Frequently asked questions regarding the conversion of the FRM II to low enriched uranium

The FRM II will convert from highly- enriched uranium (HEU) to a fuel with significantly lower enrichment.

Why is the conversion of HEU (highly- enriched uranium: HEU) to low-enriched uranium (LEU) at the FRM II not possible?

Highly -enriched uranium contains up to 93 percent of the fissionable uranium 235. Low-enriched uranium contains less than 20 percent uranium 235. The remaining 80 percent is almost exclusively uranium 238. Only the fission of uranium 235 creates neutrons, which the FRM II uses for scientific experiments. In order to obtain the same high flux of neutrons with reduced enrichment of the fissile uranium in the fuel, the uranium must be dispersed with at least this much density in the fuel element. However, since the admixed uranium 238 additionally absorbs neutrons, this packing must be disproportionately higher. If the current compact core of the FRM II were to be converted directly to LEU, the amount of uranium 235 would increase from the current 8.1 kg to more than 60 kg and require a density of uranium of 40 g/cm3. The theoretical maximum is the density of metallic uranium of 19,05 g/cm3. The direct conversion of the existing reactor core of the FRM II to LEU is therefore physically impossible. At the present time, fuels with a maximum uranium density of 4.8 g/cm3 are qualified. International research efforts aim for densities of 8-16 g/cm3. Assuming that such a fuel exists, converting the FRM II to a LEU core would make it necessary to increase the core volume and thermal power.

What specific steps are currently being undertaken by the Technische Universität München towards conversion?

Immediately after the operating license was granted in 2003, a working group at TUM embarked on the exploration of high-density uranium fuels. It is currently investigating two possible fuels made of uranium molybdenum: UMo powder mixed with aluminium ("dispersed") and a solid foil ("monolithic"). In both cases, the actual fuel zone is still enclosed in a "picture frame" made of aluminum. Test irradiations of the fabricated fuel plates are being carried out at other reactors in Europe. Together with the other high-flux research reactors (SCK-CEN, ILL, CEA) and the fuel manufacturer AREVA-CERCA, TUM is investigating both solutions within the HERACLES collaboration. This also involves close cooperation with partners from the U.S. and Korea. TUM researchers uniquely simulate the radiation damage in uranium molybdenum fuel elements by irradiating them at the Maier-Leibnitz Laboratory (MLL) of LMU and TUM. In extensive computer simulations, scenarios for the use of this nuclear fuel are being developed.

Why does the development of the new fuel take so much time?

When the federal government and the state of Bavaria agreed upon the conversion of the FRM II in 2003, the uranium molybdenum fuel in powder form seemed to be a promising candidate to the international fuel development community. These hopes were first thwarted in late 2004 when some experimental plates of this fuel showed break-away swelling and burst open in test irradiations in dedicated test reactors in the U.S. and in Europe. Nowadays, new plates with a modified fuel material that are produced using improved manufacturing techniques are tested. The granting of approval for a test irradiation takes about a year. This is followed by an irradiation time of one to one and a half years in a dedicated test reactor. The highly radioactive fuel plates take up to a further year to cool down. Only then can the necessary post-irradiation examinations be carried out. Due to the high costs associated with an irradiation test, such tests are performed serially.

Is the uranium of the FRM II of Russian origin?

Not solely, the U.S. also being a source. The fuel is delivered exclusively under the Nuclear Non-Proliferation Treaty and after the conclusion of bilateral treaties.

Is it really possible to build a nuclear weapon using an HEU fuel element from the FRM II?

8 kg of uranium are located in the chemical form of a ceramic diluted to 3 g uranium/cm3 in a fuel element of the FRM II. Such a fuel cannot be directly used in nuclear weapons. Furthermore, the mass is not sufficient for a potential proliferator to build a crude weapon. Fuel has never been stolen from research reactors, because here the International Atomic Energy Agency in Vienna takes complete control.

Is the Technische Universität München the only institute in search of a new, high-density and low-enriched fuel?

Research on this fuel is carried out in cooperation with France and Belgium ("HERACLES"). The U.S. is also engaged in an extensive research program, so the results are the subject of mutual exchange. The TUM also reciprocates with their non-European partners in the U.S. and Korea. There are still research reactors worldwide currently (outside Russia) operating using HEU. In about a dozen of these powerful research reactors, there is no high-density fuel in order to convert to lower enrichment. Approximately half of these as yet non-convertible research reactors are located in the United States.

What was the reaction of the U.S. to the new FRM II?

The U.S. Deputy Consul General, Dr. Daniel E. Turnbull, emphasized in the name of the U.S. government in a letter to the former Bavarian Minister of Science, Hans Zehetmair, in 2002 that they had "never considered the FRM II a proliferation risk". The Deputy Consul General wrote that the U.S. had no concerns regarding nuclear materials.

How much does it cost to develop the new fuel for the FRM II?

A two-digit million Euro sum is shared equally by the Federal Republic of Germany and the State of Bavaria.

Why do the German neutron researchers not simply go to the international ILL neutron source in Grenoble, France?

Moving research abroad is not a solution. Incidentally, the research neutron source of ILL - a particularly powerful one- is also operated using HEU. The FRM II is necessary not only to German researchers. Every year, 1000 visiting scientists from around the world arrive in Garching to perform their experiments with neutrons. At the FRM II as well as at the institute 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 that available. It is for this reason that a European Spallation Neutron Source is being constructed.

Which is more radioactive, LEU or HEU?

A fresh fuel element, whether made of LEU or HEU, presents no danger to humans. It is only very weakly radioactive. Used fuel elements are, however, highly radioactive and require special shielding in the long term. The radioactivity of a spent highly enriched fuel element stems mainly from the fission products that have a long dominant decay time of 30 years. A spent low-enriched fuel element contains substantially more plutonium with a long dominant decay time of 24,000 years. Therefore, the radioactive burden of an HEU fuel element is significantly lower.