Potential role of FF hybrids Massimo Salvatores CEA-Cadarache- France Fusion-Fission Hybrids have a potential role (in principle and independently from any technological readiness consideration) for nuclear fuel breeding and as an option within radioactive waste management strategies in order to: a)reduce the potential source of radiotoxicity, as a potential mitigation to the consequences of accidental scenarios (e.g. human intrusion) in the repository evolution with time, b) reduce the heat load in the repository and c) reduce the volume of the repository itself. This application can (should) be coupled (in principle) to electricity production. Different objectives and policies can be gathered into three broad categories and associated scenarios:

Scenario a): Sustainable development of nuclear energy for electricity production and waste minimization Scenario b): Reduction (elimination) of MA inventory (pure waste management objective) Scenario c): Reduction (elimination) of TRU inventory as unloaded from LWRs

Scenario a): Sustainable development of nuclear energy for electricity production and waste minimization a1) Homogenous or heterogeneous TRU recycling in a critical fast reactor. The fuels are standard mixed oxide or dense fuels (metal, nitride, carbide), with MA content of a few percent (e.g. definitely < 5-10%). a2) Use of a FFH, with similar fuel types and minor actinide content in the fission blanket. In the past, an ADS (or “Energy Amplifier”) has been proposed. However the subcriticality is not an issue (the effective delayed neutron fraction and the Doppler effect can be kept as high as needed since the MA content is <10%) and the economy was found not to be attractive.

a3) An alternative: the LIFE concept LIFE

Plutonium recycling Spent Fuel Direct disposal Uranium Ore (mine) Time (years) Relative radiotoxicity P&T of MA Pu + MA + FP MA + FP ~300 years after discharge 99.9% BU is ~ equivalent to multireprocessing of FR fuel with 99.9% recovery factor! Provided by H. F. Shaw, LLNL 99.9% Recovery factor

Another alternative: the WISE concept Use of « mobile » fuel, e.g. molten metals in a critical reactor

Scenario b): Reduction (elimination) of MA inventory(pure waste management objective) The objective is to reduce drastically the MA inventories, while Pu is still considered a resource. With respect to scenario a), the implementation of advanced (e.g. fast) reactors is somewhat delayed in time and a transition scenario has to be envisaged, in order to avoid a build up of MA. Need separation of Pu from MA, to be kept together, or separation of Cm from Am, and Cm storage. To implement this scenario (“double strata” strategy) : MA fuels could be transmuted in external neutron source-driven (like ADS or FFH ). For ADS, the MA-loaded fuels should contain some Pu (e.g. Pu/MA~1) to keep ~ constant the reactivity of the sub-critical core (i.e. the accelerator current ~constant during the cycle, with both safety and economic advantages). If Inert Matrix Fuel (IMF) is envisaged, the conversion ratio of the sub-critical core is CR=0. However, a U-matrix can be considered as alternative to U-free IMF fuels. “Critical” burner FR with very low CR can then be envisaged.

Scenario c): Reduction (elimination) of TRU inventory as unloaded from LWRs c1) reduction of TRU stockpiles as a legacy of previous operation of LWRs. The ratio MA/Pu is ~0.1. As for reprocessing, grouped TRU recovery without separation of Pu from MA. To maximise consumption, a U-free fuel (inert matrix) in a fast neutron spectrum (i.e. an external neutron source-driven system, ADS or FFH ) with conversion ratio CR=0, can be envisaged. However, a conversion ratio CR ~ 0.5 or less, allows ~75% (or more) of the maximum theoretical TRU consumption, can also be envisaged in a “critical” burner FR.

c2): Reduction (elimination) of TRU inventory within a continuous use of LWR- only nuclear power The objective is to reduce the burden on a deep geological storage, as an alternative to direct storage of the spent fuel. Here again, use of dedicated transmuters (e.g. ADS, FFH or critical, low CR FR) As an option, it can be envisaged to transmute at first the largest TRU amount possible in a “deep-burn” reactor and to send the “leftovers” to the dedicated transmuters:

Define:  objective(s)  corresponding scenario caracteristics  caracteristics of the different systems involved (critical FR, external source driven systems etc)  isotopic compositions and fuel forms  caracteristics of the fuel cycle installations (reprocessing, fuel fabrication etc)  parameters of interest for the overall fuel cycle (e.g. mass flows, radiotoxicity, decay heat, neutron sources etc.) Then, run a scenario code in a dynamic mode (i.e. to account for transition phase towards equilibrium) How to compare a) performances with respect to: a) objective(s) and b) impact on the fuel cycle?

An example: a regional (European) scenario with ADS The scenario considered two groups of countries: Group A is in a stagnant or phase-out scenario for nuclear energy and has to manage his spent fuel, and especially the Plutonium and the minor actinides (MA). Group B is in a continuation scenario for the nuclear energy and has to optimize the use of his resources in Plutonium for the future deployment of fast reactors. The deployment of Fast reactors is delayed and there is need to manage MA inventory increase. The Scenario: P&T within a double strata approach  deployment of a number of ADS shared by the two groups of countries.  The ADS will use the Plutonium of the Group A and will transmute the minor actinides of the two groups.  The Plutonium of the Group B is continuously recycled in PWRs. The main objective of this scenario is to decrease the stock of spent fuel of countries of Group A down to ~0 at the end of the century, and to stabilize both Pu and MA inventories of Group B.

Regional Facilities Reprocessing A Countries Group A Spent Fuel A Countries Group B MOX FabricationPWR MOX Spent Fuel ADS Spent Fuel B Pu+ MA Reprocessing B ADS Fuel Fabrication ADS ADS Fuel Reprocessing Pu+ MA MA Pu UOX FabricationPWR UOX Enriched U Scenario lay-out (Double strata) Actual data (e.g. spent fuel inventories) have been provided from Belgium, Czech Republic, France, Germany, Spain, Sweden and Switzerland

Examples of results The required number of ADS (~400 MWth) was determined to be 27 units A total reprocessing capacity of 3300 tonnes is needed : 850 t/y for ADS reprocessing plant, 850 t/y for Group A spent fuel legacy, and 1600 t/y for Group B.

At present, for the same scenario ADS and critical, low conversion ratio FR are compared We are investigating how to enlarge this type of studies to FFH. First discussion to include SABR (GA-Tech). Data from an external source driven system are easily implemented in the scenario code (COSI), widely used in Europe and a reference for most international studies. Δm Kg/TWh ADS (k=0.97) Low CR (=0.58) Critical FR Pu Np Am Cm Total

Impact on some fuel cycle parameters of different transmutation strategies. A crucial issue: the impact on the fuel cycle parameters Mostly a Cf-252 effect Cm-244, Cm-246 effect Cm-244, Am-241, Pu- 238 effect

Within different scenarios and according to different objectives, there is a potential role for FFH to be investigated.  However, to judge of the realism and cost/benefits of each option, a detailed in-depth comparative analysis (that should include the full fuel cycle) is needed.  The experience of the past for similar cases has shown that qualitative statements do not help the credibility of a particular concept.  Comparative analysis and collaborative initiatives can be set-up now, independently from the equally needed assessment of technological readiness and implementation horizon of the different options. Summary

Summary of typical results  The spent fuel stock of Group A can be decreased, as required, down to 0 by 2100 : all the fuel was reprocessed by that date.  In order to stabilize the MAs production from Group B, the required number of ADS (~400 MW th ) was determined to be 27 units  The plutonium inventory of Group B is stabilized starting from 2100 at ca. 100 tonnes As for the Regional facilities:  A total reprocessing capacity of 3300 tonnes is needed : 850 t/y for ADS reprocessing plant, 850 t/y for Group A spent fuel legacy, and 1600 t/y for Group B.  The needed fabrication capacity is : 690 t/y for UOX, 390 for MOX, and 40 for ADS.

Minor Actinides total mass (in tonnes) in all facilities Spent fuel cumulative inventory (in tonnes) in Group A spent fuel interim storage ADS electric power production vs. time