Page 233 - Dynamics and Control of Nuclear Reactors

232 CHAPTER 16 Nuclear plant instrumentation

See Refs. [9–11] for more details of the liquid flow system and instrumentation in
a SFR. Some specific sensors for the 500 MWe prototype fast breeder reactor (PFBR)
include the following [9]:
• Core inlet temperature is measured by six thermocouples. Each sub-assembly
coolant outlet temperature is measured by two thermocouples.
• High-temperature in-core fission chambers are used for neutron flux
measurements.
• Sodium flow rate is measured by eddy current flow meters at the outlet of the
primary pumps.
• Level of sodium in the reactor pool is measured by continuous level probes.
• In addition, there is leak detection instrumentation in the steam generators.
Other instrumentation includes sensors for cover gas hydrogen metering, electro-
chemical in-sodium hydrogen measurement, electrochemical carbon meter, sodium
ionization detector, etc.

16.6.2 High temperature gas-cooled reactor (HTGR) instrumentation
Instrumentation needed for HTGRs is influenced by the plant characteristics (very
high temperature, inert coolant, and large heat capacity that causes slow response
in a transient).
Asummaryofthevarioussensorsusedformeasurementsfollowswithoutreferenceto
aspecificcommercialHTGRplant.FollowingaretypicalmeasurementsforHTGRs[12].
• Primary coolant core inlet and outlet temperatures, along with core internals are
measured using Type-N thermocouples.
• Graphite block temperatures are measured using tungsten-rhenium thermocouples.
• The mass flow rate of the primary coolant is calculated from data of the pressure
head of the helium blower, coolant temperature, coolant pressure, and the
compressor rotational speed. This is an inferred quantity.
• High-temperature Coriolis gas flow meters may be used in the future for coolant
flow measurement.
• Two types of neutron detectors are used: fission counters for wide-range
monitoring system (WRMS) and uncompensated ionization chambers for
power range monitoring system (PRMS), which can detect a low neutron flux
level outside the reactor pressure vessel. WRMS are installed on the internal
surface of the pressure vessel.
• Primary coolant pressure is monitored by safety-grade pressure transmitters.
• The primary coolant flow through the reactor core is measured by a differential
pressure transmitter that monitors the core inlet and out let pressure difference.
This measurement is also used by the safety (protection) system.
• Other measurements include gas properties, moisture ingress (from circulation
through the steam generator), gas leak detection, and strain gauges on the
internal vessel structure and on the vessel external surface.

Certain sensors are unique to HTGRs as compared to water-cooled reactors.