To compensate the lower enrichment, the fissile Uranium has to be physically packed more tightly in order to be able to continue providing the users with neutrons without disproportionate losses. Such a fuel is currently not available worldwide and must be qualified for the use at FRM II. At the FRM II, a more than fifteen-member research group is researching potential fuels and application scenarios. Among other things, this is done in a European research network funded by the EU with more than 10 million euros. In addition, there is close cooperation with the US, because also there five high-flux reactors have to be converted.
Assuming that suitable denser fuels are available, enrichment of the fissile uranium can be reduced to less than 50 % in the existing fuel assembly and with the same thermal power of the FRM II. An ancillary clause of the operating license of FRM II in 2003 states that this conversion must be completed by the end of 2010, if a suitable fuel is available. However, this conversion could not take place within this timeframe, as a suitable, qualified and denser fuel has not been found.
Immediately after the operating license was granted in 2003, a TUM working group began researching high density Uranium fuels. It is currently investigating two possible fuels from Uranium-Molybdenum: one U-Mo powder mixed with Aluminum (disperse) and the other as a continuous plate (monolithic). Furthermore, work is being carried out on a further compression of the actual fuel U3Si2. The test irradiations of the manufactured fuel plates are carried out in material test reactors in Europe and the USA.
Together with the operators of the high flux research reactors in Europe, (SCK-CEN, ILL und CEA) and the fuel assembly manufacturer Framatome-CERCA, TUM is conducting research on all three solutions within the HERACLES cooperation and together with partners in the USA and Korea.
As unique key-stone technology, TUM researchers simulate the radiation damage in the new uranium alloys with high energy heavy ions at the Maier-Leibnitz-Laboratory (MLL) of LMU and TUM. Complex computer simulations are used to develop scenarios for the use of nuclear fuel.
When the agreement on the conversion in 2003 of the FRM II between the federal government and the state of Bavaria was signed, powered Uranium Molybdenum fuel appeared internationally as a promising candidate for fuel development. These hopes were first dashed in late 2004 when some test plates of this fuel swelled and burst during test irradiation in test reactors in US and Europe. This was followed by significant metallurgical improvements of the fuel proved in turn in test irradiations around 2023 as not yet sufficient for a nuclear regulatory approval.
Now new plates made of modified material are being produced worldwide with further improved production techniques. For a test irradiation, the application approval process takes about a year. This is followed by an irradiation for one and a half years in a material test reactor. The cooling of the highly radioactive fuel plates takes once again up to a year. Afterwards, the necessary follow-up examinations can be carried out. Due to high costs associated with an irradiation test, the tests are performed serially.
Not only Russia, but USA as well. The fuel is supplied exclusively under the Non Proliferation Treaty and under bilateral treaties.
The simple comparison between fuel elements from FRM II and nuclear weapons is not scientifically supportable. The IAEA guideline for weapon-grade uranium requires highly pure, metallic uranium with a density of more than 19 g/cm³. Extracting weapon-grade material from fresh or used fuel elements requires complex physical and chemical processes that are only possible in large scale facilities. The fresh as well as the used fuel elements from FRM II are therefore not weapon-capable.
The TUM conducts research in the European association "HERACLES" together with institutions from France and Belgium. The US is also undertaking a great deal of research, with the research groups from both continents exchanging ideas on the results. Furthermore, TUM is in constant contact with partners in Korea. At present, some research reactors (outside Russia) are still operated with HEU worldwide. For more than a dozen of these powerful research reactors, there is still no high density fuel to convert to lower enrichment. About half of these not-yet-convertible research reactors are in the USA.
In a letter to the Bavarian Minister of Science Hans Zehetmair in 2002, the Deputy American Consul General Dr. Daniel E. Turnbull, on behalf of the US government, said that the FRM II was "never seen as a proliferation risk." The deputy Consul General wrote that the US has no concerns about nuclear materials.
After a meeting in the year 2019 with the US Department of Energy, a representative stated: “The meeting […] with experts from the FRM II reactor and the Bavarian State Ministry for Science and Art was an important step forward in our joint cooperation on the conversion of the FRM II to use LEU fuel. All parties agreed to develop a technical program between FRM II and U.S. national laboratories, as well as to establish a government-to-government oversight group to help achieve a successful conversion of the FRM II reactor. The United States looks forward to working closely with Germany and the FRM II reactor, as well as with our other partners around the world, to eliminate the civil use of HEU.
Migrating research abroad is not a solution. Incidentally, the research neutron source of the ILL is also being operated using HEU since it is particularly powerful. The FRM II is not only necessary for German researchers. Every year, 1,000 visiting scientists from all over the world come to Garching to carry out their experiments with neutrons. Both at FRM II and at the facility in France, the demand for research opportunities is so great that both neutron sources are urgently needed. The demand for measuring time is twice as high as the available time. Therefore even another facility, the European Spallation Source (ESS), is being built in Sweden.
From a fresh fuel element, whether from LEU or HEU, there is no danger to humans. It is only very weakly radioactive and emits, almost exclusively, shieldable α-radiation. Spent fuel elements are highly radioactive due to the generated fission products and require special long-term shielding measures. The radioactive radiation of a spent highly enriched fuel element essentially results from the fission products with a long-term dominating decay time of 30 years. A used low enriched spent fuel contains significantly higher amounts of plutonium with a long-term dominating decay time of 24,000 years. Therefore, the radioactive burden of an original HEU fuel assembly is significantly lower.
In such an installation, the fuel assemblies would either have to be chemically dissolved or melted. Afterwards, the remaining highly enriched uranium would have to be irreversibly mixed with depleted enriched uranium. During this process, the gaseous and volatile radioactive fission products are freed and therefore, retaining measures would have to be taken. The technology of this plant would be similar to that of a reprocessing plant like the ones should be built in the 1980s in Wackersdorf and was built in La Hague used for fuel elements from power plants. It is surprising that the construction and operation of such a plant in Garching is seriously considered.
If such a processing step is sought, it would be more reasonable and technically feasible to use FRM II fuel elements, e.g. in the existing plant in La Hague. The small amount of highly enriched nuclear fuel from the FRM II fuel element would be mixed there with the large quantities of low enriched uranium from the nuclear power plants, thereby diluted and at the same time put to meaningful reuse.