ADS (Accelerator Driven Systems) e LFR (Lead Fast Reactor)

Transcription

1 ADS (Accelerator Driven Systems) e LFR (Lead Fast Reactor) L. Mansani luigi.mansani@ann.ansaldo.it Workshop: La Trasmutazione ed i Cicli Innovativi del Combustibile Nucleare Roma 20 Dicembre 2010

2 Origin of Nuclear Waste Most of the reactors operative in the world today are thermal spectrum reactors 265 PWRs, 92 BWRs, 48 CANDU, 18 AGRs, 15 LGR and only one LMFBR Currently dominant open fuel cycle, in which uranium fuel is irradiated, discharged and replaced with new uranium fuel, has resulted in the gradual accumulation of large quantities of highly radioactive or fertile materials in the form of Depleted Uranium, Plutonium, Minor Actinides (MA) and Long-Lived Fission Products (LLFP) 2500 tons of spent fuel are produced annually in the EU containing 25 tons of Pu, 3.5 tons of MAs (Np, Am, and Cm) and 3 tons of LLFPs (Tc, Cs and I) Typical annual discharge inventory from a 900 MWe PWR fuelled with about 72 tons of U (3.7% 235 U) is 200kg of Pu, 11kg of Np, 10kg of Am, 1kg of Cm, 17kg of 99 Tc, 10kg of 135 Cs, and 4kg of 129 I In EU spent fuel is reprocessed and some of the separated products have already been utilized in the form of MOX (Mixed Pu/U Oxide) fuels, but not yet in sufficient quantities to significantly slow down the steady accumulation of these materials in storage

3 Debate on Waste Management Strategy for Sustainability of Nuclear Energy P&T is essential for the sustainability of nuclear energy GD is indispensable for radioactive waste management Both communities should work together for the future of nuclear energy

4 Partitioning and transmutation (P&T) The radio-toxicity of the fission products dominates the total radio-toxicity during the first 100 years and reaches the uranium ore mine level at about 300 years The long-term radio-toxicity is dominated by the actinides (mainly by the Pu and Am isotopes) and the uranium ore mine level is reached only after more than 100,000 years By recycling and then burning all the MA, the period over which highlevel radioactive waste remains hazardous could theoretically be reduced from hundreds of thousands of years down to a few hundred years

5 Strategy for Sustainability of Nuclear Energy Once-through cycle (disposal of spent fuel as it is) does not appear to be more sustainable Reprocessing of the spent fuel and transmutation of MAs in dedicated devices reduces radio-toxic inventory of the disposed waste in geological repositories Geological disposal of the remaining waste (separation/transmutation losses) will be required

6 Transmutation Transmutation chain for the main Minor Actinides Th (n, γ) β- decay β+ decay γ decay (n, 0) α decay (n, 2n) 233 U Fissile 234 U 235 U 236 U 237 U 238 U T 1/2:9e5y 6.7d T 1/2:2.14e6y via Pa Np 238 Np 239 Np T 1/2:7e3y T 1/2:2.5e4y T 1/2:6.5e3y 2000d 2300d 238 Pu 239 Pu Fissile 240 Pu 241 Pu Fissile 242 Pu 243 Pu T 1/2:87.7y 14.4y < 30d 5h Pu242/243 (7.4e3y/1.6e7y) T 1/2:432.9y 241 Am 242 Am 242m Am Fissile 243 Am 244 Am 244m Am < 30d < 30d < 30d T 1/2:162.9d 242 Cm 243 Cm 244 Cm 245 Cm Fissile 246 Cm 247 Cm T 1/2:30y T 1/2:18.1y T 1/2:8.4e3y y Bk Transmutation chain indicates that following a prolonged period of time out of reactor (over timescales ranging from a few years to millions of years), isotopes of Np, Am and Cm can, by various captures or decays, transmute into a number of fertile or fissile isotopes, including those of Pu and U The only effective method to reduce MA both in mass and activity is via fission (or incineration, perhaps following a number of intermediate transmutations) and not solely transmutation Fast spectrum reactor gives better flexibility to transmute and to fission MA (high fast flux can be attained with a useful neutron surplus)

7 Transmutation in Fast Reactors Both fast spectrum critical reactors and sub-critical ADS are potential candidates for dedicated transmutation systems Critical reactors, however, loaded with fuel containing large amounts of MAs pose safety problems caused by unfavourable reactivity coefficients and small delayed neutron fraction Core fuelled with only MA (Uranium free) has no Doppler nor Delayed Neutrons The main characteristic of ADS (i.e. sub-criticality) is particularly favourable and allows a maximum transmutation rate while operating in a safe manner An advantage of ADS is that the lack of criticality condition to fulfil gives an additional freedom for the choice of fuel

8 Strategy for Sustainability of Nuclear Energy with ADS Double-strata approach with Sub-critical Accelerator Driven Systems (ADS) and Critical Thermal Reactors can be considered U nat. LWR First Stratum ENRICHMENT MOX Pu REPROCESSING PARTIONNING MA Second Stratum ADS FABRICATION REPROCESSING FP Actinides MA

9 ADS Structures In contrast to conventional nuclear reactors in which there are enough neutrons to sustain a chain reaction, sub-critical cores used in ADS need an external source of neutrons to sustain the chain reaction Extra" neutrons are provided by an accelerator (accelerator produces high energy protons which produce neutrons via a spallation source) ADS is made by coupling three systems: Proton Accelerator: a high intensity proton machine, delivering a proton beam on a spallation target to provide an external neutron flux source for a sub-critical core Spallation Target: a mechanical component which provides the driving neutron source by spallation process and constitutes the mechanicalfunctional interface between the high power proton accelerator and the sub-critical core Sub-critical Core: a fuel assembly zone where nuclear (fission, capture, etc) reactions are caused both by the external neutrons source and by the neutrons produced by the fission reactions itself

10 Proton Accelerator Scheme for ADS

11 ADS development in Ansaldo Nucleare and in Europe (PDS-XADS project) Following a preliminary design developed in 1998, which was based on the Energy Amplifier concept proposed by CERN, a first configuration of a Lead-Bismuth Eutectic cooled Experimental ADS (LBE-XADS) was worked out in the period by a group of Italian organizations led by Ansado Nucleare, with the aim of assessing the feasibility of a small-sized (80 MWth) ADS The design activities of the Italian organizations (ANSALDO, ENEA, INFN, CRS4, CIRTEN, SIET and SRS) were carried out under the aegis of MURST (the former Italian Ministry of University and of the Scientific-Technological Research) The design activities continued within the 5 th FP of the European Commission, in the context of the research on Fission Reactors Safety, that funded a project named PDS-XADS (Preliminary Design Studies of an Experimental Accelerator Driven System) with a threeyear contract ( ) involving the participation of 25 European partners (industries, research organizations and Universities)

12 ADS development in Ansaldo Nucleare and in Europe (PDS-XADS project) The experimental Accelerator-Driven Systems (XADS) in the 5 FP of the EU 80 MW LBE-cooled XADS 80 MW Gas-cooled XADS 50 MW LBE-cooled XADS (MYRRHA)

13 ADS development in Ansaldo Nucleare and in Europe (IP-EUROTRANS Project) In 2005 the EC partially funded, within the FP6, the integrated project IP-EUROTRANS with the objective to demonstrate the possibility of nuclear waste transmutation/burning in ADS at industrial scale XT-ADS/MYRRHA The focus during this 5 years program was on: the development of a conceptual design of a generic European Transmutation Demonstrator (EFIT- European Facility for Industrial Transmutation) to be realized in the long term; the design of an experimental Transmuter and irradiation facility based on ADS concept (XT-ADS) to be realized in the short term. Both EFIT and XT-ADS designs have beneficed of the experience acquired in the previous PDS-XADS project of EC FP5 EFIT

14 Pure Lead as the Coolant for ADS and LFR Lead does not react with water or air Possibility to eliminate the intermediate loop; SGU installed inside the Reactor Vessel Need R&D on effects of water-lead interaction in case of SGTR accident Less stringent requirements on reactor leak tightness Lead has very high boiling point Reduced core voiding risk (Lead boiling point is 1745 C ) Lead has a higher density than the oxide fuel No need for core catcher to face core melt (molten clad and fuel float) No risk of re-criticality in case of core melt Lead is a low moderating medium and has low absorption cross-section. No need to have a very compact Fuel Assemblies (FA can have fuel rods spaced large apart; Core pressure loss drastically reduced in spite of the higher density of lead resulting in lower pumping power and higher natural circulation capability) Lead has a very low 210 Po production Lead is compatible with existing clad material T91 Operation over long irradiation period and under Oxygen control up to 500 C More margins with surface treatment (e.g. GESA) up to 550 C

15 ADS: the EFIT Reactor Assembly 1 Reactor Core 2 Active Zone 3 Diagrid 4 Primary Pump 5 Cylindrical Inner Vessel 6 Reactor Vessel 7 Reactor Cavity 8 Reactor Roof 9 Reactor Vessel Support 10 Rotating Plug 12 Above Core Structure 13 Target Unit 14 Steam Generator Unit 15 Fuel Handling Machine 16 Filter Unit 17 Core Instrumentation 18 Rotor Lift Machine 19 DHR Dip Cooler

16 ADS: the EFIT Sub-criticality level The ADS core is designed to remain sub-critical under all plant conditions (Design Basis Conditions (DBC) and Design Extension Conditions (DEC)) It is assumed that a margin of K to criticality, a figure that includes allowance for measurement errors, be required at DBC, akin to standard practice for light water reactors. K eff shall hence not exceed at any time during DBC It is further assumed that a thinner margin is acceptable for DEC, owing to their postulated very low frequency, and that K eff shall not be greater than 0.95 during Refuelling or Target Unit removal for replacement K eff = 0.97 has been preliminary assumed for EFIT as the upper limit of normal operation

17 ADS: the Core Design Strategy for EFIT Main design missions of EFIT are effective transmutation rate of the Minor Actinides (MA) and effective electric energy generation Fuelled with only MA (Uranium free fuel) CER-CER (Pu,Am,Cm)O2-x MgO CER-MET (Pu,Am,Cm)O2-x 92Mo Minimize the burn-up reactivity swing without burning and breeding Pu The requirement of nearly zero burn-up reactivity swing is dictated by the whish to specify a narrower range of proton beam current with associated benefit of no risk of accidental reactor overpower and to avoid over-sizing the accelerator The requirement of Pu breeding ratio 1 implies that Pu is required for the first cycles only, a feature that limits to a minimum inter-sites Pu handling and does not contribute to pile-stocking of Pu, in times of surfeit of it, considering also that Pu can be advantageously fissioned in critical fast reactors, possibly new-generation fast reactors, all facilities that are predictably less expensive than ADS EFIT

18 ADS: the EFIT Core Performances pcm [ kg ] Tot Pu Tot MA Proton Current = f (k eff (t), ϕ*, P th ) 13,5 ma (almost constant) MA / MA (BOC) -13,9% Pu / Pu (BOC) -0,7% 0 1 [ years ] 2 3 BOL BOC EOC FA EOL 3 years BU = 78,28 MWd / kg (HM) BU -40,17 kg (MA) / TWh Total E = 10,0915 TWh th -1,74 kg (Pu) / TWh

19 LFR development in Ansaldo Nucleare and in Europe (ELSY, LEADER projects) In 2006 the EC partially funded, within the FP6 programme, the project ELSY (European Lead-cooled System) The ELSY project has been conducted by a large consortium of European organizations to demonstrate the feasibility of designing a competitive and safe Lead Fast (critical) Reactor using simple engineered features, while fully complying with Generation IV goals, including that of MA burning capability ELSY project is terminated on February 2010, but LFR development will continue within the Lead-cooled European Advanced DEmonstration Reactor (LEADER) project in the EC FP7 started on April 2010 LEADER project will be built on the ELSY results with the objective to finalize the design of a large size LFR and to develop the conceptual design of a scaled demonstrator (ALFRED)

20 LFR: the ELSY Reactor Assembly B C Steam Generato r B C Primary Pumps Primary Coolant Flow Path Core Reactor Vessel

21 LFR: the ELSY Core Performances Power: 1500 MW th (~650 MWe) Inventory: Uranium: kg; Plutonium: 6161 kg. Average enrichment: 17.6 wt% Burn-up performances (5 years resident time): Breeding Ratio (referred to the 239 Pu equivalent mass at EoL): 0.94; Reactivity swing: 900 pcm (per 1.25 years cycle); Average burn-up: 78.1 MWd/kg (HM); Maximum FA burn-up: 94 MWd/kg (HM); Uranium balance:-9.6% / kg/twh th ; Pu balance: -1.6% / kg/twh th ; MAs balance : Exponential trend toward an equilibrium content of about 240 kg (~ 4% on Pu and < 1% on the total HM inventory); (i.e. 100 kg of initial accumulation in 5 years, starting from a clean fuel).

22 LFR: the Closed Fuel Cycle MOX first loads (U:82.5%; Pu: 17.5%) Fabrication LFR Adiabatic Reprocessing FP: 1g/MWD + losses MOX equilibrium (U: 82%; Pu: 17%; MA: 1%) U nat/dep : 1g/MWD + reintegration of losses All Actinides (Expected MA: 1% of which 20% Cm) LFR can be operated as adiabatic: Waste only FP, feed only U nat/dep Pu vector slowly evolves cycle by cycle MA content increases and its composition drift in the time LFR is fully sustainable and proliferation resistant (since the start up) Pu and MA are constant in quantities and vectors Safety - main feedback and kinetic parameters vs MA content

23 LFR development in Ansaldo Nucleare and in Europe (LEADER project) Advanced nuclear systems for increased sustainability FP7-Fission Conceptual Design for Lead Cooled Fast Reactor Systems (LEADER) 18 European Organization are participating to the project Ansaldo Nucleare is the Project Coordinator 3 year Project ( ), started 1 of April 2010 LEADER Objectives Deep analysis of the hard points of the ELSY design in order to identify possible improvements with the goal to reach a feasible and improved LFR configuration Definition of a new frozen LFR configuration to be used as a reference plant Conceptual design of a scaled down facility respect to the reference plant (the ALFRED demonstrator) of a size of the order of 120 MWe (to be representative with limited cost)

24 ADS and LFR development in Ansaldo Nucleare and in Europe (CDT project) In the frame of the project CDT of the 7th FP of the EU, 20 European Organizations (coordinated by SCK CEN) have the strategic objective to further develop the design of a FAst Spectrum Transmutation Experimental Facility (FASTEF) able to demonstrate efficient transmutation and associated technology through a system working in subcritical and/or critical mode (Pilot Plant for both ADS and LFR) The aim of the 3-year lasting CDT program (started on April 2009) is to: develop the engineering design based on the resulting MYRRHA/XT-ADS facility of the FP6 IP-EUROTRANS project define the new R&D activities needed to aid the detailed design and the construction conduct a detailed analysis of the hosting site specifications and regulatory requirements

25 European Industrial Initiative of the SET Plan dedicated to the demonstration of Gen IV technologies