atw 2018-05v6


atw Vol. 63 (2018) | Issue 5 ı May


experiments, only negligible interaction

occurred near the interface

[21] and no indications for spinodal

decomposition were found [26].

UMo phase behaviour

Few experiments have been carried

out so far using heavy ions that

directly target effects in the UMo

kernels. One major finding was the

reduction of the orthorhombic

α-phase of Uranium during irradiation,

i.e. the stabilization of the bcc

γ-phase [8]. This is an imperative

requirement for the fuel. The same

effect was observed in-pile [34],

though quantitative comparisons are

still outstanding.

Ternary alloys like U 8 wt % Mo

1 wt % Pt which originally were

considered to improve irradiation

behaviour showed no improvement

and partially even a destabilisation

of the γ-phase of the fuel and were

therefore discarded, too [32].


Altogether, the experiments very well

demonstrate the applicability of the

approach to use Iodine-127 irradiation

for qualitative and even quantitative

experiments to reliably simulate

numerous in-pile irradiation effects.

Even though the burn-up equivalent

that has been reached up to now

with ions was comparably low

(n < ∼ 6 ∙ 10


) for HPRR conditions,

important contributions were made to

the development of UMo fuels.

In the future, improved ion beam

diagnostics will open the door to the

analysis of high-burn-up effects like

the recrystallization of UMo kernels.

The necessary fission density equivalents

can be reached with only a few

days of beam time, depending on the

influence of fission rate/ion flux.

Subsequent fission gas implantation

additionally allows studying gasdriven

effects – first demonstration

experiments were successfully carried

out with Kr ions.

The main advantage of this

technique is its effectiveness: No

additional radioactivity is involved,

the complete cycle from experiment

design over irradiation to post irradiation

examinations can be carried

out in a few weeks. Even though the

method has obvious limitations, it is

well able to minimize the number of

costly and time consuming in-pile

irradiation experiments.


The authors would like to thank the

MLL staff for their great support

during our beam-times and also in

the times in-between as well as all

members of the working group

“Hochdichte Kernbrennstoffe”.

The work was supported by a

combined grant (FRM1318) from the

Bundesministerium für Bildung und

Forschung (BMBF) and the Bayerisches

Staatsministerium für Bildung und

Kultus, Wissenschaft und Kunst



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Publication in preparation.

Research and Innovation

Heavy Ions Irradiation as a Tool to Minimize the Number of In-Pile Tests in UMo Fuel Development ı H. Breitkreutz, J. Shi, R. Jungwirth, T. Zweifel, H.-Y. Chiang and W. Petry

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