[en] With a compact core power of 20 MW, the conceived Munich Research Reactor II is designed to offer experimental possibilities, with about half the utilizable neutron flux, which would be comparable to the Grenoble HFR. The most important criteria, such as coolability, operating cycles with one fuel element, maximum fission density, and core design, are dealt with. Geometry calculations, design studies for a compact core for 93% uranium enrichment, temperature and boiling coefficients, and transport calculations are presented. (DG)

[en] The project of a new research reactor in Germany aims at realizing an efficient neutron source optimized primarily for neutron beam applications. Since the reactor power has to be low from reasons of economy and public acceptance, the optimization studies have resulted in a particularly compact, light water cooled reactor core which is surrounded by a large heavy water moderator tank. This concept leads to high values of the thermal neutron flux in a large useable volume outside of the core - with an unperturbed flux maximum of about 8 x 10¹⁴cm^-2s^-1 at only 20 MW power

[en] The project of a new research reactor in Germany aims at realizing an efficient neutron source optimized primarily for neutron beam applications. Since the reactor power has to be low from reasons of economy and public acceptance, our optimization studies have resulted in a particularly compact, light water cooled reactor core which is surrounded by a large heavy water moderator tank. This concept leads to high values of the thermal neutron flux in a large useable volume outside of the core - with an unperturbed flux maximum of about 8·10¹⁴ cm^-2s^-1 at only 20 MW power

[en] Published in summary form only

[en] We are planning to modernize the research reactor FRM at Munich using a novel 'compact core'. This cylindrical fuel element has about 20 cm diameter and 70 cm height, is cooled by light water and surrounded by a large heavy water tank. Using the new U₃Si/AI fuels with high enrichment (93%) and with an uranium density of 2.8 g/cm³ a maximum thermal neutron flux θ_th^max above 8·10¹⁴ cm^-2 s^-1 can be achieved in the D₂O-tank at only 20 MW reactor power. A reduction of enrichment to about 45% can be mostly compensated by an increase in uranium density up to 6.5 g/cm³ and θ_th^max is 8% smaller, then. In the case of 20% enrichment, however, the core volume must be enlarged significantly and θ_th^max decreases by 32%. While these results have been obtained for a compact core with 18 concentric fuel plate rings, we also started to investigate an alternative version with 104 involute-type fuel plates. The first results are very promising, too. (author)

[en] A novel compact core has been proposed for a project of substantially modernizing the research reactor FRM at Munich. This core has about 20 cm diameter and 70 cm height, is cooled by H₂O and surrounded by a large D₂O moderator tank. It makes essential use of the new U₃Si/Al dispersion fuel with very high uranium density now available. The authors present the results of new, two-dimension neutronic calculations and give an estimate of the probable burnup and reactivity behavior of the compact core. It is expected that this core can be effectively operated with an unperturbed multiplication factor of about 1.22, and that a maximum thermal neutron flux of 7 to 8 x 10^-14 cm^-2 s^-1 can be achieved in the D₂O tank at 20 MW reactor power

[en] Published in summary form only

[en] We present the time averaged temperature distribution of the fuel in the FRM II over a full operation cycle. Because of the single fuel element design the power distribution over the cycle changes clearly as the single control rod moves more and more away from the core centre. Any evaluation of the time averaged temperature distribution must take this into account. Therefore the early developed module sequence Mf2dAb that led to the design of the fuel element of FRM II, was used to predict the power density distribution for different time steps of now fully 60 days of full power operation. For any of this time steps there was performed a quasi static temperature evaluation over and through the full fuel plate of FRM II compact core that is cooled with a typical inlet temperature of the primary light water cooling circuit. As a result it can be given the location of the hot temperature maximum, now at different burn up states (or cycle averaged) and not only for the moment of reactor start (BOC) that is the main point of regard for reactor safety evaluations. (author)

[en] The newly developed X² program system is intended to be used for high-detail 3D calculations on compact research reactor cores. Using this system, the efforts to calculate scenarios for a new fuel element for FRM II using disperse UMo (8wt% Mo, 50% enrichment) are continued. By now, a radial symmetric core model with averaged built-in components for the D₂O tank is used. Two different scenarios are compared: The minimum fuel density of 7.5 g U/cm³ and 8.0 g U/cm³ with 60 days cycle length. In addition, two 'flux loss compensating' scenarios based on 8.0 g U/cm³ with 10% higher power/longer reactor cycles are regarded. (author)

[en] In 2005 the high-flux research reactor FRM II in Garching started routine operation using U₃Si₂ fuel with an enrichment of 93 %. As committed in the nuclear license for FRM II its fuel has to be converted to medium enriched uranium until end of 2010 -- so far the scientific aims are met. This paper presents new studies with UMo monolithic despite of all the fabrication questions with this fuel. To open a new parameter of freedom a continuous thickness variation over the radius of the fuel element was studied. FRM II could overcome the problem of high local power peaking with monolithic fuel, presumed that it is possible to fabricate monolithic plates of this type in future. The presented monolithic element study takes especially care of the reactor operational aspects like fuel inventory questions, reach-able 'full power days' and local power peaking factors while keeping the outer fuel element dimensions constant. (author)