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WP 4 : Fuel performance evaluation and validation of methodologies and codes

WP4 encompasses the feasibility study for the introduction of innovative fuels for efficient plutonium burning in a NPP. The work package addresses in addition the outstanding questions on the consequences for reactor safety, burn-up behaviour and fuel performance under existing LWR-neutronic conditions when introducing innovative fuels targeting on transmutation of Pu. The accuracy of numeric analyses and methods will be proved by simulations of irradiation experiments as well as by benchmarking, based on the results from PIE and radiochemical analyses (Th-Pu-MOX- from WP3).

To achieve these objectives, the working package consists of 3 tasks:

• T4.1 Feasibility study of introducing innovative Pu-burning fuels in the nuclear fuel cycle
• T4.2 Performance and safety assessment for novel fuels
• T4.3 Comparison and validation of codes and methodologies

The following task-breakdown gives a description of the contents and shows the anticipated contributions of each contractor in this working package.

• T4.1: Feasibility study of introducing innovative Pu-burning fuels in the nuclear fuel cycle. This task addresses the feasibility to introduce innovative Pu-burning fuels (e.g. Pu-IMF, Th-Pu MOX) in NPP as a means to minimise plutonium stockpiles. An essential part of this study is an assessment of the stakeholders’ position (utilities, governments in various member countries) with regard to the use of these efficient Pu-burning fuels. This assessment will be performed in the countries of the partners in the consortium, i.e. Belgium (SCK•CEN), Germany (FZJ), Netherlands (NRG), Slovakia (VUJE), and United Kingdom (Nexia Solutions).

NRG contributes further in collecting results and issuing the report “Introduction of innovative Pu-burning fuels in the nuclear fuel cycle”, where the prospects and limitations of the use of efficient Pu-burning (Inert Matrix) Fuels, that are investigated in LWR-Deputy, on an industrial level are discussed.

• T4.2: Performance and safety assessments aim to quantify the potential to increase the transmutation rate for Pu in different fuel types (CERCER, CERMET) and fuel compositions (e.g. IMF-PuO2, Th-Pu-MOX). Full core neutronic analysis for steady state conditions will be performed to determine reactivity coefficients and safety parameters. The task also encompasses some safety and transient analysis of Pu-IMF CERMET fuel and Th-Pu-MOX in different reactor cores (PWR, VVER).

• FZJ contributes to the assessment of selected innovative fuel concepts (CERMET) and calculates the burn-up behaviour, transmutation performance and safety parameters (reactivity feed back coefficients) by using the SCALE5 and MCNP/ORIGEN codes. These assessments will be performed on pin cell or/and assembly level.

• FZK contributes to the assessment of CERMET transmutation fuels and computes reactivity coefficients in a core containing these fuels by using deterministic and Monte-Carlo codes. C4P, a recently at FZK developed code and multigroup cross-section management system, and the ZMIX code will be used for preparing multigroup cross-sections. Cell/subassembly/core calculations will be performed by the DANTSYS and VARIANT codes. Results of deterministic calculations will be compared with those obtained by Monte-Carlo (MCNP) modelling.

• FZR contributes to the steady-state and safety assessment by reactor physics calculations. The calculations will be focused on 3D reactor core simulations using the DYN3D code. Especially, the reactivity feedback and transient behaviour of a VVER-440 core containing Th-Pu-MOX fuel will be studied. For this aim input cross sections will be generated by HELIOS.

• NEXIA Solutions contributes to performance analyses of the selected innovative fuel options (Pu-IMF CERMET fuel) applying the codes CASMO-4 and SIMULATE-3. Additionally NEXIA brings in experiences and results from studies performed for the IAEA and the British government.

• NRG contributes by defining a representative CERMET Pu-IMF assembly, based on (depleted) molybdenum. This assembly definition is used as input for the steady state burup and reactivity analysis of the assembly by FZJ and for the full core steady state analyses by FZK. The task encompasses also the full core safety assessment on the targets set within the FP5 THORIUM project (Th-Pu-O2 fuel), which did not include safety analysis. The safety analysis of the proposed design (Westinghouse-3 loops with full pellets) will be studied.

• VUJE contributes to performance and safety assessments of cores with the selected IMF-PuO2 fuel types for inclusion into the VVER-440 reactors. (RELAP5, DYN3D, cross sections generated by HELIOS). 3D core simulations will be performed by BIPR7 and DYN3D codes. Input cross sections will be generated by spectral code HELIOS.

• T4.3: Comparison and validation of codes and methodologies aim at quantifying the accuracy of results from numerical simulations of innovative fuels by neutronic codes. Benchmarking is performed by simulation of the irradiation history and comparison with PIE-results. A dedicated benchmark to the (Th,Pu)O2 fuels is defined using the results of the radiochemical analyses of KWO-irradiation (WP3). Particular attention is given to the key isotopes produced in process of breeding/chain of 232Th, the depletion of the Pu vector and the build-up of higher actinides

• FZJ will perform integral neutronic analysis for comparison with the results of PIE which are obtained in the framework of WP3 on the basis of irradiations performed at KWO Obrigheim. Using the results of PIE, FZJ will define a detailed benchmark for use by all WP4-institutes to check and validate their own numerical codes and data libraries. Finally an evaluation of the results of the different calculations and code systems is performed by FZJ.

• Nexia Solutions, FZJ, FZK, FZR, SCK•CEN and VUJE will perform the benchmark calculations using their codes and deliver the results in a template form provided by FZJ.

This WP has links to FP5- and FP6-projects as well as to other WPs of the existing project; their nature and relevance are explained in more detail:

• T4.1 Pu-IMF and Pu-Th MOX have been studied in numerous investigations and test irradiations, such as FP5 Thorium cycle and in the IFA-651 (Halden) and OTTO studies (HFR). Knowledge about these innovative fuels is on such a level, that introduction on an industrial level becomes foreseeable in the near to medium-term future. However, performing a test irradiation in a commercial NPP was, at the moment, not considered feasible. The study in task 4.1 is performed to assess still missing links, and to identify the needs and views in various countries on medium-term plutonium management and industrial deployment of innovative fuels for enhanced plutonium burning.

• T4.2 uses the experiences gained from FP5 projects when the relevant cores and fuels are defined. The transient core analysis by NRG will be based on the selected core design from the FP5 THORIUM-project. A close link to the outcome is assured by the contractors FZJ, Nexia Solutions and NRG, which contribute to the THORIUM-project.
Full core analyses of the behaviour of CERMET Pu-IMF fuels have a close relation to the screening irradiation being performed in WP2.

• T4.3 is linked to WP3 and requires input from the radiochemical analyses of the irradiated FP5-fuel samples. The benchmark set-up relates strongly on the irradiation data (e. g. power history, flux distribution, residence time), which are provided from the conducted FP5-irradiations.