Contact

Porträt Dr. Merk, Bruno; FWOR

Dr. Bruno Merk
Reactor Safety
b.merkAthzdr.de

Transmutation


Transmutation represents the technological foundation of the sustainable use of nuclear power. The overarching objective of the research in the field of isotope transmutation is the reduction of the longevity of the transuranium isotopes in the nuclear waste involving significant mitigation of the challenges in respect of radioactive waste repositories. The main thrusts of transmutation research are directed towards the evaluation of the safety and efficiency of transmutation facilities as well as the optimization of fuel cycles in relation to transmutation. The enhancement of a nuclear data base helping confirm simulation results, the assessment of the impact of transmutation on the final disposal situation, and the dimensioning of future radioactive waste repositories are main areas of research in the filed of transmutation. Reactor physical analyses, safety studies of transmutation systems and the evaluation of the degradation and activation of materials in transmutation facilities provide a strong link to reactor safety.

Currently, the transmutation groups work on several small, but well characterized problems appearing in research topic transmutation

Selected pulications:

  1. R. Beyer et al: Characterization of the neutron beam at nELBE, Nuclear Instruments and Methods in Physics Research A 723 (2013) 151–162
  2. Merk, B.: “Moderating material to compensate the drawback of high minor actinide containing transmutation fuel on the feedback effects in SFR cores”, invited to special edition Science and Technology of Nuclear Installations (2012), Article ID 172518
  3. B. Merk and V. Glivici-Cotruţă: “Solutions without space-time separation for ADS experiments: Overview on Developments and Applications“, invited Science and Technology of Nuclear Installations (2012), Article ID 140946

German study on P&T

the group is one of the main contributors to the “German study on P&T”. Here the HZDR coordinates the work package ‘Study on Partitioning and Transmutation (P&T) of high-level waste - Status of R&D‘ of the study and contributes to most of the other work packages. Additionally, one member of the group is involved in the development of the ‘Acatech Positionen’, a conclusion of the study including political recommendations on the future of the P&T research in Germany.


Measurement of nuclear cross sections

The group is engaged in the measurement of cross sections to provide improved data on neutron-induced reactions which has been expressed especially in the fast, intermediate- and high energy domains of the neutrons (En = 1 keV to 50 MeV). The accurate knowledge of neutron and proton induced nuclear reactions is of crucial importance for predicting the capabilities of reducing the inventory of plutonium, minor actinides, and long-lived fission products. Nuclear data are being measured and evaluated on an international scale. The European efforts include the ERINDA project (coordinated by HZDR) that focuses on transnational access to modern neutron facilities. The new photoneutron source nELBE and the bremsstrahlung facility nELBE at HZDR’s Center for High-Power Radiation Sources attract various users for nuclear data measurements due to their favorable beam properties and experimental conditions. Also a national joint research project on nuclear data measurements relevant to transmutation (TRAKULA 02NUK13) is being coordinated by HZDR.


Subcriticality determination for accelerator driven systems

The group is working on the subcriticality determination during operation of an ADS as an important safety feature. The currently used zero dimensional methods have shown some deficiencies which require the use of strong, spatially dependent correction factors to get acceptable results. New analytical methods have been derived without separation of space and time during the solution of the partial differential equations. Currently solutions tailored for the GUNIEVERE experiment have been derived using a coupled system consisting of a core surrounded by reflector. The analytical solutions provide a very efficient new method for the analysis of experiments and thus an important step for the use of improved methods for the safety related subcriticality determination. The insertion of transmutation fuel containing TRUs challenges the safety related feedback effects in critical fast reactors. The use of fine distributed moderating material has been demonstrated to be a method to compensate these negative effects thus improving the safety of future transmutation systems. Incore experience is already available for the proposed moderating material. Thus fine distributed moderating material opens the possibility to improve the transmutation potential of critical fast reactors without compromising the safety. (See: B. Merk and V. Glivici-Cotruţă: “Solutions without space-time separation for ADS experiments: Overview on Developments and Applications“, invited Science and Technology of Nuclear Installations (2012), Article ID 140946)


Molten salt reactors for transmutation

As consequence of the “German study on P&T” the group has focused a part of the work on the very specific situation for P&T defined by the nuclear phase out decision in Germany. The work is concentrated on molten salt fast reactors which show some very specific advantages as transmutation systems in operation and especially in safety due to the use of liquid fuels. Some major hurdles of transmutation like multi recycling and solid fuel production could be overcome with this reactor type. Some studies have been performed about the potential of molten salt reactors to fulfill the tasks given by the phase out decision providing very efficient transmutation in conjunction with a solution of the last transmuter problem. The idea of a twofold lifecycle consisting of a transmuter mode and a deep burn mode to solve the last transmuter problem has been investigated demonstrating the very promising opportunities of molten salt fast reactors.


Safety of sodium cooled fast reactors with transmutation fuel

The group works safety of fast reactors and enhancement of the negative feedback effects to improve the transmutation performance in critical fast reactors. In the frame of European research, sodium cooled critical fast reactors like the French ASTRID reactor project provide the backbone of the first generation of the planned transmutation of minor actinides. The insertion of minor actinides, americium especially, has negative consequences on the safety related feedback effects in this kind of reactors. The method of introducing fine distributed moderating materials into the fuel assemblies of the reactor core has been proposed and investigated. It has been shown that the method has the potential to enhance the negative feedback effect while reducing the positive feedback effects. Thus the insertion of moderating material can compensate the effects of an americium insertion and opens the potential to increase the americium amount in the reactor core. Thus the insertion of moderating material gives the possibility to enhance the transmutation of americium significantly. (See: Merk, B.: “Moderating material to compensate the drawback of high minor actinide containing transmutation fuel on the feedback effects in SFR cores”, invited to special edition Science and Technology of Nuclear Installations (2012), Article ID 172518)

This work provides a close link to Nuclear Reactor Safety.



Contact

Dr. Bruno Merk
Reactor Safety
b.merkAthzdr.de