1. MA and LLFP Transmutation Performance Assessment in the MYRRHA eXperimental ADS P&T: 8th IEM, Las Vegas, Nevada, USA November 9-11, 2004 E. Malambu, W. Haeck, V. Sobolev and H. Aït Abderrahim SCK·CEN, Boeretang 200, Mol, Belgium

2. Contents 1.Introduction: MYRRHA-XADS 2.Typical core configuration for MA and LLFP transmutation studies 3.MA and LLFP targets loading 4.Computational tools 5.Geometrical model features 6.Target irradiation conditions 7.Preliminary results 8.Conclusions

3. 1. Introduction  Since 1998, the Belgian nuclear research Centre, SCK·CEN, is developing the MYRRHA ADS project.  In 2004, SCKCEN is finalizing the pre- design phase of MYRRHA.  In the framework of the EC FP6 IP- EUROTRANS project, SCKCEN is willing to adapt the design options of MYRRHA to fit out the objectives of the ETD/XT- ADS project (experimental demonstration of the technological feasibility of Transmutation in an ADS).

4. 2.Typical core configuration for MA and LLFP transmutation studies

5. 3. MA and LLFP targets composition

6. 4. Computational tools  MCNPX 2.5.e code used to:  Define the sub-critical core configuration such as:  Keff-value close to 0.95  Total power close 50 MWth  Calculate neutron fluxes and spectra at each burn-up step through the ALEPH code flowchart  Libraries: JEF2.2 (MCB) combined to LA150n for Pb, Bi and steel elements); LA150h for protons.  ALEPH code (coupling MCNPX and ORIGEN2.2) to carry out the MA evolution calculation

7. 4. Computational tools (cont’d) ALEPH MCNPX calculates the spectrum in cells to be burned in an arbitrary group structure The spectra are used to calculate reaction rates outside MCNPX using data read directly from ENDF files The updated library is used to calculate new material compositions and densities This entire process is repeated until the entire burn up history is calculated MCNPX calculate multigroup spectra ORIGEN 2.2 burn up calculation ORIGEN LIBRARY use data directly from ENDF files preprocessed by NJOY 99.90 NEW MCNP(X) INPUT update densities and composition

8. 5. Geometrical model features : MYRRHA MODEL for MCNPX calculations

9. 5. Geometrical model features (cont’d): Modelled details of various assemblies

10. 6. Irradiation conditions  Irradiation history:  One-year operational period 3 cycles  Cycle time-span 90 (EFP) days  Shutdown between cycles 30 days  Neutron flux :  Constant level assumed over 30 days sub-cycles  Cycle-and-volume averaged neutron flux  MA targets in channel A: 3.17·10 15 n/cm²s  MA targets in channel D: 2.78·10 15 n/cm²s  99 Tc targets : 1.08·10 15 n/cm²s

11. 7. Preliminary results: Core physics static parameters

12. 7. Preliminary results (cont’d) Neutron spectra in MOX fuel and MA assemblies

13. 7. Preliminary results (cont’d) Neutron spectrum in 99 Tc target

14. 7. Preliminary results (cont’d) 99 Tc incineration  Mass incinerated: 431 grams (1.75% of initial mass)  Burnout half-life ( T 1/2 =Ln(2)/  a  ):  13.9 yrs vs T 1/2 = 2.11 x 10 5 yrs for natural decay 99 Tc Irradiation history

15. 7. Preliminary results (cont’d) Mass evolution of Am, Pu and Cm in MA targets

16. 7. Preliminary results (cont’d) Time-evolution of Am mass

17. 7. Preliminary results (cont’d) Time-evolution of Pu mass

18. 7. Preliminary results (cont’d) Time-evolution of Cm mass

19. 8. CONCLUSIONS  The fast spectrum available in the MYRRHA sub- critical core is very efficient for the transmutation of (Pu, Am) targets due to a better fission-to-absorption ratio than in fast reactors  The incineration of Cm pre-requires a Partitioning step to separate Cm and Am  The incineration of long-lived fission products, such as the 99 Tc, in a resonance capture region is demonstrated.  Further studies are underway to enhance the epithermal tail of the neutron spectrum by optimizing the target design and choosing more appropriate spectrum softening materials.