“PROCESS”: A systems code for fusion power plants – Part 2: Engineering

Abstract

PROCESS is a reactor systems codeit assesses the engineering and economic viability of a hypothetical fusion power station using simple models of all parts of a reactor system. PROCESS allows the user to choose which constraints to impose and which to ignore, so when evaluating the results it is vital to study the list of constraints used. New algorithms submitted by collaborators can be incorporatedfor example safety, first wall erosion, and fatigue life will be crucial and are not yet taken into account. This paper describes algorithms relating to the engineering aspects of the plant. The toroidal field (TF) coils and the central solenoid are assumed by default to be wound from niobium-tin superconductor with the same properties as the ITER conductors. The winding temperature and induced voltage during a quench provide a limit on the current density in the TF coils. Upper limits are placed on the stresses in the structural materials of the TF coil, using a simple two-layer model of the inboard leg of the coil. The thermal efficiency of the plant can be estimated using the maximum coolant temperature, and the capacity factor is derived from estimates of the planned and unplanned downtime, and the duty cycle if the reactor is pulsed. An example of a pulsed power plant is given. The need for a large central solenoid to induce most of the plasma current, and physics assumptions that are conservative compared to some other studies, result in a large machine, with a cryostat 36 m in diameter. Multiple constraints, working together, restrict the parameter space of the optimised model. For example, even when the ratio of operating current to critical current in the TF coils is increased by a factor of five, the total coil cross-section decreases only a little, because of the need for copper stabiliser, insulation, and structural support. The result is that the plasma major radius hardly changes. It is these surprising results that justify the development of systems codes.

Determination of the tolerable impurity concentrations in a fusion reactor using a consistent set of cooling factors

“…We rather will focus on the EU DEMO1 2015 design and what impurity limits can be evaluated by our model including further improvements and a more advanced model. Nevertheless, the calculation of the operation windows in the present section demonstrates that complex design codes like PROCESS [25,26], which consider many details and which came up with the EU DEMO1 2015 design, must move within the general frame work which can be identified with the tools developed in the present work. Note, that if the operation point of the EU DEMO1 2015 design was not indicated in figure 12(a), one would still like to design a reactor in this region of the nT τ E versus T plane: For points in the nT τ E versus T plane which feature larger W-or Xe-impurity concentrations, i.e.…”

Overview of the DEMO staged design approach in Europe

“…System codes (see for example [6][7][8]) representing the full DEMO power plant, are currently being used in Europe to underpin DEMO design studies to find meaningful design points [9]. For DEMO, these codes have been used to find solutions with a minimum tokamak size.…”

Implications of uncertainties on European DEMO design

“…The currently implemented options are Correlations currently cannot be modelled and are therefore not taken into account. The uncertainties cannot be specified for parameters used as iteration variables in PROCESS as these are varied within the code to determine a constrained optimal design point [4,5]. The output of the method is then the distribution of optimised design points based on the ensemble of randomly varied input points.…”

“…Other uncertainty quantification software like IAEA-CN-123/45 [Right hand page running head is the paper number in Times New Roman 8 point bold capitals, centred] COSSAN-X [3] is routinely used for a wide spectrum of uncertainty quantification in engineering problems. The top-level European DEMO baseline designs are determined by the system modelling code PROCESS [4,5]. It optimises a figure of merit (e.g.…”