Key Technological Breakthrough and Engineering Practice of Accelerator-driven Subcritical System in China Institute of Atomic Energy

Accelerator-driven subcritical system (ADS), as an innovative nuclear energy technology, is designed to break through two major limitations of conventional reactors: low uranium utilization (＜1%) and high-level waste requiring more than 100 000 a of decay. By enabling efficient waste transmutation, improving fuel use, and supporting closed fuel cycles, ADS offers a pathway to safer, low-carbon nuclear energy. This paper reviews two decades of ADS research and engineering practice led by the China Institute of Atomic Energy (CIAE), focusing on the progress of the China Initiative Accelerator-driven System (CiADS) and its relevance for international development. Since the early 2000s, CIAE has led ADS research in China. The Venus zero-power facilities were constructed to support basic studies: Venus-Ⅰ (2005) and Venus-Ⅱ (2016). To address key challenges, CIAE conducted targeted R&D (research and development). In spallation target design, a solid metal composite target was optimized and an integrated “reactor-target” scheme was proposed, lowering costs relative to separated designs. For coolant chemistry, an electrochemical oxygen sensor (zirconia electrolyte) and gas-phase control system were developed to maintain dissolved oxygen in lead-bismuth eutectic (10⁻⁴%-10⁻⁶%). In collaboration with ENEA (Italy) and PSI (Switzerland), long-term corrosion tests of CLAM steel and 316LN stainless steel were carried out in flowing lead-bismuth at 550 ℃ for up to 10 000 h. In core design, a 12-core subsystem (9.75 MW, 69 fuel assemblies, k_eff=0.97) was completed and its safety was validated. Since 2016, CiADS has advanced to engineering-scale demonstrations. Key achievements include ton-scale solid-phase oxygen control, a combined “magnetic+deep-bed filtration” method for corrosion product removal, and a prototype ²¹⁰Po purification system with ＞0% efficiency. The integrated “reactor-target” design simplified plant layout, reduced land area by over 30%, and aligned with international development trends. Lead-bismuth coolant technologies were qualified to ensure structural safety, while the primary loop design and major component fabrication have been completed, enabling upcoming accelerator-target-reactor coupling tests of at least 1 h. Through these efforts, CIAE has established an independent ADS platform. The Venus facilities serve as international benchmarks, providing high-quality data for heavy-metal coolant systems. CiADS demonstrates that ADS can reduce the hazardous lifetime of nuclear waste to hundreds of years, raise uranium utilization above 95%, and provide a route to inherently safe, low-carbon power. Looking ahead, CIAE is exploring artificial intelligence for ADS simulation and control to further optimize design. These achievements represent substantial progress in China’s ADS program and offer valuable reference for international peers advancing advanced nuclear technologies.