Nuclear safety is one of the key issues for a nuclear power plant (NPP). The alarm system plays a critical role for the safe and efficient operation of an NPP which is a significant human-machine interface in the main control room. The multi-modular NPPs have multiple reactor modules coupled to one steam turbine. One critical problem for the multi-modular NPP is that the complexity of the alarm system is greatly increased, which threatens the human-factor safety and the operation reliability. On the other hand, the main control room usually suffers from too many alarms to be handled at the same time after the accident, which is difficult for the operator to find out specific initiating event and may cause severe accident. The High Temperature Gas-Cooled Reactor - Pebble bed Module (HTR-PM) which is under construction in Shandong province of China, is a typical multi-modular NPP with two reactor modules coupled to one steam turbine. In this paper, the architecture of the alarm system of HTR-PM is introduced. Different from conventional full-digital alarm system in the NPPs, a set of alarm tiles which are set up at the top of the large display panel are adopted to improve the alarm identification, and the alarm tiles are classified to groups of reactor 1#, conventional island, and reactor 2#, respectively. These alarm tiles cooperates with the alarm indication on the visual display unit to help to locate the accident location as soon as possible. The suppression design in case of alarm overloading are also discussed in this paper. Techniques like the dead band and first alarm indication are adopted in the alarm system of HTR-PM. Two kinds of suppression logics on condition and priority are discussed in the end of this paper. The work showed in this paper can contribute to improve the design of alarm systems in other NPPs, especial the multi-modular NPPs.

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