Nuclear Power Reactors – An Example of Improvements in

Reliability and Potential for Improvement

Dr. Jess Gehin Director, Consortium for Advanced Simulation

of Light Water Reactors

Oak Ridge National Laboratory

5th Accelerator Reliability Workshop (ARW 2015) Knoxville, Tennessee

April 26 to May 1, 2015

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Outline

• Nuclear Energy in the United States

• Availability and Reliability in Nuclear Plants

• Historical Experience on Key Performance Indicators

• Reliability of Nuclear Fuel

• CASL Research to Improve Operations

• Conclusions

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There are 100 Commercial Nuclear Power Reactors in the

U.S.

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Five Nuclear Reactors are Currently Under Construction

in the US TVA Watts Bar Unit 2

V.C. Summer Units 2 & 3

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Several More Reactors have been Previously Proposed

Most of the Plants Delayed Because of Low 2008 Economic Downturn and Low Natural Gas Prices

Source: U.S. NRC

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New Reactor Designs Being Developed/Certified by NRC

• Westinghouse AP1000® - Design Certified

• General Electric ESBWR - Design Certified (2014)

• NuScale Small Modular Reactor - Certification application to be submitted in 2016

• mPower Small Modular Reactor – Certification application suspended

• AREVA EPR – Design certification suspended

• Mitsubishi USAPWR – Design certification delayed

• Korea APR-1400 – Schedule TBD

Most Schedules Delayed Because Scale Back in Planned Construction

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Availability and Reliability of Commercial Reactors

• Utilities require high availability and capacity factors for nuclear power plants – Availability Factor – fraction of the of time a reactor is able to produce

electricity

– Capacity Factor – ratio of the actual energy output to the potential output

• Desire for high capacity factors is driven by: – Large capital costs for nuclear plants

– Large cost of replacement power when the plant is shutdown

– Very low production costs compared to other sources

• Factors that affect Availability/Capacity – Planned refueling outages

– Unplanned shutdowns due to mechanical failures or offsite issues

– Major outages for maintenance, upgrades, component replacements

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Nuclear Energy Has a High Capacity Factor Compared to

Other Energy Sources

Source: NEI, updated 4/14

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Capacity Factors Have Increased Significantly

2014 Capacity Factor 91%

Source: NEI, updated 4/14

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The US Nuclear Fleet as a Whole is Performing Well

Source: NEI, updated 4/14

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Improvements in Capacity Factors Largely Driven by Optimization of Refueling

Outages

Outages are planned for spring/fall – time of low demand

Source: NEI, updated 4/14

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Significant Power has Been Added Through Uprates

Plant power uprates range from 1 – 20%

Source: NEI, updated 4/14

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Reliability of Nuclear Power Plants

• Reliability – A measure of plants expected generation when expected to be available.

• Scheduled Outage - The shutdown of a generating unit, transmission line, or other facility for inspection, maintenance, or refueling, which is scheduled well in advance (even if the schedule changes)

• Forced Outage - The shutdown of a generating unit, transmission line, or other facility for emergency reasons, or a condition in which the equipment is unavailable as a result of an unanticipated breakdown. – An outage is considered "forced" if it could not reasonably be delayed beyond 48 hours from

identification of the problem, if there had been a strong commercial desire to do so. In particular, the following problems may result in forced outages

– Any failure of mechanical, fuel handling, or electrical equipment or controls within the generator's ownership or direct responsibility (i.e., from the point the generator is responsible for the fuel through to the electrical connection point)

– A failure of a mine or fuel transport system dedicated to that power station with a resulting fuel shortage that cannot be economically managed

– Inadvertent or operator error

– Limitations caused by fuel quality

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Several Performance Indicators are used

• U.S. NRC (primarily safety focused, but informs on reliability): – Automatic Reactor Scrams While Critical (IE)

– Significant Events (IE)

– Safety System Actuations (MS)

– Safety System Failures (MS)

– Forced Outage Rate (MS)

– Equipment Forced Outage Rate/1000 Critical Hours (MS)

– Collective Radiation Exposure (OR)

• World Association of Nuclear Operators– performance & safety – Capability factor

– Unplanned capability factor loss

– Fuel reliability

– Thermal performance

– Chemistry performance

– Collective radiation exposure

– Volume of solid radioactive waste

– Forced Loss Rate

– Unplanned automatic scrams

– Industry safety accident rate

– Safety system performance

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Unplanned Automatic Scrams (Worldwide)

Source: WANO 2013

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Unplanned Capability Loss Factor (Worldwide)

Source: WANO 2013

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Forced Loss (of capacity) Rate (Worldwide)

Source: WANO 2013

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Forced outage rate of U.S. nuclear reactors from FY 2000

to FY 2013 4.24%

3%

1.7%

3.04%

1.88%

2.34%

1.47% 1.41%

1.34%

2.21%

1.74% 1.8%

2.77%

2.98%

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

2000* 2001* 2002* 2003* 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Forc

ed

ou

tag

e r

ate

Source: US NRC

Force Outage Rate: Fraction of total generation time that plant is not available

to operate

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The U.S. Industry has a Focus in Improving Nuclear Fuel

Reliability

• Improving the economics by reducing the requirements to replace failed fuel

• Increase fuel utilization and lifetime

• Reduced unplanned outages to replace fuel avoiding operation and replacement power costs

Fuel Failure – cladding breach and release of fission products into coolant water

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Anatomy of a Nuclear Reactor Example: Westinghouse 4-Loop Pressurized Water Reactor (PWR)

Reactor Vessel and Internals

17x17 fuel assembly

Core • 11.1’ diameter x 12’ high • 193 fuel assemblies • 107.7 tons of UO2 (~3-5% U235)

Fuel Assemblies • 17x17 pin lattice (14.3 mm pitch) • 204 pins per assembly

Fuel Pins • ~300-400 pellets stacked within 12’ high x 0.61

mm thick Zr-4 cladding tube Fuel Pellets • 9.29 mm diameter x ~10.0 mm high

Operating Conditions • 2200°C – max fuel centerline • 350°C – max clad surface) • 300°C, 15 MPa – coolant water • Radiation environment • 6 year residence time

~50,000 fuel pins and over 16M fuel pellets in the core of a PWR

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Details of a Nuclear Fuel Assembly

US Plants require ~1.5M fuel rods/year (500M pellets)

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Reported Fuel Failures

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Causes of Fuel Failures (2000 – 2008)

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Approaches for Improving Fuel Reliability

• Improve fabrication quality to reduce fuel pellet and cladding defects

• Reactor operations that improve fuel performance – Slower power ramp rates to reduce strain

– Additional of chemicals to coolant reduce corrosion

• Improvements in fuel designs – Add lower nozzle strainers to filter out debris

– Improved grid designs to minimize flow induced vibration

– Improved core designs to minimize power peaking to reduce corrosion

• Research and development – Improved modeling and simulation to predict failures

– Improved materials that are more tolerant of conditions

– Experimental investigations of performance in laboratories

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CASL was the first DOE Innovation Hub

Core partners

Oak Ridge National Laboratory

Electric Power Research Institute

Idaho National Laboratory

Los Alamos National Laboratory

Massachusetts Institute of Technology

North Carolina State University

Sandia National Laboratories

Tennessee Valley Authority

University of Michigan

Westinghouse Electric Company

Contributing Partners

ASCOMP GmbH

CD-adapco

City College of New York

Florida State University

Imperial College London

Rensselaer Polytechnic Institute

Texas A&M University

Pennsylvania State University

University of Florida

University of Wisconsin

University of Notre Dame

Anatech Corporation

Core Physics Inc.

G S Nuclear Consulting, LLC

University of Texas at Austin

University of Texas at Dallas

University of Tennessee – Knoxville

Pacific Northwest National Laboratory

A Different Approach

• “Multi-disciplinary, highly collaborative teams ideally working under one roof to solve priority technology challenges” – Steven Chu

• “Create a research atmosphere with a fierce sense of urgency to deliver solutions.” – Kristina Johnson

• Characteristics – Leadership – Outstanding, independent, scientific

leadership – Management – “Light” federal touch – Focus – Deliver technologies that can change the

U.S. “energy game”

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CASL Scope: Develop and apply a “Virtual Reactor” to assess fuel design, operation, and safety criteria

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• Deliver improved predictive simulation of PWR core, internals, and vessel

– Couple Virtual Reactor to evolving out-of-vessel simulation capability

– Maintain applicability to other NPP types

• Execute work in six technical focus areas to:

– Equip the Virtual Reactor with necessary physical models and multiphysics integrators

– Build the Virtual Reactor with a comprehensive, usable, and extensible software system

– Validate and assess the Virtual Reactor models with self-consistent quantified uncertainties

Focus on Addressing Challenge Problems to Drive Development and Demonstration

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CRUD Predict CRUD Thickness Boron Uptake and Impact

on Core Power Distribution (CIPS) and Cladding

Corrosion (CILC)

Neutronics, Thermal-hydraulics/Fluid Flow, Chemistry

Our Challenge Problems are Focused on Key Industry Reactor

Performance Areas

Pellet-Clad Interaction Predict Core Wide PCI Margin and Missing

Pellet Surface PCI

Neutronics, Thermal-hydraulics, Fuel/Cladding Performance

Core

Operation Environment

Conditions for fuel rod depletion

over operating cycle

Neutronics, Thermal-Hydraulics,

Fuel Performance

Departure from Nucleate Boiling

Predict DNB Margin for Steam Line Break and RIA

and Predict Mixing & DNB

Neutronics, Thermal-hydraulics/Fluid Flow

Grid-to-Rod Fretting Predict Fluid-Structure Excitation Forces,

Grid Gap, and Cladding Wear

Fluid flow, Fuel/Clad Performance, Materials

Performance

Cladding Integrity

Reactivity Insertion Accident

Predict Pellet-Clad Mechanical Interaction

Reactor kinetics, Transient fuel/cladding

Performance

Cladding Integrity

Loss of Coolant Accident Predict Peak Clad Temperature and

Oxidation Margin given Thermal-Hydraulic

Conditions

Fuel/cladding performance

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CASL Is Developing a High-Fidelity Virtual Environment for

Reactor Applications (VERA)

VERA

Hydra-TH COBRA-TF

Thermal-Hydraulics

Fuel Performance

Bison-CASL

Shift

Neutronics

Insilico

Chemistry

MAMBA Common Input /

Output

front-end & back-end

(workflow / analysis)

Trilinos

DAKOTA

MOOSE

PETSc

Solvers / Coupling / SA / UQ

libMesh

DTK

STK

Geometry / Mesh / Solution

Transfer

Industry Codes

Interoperability with

External Components

Reactor System

Commercial CFD

MPACT

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CASL is Modeling Watts Bar Unit 1 Cycles 1 and 2

• Benchmark Spec provides data for WBN1 zero power physics tests, first cycle operation and second cycle shuffle

• Watts Bar Unit 1, Cycle 2 BOC – 4 new fuel assembly types – include different IFBA loadings – Tritium Producing Burnable Poison Rods

(TPBARS)

NP M L K J H FG ER D C B A

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45678

109

11

1

12131415

NP M L K J H FG ER D C B A

32

45678

109

11

1

12131415

EOC1

BOC2

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90 EFPD

270 EFPD

360 EFPD

We Are Now Focusing on Advanced Multi-Physics Capabilities:

MAMBA capability Integrated with COBRA-TF For CIPS Challenge Problem

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CILC Requires Coupling Local Flow Conditions with CRUD Deposition

Investigations performed with coupling of Chemistry and CFD

• First high-fidelity, two-way coupled CFD/CRUD simulation of an plant cycle

• Axial and azimuthal thermal hydraulic effects dramatically affect CRUD deposition patterns

• Axial and azimuthal CRUD deposition patterns were consistent with plant data

Now Integrating Chemistry as Subgrid Model in CFD

• CRUD deposition simulated directly on fuel rod surfaces.

• Will be applied for subregion of core using CIPS calculation of power history

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Technology Deployment We have now deployed 3 Test Stands

• Early deployment to industry for rapid and enhanced testing, use, and ultimate adoption of VERA to support real-world LWR applications Westinghouse (Mar 2013): Test VERA core

simulator’s ability to analyze AP1000 first core startup

EPRI (Nov 2013): Benchmark VERA fuel performance (Peregrine) on PCI applications utilizing new EPRI’s computing platform

TVA (Mar 2014): Test VERA CFD capability (Hydra-TH) on lower plenum flow anomaly observed in operational reactors

• CASL Test Stands have exposed technology gaps, deployment needs, and driven continuous improvement Have become a best practice for us

• More Test Stands on the horizon

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Conclusions

• Because of economic and safety drivers reliable operation of nuclear plants is essential.

• The nuclear industry has continually improved operation of their plants over time as well.

• Nuclear fuel reliability has also significantly improved resulting in reduce down time and replacement fuel costs

• On-going research has the potential to support continual improvements.

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Questions?