European Facility For Industrial Transmutation Research Articles

Oxygen for protective oxide scale formation on pins and structural material surfaces in lead-alloy cooled reactors

Oxygen dissolved in liquid Pb alloys prevents dissolution attack on structural steels by formation of oxide scales on the surface. The required amount of oxygen for continuous scale formation depends on temperature on the kind of steel and its oxidation behavior. Compatibility of the steels in reactor systems with liquid lead alloys can only be maintained if the oxygen consumed by the growing oxide scales is replaced. Calculation of the oxygen consumed is performed on the basis of experiments on the oxide scale growth on steels in liquid Pb alloys. These calculations consider also the change in surface temperature caused by the growth of the oxide scales. The design data of EFIT (European Facility for Industrial Transmutation) and a realistic start-up scenario for such a system was used in the investigation. Also the impact of fuel element exchange and the replacement of heat exchangers were considered.The oxygen consumption is very high in the beginning, when the metals get into contact with the lead alloy. It is a great advantage to employ structures that have already protective oxide scales or can form those during a commissioning phase at 400°C inside the reactor. Otherwise, the oxygen consumption rate would be difficult to handle. A further great improvement would be to alloy the surface of heavy loaded structure parts like the high temperature parts of fuel pins and the heat exchanger tubes with Al to form thin stable oxide films, which, furthermore, have the advantage of a low thermal resistance. This surface treatment would cut down the overall oxygen consumption to less than the half of it.It may be not possible to provide the reactor completely with oxygen via the gas phase because even the surface of the whole pool may not be large enough to transfer the required oxygen. An additional transfer of oxygen by solution of PbO could support the gas phase transport during the peak times of the consumption rate.

Propagation of Nuclear Data Uncertainties in Transmutation Calculations Using ACAB Code

Departamento de Ingeniera Energetica, Universidad Nacional de Educacion a Distancia (UNED), 28004 Madrid, Spain(Received 26 April 2010)The assessment of the accuracy of parameters related to the reactor core performance (e.g.,ke ) and fuel cycle (e.g., isotopic evolution/transmutation) due to the uncertainties in the ba-sic nuclear data (ND) is a critical issue. Di erent error propagation techniques (adjoint/forwardsensitivity analysis procedures and/or Monte Carlo technique) can be used to address by computa-tional simulation the systematic propagation of uncertainties on the nal parameters. To performthis uncertainty assessment, the ENDF covariance les (variance/correlation in energy and cross-reactions-isotopes correlations) are required.In this paper, we assess the impact of ND uncertainties on the isotopic prediction for a concep-tual design of a modular European Facility for Industrial Transmutation (EFIT) for a dischargeburnup of 150 GWd/tHM. The complete set of uncertainty data for cross sections (EAF2007/UN,SCALE6.0/COVA-44G), radioactive decay and ssion yield data (JEFF-3.1.1) are processed andused in ACAB code.

Comparative studies of CERCER and CERMET fuels for EFIT from the viewpoint of core performance and safety

The European Facility for Industrial Transmutation (EFIT) has been developed within the 6th EU Framework by the EUROTRANS Program, aiming at a generic conceptual design of an accelerator driven transmuter. This paper deals with assessments of EFIT cores with CERCER and CERMET fuels from the viewpoint of core performance and safety. The conclusive remarks can be drawn as follows. Because of its much better thermal conductivity, the CERMET core can be designed by using thicker pins, so that it has the same or even better transmutation performance compared to the CERCER core. Both CERCER and CERMET fuels fulfill safety requirements. Moreover the CERMET fuel has higher fuel safety margins than the CERCER one. Preliminary analyses show that the CERMET total core power can be further increased by 50% at least without exceeding fuel and clad temperature limits.

Prognosis and comparison of performances of composite CERCER and CERMET fuels dedicated to transmutation of TRU in an EFIT ADS

The neutronic and thermomechanical performances of two composite fuel systems: CERCER with (Pu,Np,Am,Cm)O 2− x fuel particles in ceramic MgO matrix and CERMET with metallic Mo matrix, selected for transmutation of minor actinides in the European Facility for Industrial Transmutation (EFIT), were analysed aiming at their optimisation. The ALEPH burnup code system, based on MNCPX and ORIGEN codes and JEFF3.1 nuclear data library, and the modern version of the fuel rod performance code TRAFIC were used for this analysis. Because experimental data on the properties of the mixed minor-actinide oxides are scarce, and the in-reactor behaviour of the T91 steel chosen as cladding, as well as of the corrosion protective layer, is still not well-known, a set of “best estimates” provided the properties used in the code. The obtained results indicate that both fuel candidates, CERCER and CERMET, can satisfy the fuel design and safety criteria of EFIT. The residence time for both types of fuel elements can reach about 5 years with the reactivity swing within ±1000 pcm, and about 22% of the loaded MA is transmuted during this period. However, the fuel centreline temperature in the hottest CERCER fuel rod is close to the temperature above which MgO matrix becomes chemically instable. Moreover, a weak PCMI can appear in about 3 years of operation. The CERMET fuel can provide larger safety margins: the fuel temperature is more than 1000 K below the permitted level of 2380 K and the pellet-cladding gap remains open until the end of operation.

ADS Fuel Developments in Europe: Results from the EUROTRANS Integrated Project.

Fuels to be used in Accelerator Driven Systems dedicated to Minor Actinides transmutation can be described as highly innovative in comparison with those used in critical cores. Indeed, ADS fuels are not fertile, so as to improve the transmutation performance and they contain high volumetric concentrations (~50%) of minor actinides and plutonium compounds. This unusual fuel composition results in high gamma and neutron emissions during its fabrication, as well as degraded performances under irradiation. Ceramic-Ceramic and Ceramic Metallic composite fuels consisting of particles of (Pu,MA)O2 phases dispersed in a magnesia or molybdenum matrix were investigated within the European Research programme for Transmutation, as driver fuels for a prospective 400MWth transmuter: the European Facility for Industrial Transmutation. Fuel performances and safety of preliminary core designs were evaluated to support the project. Out -of-pile as well as in-pile experiments were carried out to gain essential knowledge on properties and behaviour under irradiation of these types of fuel. This paper gives an overview of experimental results within the project. © 2010 Published by Elsevier Ltd

Predicting thermo-mechanical behaviour of high minor actinide content composite oxide fuel in a dedicated transmutation facility

The European Facility for Industrial Transmutation (EFIT) of the minor actinides (MA), from LWR spent fuel is being developed in the integrated project EUROTRANS within the 6th Framework Program of EURATOM. Two composite uranium-free fuel systems, containing a large fraction of MA, are proposed as the main candidates: a CERCER with magnesia matrix hosting (Pu,MA)O 2− x particles, and a CERMET with metallic molybdenum matrix. The long-term thermal and mechanical behaviour of the fuel under the expected EFIT operating conditions is one of the critical issues in the core design. To make a reliable prediction of long-term thermo-mechanical behaviour of the hottest fuel rods in the lead-cooled version of EFIT with thermal power of 400 MW, different fuel performance codes have been used. This study describes the main results of modelling the thermo-mechanical behaviour of the hottest CERCER fuel rods with the fuel performance code MACROS which indicate that the CERCER fuel residence time can safely reach at least 4–5 effective full power years.

Optimisation of composite metallic fuel for minor actinide transmutation in an accelerator-driven system

A potential option for neutralization of minor actinides (MA) accumulated in spent nuclear fuel of light water reactors (LWRs) is their transmutation in dedicated accelerator-driven systems (ADS). A promising fuel candidate dedicated to MA transmutation is a CERMET composite with Mo metal matrix and (Pu, Np, Am, Cm)O 2− x fuel particles. Results of optimisation studies of the CERMET fuel targeting to increasing the MA transmutation efficiency of the EFIT (European Facility for Industrial Transmutation) core are presented. In the adopted strategy of MA burning the plutonium (Pu) balance of the core is minimized, allowing a reduction in the reactivity swing and the peak power form-factor deviation and an extension of the cycle duration. The MA/Pu ratio is used as a variable for the fuel optimisation studies. The efficiency of MA transmutation is close to the foreseen theoretical value of 42 kg TW −1 h −1 when level of Pu in the actinide mixture is about 40 wt.%. The obtained results are compared with the reference case of the EFIT core loaded with the composite CERCER fuel, where fuel particles are incorporated in a ceramic magnesia matrix. The results of this study offer additional information for the EFIT fuel selection.

Nuclear data requirements for the ADS conceptual design EFIT: Uncertainty and sensitivity study

In this paper, we assess the impact of activation cross-section uncertainties on relevant fuel cycle parameters for a conceptual design of a modular European Facility for Industrial Transmutation (EFIT) with a “double strata” fuel cycle. Next, the nuclear data requirements are evaluated so that the parameters can meet the assigned design target accuracies. Different discharge burn-up levels are considered: a low burn-up, corresponding to the equilibrium cycle, and a high burn-up level, simulating the effects on the fuel of the multi-recycling scenario. In order to perform this study, we propose a methodology in two steps. Firstly, we compute the uncertainties on the system parameters by using a Monte Carlo simulation, as it is considered the most reliable approach to address this problem. Secondly, the analysis of the results is performed by a sensitivity technique, in order to identify the relevant reaction channels and prioritize the data improvement needs. Cross-section uncertainties are taken from the EAF-2007/UN library since it includes data for all the actinides potentially present in the irradiated fuel. Relevant uncertainties in some of the fuel cycle parameters have been obtained, and we conclude with recommendations for future nuclear data measurement programs, beyond the specific results obtained with the present nuclear data files and the limited available covariance information. A comparison with the uncertainty and accuracy analysis recently published by the WPEC-Subgroup26 of the OECD using BOLNA covariance matrices is performed. Despite the differences in the transmuter reactor used for the analysis, some conclusions obtained by Subgroup26 are qualitatively corroborated, and improvements for additional cross sections are suggested.

Transient analyses of the 400MWth-class EFIT accelerator driven transmuter with the multi-physics code: SIMMER-III

In the EUROTRANS Programme of the 6th FP of the EC, EFIT, the European Facility for Industrial Transmutation, a generic conceptual design of a 400MWth ADS transmuter loaded with a CERCER U-free fuel with an MgO matrix, is developed. The safety objectives for the EFIT are achieved on the basis of the defense-in-depth concept. For the safety assessment various protected and unprotected design basis conditions (DBC) and design extension conditions (DEC) transients have been analyzed as e.g. the protected and unprotected loss of flow (PLOF/ULOF), beam trip transients, over power transients and especially the unprotected blockage accidents (UBAs). Key safety analyses of the EFIT core have been performed with the SIMMER-III code, currently the only code which can handle core disruptive conditions for heavy liquid metal cooled reactors. Unprotected transients set upper safety limits and play an important role in the overall safety assessment and transient behaviors of an ADS with MgO based fuel and T91 cladding. The high temperature range is still affected by significant uncertainties, therefore, unprotected accidents with a potential of fuel failure and fission gas release deserve special attention. In this paper, analyses of important and challenging transient cases will be presented. The SIMMER-III simulated results indicate that under the current conditions, the EFIT core can survive in most of the transient cases without pin failure except in the UBA cases. The analyses thus demonstrate the general high safety potential of an ADS like EFIT. Results of the UBA cases show that pin failure happens in the core center and propagation of the pin failure could be possible, while the core will finally arrive at a lower power condition because of the sweeping out of the fuel from the active core.

Heterogeneous fuels for minor actinides transmutation: Fuel performance codes predictions in the EFIT case study

Abstract Plutonium recycling in new-generation fast reactors coupled with minor actinides (MA) transmutation in dedicated nuclear systems could achieve a decrease of nuclear waste long-term radiotoxicity by two orders of magnitude in comparison with current once-through strategy. In a double-strata scenario, purpose-built accelerator-driven systems (ADS) could transmute minor actinides. The innovative nuclear fuel conceived for such systems demands significant R&D efforts in order to meet the safety and technical performance of current fuel systems. The Integrated Project EUROTRANS (EUROpean research programme for the TRANSmutation of high level nuclear waste in ADS), part of the EURATOM Framework Programme 6 (FP6), undertook some of this research. EUROTRANS developed from the FP5 research programmes on ADS (PDS-XADS) and on fuels dedicated to MA transmutation (FUTURE, CONFIRM). One of its main objectives is the conceptual design of a small sub-critical nuclear system loaded with uranium-free fuel to provide high MA transmutation efficiency. These principles guided the design of EFIT (European Facility for Industrial Transmutation) in the domain DESIGN of IP EUROTRANS. The domain AFTRA (Advanced Fuels for TRAnsmutation system) identified two composite fuel systems: a ceramic–ceramic (CERCER) where fuel particles are dispersed in a magnesia matrix, and a ceramic–metallic (CERMET) with a molybdenum matrix in the place of MgO matrix to host a ceramic fissile phase. The EFIT fuel is composed of plutonium and MA oxides in solid solution with isotopic vectors typical of LWR spent fuel with 45 MWd/kg HM discharge burnup and 30 years interim storage before reprocessing. This paper is focused on the thermomechanical state of the hottest fuel pins of two EFIT cores of 400 MW (th) loaded with either CERCER or CERMET fuels. For calculations three fuel performance codes were used: FEMALE, TRAFIC and TRANSURANUS. The analysis was performed at the beginning of fuel life. Presented results were used for testing newly-developed models installed in the TRANSURANUS code to deal with such innovative fuels and T91 steel cladding. Agreement among codes predictions was satisfactory for fuel and cladding temperatures, pellet-cladding gap and mechanical stresses.

Safety and design concepts of the 400 MW th-class EFIT accelerator driven transmuter and considerations for further developments

European R&D for ADS design and fuel development is driven in the 6th FP of the EU by the EUROTRANS Programme. In EUROTRANS, the longer-term EFIT development, the european facility for industrial transmutation, aims at a generic conceptual design of a full transmuter. A CERCER U-free fuel core with an MgO matrix and a CERMET core with a Mo-92 matrix have been designed. Both the CERCER and the CERMET EFIT concept were optimized towards: a high transmutation efficiency, high burn-up, low reactivity swing, low power peaking, adequate subcriticality, reasonable beam requirements and a high level of safety. Protected and unprotected transients which are initiated by a mismatch of power-to-flow or resulting from a beam disturbance or overpower situation were analyzed. Potentials which can lead to the introduction of positive reactivity into the core were identified, as e.g. the steam generator tube rupture (SGTR) accident or the pin failure with a gas release from the fission gas plena. Both for the CERCER and the CERMET fuelled core the design and safety analyses are close to completion in EUROTRANS and thus a first preliminary résumé can be drawn on the achieved design and safety goals. In addition, scenario studies in the framework of the PATEROS CA project of the 6th FP highlighted the specific needs on transmutation machines serving in countries with different nuclear options. Based on these studies in the 6th FP first reflections can be performed on needs or options for further optimizing an EFIT type ADS.

A source efficient ADS for minor actinides burning

Taking advantage of the good neutron economy of nitride fuel, a compact accelerator-driven system (ADS) for burning of minor actinide fuels has been designed, based on the fuel assembly geometry developed for the European Facility for Industrial Transmutation (EFIT) within the EUROTRANS project. The small core size of the new design permits reduction of the size of the spallation target region, which enhances proton source efficiency by about 80% compared to the reference oxide version of EFIT. Additionally, adoption of the austenitic steel 15/15Ti as clad material allows to safely reduce the fuel pin pitch, which leads to an increase of fuel volume fraction and therefore makes the neutron energy spectrum faster, consequently increasing minor actinides fission probabilities. Our calculations show that one can dramatically increase neutron source efficiency up to 0.95 without a significant loss of neutron source intensity, i.e. having high proton source efficiency. Consequently, the accelerator current required for operation of the ADS with a fission power of 201 MWth and a burn-up of 27 GW d/t per year (365 EFPD) is reduced by 67%.

T/H and transient analyses to confirm EFIT preliminary design

One of the main objectives of the EUROTRANS Integral Project is the design of a several hundreds MWth transmutator based on the accelerator driven system (ADS) concept. The preliminary layout of European Facility for Industrial Transmutation (EFIT) has started with a set of basic options derived from the previous ADS demo design (PDS-XADS) with the adoption of U-free fuel instead of MOX and taking into account the economic requirements needed for an industrial power plant. To support the project, a thermal-hydraulic numerical model of the reactor has been developed for the RELAP5 system code with the support of multidimensional SIMMER code to improve the representation of the natural circulation paths in the reactor vessel. The presented analyses, addressed to verify the capability of EFIT to face up the high power densities and temperatures, have allowed a first positive evaluation of the inherent safety behavior of the plant mainly relying on the natural circulation.

Accelerator driven systems for transmutation: Fuel development, design and safety

European R&D for ADS design and fuel development is driven in the 6th FP of the EU by the EUROTRANS Programme. In EUROTRANS two ADS design routes are followed, the XT-ADS and the EFIT. The XT-ADS is designed to provide the experimental demonstration of transmutation. The EFIT, the European Facility for Industrial Transmutation, aims at a conceptual design of a full transmuter. A key R&D issue is the choice of an adequate fuel. Various fuel forms have been assessed and CERCER and CERMET fuels, specifically the matrices MgO and Mo, have finally been selected. Within EUROTRANS, the domain ‘AFTRA’ is responsible to more deeply assess the behavior of these dedicated fuels and to provide the fuel database for the EFIT. The EFIT is optimized towards: a good transmutation efficiency, high burnup, low reactivity swing, low power peaking, adequate subcriticality, reasonable beam requirements and a high safety level. In the current paper the fuels under investigation are described, including their production route and their safety limits. First core designs of CERCER and CERMET fuelled 400 MWth EFITs have been developed within AFTRA. The trends found in the design studies and first safety analyses are presented.