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TISCO advanced material applied in neutrino exploration

By CHEN Qiang, YIN Wei and WANG Yongze UpDate 2022-07-22

TISCO Group delivered nearly 2,000 tons of stainless steel plates and bars with low background to Guangdong Jiangmen Neutrino Project of Chinese Academy of Sciences, for the manufacture of stainless steel spherical reticulated shells for the main structure of the experimental station. With the recent completion of the shell, the construction of this project has entered a new stage. This is another achievement made by TISCO, aiming at the major national demand and "sticking neck" product technology, continuously increasing R&D and tackling key problems in science and technology, and vigorously developing high-precision special steel products.

Jiangmen Neutrino Experiment Station is the second large-scale neutrino experiment project hosted by China after Daya Bay Neutrino Experiment, as well as an important scientific experiment project of high energy physics research. The construction of the project started in 2015 and is expected to be completed in 2022. The experimental station is built at a depth of 700 meters underground. The scientific target of the experiment is to determine the mass order of neutrinos by using the reactor neutrino oscillation, which is of great significance for humans to understand the microscopic basic structure of matter and the origin and evolution of the universe.

The key device of the station is a liquid scintillator detector with about 20,000 tons of alkylbenzene in a glass sphere surrounded by a stainless steel spherical reticulated shell, which is the largest liquid scintillator detector with the highest energy accuracy in the world. In order to ensure the accuracy and sensitivity of the detector, the detector is supported by a stainless steel spherical reticulated shell and placed in the center of a huge pool, surrounded by water to shield the background of the surrounding environment. Background refers to a characterization of the radioactivity of an object. The lower the background, the lower the radioactivity. The spherical reticulated shell will be the largest stainless steel spherical reticulated shell structure in the world and the first large stainless steel structure in China.

In order to control the background level of the device itself, corrosion-resistant stainless steel with low content of radioactive elements is required for manufacturing spherical reticulated shells. Experts from the Institute of High Energy Physics, Chinese Academy of Sciences, who are in charge of the design of this project, made thoroughly investigation to domestic stainless steel material before finding TISCO’s nuclear grade stainless steel, which has relatively low background but not low enough to meet the requirements of the spherical reticulated shell of the main structure of the detector. The experts led a team to visit TISCO to see if the later could reduce background level of stainless steel further.

After knowing the project requirements, the stainless steel team of TISCO immediately arranged an investigation to the background levels of all raw and auxiliary materials used in three production lines of nuclear grade stainless steel, including lime, dolomite, molten iron from blast furnace, ferrochrome, electrolytic nickel, and etc., and finally found the best one. They made background test for each heat of steel and send the qualified heat to caster as the material for neutrino project. Through careful organization of smelting, the background level was well controlled to meet the specification of the neutrino project in terms of single weight, contract quantity, consistency and stability among batches, and successfully completed the delivery, once again reflecting TISCO's fulfillment of responsibility and commitment.