Irradiation performance of U–Mo–Ti and U–Mo–Zr dispersion fuels in Al–Si matrixes

doi:10.1016/j.jnucmat.2012.05.006

Journal of Nuclear Materials

Volume 427, Issues 1–3, August 2012, Pages 233-238

https://doi.org/10.1016/j.jnucmat.2012.05.006 Get rights and content

Abstract

Performance of U–7 wt.%Mo with 1 wt.%Ti, 1 wt.%Zr or 2 wt.%Zr, dispersed in an Al–5 wt.%Si alloy matrix, was investigated through irradiation tests in the ATR at INL and HANARO at KAERI. Post-irradiation metallographic features show that the addition of Ti or Zr suppresses interaction layer growth between the U–Mo and the Al–5 wt.%Si matrix. However, higher fission gas swelling was observed in the fuel with Zr addition, while no discernable effect was found in the fuel with Ti addition as compared to U–Mo without the addition. Known to have a destabilizing effect on the γ-phase U–Mo, Zr, either as alloy addition or fission product, is ascribed for the disadvantageous result. Considering its benign effect on fuel swelling, with slight disadvantage from neutron economy point of view, Ti may be a better choice for this purpose.

Introduction

U–Mo particle dispersion in an aluminum matrix, termed as U–Mo/Al hereafter, has been under development for the use of high-power research and test reactors because of its potential for high U-density. Interaction layer growth and occasional porosity formation in the matrix, however, has been hampering its qualification [1]. An example of excessive interaction layer growth and pore formation in the interaction layers observed in this fuel is shown in Fig. 1, and a more detailed discussion of behavior of interaction layers (ILs) during irradiation and the problem of large pore formation in U–Mo/Al have been presented elsewhere [2]. The addition of a small amount of silicon to the aluminum matrix was proposed as a possible solution [3], [4], [5] and a beneficial result was observed from irradiation tests [6], [7].

Other elemental additions to the U–Mo fuel phase, not in the matrix, are also proposed to help further reduce interaction layer (IL) growth, possibly having a synergistic effect with the Si addition [3], [5]. Transition elements just to the left of Mo in the periodic table are the most likely candidates from a metallurgical standpoint. Elements such as Nb, Ti and Zr form, at most, one weak compound with U, but multiple strong compounds with Al. By forming stronger compounds with Al than U, these elements can reduce the reaction between U and Al. A detailed thermodynamic analysis was performed to evaluate the stabilizing effect of the candidate elements [3], [5]. Based on a previous irradiation test, Nb was excluded chiefly because of its negative effects on fuel swelling [8]. Phase stability and IL growth tests of Ti and Zr added in U–Mo were out-of-pile tested [9], [10], [11], which showed results consistent with theoretical predictions.

The promising out-of-pile results supported several test plates with Ti or Zr addition to be included in the RERTR-8 irradiation test in the Advance Test Reactor (ATR). Two plates, one with Ti addition and the other with Zr addition, achieved high burnup, and were examined after the irradiation. Another test, KOMO-4, was conducted in the HANARO reactor at KAERI, Korea. This test differs from the RERTR-8 test in that it was higher in test temperature but slightly lower in burnup. Most remarkable difference is, however, in sample geometry: the KOMO-4 test samples are rodlets while those for the RERTR-8 were mini-plates. Because of the rod type geometry, KOMO-4 samples have higher external constraints that can better suppress fission gas bubble growth than the plate type samples.

This paper discusses the post-irradiation examination (PIE) results of the RERTR-8 test and the KOMO-4 test regarding the effect of Ti or Zr addition in U–Mo on IL growth and fission gas swelling. Ti or Zr addition appears to be effective in suppressing interaction layer (IL) growth during irradiation. The change by the Ti addition on U–Mo fuel swelling was minimal, whereas the Zr addition clearly affected U–Mo’s fuel swelling behavior. However, the observation for the Zr addition provided some insights that could explain pore formation behavior of U–Mo/Al dispersion fuel at high burnup.

Section snippets

Irradiation experiments

Two test plates including Ti or Zr addition were included in the RERTR-8 test irradiated in the ATR. A U–Mo dispersion fuel plate without Ti or Zr addition, irradiated in the RERTR-7 test, was added for comparison. A data summary of test plates discussed for the present study is given in Table 1.

The plate dimensions are 101.6 × 25.4 × 1.4 mm and the meat (i.e., the fueled zone with fuel particles embedded in the matrix aluminum) dimensions are 81.3 × 18.5 × 0.64 mm. A schematic showing the design of the

Results

RERTR test results are compared in Fig. 7. Micrographs were taken at two locations, one on the higher-power side and the other on the lower-power side, schematically shown in Fig. 2 and indicated by arrows in Fig. 4. For comparison, micrographs of R3R050 from the RERTR-7 test, which was irradiated at similar condition, is also included in Fig. 7.

As indicated in Fig. 7, there appears to be a beneficial effect of adding Ti and Zr on IL growth, albeit small in absolute terms, because of the

Discussion

The effectiveness of Ti or Zr addition to U–Mo in suppressing IL growth is observed. In the lower temperature RERTR-8 test, the extent of reduction is not significant in terms of absolute amount because the high Si addition reduced IL growth drastically [6], [7]. The effect is more clearly noticeable from the KOMO-4 test where IL growth is higher because of the higher test temperatures (see Fig. 8, Fig. 9). This implies that Ti or Zr addition to U–Mo is beneficial for high temperature

Conclusions

The effect of Ti and Zr additions to U–7 wt.%Mo on the extent of fuel-matrix interdiffusion is small in absolute terms in the lower temperature RERTR-8 test because of the overwhelming reduction effect on IL growth of the 5%Si addition to the Al matrix. In the higher temperature KOMO-4 test, the effect was considerable. Therefore, the addition of Ti or Zr may be recommendable to reduce the burden of a large amount of Si addition in the matrix in high power reactor applications where the IL

Acknowledgments

This paper contains information on the development of U–Mo/Al gathered from reduced-size plate tests, RERTR-7, and -8, irradiated in the Advanced Test Reactor (ATR), for the GTRI-Conversion program (formerly known as the RERTR program), and information from the rod-type KOMO-4 test irradiated in the HANARO at KAERI, South Korea. For design and fabrication of the RERTR-7 and -8 test plates, Mr. C. Clark and Mr. G. Moore are acknowledged. The physics data were available by Dr. G. Chang and Ms. M.

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^☆: Work supported by the US Department of Energy, Office of Global Threat Reduction, National Nuclear Security Administration (NNSA), under Contract DE-AC-02-06CH11357. The submitted manuscript has been authored by a contractor of the U.S. Government under Contract DE-AC-02-06CH11357. Accordingly, the U.S. Government retains a nonexclusive royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

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Irradiation performance of U–Mo–Ti and U–Mo–Zr dispersion fuels in Al–Si matrixes☆

Abstract

Introduction

Section snippets

Irradiation experiments

Results

Discussion

Conclusions

Acknowledgments

J. Nucl. Mater.

J. Nucl. Mater.

J. Nucl. Mater.

J. Nucl. Mater.

J. Nucl. Mater.

J. Nucl. Mater.

J. Nucl. Mater.

J. Nucl. Mater.