Xe stability is the core size

large cores have small subcritical reactivities for higher neutron fluxharmonics, which is destabilizing

ff

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Dynamic Instabilities9 Natural circulation instability

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Coupled Instability Modes" More complex than pure instability modes

" Instability modes may become combined

" Additional feedback mechanisms may alter the behaviorof a pure instability mode

* Example of coupled modes

- parallel channel instability

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Coupled Instability Modes

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3. Stability Model Description

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CONTROL RODDRIVE MECHANISM

PRESSURIZER

MAIN STEAM

RISER(PRIMARY FLOW)

STEAM GENERATOR(SECONDARY FLOW)

CONTAINMENT VESSEL----- FEEDWATER

DOWNCOMER(PRIMARY FLOW)

REACTORPRESSURE VESSEL

-CORE(PRIMARY FLOW)

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3. Stability Model Descriptione Heat conduction in fuel rods

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* Heat transfer models for heat sink (steam generator)

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3. Stability Model Description9 Closing relations and correlations

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3. Stability Model Description* Numerical solution

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3. Stability Model DescriptionNumerical solution procedure

- steady state initialization

- transient calculations

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- output at discrete time steps includes

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Summary of Model Assumptions* Model assumptions suitable for the target application

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Summary of Model Assumptions

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4. Stability Analysis Sample Applications

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Sample Applications

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Stability Under Transient Conditions

" Requires boundary conditions (time-dependent forcing functions)- primary system pressure

- steam generator secondary side pressure,feedwater flow rate and temperature

- reactivity forcing function, as needed tosimulate reactivity-induced transients

" Initial core power specified

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Stability Under Transient Conditions9 Types of transients

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* Selected representative results in the next slides

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5. Observations and ConclusionsNuScale stability characteristics differ from large PWRs and BWRswith or without recirculation pumps

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a NuScale operation is nonlinear because of natural circulation

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6. Elements of Stability Protection Methodology

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•Region exclusion for BWR

- exclusion region is defined on power vs. flow operation space (two-dimensional)

- exclusion region is calculated analytically for the least stable point in each cycle

- a buffer region is defined for immediate manual exit (to avoid automatic scram)

- protected by automatic scram

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Detect and suppress for BWR- online detection of coherent oscillations using a period-based algorithm analyzing groups of

local power range monitor signals

- relationship between critical power response and power oscillation magnitude (DIVOM curve).DIVOM curve is calculated once for each reload cycle.

- trip setpoint is plant-specific

- automatic scram when coherent oscillations are detected and setpoint reached

- reactor trip prevents oscillation growth

- spurious scrams are possible

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9 Generic stability protection methodology

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Summary and Path Forward

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Enclosure 3:

Affidavit, AF-0515-14244

NuScale Power, LLC1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928

www.nuscalepower.com

NU SCALE AF-051 5-14244'POWER- Revision 0

Page 1 of 2

AFFIDAVIT of Thomas A. Bergman

STATE OF OREGON

CITY OF CORVALLIS

I, Thomas A. Bergman, state as follows:

(1) I am the Vice President of Regulatory Affairs of NuScale Power, LLC (NuScale), and as suchI am authorized to apply for withholding of information transmitted with this letter from publicdisclosure and to execute this affidavit on behalf of NuScale.

(2) I am knowledgeable of the criteria and procedures used by NuScale in designating confidentialcommercial information as proprietary and have been specifically delegated the function ofreviewing the information described in this affidavit that NuScale seeks to have withheld frompublic inspection.

(3) The harm that would result if the information sought to be withheld is disclosed to the public is asfollows:

(a) The presentation discloses information about the processes, components, structures,tools, methods, or other trade secrets by which NuScale develops Reactor Stability.NuScale has performed significant research and evaluation to develop a basis for theseprocesses, components, structures, tools, methods, or other trade secrets and hasinvested significant human and financial resources in such development.

(b) NuScale's unique process, component, structure, tool, method, or other trade secretsprovide NuScale with a competitive economic advantage over other companies. Publicdisclosure of the information would cause substantial harm to NuScale's competitiveposition and reduce or foreclose opportunities for NuScale to generate a return on itsinvestment in research and development. Although the exact financial value of theinformation is difficult to quantify, it is a key element of the design basis for a NuScaleplant and, therefore, has substantial value to NuScale.

(c) If the information were disclosed to the public, NuScale's competitors would have accessto the information without having been required to undertake a similar expenditure ofresources. Such disclosure would constitute a misappropriation of NuScale's intellectualproperty, would unfairly provide NuScale's competitors with a windfall, and would depriveNuScale of the opportunity to seek an adequate return on its investment.

(4) The information sought to be withheld is contained in the enclosed presentation scheduled forJune 2, 2015 entitled NuScale Reactor Stability. The enclosure contains the designation"NuScale Proprietary Class 2" at the top of each page containing proprietary information. Theinformation considered by NuScale to be proprietary is identified within double braces, {{ }}" inthe document.

(5) The basis for proposing that the information be withheld is that NuScale treats the information astrade secrets and commercial or financial information that are privileged and confidential.NuScale relies upon the exemption from disclosure set forth in the Freedom of Information Act("FOIA"), 5 USC § 552(b)(4), as well as exemptions applicable to the NRC under 10 CFR §§2.390(a)(4) and 9.17(a)(4).

(6) With respect to the considerations set forth in 10 CFR § 2.390(b)(4):J

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(a) The information sought to be withheld has been held in confidence by NuScale.

(b) The information is of a sort customarily held in confidence by NuScale and, to the best ofmy knowledge and belief, consistently has been held in confidence by NuScale. Theprocedure for approval of external release of such information typically requires review bythe staff manager, project manager, chief technology officer or other equivalent authority,or the manager of the cognizant marketing function (or his delegate), for technicalcontent, competitive effect, and determination of the accuracy of the proprietarydesignation. Disclosures outside NuScale are limited to regulatory bodies, customers andpotential customers and their agents, suppliers, licensees, and others with a legitimateneed for the information, and then only in accordance with appropriate regulatoryprovisions or contractual agreements to maintain confidentiality.

(c) The information is being transmitted to and received by the NRC in confidence.

(d) No public disclosure of the information has been made, and it is not available in publicsources. All disclosures to third parties, including any required transmittals to NRC, havebeen made, or must be made, pursuant to regulatory provisions or contractualagreements that provide for maintenance of the information in confidence.

(e) Public disclosure of the information is likely to cause substantial harm to the competitiveposition of NuScale, taking into account the value of the information to NuScale, theamount of effort and money expended by NuScale in developing the information, and thedifficulty others would have in acquiring or duplicating the information. The informationsought to be withheld is part of NuScale's technology that provides NuScale with acompetitive advantage over other firms in the industry. NuScale has invested significanthuman and financial capital in developing this technology and NuScale believes it woulddifficult for others to duplicate the technology without access to the information sought tobe withheld.

I declare under penalty of perjury that the foregoing affidavit and the matters stated therein are true andcorrect to the best of my knowledge, information, and beli f.

Thomas A. Ber m•an

State of Oregon, County of Benton OFFICIAL SEALELIZABETH JANE LUCASON

SNOTARY PUBLIC-OREGONSubscribed and sworn to before me this leday of May 2015 COMMISSION NO. 466711

S MY COMMISSION EXPIRES MARCH 14, 2016

Notary Public

My commission expires: ?12o~~Jh ,M/ A~/1L9

n•. nuscale power- · 2015-06-02 · dynamic instabilities" dynamic instabilities require...

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