I. The Purity Threshold: The "Passing Line" for Nuclear-Grade Boron Carbide

Whether boron carbide powder is "qualified" is clearly defined by international standards. According to the latest ASTM C750-24 specification published in 2024, nuclear-grade boron carbide powder is strictly classified into three types based on application scenarios: Type 1 for reactor core particulate materials, Type 2 for further processing into shapes or applications that may adversely affect structural components, and Type 3 for non-core or special core applications. The accompanying ASTM C791-24 test methods specify the testing procedures for total carbon, total boron, isotopic composition, chlorine, fluorine, water, metallic impurities, and other indicators. In actual industrial testing, common control indicators include B₄C content ≥95%, free carbon ≤0.5%, oxygen content ≤0.8%, and iron ≤0.1%.

II. Isotopic Enrichment: How Difficult Is It to "Pick Out" ¹⁰B?

¹⁰B and ¹¹B are "twin brothers," differing by only one neutron, with extremely close relative atomic masses, making separation highly difficult. In natural boron, ¹⁰B abundance is less than 20%, while fast neutron reactor control rod materials may require ¹⁰B abundance of 65% or even 90%. Starting from natural boric acid, raising ¹⁰B abundance to this level requires multi-stage separation and enrichment.

For a long time, the core technology and high-end market for high-abundance ¹⁰B isotopes worldwide have been monopolized by foreign enterprises. China's high-abundance boron-10 products relied on imports, posing a clear "bottleneck" risk in critical fields. China began boron isotope research in the 1950s and 1960s, but had never overcome the core technology for large-scale mass production, unable to stably produce qualified products meeting nuclear-grade standards.

III.From Enriched Boron to Boron Carbide: The Complete Material Chain

It is worth noting that isotopic enrichment is only the first step. The enriched boron-10 must be further converted into boron carbide powder before it can be used for control rod pellet preparation. Patent technology shows that the route for preparing enriched ¹⁰B boron carbide powder includes: using enriched ¹⁰B boric acid as the boron source, mixing with a composite carbon source (carbon black + carbon nanotubes/graphene) and a removable reaction medium (alkali metal halides), pressing into green bodies, and subjecting them to a three-step heat treatment of dehydration–medium-temperature activation–high-temperature carbothermal reduction, ultimately obtaining high-purity B₄C powder with high ¹⁰B abundance retention.

In large-scale carbothermal reduction production, the purity control of boron carbide also relies on a refined classification and purification process: using a cyclone to classify acid-washed materials by particle size, collecting the high-purity core material from the underflow, and removing fine particle impurities, thereby improving the final product purity.

IV. Application Extension: Beyond Control Rods

The application scenarios for enriched boron-10 are continuously expanding. In the nuclear power sector, enriched boric acid is added to primary coolant as a neutron absorber. Compared with natural boric acid, the total dosage can be greatly reduced, significantly lowering equipment corrosion risks. It has become a key material for "Hualong One" nuclear power units. Domestically produced nuclear-grade enriched boric acid was officially delivered to Lufeng Nuclear Power Unit 5 in 2025, marking the achievement of an independent and controllable supply chain.

In the national defense sector, boron-10 is an irreplaceable key material in the process of reactor miniaturization. In the high-end medical field, boron-10 is the core raw material for boron neutron capture therapy (BNCT) technology.