This article aims to address the DO module failure issue of a certain type of rod control rod position equipment in the GJB 151B-2013 standard’s CS116 test. By establishing an equivalent circuit model and laboratory simulation verification, the coupling mechanism between the shielding layer grounding method and relay breakdown is revealed. Experimental results have shown that the shielding effectiveness of single ended grounding decreases in the high-frequency range above 1 MHz, resulting in an induced voltage of 177 V. The use of double ended grounding combined with braided copper strap connection can reduce the interference voltage to 26 V. A dual-level rectification plan (module protection + system shielding) was proposed, and engineering verification showed that the equipment successfully passed CS116 testing after rectification, providing a reference frame work for nuclear-grade electromagnetic compatibility (EMC)design of nuclear power plant instrumentation and control equipment.