3rd International Workshop on ACCELERATOR DRIVEN SUB-CRITICAL SYSTEMS & THORIUM UTILIZATION VCU - Virginia Commonwealth University Richmond, Virginia, USA - October 14-17, 2014 Personal perspectives on ADS history Carlo Pagani Università degli Studi di Milano & INFN LASA carlo.pagani@mi.infn.it
Introduction In spite of the construction so far of ~ 400 nuclear power plants, the radioactive waste represents a problem that is not yet properly solved, especially in terms of social acceptability and long term environmental impact. After Fukushima also safety issues are very hot. But, planet in equilibrium with 7 to 10 billions of human beings, will possibly require a few thousands of high power plants to be integrated in a network of smaller localized electric power sources from renewable resources. Fission nuclear power respects in principle most of the requirements should a new generation being developed, now generically called Generation IV, with fuel regeneration, breading, and ultimate waste with a long term acceptable radiotoxicity, i.e. which remains in equilibrium with the planet life. Electricity generation worldwide (OECD, 2007) Carlo Pagani N
From Physics Today, May 2006 (Yucca Mountain) 55000 tons in >100 temporary repositories in 39 States 2000 tons/y produced in USA 70000 tons is the total Yucca Mountain capacity Safety analysis after 1 My required for licensing! Carlo Pagani N
The end of the US Repository Las Vegas Sun Funds cut to zero in 2011 Carlo Pagani 4
Since mid ninetieth new proposals C. Rubbia proposal for the Energy Amplifier Pb-Bi cooled subcritical reactor driven by fast neutrons produced by spallation. The scheme was using a high power proton cyclotron delivering a few MW proton beam Partitioning & Transmutation via ADS (Accelerator Driven System) Evolution of the previous scheme. The focus is now on the waste partitioning, fuel preparation and accelerator design for reliability. The scope is to study and optimize the waste transmutation process. The subcritical reactor is generally a Pb-Bi cooled fast reactor The proton accelerator is generally a superconducting linear accelerator Generation IV A global process to develop a completely new nuclear power scenario that includes: fuel regeneration, breading, and ultimate waste in equilibrium with the planet life. Carlo Pagani 5
Partitioning & Transmutation ADS = Accelerator Driven System Problem: Disposal of Nuclear Waste Reduce radiotoxicity of the waste Minimize volume/heat load of waste Strategy: Partitioning and Transmutation Separate the waste (Pu, MA, LLFF,) Use the waste as part of the fuel in dedicated transmutation systems that include: A subcritical reactor (k<1): chain reaction not self-sustained, more freedom for transmutation (mainly MA) An intense spallation source: high proton flux on liquid target (Pb, Pb-Bi) : provides missing neutrons to keep the reaction going, with a broad energy spectrum (good for MA burning) Carlo Pagani 6
Partitioning & Transmutation Concept Carlo Pagani 7
The ADS Program in US (Sep 1999) ATW = Accelerator Transmutation of Waste Carlo Pagani 8
Others reference documents Carlo Pagani 9
P&T Program in Japan (as in 2004) Carlo Pagani 10
Radio-toxicity Reduction Carlo Pagani 11
ADS in Europe Early Stage: National Programs TRASCO in Italy / ASH in France European Programs FP5 PDS-XADS «Preliminary Design Studies for an experimental Accelerator Driven System» Accelerator/target/core/material FP6 EUROTRANS «EUROpean Research Programme for the TRANSmutation of High Level Nuclear Waste in an Accelerator Driven System» System analysis, coupling, base option FP7 CDT, towards design and licensing «Central Design Team for a Fast Spectrum Device in Europe» MAX program dedicated to accelerator activities Carlo Pagani 12
The role of OECD-NEA 2000-2005: Working Party on Partitioning and Transmutation (WPPT) Several workshops on the different topics Several reports from international expert groups ADS as one of the parallel lines to be pursued Accelerator feasibility demonstrated and beam parameters defined and agreed 2005-2010: Working Party on Fuel Cycle (WPFC) Follows the program of the previous WPPT More attention to the specific items related to the complete fuel cycle Focusing on Generation IV ADS as integral part of the Generation IV cycle The accelerator is considered as feasible with required performances 2010-2015: Working Party on Fuel Cycle (WPFC) - Continuation Carlo Pagani 13
Why an Accelerator Driven System To transmute MA effectively, fission reactions of MA in fast neutron system fueled with high MA content is desirable Fast critical reactor (FR) with high MA content is the most effective burner of MA from the above viewpoint Operation of such a critical burner is not straitforward because of: Small delayed neutron fraction Large positive reactivity effect by coolant void Small negative reactivity feedback by Doppler effect To overcome these problems two methods are considered: make the core subcritical ADS reduce the MA concentration and possibly add 238 U Carlo Pagani 14
From the ADS Italian Design Funded by EU FP5 - PDS-XADS Carlo Pagani 15
Neutron Spallation Scheme Spallation reaction A heavy metal target hit by a high energy proton generates neutrons At 1 GeV 1 proton generates 20-30 neutrons Characteristics: High conversion neutrons/protons factor Wide neutron energy spectrum For high neutron production efficiency, high energy proton beam is required Carlo Pagani 16
What is a Particle Accelerator? A particle accelerator is a machine designed to transfer energy to a charged particle beam. In most cases the particle beam extracts energy from an electromagnetic field that is stored or traveling in low losses structures, called cavities. E gain [ev] = q [e] V [Volt] Particles are taking energy from the electric field, E, and are guided by the magnetic field, B, according to the Lorentz equation: F = q (E + v x B) The charged accelerated particles can be: electrons (& positrons) [i.e. leptons: elementary particles] protons (& antiprotons) [i.e. hadrons, composite particles] ions (i.e. ionized atoms) An intense primary beam can be used to produce a secondary beam that could not be accelerated: photons, neutrons, neutrinos, etc. Carlo Pagani 17
Linac or Cyclotron? Cyclotron No remarkable R&D programs Its cost scales quadratically with the output energy Very high reliability and availability at PSI, but further improvement looks very difficult Not applicable concepts of redundancy and spare on line Linear Accelerator (Linac) A worldwide R&D effort is in progress High potentiality of these machines has been proven: Sources, RFQs and SRF technology successfully in operation cost per MeV is decreasing with energy Linac (except front end) has intrinsic modularity: Easy redundant and spares on line design Carlo Pagani 18
CEBAF and LEP II, end of 80s CEBAF 338 bulk niobium cavities Produced by industry Processed at TJNAF in a dedicated infrastructure 5-cell cavities 1.5 GHz, L act =0.5 m 4-cell cavities 352 MHz, L act =1.7 m LEP II & CERN 32 bulk niobium cavities Limited to 5 MV/m Poor material and inclusions 256 sputtered cavities Magnetron-sputtering of Nb on Cu Completely done by industry Field improved with time <E acc > = 7.8 MV/m (Cryo-limited) Carlo Pagani 19
The TESLA Collaboration Mission Develop SRF for the future TeV Linear Collider Basic goals Increase gradient by a factor of 5 (Physical limit for Nb at ~ 50 MV/m) Reduce cost per MV by a factor 20 (New cryomodule concept and Industrialization) Make possible pulsed operation (Combine SRF and mechanical engineering) Major advantages vs NC Technology Higher conversion efficiency: more beam power for less plug power consumption Lower RF frequency: relaxed tolerances and smaller emittance dilution as in 1992 Björn Wiik Carlo Pagani 20
TESLA Technology: SRF Cavities Major contributions from: CEA-Saclay, CERN, Cornell, DESY and INFN-LASA (Alphabetic order) Bulk Nb, 9-cell, 1.3 GHz TESLA cavity parameters R/Q 1036 Ω E peak /E acc 2.0 B peak /E acc 4.26 mt/(mv/m) f/ l 315 khz/mm K Lorentz -1 Hz/(MV/m) 2 Carlo Pagani 21
TESLA Technology: the Cryomodule International collaborative Effort in the three regions for ILC Design changes are towards nailing down slot length of components Costing should be straight-forward from TTF and XFEL experience Carlo Pagani 22
From the ILC Cryomodule drawings Carlo Pagani 23 O & O Seminar Milano, June 14, 2011
Acceleration inside an ILC Cavity An electromagnetic field is resonating inside the cavity. The electric field inverts its direction according to the frequency determined by the cavity resonator shape. If the charged particle beam has the proper synchronism, moving from one cell to the other it sees always the field in the right direction and gains energy: E gain = q * V Electric 電場 Field Particle ( 陽 ) 電子 Carlo Pagani 24
ADS for Transmutation Carlo Pagani 25
Why Superconductivity in RF linacs? In normal conducting linac a huge amount of power is deposited in the copper structure, in the form of heat, that needs to be removed by water cooling (in order not to melt the structures) Dissipated power can be much higher than the power transferred into the beam for acceleration Superconductivity, at the expenses of higher complexity, drastically reduces the dissipated power and the cavities transfer more efficiently the RF power to the beam In short: NC linac: lower capital cost, but high operational cost SC linac: slightly higher capital cost, but low operational cost Carlo Pagani 26
Superconductivity whenever possible Superconductivity, drastically reduces the dissipated power. But some drawbacks Higher complexity: 1.0E-04 refrigeration and cryomodules Carnot and refrigeration plant efficiencies η tot Ratio between Nb and Cu Rs = η η 1.0E-03 1.0E-05 C th 1.0E-06 250W at 300K for 1W at T 800W at 300K for 1W at T Higher technology: 1.0E-07 cavity treatments Simpler geometries: lower shunt impedance 1.0E-08 And two big advantages: Large bore radius: less beam losses CW or high duty cicle preferred = 4.2K = 2K 0 500 1000 1500 2000 2500 3000 f [MHz] 2 K 4.2 K Carlo Pagani 27
ADS proton beam requirements Very high duty cycle, possibly CW Energy of the order of 1 GeV, determined by neutron production rate per GeV and per proton (optimum value reached at ~1 GeV) energy dissipated in the input window (rapidly decreasing with energy, when E < few GeV) beam power from several MW up to tens of MW few MW for a demo plant of ~100 MWth ~20 MW for an industrial burner of ~1500 MWth Very few beam trips per year longer then 1 second No limitation for very short beam trips: << 1 second yield / E p (neutrons/gev) 50 40 30 20 10 0 0 0.5 1 1.5 2 2.5 proton energy, E_p (GeV) Carlo Pagani 28
The ADS Linac Linac benefits of impressive progresses on SC cavities: SC technology can be extended to proton linac down to few MeV Intrinsic modularity simplify reliability issues Redundant design strategy based on the spare-on-line concept Strong focusing and large beam aperture produce negligible losses The scheme generally considered consists of four different sections The proton source: proton energy 50-100 kev The Radio Frequency Quadrupole (RFQ): up to 3-5 MeV A low energy section, low beta SC structures up to 100-200 MeV A high energy section, made of SC elliptical RF cavities: up to final energy 1 GeV (most of the linac is here!) Carlo Pagani 29
The Reliability Issue The small number (few per year) of beam trips allowed during the accelerator operation, requires a detailed analysis of the accelerator availability and reliability, much deeper that in the past applications The reliability analysis of a complex system is an iterative process, which starts from a preliminary design of the whole system and its components and is followed by the development of the Reliability Block Diagram (RBD). Carlo Pagani 30
Outcome of FP5 PDS-XADS activities Three project deliverables dedicated to reliability assessments Qualitative FMEA RBD analysis Assessment of (lack of) existing MTBF database for components Identification of redundant and fault tolerant linac configurations intended to provide nominal reliability characteristics Carlo Pagani 31
EU Linac Design (2000) Accelerator design performed in the EU PDS-XADS program (5 FWP) Choice of superconducting linac Modular: same concept for Prototype and Industrial scale Carlo Pagani 32
High energy section: the test module Z501 Test #1 Z502 E acc =8.5 MV/m @ Q 0 =10 10 10 Q 10 0 multipacting barriers start of electron emission 10 9 0 2 4 6 8 10 12 14 16 18 20 E acc [MV/m] Elliptical β=0.47 cavities have been produced, vertically tested and finally tested in a horizontal test module (at IPM- Orsay) by INFN - LASA Carlo Pagani 33
EU Planning at Eurotrans time EUROTRANS 2010? 2015? 2020? Carlo Pagani 34
MYRRHA & FP7 (2010) The purpose of MYRRHA is to serve as a multipurpose irradiation facility for research to address: ADS technological demonstration Waste transmutation studies of minor actinides and long lived fission products Structural material studies for PWR, fusion and ADS type reactors Nuclear fuel behaviour studies for PWR, BWR and ADS type reactors Radioisotopes production for medical & industrial applications Proton beam applications Taking into account the above catalogue of applications and the objective to put in service the facility around 2014-2015, the choice of MYRRHA components and parameters are as follows: A proton beam power of 1.5 MW (600 MeV * 2.5 ma) A windowless liquid Pb-Bi spallation target A sub-critical core (about 60 MW) made of MOX fuel with a plutonium content limited to 35 wt%, cooled with Pb-Bi and a Keff value of 0.95. Carlo Pagani 35
Concluding Remarks High power linear accelerators have been developed for other applications. They represent the minor problem When needed they will be there P&T together with ADS are now parts of the Generation IV strategy whose future is not clear in the Western Countries Carlo Pagani 36
A real ADS on the way Carlo Pagani 37
and development is going fast Carlo Pagani 38