S

 ISR

In charge: Prof. K. Kugeler, ISR, k.kugeler@fz-juelich.de

In programme topic Safety Research for Nuclear Reactors aspects related to a nuclear technology with the highest safety standards ("catastrophe-free") are investigated. Proof of the thermal, nuclear, chemical and mechanical stability of concepts of nuclear plants is being established, also for extreme accident conditions. The safety research includes also contract work on the safety of the PBMR (= Pebble Bed Modular Reactor) of the company ESKOM, South Africa. Their project has the objective of the realisation of a catastrophe free nuclear energy technology as mentioned before.

Work on Safety Research for Nuclear Waste Disposal includes conditioning and storage of radioactive waste as well as the behaviour of irradiated fuel elements from HTR and research reactors in a final repository. The potential of new immobilisation materials, especially of ceramics, for the final disposal is investigated. Minimisation and transmutation of plutonium and minor actinides are further activities. Moreover, work is concerned with the handling of practical radiation protection problems derived from work with radioactive substances in the Research Centre Jülich with the aim of improving dosimetry, analysis of measurements and radiological assessment.

The maintenance of competence in nuclear technology is a central aspect of both topics and requires large efforts.

Significant Results in 2003

Safety Research for Nuclear Reactors

• Within the scope of the research on control of hydrogen released during a severe accident in Light Water Reactors the final summary report for the EC Project THINCAT was completed under co-ordination of ISR and was presented at the FISA conference in Luxembourg. Studies on heat radiation effects inside catalytic recombiners showed high potentials for the reduction of temperature. Optimised catalyst coatings to prevent unintended ignitions in catalyst elements were tested and prepared for application in a modular recombiner set-up.
• The database for SiC-encapsulated LWR-fuel has been updated. The heat transfer in the gap between fuel and cladding has been modelled more precisely. First transient calculations indicate that maximal fuel centreline temperatures can be reduced when using SiC-encapsulated fuel.
• Cell calculations for a dispersion LWR fuel indicate the principle feasibility of such a fuel design. According to FEM calculations the thermal conductivity within the heterogeneous structure of the dispersion fuel can be approximated by an analytical formula for simple geometries.
• Activities in several projects partly EU-financed lead to the following significant results:
  • The dynamics of the MUSE-4 subcritical experiment was successfully described by use of the Monte-Carlo-code MCNP-4C3
  • Ceramic encapsulation of burnt fuel elements can be performed by joining of SiC parts using two new methods. The ‚friction-welding' technology works best with small geometries, the ‚laser-welding' method is suitable for larger parts, like SiC-containers with lids. The proof of the final corrosion-stability is still open for both methods.
  • Analyses on SiC-coating of graphite pebbles have been terminated and documented after successful completing of post irradiation tests. The coating of graphite species IG-110 shows excellent irradiation and corrosion stability.
  • Small differences in calculated control rod reactivities using the VSOP-99 code system to the measured figures are not due to n-streaming effects in the empty rod holes.
  • The HTR Fuel Data Bank has been implemented as a preliminary prototype Web-enabled database application for experimentally measured HTR fuel data.
• Within the frame of preservation of competence with respect to effective advertising of third-party funding by contracts and licence agreements with international partners in the field of safety analyses for modular high-temperature reactors theoretical models and the computer code systems VSOP-99 and TINTE have been adapted to new international standards and validation processes. For VSOP-99 another licence has been taken by an abroad company.

Programme topic Safety Research for Nuclear Waste Disposal

• A software module for the numerical simulation of the efficiency of collimated HPGe detectors was set up in the framework of a R&D project funded by the BMBF. It will enable numerical variance analyses of gamma-scanning and tomography data.
• In collaboration with the ITU/Karlsruhe a process for actinide(III) separation from the high active reprocessing waste before its vitrification was jointly developed and successfully tested.
• A process to separate the trivalent actinides (Americium and Curium) from the trivalent lanthanides and the consecutive separation of Am from Cm was developed and applied for patent.
• Trivalent actinides, simulated by Ce and Nd, were immobilised homogeneously in Zr- and Th-based ceramics. The parameters of fabrication were optimised and important properties (density, structure etc.) of the synthesised ceramics were investigated.
• Changing from U/Pu-MOX fuels to Th/Pu-MOX-fuel in the PWR-core maintains the safety characteristics well known from U/Pu-MOX cores. Applying Th/Pu-MOX fuel with the reference assembly layout, reduces the contents of trans-uranium elements (TRU) in spent fuel by 41% compared to 24% with U/Pu-MOX fuel. An optimized Th/Pu-MOX-assembly reduces the TRU-contents even by 49%.
• A twin-layer pellet design (a central Th/Am-MOX column with surrounding Th/U-MOX shell) of selected pin in a PWR-assembly reduces up to 84% of the initial Am, while about 39% of them form Cm. Finally the net reduction of minor actinides becomes about 45%.
• Syntheses of Mg/Al-Cl hydrotalcites, which were identified as crystalline phase components of the corrosion products of metallic U/Al research reactor fuel elements in saline brines, were successfully performed and a complete analytic data set was determined.
• Experiments with smooth surface oxidation of graphite from the thermal column of the research reactor FRJ1 resulted in a CO/CO2- off gas enriched with C-14.
• Experiments with U/Th mixed oxide fuel showed that Thorium increases the stability of the fuel matrix against leaching in a repository, compared to pure Uranium oxide.
• In investigations of the long-term development of the population dose in the highly contaminated regions of Belarus it was found that for determining of the external dose the organic bound and retransfer activity into plants cannot be neglected. The phenomena observed are described in a model, which permits an analytical calculation of the contamination profile in soil, taking migration and transfer effects into account.
• Quantum mechanical investigations on the radiation action mechanism of DNA-bound Auger emitters confirm recent experimental data demonstrating a non-radiation component playing a significant role in strand break induction. Semi-empirical calculations on the PM3 level to study the stability of I-125UdR strongly indicate the possibility of a Coulomb explosion when the I-125 decay induced molecular charge is equal or greater than +5e.