A Low-Enriched Uranium (LEU) option for the conversion of FRM II - Scientific possible using monolithic U-10Mo fuel

Sep 2, 2026

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Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) is Germany’s most powerful research reactor and currently uses highly enriched uranium (HEU) fuel enriched at 93%, operated by the Technical University of Munich (TUM). TUM is mandated to convert FRM II to lower-enrichment fuel and is evaluating multiple conversion scenarios ahead of a planned downselection in 2023. This paper demonstrates that conversion to low-enriched uranium (LEU) is scientifically feasible with novel monolithic U-10Mo fuel. Neutronic and thermal-hydraulic coupled models, built from technical drawings and material properties, enable a systematic parameter study that identifies multiple viable LEU designs meeting safety, compatibility, and performance requirements.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages19

Reading Time48 min

AccessFree to download

Abstract

Conversion objective and timeline

Modeling approach and coupling schemes

Parameter study and viable LEU designs

Example LEU solution

| A Low-Enriched Uranium (LEU) option for the conversion ofFRM II | | | | | --- | --- | --- | --- | | C. Reiter a,∗, A. Bergeron b, D. Bonete-Wiese a, M. Kirsta, J. Mercza, R. Schönecker a, K. Shehua, B. Ozarb, F. Puig b, J. Lichtb, W. Petrya, P. Müller-Buschbaum a,c
a Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München, Lichtenbergstraße 1, 85748, Garching, Bavaria, Germany b Argonne National Laboratory (ANL), 9700 S Cass Ave, Lemont, 60439, IL, United States
c Chair for Functional Materials, TUM School of Natural Sciences, TUM School of Natural Sciences, James-Franck-Str. 1, 85748, Garching, Bavaria, Germany | | | | | A R T I C L E I N F O | | A B S T R A C T | | | Keywords: FRM II
Research reactor Neutronics Thermal-hydraulics
Coupled calculation Conversion Nonproliferation LEU fuel | | The Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) is Germany’s most powerful research reactor and uses Highly Enriched Uranium (HEU) fuel enriched at 93 %. The Technical University of Munich (TUM) operates the reactor and has been mandated to convert the FRM II to a lower-enrichment fuel. In preparation for the lower-enrichment fuel downselection, planned for 2023, TUM is evaluating multiple conversion scenarios.
In this paper, it is demonstrated that a conversion of FRM II to Low-Enriched Uranium (LEU) is scientifically possible when using the novel monolithic U-10Mo fuel system, which is currently in the qualification process. As a research reactor, safety criteria, neutron flux distribution and cycle length are key metrics. To begin, neutronic and thermal-hydraulic models were created based on current technical drawings and relevant material properties. Specifically tailored computational methods and coupling schemes have also been developed to properly evaluate all relevant characteristics for the conversion of the FRM II reactor.
Using these models and methods, a systematic parameter study was performed to explore the defined design space. The results of that study indicate that many LEU designs using monolithic U-10Mo appear tobe viable to convert FRM II to LEU. One example of an LEU solution for the FRM II reactor that fulfills the stated safety, compatibility and scientific performance requirements is discussed in more detail. | | | Mesh | Thickness | | | | Width | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | | Water | Cladding | Fuel | Tubing | Water | Cladding | Fuel | Tubing | | Mesh 1 | 10 | 4 | 5 | 33 | 150 | 15 | 120 | 15 | | Mesh 2 | 15 | 6 | 8 | 50 | 200 | 20 | 160 | 15 | | Mesh 3 | 20 | 8 | 10 | 66 | 230 | 25 | 180 | 15 | | Mesh 4 | 20 | 8 | 10 | 66 | 230 | 25 | 180 | 15 | | | Parameters | Mesh 1 | Mesh 2 | Mesh 3 | Mesh 4 | | --- | --- | --- | --- | --- | --- | | Elem.
Count | Elements at Inlet | 2.6⋅106 | 2.6⋅106 | 2.6 ⋅106 | 1.3⋅106 | | | Elements at Outlet | 1.7⋅106 | 1.7⋅106 | 1.7⋅106 | 4.6⋅106 | | | Total nr. of elements | 5.9⋅106 | 6.9⋅106 | 7.9⋅106 | 5.2⋅106 | | Abs. Diff.
to Mesh 3 | Pressure Drop (fuel)[bar] | 0.0419 | 0.04142 | Reference | 0.00959 | | | Pressure Drop (plate)[bar] | 0.0433 | 0.04078 | | 0.00073 | | | Max Heat Flux [W∕cm2 ] | 0.265 | 0.201 | | 0.002 | | | Max Temperature Fuel [◦C] | 6.538 | 1.159 | | 0.004 | | | Max Temperature Cladding [◦C] | 0.678 | 0.473 | | 0.006 | | | Max Temperature Water [◦C] | 0.256 | 0.375 | | 0.002 | | Material | Density
(kg∕m3 ) | Specific heat capacity (J∕kg K) | Thermal conductivity CFX (W∕m K) | Thermal conductivity CD3CL2/PLTEMP (W∕m K) | | --- | --- | --- | --- | --- | | AlFeNi | 2702 | 903 | | 216 | | U-10Mo | 17130 | 412 | temperature dependent (Jamisonet al., 2020) | 15.0 |

FAQs

What conversion is evaluated for FRM II?

The document evaluates converting FRM II from highly enriched uranium (HEU) to low-enriched uranium (LEU).

What fuel system enables the LEU conversion in this study?

It demonstrates feasibility using a novel monolithic U-10Mo fuel system currently in qualification.

How is the feasibility of the conversion assessed?

The work builds neutronic and thermal-hydraulic models from technical drawings and material properties, then performs a coupled evaluation with a systematic parameter study.

Sep 2, 2026

Upload by Eliana