1. R. NABBI, P. BOURAUEL, G. DAMM
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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

2. The main design data of the FRJ-2 Research Reactor
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The main design data of the FRJ-2 Research Reactor
Type: Tank
Operation:
Thermal Power: /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 …..

3. MCNP: Arrangement of the beam tubes in the structures
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MCNP: Arrangement of the beam tubes in the structures
Nab-April2007

4. MCNP: FRJ-2 model with the nodalized reactor core
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MCNP: FRJ-2 model with the nodalized reactor core

5. MCNP: FRJ-2 model with the nodalized reactor core
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MCNP: FRJ-2 model with the nodalized reactor core

6. 3-d Distribution of the n-flux in the reactor core midplane and fuel element (MCNP-BURN)
Core Fuel element
Core center

7. MCNP: Nodalization of the whole reactor block
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MCNP: Nodalization of the whole reactor block

8. Visualization of the streaming effect
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Cd-layer
Visualization of the streaming effect

9. MCNP: Distribution of thermal N-flux
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MCNP: Distribution of thermal N-flux

10. Neutron flux distribution in the structures
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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 …..

11. Detailed neutron flux distribution in the structure

12. Distribution of N-flux above the Cd-layer
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Distribution of N-flux above the Cd-layer
Nab-April2007

13. Distribution of thermal N-flux in the steel tank
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Distribution of thermal N-flux in the steel tank

14. Total activity in the structures of the reactor
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Total activity in the structures of the reactor

15. Nuclide activity in different structures after 5 years cooling time
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Nuclide activity in different structures after 5 years cooling time

16. Distribution of the total activity in radial structures
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Distribution of the total activity in radial structures

17. Optimum dismantling process with minimum radiation effect
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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

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