atw 2018-09v3

inforum

atw Vol. 63 (2018) | Issue 8/9 ı August/September

442

FUEL

Innovations for the Future

Westinghouse EnCore® Accident

Tolerant Fuel

Gilda Bocock, Robert Oelrich, and Sumit Ray

EnCore® and

ADOPTTM are trademarks

and registered

trademarks of Westinghouse

Electric

Company LLC, its

affiliates and/or its

subsidiaries in the

United States of

America and may be

registered in other

countries throughout

the world. All rights

reserved. Unauthorized

use is strictly prohibited.

Other names

may be trademarks of

their respective owners

The development and implementation of accident tolerant fuel (ATF) products, such as Westinghouse’s EnCore® Fuel,

can support the long-term viability of nuclear energy by enhancing operational safety and decreasing energy costs. The

first introduction of Westinghouse EnCore Fuel into a commercial reactor is planned for 2019 as segmented lead test

rods (LTRs) utilizing chromium-coated zirconium cladding with uranium silicide (U 3 Si 2 ) pellets. The EnCore Fuel lead

test assembly (LTA) program, with LTAs planned for 2022 insertion, will introduce silicon carbide/silicon carbide

composite cladding with U 3 Si 2 pellets.

Over the past several years, the

Westinghouse EnCore Fuel features

have been tested in autoclaves, in

research reactors, at national laboratories

and in the Westinghouse Ultrahigh

Temperature Test Facility to

­confirm and fully understand the

science behind ATF materials. Based

on the positive results to date, fuel rod

and assembly design in preparation

for the LTR and LTA programs is

underway, as well as licensing efforts

with the U.S. Nuclear Regulatory

Commission (NRC). Accident analyses,

coupled with economic evaluations,

have been continuing to define the

value of ATF to utilities.

These new designs will offer

design- basis-altering safety, greater

uranium efficiency and significant

economic benefits. Adoption of the

Westinghouse ATF, in conjunction

with a transition to 24-month cycle

operation, is the recommended path

forward for implementation of the

Westinghouse EnCore Fuel.

1 Introduction

Nuclear energy remains a fundamental

component of many industrialized

nations’ energy supply mixes due to its

demonstrated reliability in baseload

electrical supply, as well as inherent

carbon-free energy production. Two

factors are critical to maintaining this

capability: (a) enhancing safety to

help safeguard the plant and public

from highly impacting events such as

that which occurred at the Fukushima

Daiichi Nuclear Power Plant and (b)

decreasing operating costs to compete

with other sources of energy. The

development and implementation

of Accident Tolerant Fuel (ATF) products,

such as Westinghouse’s EnCore®

Fuel features, can support both of

these critical factors for long-term

operation.

Development of nuclear fuels with

enhanced accident tolerance is being

accelerated to support implementation

into commercial reactors as soon

as possible. The major objectives for

ATF designs include: 1) improved

cladding reaction to high-temperature

steam; 2) reduced hydrogen generation;

and 3) reduced beyond design

basis accident source term. In addition

to improving safety margins

for light water reactors (LWRs), fuel

designs using advanced, ATF materials

can improve fuel efficiency, ­enhance

debris resistance and extend fuel

management capability. Encore Fuel,

being developed by Westinghouse

Electric Company LLC (Westinghouse),

includes two unique accident tolerant

or fault tolerant fuel designs: chromium

(Cr)-coated zirconium (Zr)

alloy cladding with uranium silicide

(U 3 Si 2 ) fuel pellets, and silicon

carbide (SiC) cladding with U 3 Si 2 fuel

pellets.

The first introduction of Westinghouse

EnCore Fuel into a commercial

reactor is planned for 2019 as segmented

lead test rods (LTRs). The

LTRs will utilize chromium-coated

zirconium cladding with U 3 Si 2 highdensity,

high-thermal conductivity

pellets. The EnCore Fuel lead test

assembly (LTA) program, planned

for 2022 insertion, will introduce

SiC/SiC composite cladding along

with chromium- coated zirconium

cladding and the high-density, /highthermal

conductivity U 3 Si 2 pellets

modified to achieve higher oxidation

resistance.

Over the past several years,

Westinghouse’s ATF test program

has tested the chromium-coated

zirconium and SiC claddings in

autoclaves and in the Massachusetts

Institute of Technology’s (MIT) reactor

and U 3 Si 2 pellets in Idaho National

Laboratory’s (INL) Advanced Test

Reactor (ATR). Tests in the Ultrahigh

Temperature Test Facility at

Westinghouse’s U.S. Materials Center of

Excellence Hot Cell Facility in Churchill,

Pennsylvania, have been carried out to

confirm the time and temperature

limits for the SiC and chromiumcoated

zirconium claddings. Additionally,

an extensive research program to

fully understand the science behind

ATF materials continues with the

Westinghouse-led International Collaboration

for Advanced Research on

Accident Tolerant Fuel (CARAT) group

and at United States (US) and United

Kingdom (UK) national laboratories.

Based on the positive results to date,

fuel rod and assembly design in preparation

for the LTR and LTA programs is

underway, as well as licensing efforts

with the U.S. Nuclear Regulatory Commission

(NRC), and accident analyses

coupled with economic evaluations

for both operating savings and fuel

savings have been continuing to define

the value of ATF to utilities.

2 Lead test rod program

LTR programs are an essential step in

the introduction of new nuclear fuel

technologies into commercial energyproducing

reactors. In the EnCore LTR

program, two Westinghouse 17x17

optimized fuel assemblies (OFA) will

contain up to 20 ATF rods with

Cr-coated Zirconium alloy cladding,

and U 3 Si 2 and enhanced ADOPT fuel

pellets in Exelon’s Byron Unit 2 in

Cycle 22. Coated tubes and U 3 Si 2 and

ADOPT pellets will be delivered to the

Westinghouse Columbia Fuel Fabrication

Facility for manufacturing of

the assemblies. The shipping date for

the assemblies containing the LTRs is

February, 2019.

Westinghouse is continuing development

work with the University of

Wisconsin-Madison to continue the

optimization of coating performance,

and also working with commercial

vendors and the U.S. Army Research

Lab (ARL) to scale-up production

to full-length tubes. The U 3 Si 2 fuel

Fuel

Westinghouse EnCore® Accident Tolerant Fuel ı Gilda Bocock, Robert Oelrich, and Sumit Ray

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