Abstract
Computationally modelling a nuclear reactor startup core for a benchmark against the existing models is highly desirable for an independent assessment informing nuclear engineers and energy policymakers. For the first time, this work presents a startup core model of the UK’s first Evolutionary Pressurised Water Reactor (EPR) based on Monte Carlo simulations of particle collisions using Serpent 2, a state-of-the-art continuous-energy Monte Carlo reactor physics burnup code. Coupling between neutronics and thermal-hydraulic conditions with the fuel depletion is incorporated into the multi-dimensional branches, obtaining the thermal flux and fission reaction rate (power) distributions radially and axially from the three dimensional (3D) single assembly level to a 3D full core. Shannon entropy is quantified to characterise the convergence behaviour of the fission source distribution, with 3 billion neutron histories tracked by parallel computing. Source biasing is applied for the variance reduction. Benchmarking the proposed Monte Carlo 3D full-core model against the traditional deterministic transport computation suite used by the UK Office for Nuclear Regulation (ONR), a reasonably good agreement within statistics is demonstrated for the safety-related reactivity coefficients, which creates trust in the EPR safety report and informs the decision-making by energy regulatory bodies and global partners.
Highlights
Maintaining electricity supplies reliably is vital during the lockdown as well as the long-term combat against the Coronavirus (COVID-19)
Office for Nuclear Regulation (ONR), a reasonably good agreement within statistics is demonstrated for the safety-related reactivity coefficients, which creates trust in the Evolutionary Pressurised Water Reactor (EPR) safety report and informs the decision-making by energy regulatory bodies and global partners
As a low-carbon energy solution, nuclear power is projected to supply more than one-third of the UK’s electricity by 2035 [1]. Based on this vision and with the design acceptance by the UK Office for Nuclear Regulation (ONR) [2,3], EDF Energy is building up the first Evolutionary Pressurised Water Reactor (EPR) in the UK, supplied by AREVA [4]
Summary
Maintaining electricity supplies reliably is vital during the lockdown as well as the long-term combat against the Coronavirus (COVID-19). EPR reference core model using a state-of-the-art Serpent Monte Carlo code for the first time for an independent review of the analyses performed by EDF, whose results rely on a deterministic code. Rates of production and loss of neutrons are closely involved in the prediction of the reactivity and power distributions This reflects the significance of the Boltzmann transport equation [9], an integro-differential equation in seven dimensions, representing the neutron balance, i.e., the number of neutrons generated, equals to those consumed by fission, capture and other losses. As compared with traditional deterministic methods, the state-of-the-art Monte Carlo method relies on fewer approximations, e.g., no discretisation of space or energy required This results in a higher computational cost and a longer running time [13], especially for 3D full-core burnup calculations. Negligible deviation does exist because of the statistical nature of the Monte Carlo approach, which can be further mitigated by simulating more neutron histories and implementing the source biasing
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