Speaker
Description
The ESS Cryogenic Moderator System (CMS) uses liquid hydrogen moderators to achieve high cold neutron brightness. Due to the use of hydrogen at cryogenic temperature and elevated pressure, dedicated protection measures are required to mitigate the consequences of potential hydrogen leaks. One of these mitigation measures is the Hydrogen Safety Interlock System (H2 SIS).
The H2 SIS has been implemented as part of the ESS Target Station gas detection system and interfaces with the CMS Basic Process Control System (BPCS) and the Fast Beam Interlock System (FBIS). The system applies an alarm escalation scheme based on the detected hydrogen concentration in the affected area. Depending on the hydrogen level, the system initiates evacuation alarms, provides alarm and status signals to the CMS BPCS, and automatically initiates protective actions such as hydrogen venting from the CMS. The escalation philosophy is primarily designed to support safe and controlled venting of hydrogen during leak scenarios.
To improve system availability while maintaining the required safety reliability, several measures have been implemented, including additional signal validation logic, redundant power supplies with UPS backup, and the use of a ring topology in the system architecture to reduce unnecessary trips and avoid protective actions caused by spurious signals, loss of a network link, or loss of a single power input. In addition, provisions were introduced to improve system maintainability during CMS operation, including maintenance modes for the hydrogen detectors and the ability to temporarily mask selected interfaces while ensuring that the necessary compensatory safety measures are in place.
This presentation describes the overall system architecture, interfaces, logic overview, operating modes, alarm handling philosophy, and implementation approach of the H2 SIS. Different operating and alarm scenarios will be discussed, together with the methodology and standards used during system development, including hazardous area considerations, detector integration, fail-safe design principles, and the approaches adopted to improve system availability and maintainability.