An off-line boron meter in a pressurized water reactor (PWR) nuclear power plant has the disadvantages of lagging data measurements and a long response time. This paper aims to shorten the response time and enhance the measurement accuracy of this type of device. First, the shortcomings of off-line boron meters were analyzed and the serpentuator system was proposed to replace the typical container system. Then, both FLUENT and GEANT simulation tools were used to demonstrate the merits of the serpentuator system. FLUENT was used to simulate the fluid response, while GEANT4 was used to obtain the f(P) curve. The simulation results from FLUENT indicate that the residence time of the fluid in the container system was approximately 9.5 times that in the serpentuator system. The simulation results obtained from GEANT4 manifest that the f(P) curve of the rectangular section was steeper than for the circular section. When the polyethylene was 8 cm thick, the f(P) curve was the steepest. Compared with a serpentuator made of titanium alloy, stainless steel, and brass, a serpentuator made of zirconium alloy or aluminum alloy achieved a steeper f(P) curve. Therefore, the serpentuator system is more applicable for PWRs using an off-line boron letdown through a chemical and volume control system.