DETECTORS FOR SAFE OPERATING NUCLEAR POWER PLANTS: RESISTANCE TEMPERATURE DETECTORS (RTDs)

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DETECTORS FOR SAFE OPERATING NUCLEAR POWER PLANTS: RESISTANCE TEMPERATURE DETECTORS (RTDs)

INTRODUCTION

The image of nuclear safety is international; a serious accident anywhere affects the public’s view of nuclear power everywhere.Hence, the dynamic response of the process sensors that supply real-time data to the safety systems in Nuclear Power Plants (NPP) plays a significant role in preventing plant accidents. nuclear engineering detecting instrumentssuch as Resistance Temperature Detectors (RTDs) is one of the most important equipment for the safety, reliability, and economic operation of nuclear power plants.TheseInstrumentsare used to detect relevant parameters in the nuclear and conventional island.They are used todetect parameters such as temperature, pressure, flow, level and along with a list of othersduring startup, shutdown, and normal operation[1]

Moreover, Instrumentation and Control (I&C) equipment, including the sensors and process-to-sensor interface, essentially constitutes the central nervous system of a nuclear power plant. I&C equipment measures thousands of variables and processes data to activate pumps, valves, motors, and other electromechanical equipment that control the plant. It also displays the plant conditions and keeps the process variables within the design limits to maintain safety, efficiency, and availability.As such, the performance of I&C equipment is vital to the operation of the plant, resulting in the protection of workers, the public, and the environment from undue radiation hazards.

A practical example is one U.S. PWR plant, which was suspected of having sluggish temperature sensors, was informed by regulators that it could operate at 100% power only if it could demonstrate that the response time of its safety system temperature instrumentation was 6.0 seconds or less. On the other hand, if the response time of its temperature instrumentation degraded to above 6.0 seconds, this plant was ordered to reduce its power production level by an amount proportional to the increased response time [1, 2]. At an operating revenue of over US$1 million per day for a 1000 MWe plant, even a 1% loss in power generation level can amount to millions of dollars in lost revenue. Today, over 50 percent of the U.S. fleet of 104 reactors has taken advantage of this provision. This process is referred to as measurement uncertainty recapture or power uprate through more accurate process measurements [1, 3]. These examples testify that the performance of the process of nuclear detecting instruments or instrumentation is critical to plant safety and economy [4].

FUNCTION OF RTDs

RTD is used for temperature measurement. The resistance of a conductor changes when the temperature is changed.

APPLICATIONS

RTDs are used in modern Pressurized Water Reactors (PWRs) to measure the reactor coolant temperature (figure 1). This measurement must be performed with the sensor installed in its normal in-plant configuration to yield the response characteristics of the sensor in service [2].

Figure 1.A step change in Temperature in the core of a Nuclear Reactor and the resulting response of an RTD sensor at the output of the Reactor

CONCLUSION

Tomeasure the true value of a process variable, the chosen sensors must fit the application and provide very accurate and stable calibration for steady-state measurements and fast dynamic response for transient measurements. A second requirement is the appropriate process-to-sensor interface. All these components must functionproperly to yield accurate and timely data to the plant control and safety systems.

REFERENCES

  • Hashemian, H.M., Measurement of Dynamic Temperatures and Pressures in Nuclear Power Plants, in Graduate Program in Electrical and Computer Engineering. 2011, Western University.
  • Hashemian, H.M. and J. Jiang, Nuclear plant temperature instrumentation.Nuclear Engineering and Design, 2009. 239(12): p. 3132-3141.
  • Montalvo, C., et al., Advanced surveillance of Resistance Temperature Detectors in Nuclear Power Plants.Annals of Nuclear Energy, 2014. 65: p. 35-40.
  • Hashemian, H.M., On-line monitoring applications in nuclear power plants.Progress in Nuclear Energy, 2011. 53(2): p. 167-181.

Writter: Emmanuel Osei Tutu
Msc. Student in Harbin Engineering University, China
College of Nuclear Science and Technology

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