JUNO boasts the world's largest stainless-steel spherical grid shell. [Photo/Southeast Space Frame Group]

Hidden 700 meters underground in South China's Guangdong province, the Jiangmen Underground Neutrino Observatory (JUNO) is the world's first next-generation, ultra-large, ultra-precise neutrino experiment.

After 17 years of planning and construction, the facility is finally operational — backed by a nationwide collaboration that includes critical contributions from Xiaoshan district, Hangzhou, East China's Zhejiang province.

At the heart of JUNO stands the world's largest stainless-steel spherical grid shell, built by Southeast Space Frame Group, a company based in Xiaoshan. With an inner diameter of 40.1 meters, the structure supports a 35.4-meter acrylic sphere, 20,000 metric tons of liquid scintillator, and over 40,000 photomultiplier tubes — earning its reputation as the experiment's "steel armor".

The main challenge lay in achieving extremes simultaneously: massive scale, millimeter-level precision, exceptional strength, and ultra-low radioactivity. Assembly tolerances were kept within 3 millimeters across the entire sphere, while 120,000 high-strength ring-groove rivets ensured flawless connections. Even the stainless steel itself underwent a "source-level revolution", with customized low-radioactivity materials jointly developed by industry and research institutes.

The high-precision connection of stainless steel beams ensures millimeter-level accuracy for the detector's main support structure. [Photo/Southeast Space Frame Group]

After seven years of technical breakthroughs, including an innovative fastening solution adapted from high-speed rail technology, the project was finally completed in October 2024. On Jan 18, the Xiaoshan-based company received the JUNO Engineering Outstanding Contribution Award.

From FAST, China's giant radio telescope, to JUNO, Zhejiang manufacturers are playing an increasingly vital role in building major national scientific instruments — demonstrating how the deep integration of industry, academia, and research is shaping the backbone of China's cutting-edge science.

Engineers work on the final closure of the stainless steel spherical lattice shell. [Photo/Southeast Space Frame Group]