New Test Facility Validates Molten Salt Reactor Pump Seals

Molten salt reactors (MSRs) offer potential advantages in energy efficiency and waste reduction compared to conventional water-cooled reactors. However, safely containing the highly corrosive and potentially radioactive molten salts is critical for their deployment. Researchers at the University of Michigan have addressed this challenge by developing a custom-built Shaft Seal Test Facility to evaluate the performance of critical pump components.

The facility was designed to replicate the demanding operating conditions of MSRs, including elevated temperatures up to 550°C (1,022°F) and the presence of molten salt vapors. The experiments focused on a commercially available circumferential graphite bushing seal, a key component designed to prevent the escape of hazardous salt vapors and radioactive gases. The seal was tested in conjunction with FLiNaK salt, a mixture that mimics the core salts used in MSRs, and various cover gases.

Results from the 2,300-hour test campaign indicated that the shaft seal operated successfully with minimal corrosion or degradation. The researchers observed that the seal underwent a 10-day wear-in period, after which it achieved a stable operating condition. Notably, the radial clearance between the shaft and the seal was found to be the most significant factor influencing seal performance, while shaft speed and temperature had minimal impact.

Among the protective cover gases tested, argon demonstrated superior performance, maintaining higher tank pressure at the same gas flow rate compared to nitrogen and helium. This finding is crucial for ensuring the containment integrity of MSRs. The successful long-duration testing of this understudied pump component in an academic setting provides valuable data and guidance for future MSR design and optimization.