Digital twins are a powerful support tool for plant opera-

tion: they provide further understanding on ongoing phe-

nomena and allow realistic projection of the current plant

state into the future. Among other twins, EDF is devel-

oping a digital twin of the chemistry of the secondary cir-

cuits of its nuclear plants. Such a tool will give access

to the pH in any point of the circuit and in any operating

condition (e.g. partial load, power transients...), outper-

forming the current, limited, monitoring techniques. It is

expected to help operators and engineers to better monitor

the circuit (e.g. for erosion corrosion) and anticipate the

consequences on equipment of different operating strate-

gies (e.g. for amines’ injection pumps maintenance).

ThermoSysPro, the EDF R&D’s thermal-hydraulic li-

brary, is the bedrock of the tool under development. To

meet the needs of the target application, modeling of

amines convection and some related chemistry, allowing

the computation of pH, are introduced in a new version

of the library. Moreover, the presented approach aims at

proposing a general framework allowing the convection

of custom substances (i.e. easily customized by the end

user following its needs). This will open the door for a

wide range of other applications: radioactive substances,

pollution (e.g. salted water ingress coming from a heat-

exchanger leak), just to cite a few, could be modeled in

ThermoSysPro to augment the scope of the digital twins.

Dynamic thermo-hydraulic simulations of district heating

networks are an essential tool to investigate concepts for

their sustainable design and operation. The way the numerous

heat consumers are modeled has crucial impact on

the simulation performance. The proposed model for heat

consumers is designed to require low computational effort

by using a simplified modeling approach, avoiding state

events and limiting its dynamics, while still reproducing

their main characteristics. It is tested for a demonstration

network, showing its ability to yield realistic results

throughout the whole range of operational states including

undersupply situations. The results show that the heat

consumer model itself requires little time to simulate but

still significantly influences the simulation time. Fast dynamics

and including a bypass in the model increase the

simulation time, so that users should sensibly choose how

to use these options. Furthermore, heat consumer models

triggering unnecessary state events result in the highest

computational effort.

This paper presents a low order aquifer thermal energy storage (ATES) model for simulation of combined subsurface and above-surface energy systems. The model is included in the Modelica IBPSA Library, which is a free open-source library with basic models for building and district energy and control systems. The model uses a lumped-component method, in which the transient conductive-convective heat and mass transfer equation is radially discretized. To verify the accuracy of the model, we present an intra-model comparison from a simulation test suite. Results show that the Modelica ATES model is in good agreement, with a normalized mean bias error for yearly variation of aquifer temperatures of 1.6×10−2 and 9×10−5 at 1 m and 10 m distance from the well.