Fusion’s Neutron Hammer: The Impact on Design

As fusion energy edges closer to commercial reality, a central engineering challenge is emerging: the extreme neutron flux bombarding the inner core of reactors, threatening the longevity of critical components, especially seals, structural materials and vacuum vessels. For some first-generation reactors like ARC, this could mean replacing key parts at a certain frequency. But design updates inside ARC propose alternative solutions, like the FLiBe liquid blankets, to mitigate this issue.

SPARC: 퓨전의 중성자 해머

SPARC, developed by Commonwealth Fusion Systems, is one of the most advanced high-field tokamak prototypes in the world. It is expected to achieve plasma breakeven (Q > 1) by 2026. It is interesting to note its compact size and high magnetic fields (up to 12 T); the neutron flux is way beyond usual rates in the industrial nuclear installations used for electricity production.

유지 관리 및 밀봉: 숨겨진 병목 현상

This flux can lead to activation of structural materials, embrittlement, helium swelling and challenges to the integrity of seal functions.

Maintaining or replacing seals under such conditions requires full shutdown and remote intervention, which is costly and time-consuming. Without a hot cell or robotic maintenance infrastructure, this becomes a critical limitation. However, because of the operation conditions of SPARC, activation will be considerably more limited than in the case of ARC.

ARC: Overcoming the Neutron Flux Impact With FLiBe

SPARC의 후속작인 ARC는 이러한 문제를 염두에 두고 설계되었습니다. FLiBe(불화 리튬과 불화 베릴륨의 혼합물)로 만든 액체 침지 블랭킷을 소개합니다.

What FLiBe Does

• 중성자 조절 및 흡수: 구조 재료와 진공 용기를 보호합니다.
• 삼중수소 번식: FLiBe의 리튬은 중성자 충격을 받아 삼중수소를 생성합니다. 이는 핵융합 반응에 필요한 삼중수소를 생산할 수 있다는 것을 의미합니다.
• Heat transfer medium: Operates efficiently at 700 to 900°C without high pressure.

새로운 소재의 도전 과제 등장

재료의 중성자 문제를 해결하는 FLiBe는 자체적인 엔지니어링 제약이 있습니다:

• 높은 작동 온도(~850°C)에는 내열성 및 내화학성이 뛰어난 소재가 필요합니다.
• 호환되는 자료는 다음과 같습니다:
  • Nickel-based alloys, like Hastelloy-N or Inconel, for better corrosion resistance in molten salt.
  • SiC/SiC 복합재: 중성자 저항성 및 FLiBe 호환성(비용이 많이 들고 깨지기 쉽지만).
  • 흑연 또는 코팅된 내화성 금속(예: 몰리브덴, 텅스텐).
• Sealing materials must resist thermal cycling, chemical corrosion and potential tritium permeation — pushing engineers toward new designs.

Maturity of FLiBe and Broader Adoption

Despite promising performance, FLiBe blankets are not yet industrially mature. Key areas of ongoing development include:

• 산화 환원 제어 시스템으로 염분 분해와 부식을 방지합니다.
• 용융 염에서 삼중수소 추출 시스템.
• 원격 처리 및 염분 정화 기술.

하지만 그 모멘텀은 점점 커지고 있습니다:

• ARC는 가장 고급 사용자입니다.
• Xcimer Energy(레이저 융합)는 중성자 방패로 FLiBe를 연구하고 있습니다.
• For the fission world, MoltexFLEX and TMSR-LF1 (China) are deploying other salts in MSR.

This trend shows a clear industry shift: liquid blankets are becoming the future of durable fusion reactor architecture, offering better uptime, shielding and integration potential, at the cost of higher chemical and thermal complexity.

The fusion industry is facing a defining moment: will reactor cores withstand their own power? While SPARC exposes the engineering pain points of first-generation tokamaks, especially in maintenance, sealing and material fatigue, next-gen designs like ARC embrace FLiBe to overcome them. But as FLiBe becomes central to fusion’s future, the industry must now solve corrosion, tritium management and high-temperature material integration.