A framework for quantum-secure communications in cyber-physical control systems with experimental demonstration in a nuclear reactor

Quantum key distribution (QKD), a cryptographic method grounded in the laws of quantum mechanics rather than computational hardness, promises provably secure communications. Its integration into critical infrastructure offers a pathway to secure resilient operation of next-generation control systems, from power-intensive data centers to remotely operated microreactors located in energy-deprived remote communities. While QKD has been demonstrated in laboratory and network settings, its use in safety-critical control systems remains unexplored where requirements on latency, key availability, and operational stability pose unique challenges. Here, we introduce a QKD-secured data acquisition and control framework for embedding quantum cybersecurity directly into safety-critical cyber-physical systems and report the first end-to-end experimental demonstration in a nuclear reactor. The framework establishes the conditions necessary to achieve secure, low-latency, real-time operation in safety-critical environments. Using a phase-encoding decoy-state BB84 system deployed on Purdue's 10 kWth fully digital research reactor (PUR-1) we validate the model and achieve real-time encryption and decryption of 2,000 reactor signals. Experiments demonstrated a stable secret-key rate of 320 kbps with a quantum bit error rate of 3.8% at 54 km, and maximum optical-fiber distances of 82 km with One-Time Pad (OTP) encryption and 140 km with AES-256. We further evaluated compliance with latency and key availability conditions using three cryptographic schemes (OTP, AES-256, ASCON), finding that all variants supported real-time operation at typical data reporting rates. Our results establish a universal framework for quantum-cybersecurity in safety-critical systems, demonstrating that quantum communication technologies can enable secure, low-latency, real-time operation of nuclear reactors and other critical infrastructure.