The European Union is developing the European Quantum Communication Infrastructure (EuroQCI) as a pan-European network to provide secure communication capabilities across Member States, including governmental and critical-infrastructure domains. While the strategic objective is defined at EU level, the required scale and structure of national quantum key distribution (QKD) networks remain largely unspecified. This work addresses the question of how to plan and size national terrestrial QKD networks to support critical infrastructure and public authorities. We propose a reproducible planning methodology that estimates network size, total fiber length, and the number of required QKD components based on a small set of explicit assumptions. The approach is demonstrated for Austria, where a synthetic but structured network model is constructed and evaluated using Monte Carlo simulation. The model focuses on terrestrial QKD infrastructure and explicitly excludes space-based segments. It estimates endpoint counts, trusted repeater node requirements, and hop-length distributions under realistic operational constraints. The Austrian case is then used as a baseline to derive scaling rules for other EU Member States based on population and geographic extent. The results provide first-order planning estimates for national QKD backbone sizes across Europe. These estimates are not intended as deployment designs but as planning-level references that support early-stage cost assessment and infrastructure dimensioning under the EuroQCI framework.

翻译：欧盟正在建设欧洲量子通信基础设施（EuroQCI），旨在构建泛欧网络，为成员国提供涵盖政府和关键基础设施领域的安全通信能力。尽管战略目标已在欧盟层面定义，但国家级量子密钥分发（QKD）网络的所需规模和结构仍基本未明确。本研究探讨如何规划并确定国家级地面QKD网络的规模，以支持关键基础设施和公共机构。我们提出一种可复现的规划方法论，基于少量显式假设估算网络规模、总光纤长度及所需QKD组件数量。该方法以奥地利为例进行验证：构建合成且结构化的网络模型，并通过蒙特卡洛模拟评估。该模型聚焦于地面QKD基础设施，明确排除天基部分，在现实操作约束下估算端点数量、可信中继节点需求及跳数分布。随后以奥地利案例为基准，根据人口和地理范围推导其他欧盟成员国的规模缩放规律。结果可为欧洲各国QKD骨干网络规模提供一阶规划估算。这些估算并非实际部署设计，而是作为规划级参考，支持EuroQCI框架下的早期成本评估与基础设施规模确定。