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Advances in Ceramics for
Environmental, Functional,
Structural, and Energy Applications

Ceramic Transactions Volume 265

Edited by

Morsi M . Mahmoud

Kumar Sridharan

Henry Colorado

Amar S. Bhalla

J. P. Singh

Surojit Gupta

Jason Langhorn

Andrei Jitianu

Navin Jose Manjooran

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Wiley Logo


This volume contains 20 manuscripts presented during the Materials Science & Technology 2017 Conference (MS&T’17), held October 8-12, 2017 at the David L. Lawrence Convention Center, Pittsburgh, PA. Papers from the following symposia are included in this volume:

These symposia provided a forum for scientists, engineers, and technologists to discuss and exchange state-of-the-art ideas, information, and technology on a dvanced methods and approaches for processing, synthesis, characterization, and applications of ceramics, glasses, and composites.

Each manuscript was peer-reviewed using The American Ceramic Society’s review process. The editors wish to extend their gratitude and appreciation to their symposium co-organizers, to all of the authors for their valuable submissions, to all the participants and session chairs for their time and effort, and to all the reviewers for their comments and suggestions.

We hope that this volume will serve as a useful reference for the professionals working in the field of materials science.

Morsi M. Mahmoud

Kumar Sridharan

Henry Colorado

Amar S. Bhalla

J. P. Singh

Surojit Gupta

Jason Langhorn

Andrei Jitianu

Navin Jose Manjooran



Frank Boylan1, Peng Xu2, Javier Romero2, and Ed Lahoda3

1Westinghouse Electric Company, Cranberry Township 16066


2Westinghouse Electric Company, Columbia, SC 29061

3Westinghouse Electric Company, Cranberry Township, PA 16066


Westinghouse is commercializing two unique accident tolerant fuels (ATFs): silicon carbide (SiC) as produced by General Atomics with uranium silicide (U3Si2) fuel and Cr coated zirconium alloy cladding with U3Si2 fuel. Testing of the cladding alternatives in autoclaves has been performed and samples have begun irradiation at the Massachusetts Institute of Technology Reactor and the Halden Project Reactor. Uranium silicide fuel is undergoing exposure in the Advanced Test Reactor and fuel pins have been removed and are undergoing post irradiation examination (PIE) at the Idaho National Laboratory (INL). This paper provides an update on these activities and a summary of results.


The Westinghouse Electric Company LLC (Westinghouse) accident tolerant fuel (ATF) program utilizes Cr coated zirconium alloy (CZA) cladding with U3Si2 high density/high thermal conductivity fuel for its lead test rod (LTR) program with irradiation beginning in 2019. The lead test assembly (LTA) program will use both SiC/SiC composites from General Atomics and Cr coated zirconium alloy claddings with the high density/high thermal conductivity U3Si2 pellet which will begin in 2022. Over the past several years, Westinghouse has tested the Cr coated zirconium and SiC claddings in autoclaves and in the Massachusetts Institute of Technology (MIT) reactor and U3Si2 pellets in the Advanced Test Reactor (ATR). High temperature tests at the state-of-the-art facilities in Churchill, PA have been carried out to determine the time and temperature limits for the SiC and Cr coated zirconium claddings.


Autoclave Corrosion Testing

Westinghouse has performed corrosion testing using the autoclave facility at the Churchill, PA site to screen various coatings and SiC preparation methods for corrosion resistance. As part of a multi-year program, over 12 types of coatings on zirconium alloys and approximately 10 versions of SiC have been tested in autoclaves. As a result of this testing, two coatings (Table I) were identified for testing in the MIT reactor.

Testing in the MIT reactor further narrowed the options to the Cr coating. Based on the positive test results, Westinghouse is now exploring methods for production of full length rods for LTRs to be constructed in 2018 for inclusion in a commercial reactor in early 2019.

Table I – Top Zirconium Alloy Coatings Autoclave Corrosion Performance At 360°C Water

Material Proces s Vendor Maximu m Days Average Corrosion rate (mg/dm2/day) Average Zr Corrosion (mg/dm2/day) Corrosion Rate ( /year)
TiN/TiAlN PVD Pennsylvani a State University 169 1.07 2.22 7.67
Cr Cold spray University of Wisconsin, Madison 20 0.03 3.27 0.14

Initial autoclave and reactor testing indicated relatively high levels of SiC corrosion. Autoclave testing with hydrogen peroxide was used to simulate more aggressive oxidation conditions of the reactor and to explore coolant conditions that would minimize SiC corrosion rates. The full battery of testing has been used to refine the manufacturing parameters of the SiC composites such that along with hydrogen addition to the primary coolant above 40 cc/kg [1], the current corrosion rates for SiC meet or exceed the target 7 microns/year recession rate. For a full core of SiC cladding, this would result in a maximum of 150 kg of SiO2 or about 300 ppm over an 18 month cycle. This is well below the solubility limit of ~700 ppm SiO2 at the coldest steam generator conditions. Note also, that resins are commercially available that could be added to the current resins used to maintain water chemistry to remove SiO2 on a continuous basis.

High Temperature Testing

The goal of the ATF program is to develop fuels that can withstand post-accident temperatures greater than 1200°C without the cladding igniting in steam or air. Therefore a crucial part of the testing carried out by Westinghouse over the previous year was aimed at quantifying the maximum temperature at which the ATF claddings could operate without excessive corrosion. The test apparatus first used current applied directly to the coated zirconium tubes. However, it was found that as the temperatures increased, issues with the connection of the test piece to the current source caused excessive resistance resulting in excessive heating and then burnout of the samples at the connection point. This direct heating method was then replaced with a graphite rod which was inserted into insulation and then into the test piece. This resulted in very stable heating of the test pieces.

CZAs have now been run at up to 1400°C. This is above the Cr-Zr low melting eutectic point of 1333°C. At 1400°C, there was noticeable reaction between the Cr and the Zr. However, there was not the rapid oxidation that uncoated Zr experiences at 1200°C, so that there is likely some reasonable residence time that the cladding could survive at temperatures above 1400°C.

At temperatures of 1300°C, the Cr coated zirconium alloy was stable for reasonable lengths of time. Combined with the lowering of zirconium oxidation at normal operating temperatures which vastly reduces the formation of zirconium hydrides and therefore embrittlement, the Cr coated zirconium has shown that it will provide significant improvement in the performance during normal operation, transients, design basis accidents and beyond design basis accidents as compared to uncoated zirconium.

Similar tests were run with SiC at temperatures from 1600°C up to 1700°C. These tests were run with the graphite heater rod and were terminated only because of excessive corrosion of the heater rod. At 1600°C, the SiC was visually untouched. At 1700°C, there were indications of small beads on the surface (presumably SiO2 from the reaction of SiC with steam) but on the whole, no significant deterioration of the SiC. Changes are being made to the heating rod to increase the flow of He cover gas and to allow accurate weight changes to be made on the SiC rodlets so that kinetic data can be obtained.

U3Si2 Testing

U3Si2 has never been utilized as pellets inside cladding in Light Water Reactor (LWR) fuel service. There is a lack of data on the behavior of U3Si2 at LWR operating temperatures (estimated to be from 600°C and up to 1200°C during transients). To remedy this lack of data, U3Si2 fuel pellets were manufactured at Idaho National Laboratory (INL) and put into rodlets in the ATR in 2015. The first rodlets came out of ATR at the end of 2016 and are due for destructive post irradiation examination in the summer of 2017 at INL [2]. Preliminary nondestructive testing from neutron radiography of the U3Si2 Pins after exposure of 20 MWd/kgU in the ATR shows very good results with a lack of pellet cracking and distortion.

U3Si2 was tested for air and steam oxidation as compared with UO2 using digital scanning calorimeters at both the Westinghouse Columbia facility [3] and at Los Alamos National Laboratory (LANL) [4]. The Westinghouse results indicate that the ignition temperatures for UO2 and U3Si2 are between 400°and 450°C (Table II). The LANL results (Table II) indicates an ignition temperature of about 400°C. The reasons for this difference are being studied. The reactivity of U3Si2 and UO2 are comparable at normal operating conditions (320°C), though the heat generated and mass generated by the oxidation of the U3Si2 is considerably higher than for UO2 at higher temperatures. The effect of this difference in heat release and mass on the stability of the rods is being investigated in rodlet tests in the Churchill autoclaves in the summer of 2017. However, the risk of any reactions between the coolant and the U3Si2 is probably much less than the current 1 to 2 ppm due to current rod failures, because the ATF claddings tend to be much harder than zirconium alloys. Therefore, it is expected that grid to rod fretting leakages will be eliminated.

Finally, LANL identified the potential for the formation of a U3Si2-H1.8 compound in the event of a leaker. Further work reported by S. Mašková et al [5] indicated that this would not likely be an issue since the operating temperature of the U3Si2 fuel will be above the decomposition temperature (~550°C) of this compound.

Table II – Comparison of Westinghouse U3Si2 and UO2 Scanning Calorimeter Results (Heating Rate 2.5°C/min)

Material UO2 (Air) U3Si2 (Air) U3Si2 (Steam)
Maximum Δmass (%) 4.1% 25% 25%
On-set Oxidation T (oC) ~410 ~450 ~500
Reaction enthalpy (-J/g) ~200 ~3200 Not available


The Westinghouse ATF concepts appear to be technically achievable as LTRs and LTAs in the 2019 and 2022 timeframe. Performance issues with SiC, coated cladding, and U3Si2 fuel have been identified and overcome through modifications, engineering, and testing. As with any revolutionary new product, technical challenges may surface, but the robust research and development program that Westinghouse has in place will be used to overcome these challenges.


  1. Ed Lahoda, Sumit Ray, Frank Boylan, Peng Xu and Richard Jacko, “SiC Cladding Corrosion and Mitigation,” TopFuel 2016, Boise, Idaho, Paper Number 17450, September 10, 2016.
  2. Jason Harp, Idaho National Laboratory, private communication, preliminary examination.
  3. Lu Cai, Peng Xu, Andrew Atwood, Frank Boylan, Edward J. Lahoda, “Thermal Analysis of ATF Fuel Materials at Westinghouse,” ICACC 2017, Daytona Beach, Florida, January 26, 2017.
  4. E. Sooby Wood, J.T. White, A.T. Nelson, “Oxidation behaviour of U-Si compounds in air from 25 to 1000 C,” Journal of Nuclear Materials, 484 (2017) pages 245-257.
  5. S. Mašková, K. Miliyanchuk, L. Havela, “Hydrogen absorption in U3Si2 and its impact on electronic properties”, Journal of Nuclear Materials, 487 (2017) pages 418-423.


This material is based upon work supported by the Department of Energy under Award Number DE-NE0008222.

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.