1. Challenges and Perspectives of Accelerator Driven Systems (ADS)
Forum für Beschleunigerphysik
TU Darmstadt
H. Podlech
Institut für Angewandte Physik
Goethe Universität Frankfurt

2. Outline Motivation for ADS Principle of ADS
Key Issues and Challenges of ADS Accelerators
European Program: MYRRHA
Summary

3. World Wide Use of Nuclear Energy (Fission)
10000 t of burned
fuel elements per year

4. Composition of Burned Fuel Elements
After 500 years the activity is dominated by Minor Actinides and few fission products!!

5. Creation of Minor Actinides Created by slow neutrons
in thermal reactors
Long life-time
High Radio-Toxcitiy

6. Use of Fast Neutrons Alternative
Use of Fast Reactors (for exampe SFR) „avoids“ creation of MA
Adding MA to Fast Reactors can „burn“ them
But: FR are technological challenging (Cooling, short reactor period)
Alternative
Use of an external source of fast neutrons (Spallation Source)
Coupling the neutron source with a sub-critical reactor
Basic idea of Accelerator Driven Systems

7. Accelerator Driven System
Proton accelerator (cw)
I≈10 mA, E≈1 GeV
Subcritical reactor
with spallation target
Keff
Spallation neutrons create fissions
Additional neutron by fission
2-5% external neutrons required
Reactor power times higher compared to beam power

8. Transmutation using ADS

9. Different studies around the world in the past
Worldwide Activities
Different studies around the world in the past
Presently the most advanced Projects:
China: C-ADS
Europe: MYRRHA

10. Multi Purpose Hybrid Reactor for High Tech Applications
MYRRHA
Multi Purpose Hybrid Reactor for High Tech Applications

11. Parameter MYRRHA Linac Extreme reliability level
Proton energy
600 MeV
Beam current
0.1 to 4.0 mA
Beam power
2.4 MW
Beam duty cycle
100%
Beam power stability
< ± 2% on a time scale of 100ms
Beam footprint on reactor window
Circular 85mm
Beam footprint stability
< ± 10% on a time scale of 1s
# of allowed beam trips on reactor longer than 3 sec
10 maximum per 3-month operation period
# of allowed beam trips on reactor longer than 0.1 sec
100 maximum per day
# of allowed beam trips on reactor shorter than 0.1 sec
unlimited
Extreme reliability level
J-L. Biarrotte, MYRTE TEC meeting, Brussels, 29 October 2015.

12. Conservative design & redundancy
Reliability Issues
Beam trips longer than 3 sec must be very rare:
 To minimize thermal stress & fatigue on the target window, reactor structures & fuel assemblies
 To ensure an 80% availability – given the foreseen reactor start-up procedures
Conservative design & redundancy

13. Schematic Layout of the MYRRHA Project
Parallel redundancy
Serial redundancy

14. Lay-Out of the MYRRHA-Linac
Courtesy J.-L. Biarrotte

15. Courtesy SCK • CEN

16. Reliability Issues – Cavity Failure
 A failure is detected anywhere
→ Beam is stopped by the MPS in injector at t0
 The fault is localized in a SC cavity RF loop
→ Need for an efficient fault diagnostic system

17.  The failed cavity is detuned (to avoid the beam loading effect)
 New V/φ set-points are updated in cavities adjacent to the failed one
→ Set-points determined in advance: via virtual accelerator application and/or during the commissioning phase
 The failed cavity is detuned (to avoid the beam loading effect)
→ Using the Cold Tuning System
 Once steady state is reached, beam is resumed at t1 < t0 + 3sec

18. Reliability Issues Example with multiple failures: Failed cavity:
 Section #1: 1 Spoke cavity
 Section #2: 1 Cryomodule (i.e. 2 cavities)
 Section #1: 1 elliptical cavity
Failed cavity:
RF off
Detuning within 1 s
Compensating cavities:
RF increase by 50%
Adjust RF phase
Setup at LPSC on March 2015

19. Beam losses - Acceptance
 Same example multiple failures example with errors (static and dynamic).
 1000 linacs simulated with 106 macro- particles
Loss power with compensation
 Longitudinal acceptance is the key point for beam loss control
 Investigate to improve the method and find a less aggressive retuning scheme (use more cavities?)

20. 17 MeV MYRRHA Injector
ECR
LEBT
RFQ
MEBT-1
CH-cavities
MEBT-2
CH-cavities
32 m
Design driven by emittance conservation (especially. longitudinally)
Conservative beam dynamics design
Cw Solid state amplifiers as RF sources (up to 150 kW)
Design philosophy: As conservative a necessary, as efficient as possible

21. 17 MeV MYRRHA Injector Constant negative synchronous phase per cavity
Smooth variations of phase advance
Minimum emittance growth

22. Radio-Frequency-Quadrupole (RFQ)
176 MHz 4-Rod RFQ
Cw operation major concern
Conservative design
Research program to optimize cooling
New fabrication technologies have been developed

23. FRANZ RFQ as MYRRHA Prototype
Frankfurt Neutron Source

25. rt CH-Cavities

26. Step 1: Construction of 100 MeV Linac (Pbeam=400 kW cw)
ECR, LEBT: operational, RFQ delivery March 2017, 2 CH-cavities end 2017
decisional hold point
for 600 MeV
milestone
date
ground breaking
2018
very first beam
2021
hold point
2024
nominal beam
2025
Parallel:
R&D for sc 600 MeV Linac and Reactor

27. Main issues for ADS accelerators (profit for other machines as well)
Summary
Main issues for ADS accelerators (profit for other machines as well)
Extreme Reliability Level
 Dynamic fault compensation
 Reliable RF sources (solid state amplifiers)
 Redundancy
 RT RF structures with high thermal load
Excellent Beam Quality and Stabiity
 Optimized beam optics/maximum acceptance
 Minimization of dynamic errors (LLRF)
 Minimization of field deviations (rt cw operation)
 Space charge compensation in LEBT
 optimized injection into RFQ

28. Thank you