1. ADS reliability requirements
Dirk Vandeplassche
Eucard-2 — Reliability for ADS Workshop, CERN
June 22-23, 2015

2. ADS reliability workshop, CERN, 22-23/06/2015
Overview
fundamental accelerator needs for ADS
the availability goal
GUINEVERE operational experience
the beam trip spectrum
pathways towards availability
ADS reliability workshop, CERN, 22-23/06/2015

3. the accelerator for ADS
Accelerator driving a subcritical fission core:
external neutron source  spallation reaction
subcritical core acts as a neutron amplifier
ADS proton beam power, rule of thumb, order of magnitude:
core power k
beam power
MYRRHA
100 MWth
.975
2.4 MW
industrial transmuter
1 GWth
.99
10–15 MW
nothing shocking ... up to now
ADS reliability workshop, CERN, 22-23/06/2015

4. the accelerator for ADS
Hence
accelerator = HPPA-class
fission core = DC device  CW beam
yes, but with holes for n-monitoring
beam energy: efficient neutron production, core geometry
MYRRHA choice: Ebeam = 600 MeV
transmuter: Ebeam = 1000–1500 MeV
Ibeam
MYRRHA: Ibeam ≈ 4 mA
transmuter: Ibeam ≈ 10–12 mA
the acceptable time structure of the beam is determined by the "target"
ADS reliability workshop, CERN, 22-23/06/2015

5. ADS reliability workshop, CERN, 22-23/06/2015
the ADS target
MYRRHA reactor rev. 1.6
ADS reliability workshop, CERN, 22-23/06/2015

6. ADS reliability workshop, CERN, 22-23/06/2015
the ADS target
ADS reliability workshop, CERN, 22-23/06/2015

7. ADS reliability workshop, CERN, 22-23/06/2015
the availability goal
effect of a beam trip in a fast core
prompt neutron population drops down to zero in tens of µs
small fraction of delayed neutrons may subsist, depending on the fuel
power delivered by core becomes instantaneously very low — its heat capacity is fairly low  temperature drops very fast
ADS reliability workshop, CERN, 22-23/06/2015

8. ADS reliability workshop, CERN, 22-23/06/2015
the availability goal
problems
thermal stresses  fatigue
structural materials, e.g. core support structures
fuel pins' cladding material
loss of integrity of oxide layer
Pb-Bi environment  corrosion, embrittlement
tolerances to fast and unexpected drops
fast reactor experience (PHENIX)  min.
fast reactor design (PHENIX)  typical ?
thermal stress modeling of structural mat.  max.
ADS reliability workshop, CERN, 22-23/06/2015

9. ADS reliability workshop, CERN, 22-23/06/2015
the availability goal
numbers for 1 MYRRHA cycle = 3 months:
PHENIX experience: 10 trips
PHENIX design: 30 trips (for 20y lifetime)
structural modeling:
t < 10s : 1000
10s < t < 5m : 100
t > 5m : 10
τmax ?
t < τmax :
thermally "transparent"
immediate restart is allowed
τmax = 3s
ADS reliability workshop, CERN, 22-23/06/2015

10. ADS reliability workshop, CERN, 22-23/06/2015
the availability goal
ADS reliability workshop, CERN, 22-23/06/2015

11. ADS reliability workshop, CERN, 22-23/06/2015
GUINEVERE
ADS reliability workshop, CERN, 22-23/06/2015

12. ADS reliability workshop, CERN, 22-23/06/2015
GUINEVERE
GUINEVERE is :
zero power SCK•CEN
electrostatic d-accelerator 230 keV (GENEPI-3C), 3H target
coupled to VENUS-F fast core
critical or subcritical operation
GUINEVERE has :
operational experience with beam trips
without bothering about structural integrity
ADS reliability workshop, CERN, 22-23/06/2015

13. ADS reliability workshop, CERN, 22-23/06/2015
GUINEVERE
operational limits
given in official licence document "core certificate"
one main safety parameter = reactor period — GUINEVERE: 10s
this limit prevents restarting (SCRAM !) if t > few s
"almost every accidental beam trip causes a scram"
recovering from a scram : 30 minutes (zero power !)
comparison PHENIX (600 MWth) : scram recovery time = 22 hours !
ADS reliability workshop, CERN, 22-23/06/2015

14. the practical beam trip spectrum
assume a conservative SCRAM recovery time of 24 hours (first of a kind !)
accept a 10% availability loss due to SCRAMs (OK for research, not for industry !)
hence, for MYRRHA: may accept 10 SCRAMs per period of 3 months
equiv.: not more than 10 accidental beam interruptions > 3s per 3 months
equiv.: beam-MTBF > 250 hours, failure = beam trip > 3s
important: purely operational argument
which luckily coincides with the "PHENIX experience"
ADS reliability workshop, CERN, 22-23/06/2015

15. the practical beam trip spectrum
ADS reliability workshop, CERN, 22-23/06/2015

16. pathways to availability
2 questions :
wishful thinking ?
how to reach ?
startpoint = gut feeling : no fundamental show stopper
recipe : main ingredient = build in fault tolerance, hence redundancy
implementation : modularity goes well with redundancy
ADS reliability workshop, CERN, 22-23/06/2015

17. pathways to availability
ADS reliability workshop, CERN, 22-23/06/2015

18. pathways to availability
initial modeling
beam dynamics : seems OK
FMEA studies : fault tolerance seems effective for gaining, say, 1 order of magnitude
today : recipe basically unchanged
advanced beam dynamics, start-to-end simulations, including errors
working reliability model
several experimental results
International Design Review : they tasted, evaluated positively and gave many recommendations
R&D program : focus on availability
ADS reliability workshop, CERN, 22-23/06/2015

19. pathways to availability
ADS reliability workshop, CERN, 22-23/06/2015

20. pathways to availability
today's confidence :
" much more than wishful thinking"
but the 2nd question remains :
" how to get there ?"
some thoughts, besides trivial issues of reliability
3s is short for doing all that has to be done
a decision taking control system is new to us
innovative functionalities
overlooked R&D item ?
ADS reliability workshop, CERN, 22-23/06/2015

21. pathways to availability
commissioning and its uncertainties
the benefits of a phased approach : a hold point at intermediate energy
evaluation
application with strongly reduced constraints
flexibility at reactor side is a must
constraints should not be magic numbers
refer to PHENIX : allowable # scrams seems to be a design parameter
unavailability in a demo context should be allowable
ADS reliability workshop, CERN, 22-23/06/2015