atw 2018-09v3


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



commercial delivery, while improving

the quality of the data and resulting

design models used to describe the

fuel. This new approach would be a

significant improvement compared

to the current, largely empirical

approach, which requires years to

obtain limited data from a very expensive

test reactor(s), as well as for the

fabricating, testing, cooling, transportation

and post-irradiation examination

of samples. To reduce the

licensing timeframe for EnCore Fuel,

Westinghouse plans to utilize:

• Atomic scale modeling:

• By utilizing first principles to

determine physical properties

of irradiated materials

• By leveraging Westinghouse

involvement in the Nuclear

Energy Advanced Modeling &

Simulation (NEAMS) Department

of Energy (DOE) program

on basic property prediction

• By leveraging Westinghouse

involvement in the Consortium

for Advanced Simulation of

Light Water Reactors (CASL) –

Virtual reactor design

• By continuing to utilize MedeA

and Thermo-Calc software

• Real-time data generation to verify

the atomic scale modeling:

• Poolside data generation


Gamma emission tomography

based on gamma-ray spectroscopy

and tomographic reconstruction

can be used for

rod-wise characterization of

nuclear fuel assemblies without

dismantling the fuel to detect

pellet swelling, pellet- cladding

interaction and pellet cracking


Potential use of a spectroscopic

detection system to select

different gamma-ray emitting

isotopes for analysis, enabling

nondestructive fuel characterization

with respect to a variety

of fuel parameters (fission gas


• Wired or wireless transmission

technology for measuring


Centerline temperature


Fuel rod gas pressure


Swelling of fuel

In addition to saving time and cost, with

this approach Westinghouse hopes to

achieve, an increased con­fidence by the

U.S. NRC due to the predictability of

performance that can be obtained since

the performance models will have a

theoretical basis in addition to an

empirical basis. There should also be

reduced time and effort due to the reduction

in the number of submissionreview-revision-

submission cycles. This

should remove the review process from

the critical path to commercialization.

Communication with the U.S. NRC

Commissioners, and coordination

between the DOE, NRC and industry

for licensing of ATF, are in progress

and continuing.

7 Conclusion

Westinghouse and its partners are

continuing to make good progress on

U 3 Si 2 fuel, SiC cladding, and chromium-coated

zirconium cladding. These

new designs will offer design-basisaltering

safety, greater uranium efficiency,

and significant economic

­benefits per reactor per year for PWRs.

While all testing and development to

date has been engineered for LWR

designs, Westinghouse believes the

technology could provide some of the

same safety and economic benefits to

CANDU and other reactor designs.

Fuel and accident modeling with

other types of reactor systems will be

required to evaluate the actual potential

for these benefits. This, together

with more beneficial power peaks,

lower impact of the transition cycles

and reduced dependence on uranium

price assumptions, make adoption of

the Westinghouse ATF, in conjunction

with a transition to 24-month cycle

operation, the recommended path

forward for implementation of the

Westinghouse ATF, EnCore Fuel.


[1] Gordon Kohse, MIT, 2016.

[2] Ed Lahoda, Sumit Ray, Frank Boylan,

Peng Xu and Richard Jacko, SiC Cladding

Corrosion and Mitigation, Top Fuel 2016,

Boise, ID, September 11, 2016, Paper

Number 17450, ANS, (2016).

[3] Jason Harp, Idaho National Laboratory

preliminary photographs.

[4] Lu Cai, Peng Xu, Andrew Atwood,

Frank Boylan and Edward J. Lahoda,

Thermal Analysis of ATF Fuel Materials

at Westinghouse, ICACC 2017, Daytona

Beach, FL, January 26, 2017.

[5] E. Sooby Wood, J.T. White and A.T.

Nelson, Oxidation behavior of U-Si

compounds in air from 25 to 1000 C,

Journal of Nuclear Materials, 484,

pages 245-257 (2017).

[6] Eugene van Heerden, Chan Y. Paik,

Sung Jin Lee and Martin G. Plys,

Modeling Of Accident Tolerant Fuel

for PWR and BWR Using MAAP5,

Proceedings of ICAPP 2017, Fukui and

Kyoto ,Japan, April 24-28, 2017.


Gilda Bocock

Robert Oelrich

Sumit Ray

Westinghouse Electric Company

5801 Bluff Road

Hopkins, SC 29061, USA

Analyses of Possible Explanations for the

Neutron Flux Fluctuations in German PWR

Joachim Herb, Christoph Bläsius, Yann Perin, Jürgen Sievers and Kiril Velkov

Revised version of a

paper presented at

the Annual Meeting

of Nuclear Technology

(AMNT 2017), Berlin.

During the last 15 years the neutron flux fluctuation levels in some of the German PWR changed significantly. During

a period of about ten years, the fluctuation levels increased, followed by about five years with decreasing levels after

taking actions like changing the design of the fuel elements [1, 2]. The increase in the neutron flux fluctuations resulted

in an increased number of triggering the reactor limitation system and in one case in a SCRAM [3].

There exist different possible explanations

how neutron flux oscillations are

caused by physical phenomena inside

a PWR. Possible explanations can be

based on complicated interactions

between thermo-hydraulical (TH),

structural-mechanical and neutron

physical processes (see Figure 1).

Yet, no comprehensive theory

exists, which can explain the neutron

flux fluctuation histories observed

in German PWR based on first ­

physical principles. Therefore, GRS

has started investigations to

explain the observed neutron flux

Operation and New Build

Analyses of Possible Explanations for the Neutron Flux Fluctuations in German PWR ı Joachim Herb, Christoph Bläsius, Yann Perin, Jürgen Sievers and Kiril Velkov

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