R. NABBI, P. BOURAUEL, G. DAMM Zentralabteilung Forschungsreaktoren ANALYSIS OF THE ACTIVITY INVENTORY FOR THE DECOMISSIONING PLAN OF THE GERMAN FRJ-2 RESEARCH REACTOR R. NABBI, P. BOURAUEL, G. DAMM Contents - The German FRJ-2 Research Reactor Operation and Decommissioning Distribution of Neutronflux and activity Geometrical Nodalization (MCNP) ORIGEN Model and Calculations - Effects of geometrical inhomogenities - Results and Summary

The main design data of the FRJ-2 Research Reactor Zentralabteilung Forschungsreaktoren The main design data of the FRJ-2 Research Reactor Type: Tank Operation: 1962 - 2006 Thermal Power: 10/15/23 MW Moderator / Coolant: D2O (Heavy Water) Vertical experimental tubes: 25 inside core and 25 inside reflector Horizontal experimental tubes: 10 inside D2O and 21 inside graphite reflector Neutron flux: core max.: 3,2*1014 1/(cm2s) reflector max.: 2,6*1014 1/(cm2s) The reactor is a tnk type rector, what means that it is completely surrounded by shielding. For contrast, the training reactor in Prague is a swimming-pool tpe reactor. Commissioning was 1962, the increase in power i talked about already and as i said before, the moderator and also the coolant is heavy water. Now, what makes a reactor a research reactor, that is the avilability of high neutron fluxes for the materials and experiments you have. Because of that the reactor has a lot of tubes that are reaching into the vicinity of the active reactor core and you have access from the outside. Neutron fluxes are …..

MCNP: Arrangement of the beam tubes in the structures Zentralabteilung Forschungsreaktoren MCNP: Arrangement of the beam tubes in the structures Nab-April2007

MCNP: FRJ-2 model with the nodalized reactor core Zentralabteilung Forschungsreaktoren MCNP: FRJ-2 model with the nodalized reactor core

MCNP: FRJ-2 model with the nodalized reactor core Zentralabteilung Forschungsreaktoren MCNP: FRJ-2 model with the nodalized reactor core

3-d Distribution of the n-flux in the reactor core midplane and fuel element (MCNP-BURN) Core Fuel element Core center

MCNP: Nodalization of the whole reactor block Zentralabteilung Forschungsreaktoren MCNP: Nodalization of the whole reactor block

Visualization of the streaming effect Zentralabteilung Forschungsreaktoren Cd-layer Visualization of the streaming effect

MCNP: Distribution of thermal N-flux Zentralabteilung Forschungsreaktoren MCNP: Distribution of thermal N-flux

Neutron flux distribution in the structures Zentralabteilung Forschungsreaktoren Neutron flux distribution in the structures The reactor is a tnk type rector, what means that it is completely surrounded by shielding. For contrast, the training reactor in Prague is a swimming-pool tpe reactor. Commissioning was 1962, the increase in power i talked about already and as i said before, the moderator and also the coolant is heavy water. Now, what makes a reactor a research reactor, that is the avilability of high neutron fluxes for the materials and experiments you have. Because of that the reactor has a lot of tubes that are reaching into the vicinity of the active reactor core and you have access from the outside. Neutron fluxes are …..

Detailed neutron flux distribution in the structure

Distribution of N-flux above the Cd-layer Zentralabteilung Forschungsreaktoren Distribution of N-flux above the Cd-layer Nab-April2007

Distribution of thermal N-flux in the steel tank Zentralabteilung Forschungsreaktoren Distribution of thermal N-flux in the steel tank

Total activity in the structures of the reactor Zentralabteilung Forschungsreaktoren Total activity in the structures of the reactor

Nuclide activity in different structures after 5 years cooling time Zentralabteilung Forschungsreaktoren Nuclide activity in different structures after 5 years cooling time

Distribution of the total activity in radial structures Zentralabteilung Forschungsreaktoren Distribution of the total activity in radial structures

Optimum dismantling process with minimum radiation effect Zentralabteilung Forschungsreaktoren Summary & Conclusions A sophisticated MCNP model is generated on the basis of detailed material composition and geometrical design data Using the MCNP model the neutron flux was determined with a high level of accuracy and low standard deviations Using ORIGEN, the activity inventory in different components could be determined. The calculations resulted in a detailed activity map allowing The determination of the low and high level activity zones Reduction of waste material mass and volume Optimum dismantling process with minimum radiation effect The main source of activity are H3, Fe55 and Co60 resulting from the activation of impurities

Horizontal cut view of the whole reactor block Therm. Power Central FE