Control rod drive system instrumentation
In the control rod drive system, appropriate process instrumentation
is provided for the driving water system, the scram accumulators,
the scram discharge volume, and the control rod positions.
Measured items of the control rod drive system include driving pump
outlet pressures, filter pressure drops, differential pressures
between the reactor pressure and driving water pressures, drive
header flows, control rod drive temperatures, accumulator nitrogen
gas pressures, accumulator leakage flow rates, and scram discharge
volume water level. Alarm annunciation is actuated for low driving
pump inlet pressure, high filter pressure drop, low accumulator
nitrogen gas pressure, high accumulator leakage flow rate, and high
scram discharge volume water level. Hie
reactor shutdown system is initiated at a suitably high water level
of the scram discharge volume, since too high a water level of the
scram discharge volume may jeopardize scram capability. Control rod
positions are measured with reed switches in the indicator tube
installed in the center area of the control rod drive, and indicated
as well.
In an ABWR plant, since there is the motor- driven fine motion
control rod drive system (FMCRD), control rod motion is measured
with a synchro directly connected to the motor, and control rod
positions thus obtained are used in the rod control and information
system.
Primary containment vessel (PCV) atmosphere instrumentation
The main measured items of the PCV are pressures, temperatures,
humidities, hydrogen and oxygen concentrations, and radiation
levels. Pressures, temperatures and oxygen concentrations in the PCV
are continuously measured, and indicated or recorded. Hydrogen
concentrations, oxygen concentrations and radiation levels in the
PCV are also measured and recorded following a LOCA event. In
addition, drywell temperatures, suppression pool water levels and
temperatures are continuously measured, and indicated or recorded.
Alarm annunciation is actuated for high drywell pressure, high
oxygen concentration and high hydrogen concentration. The reactor
shutdown
system and the ESFs are initiated at higher drywell pressure.
Erroneous trip actuation caused by drain water in the
instrumentation line should be avoided, though the set point for
this drywell pressure trip maybe
low enough for an erroneous trip. With respect to the suppression
pool, alarm annunciation is actuated for low water level, high water
level, high water temperature, high oxygen concentration and high
hydrogen concentration. Nitrogen supply flow to the PCV is
continuously measured and recorded.
Leak detection system instrumentation
Coolant leakage from the reactor coolant pressure boundary is
measured and indicated. High leakage flow actuates alarm
annunciation.
Other instrumentation
In the standby liquid control (SLC) system, levels and temperatures
of borated water in the boron injection tank and pump outlet
pressures are measured. Alarm annunciation is actuated for low tank
level, etc. In the LPCS and the RHR, pump outlet pressures and flows
are measured and indicated. Pump outlet pressures and flows are also
measured and indicated with respect to the RCIC and the HPCS.
The radiation monitoring system consists of process radiation
monitoring systems, area radiation monitoring systems, environmental
monitoring systems, and radiation survey devices; and has the
following functions.
To detect abnormal radioactivity in each system and each area of
the plant, and provide alarm annunciation.
To monitor radioactive materials that are controlled and released
to the area around the site.
The containment atmospheric radiation monitoring system monitors
radiation inside the PCV, and has appropriate redundancy and
independency to monitor even in accident conditions.
Process radiation monitoring systems
The process radiation
monitoring systems continuously measure radiation,
provide relevant recording and indication in the MCR and the
radioactive waste (radwaste) disposal system
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Radiation monitoring system
Chapter
2 Systems of BWR Nuclear Power Plants
control room, and it initiates alarm annunciation if a measured
value exceeds the limit
The main process radiation
monitoring systems are described below. An example layout of process
radiation monitors is shown in Figure 2.6.15,
and typical process radiation monitors are shown in Table 2.6.4.
Containment atmospheric radiation monitoring system
Radiation in the PCV area is monitored to grasp the effectiveness of
the radiation barrier against radioactive materials in accident
conditions. Ion chambers are used for detectors.
Stack monitor
Radioactive gases released from the stack are monitored.
Scintillation (Nal)
counters and ion chambers are used for detectors. Iodine filters,
particle filters and tritium collectors are installed to
continuously capture, periodically collect and measure radioactive
iodine, particulate radioactive materials and tritium.
Off-gas Monitor
Radioactive gases are monitored in the exhaust from the steam jet
air ejectors (SJAEs) before and after passing through the rare gas
holdup
equipment. Ion chambers are used for detectors at the former
location and scintillation (Nal)
counters at the latter.
Gland steam condenser and vacuum pump exhaust radiation monitor
Radioactive gases discharged from the vacuum pump are monitored.
Scintillation (Nal)
counters are used for detectors.
Main steam line radiation monitor
Fission products leaked from fuel are monitored, and a reactor scram
signal is initiated if rapid increase in radiation is detected. Ion
chambers are used for detectors.
Reactor building heating ventilating and air conditioning system
(HVAC) exhaust monitor Radioactive gases are monitored in the
reactor
building exhaust from the reactor building HVAC system. The standby
gas treatment system (SGTS) is initiated when excessive
radioactivity is detected. Solid state detectors are used.
Off-gas treatment system area exhaust radiation monitor
Radioactive gas is monitored in the exhaust from the off-gas
treatment system. Solid state detectors are used.
Reactor
building
Reactor
building annex
Figure
2.6.15
Layout of process radiation monitors
2-77
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Table
2.6.4 Process radiation monitors (example) |
Detector Type |
Measuring Range |
Main steam line radiation monitor |
Ion chamber |
1013tol0*A |
Off-gas monitor |
Ion chamber |
IO13 to 105 A |
Scintillation counter |
10'1 to 106 cps |
|
Off-gas linear radiation monitor |
Ion chamber |
Oto3.3 x 103A |
Gland steam condenser and vacuum pump exhaust monitor |
Scintillation counter |
101 to 106 cps |
Refueling area exhaust radiation monitor |
Solid state |
10n to 10 mSv/h |
Off-gas treatment system area exhaust radiation monitor |
Solid state |
10'* to 1 mSv/h |
Reactor building II VAC exhaust monitor |
Solid state |
101 to 1 mSv/h |
SGTS exhaust radiation monitor |
Ion chamber |
10I3tol0*A |
Scintillation counter |
101 to 106 cps |
|
Stack monitor |
Ion chamber |
10-13 to Iff6 A |
Scintillation counter |
Iff1 to 10G cps |
|
Reactor building closed cooling water system radiation monitor |
Scintillation counter |
101 to 106 cps |
HPCS diesel generator cooling water radiation monitor |
Scintillation counter |
Iff1 to 106 cps |
liquid waste treatment system drain radiation monitor |
Scintillation counter |
0 to 3.3 x 101 cps |
Drywell drain radiation monitor |
Ion chamber |
1013 to 10* A |
Containment atmospheric radiation monitor |
Ion chamber |
Iff2 to 105Sv/h |
Leak detection system dust radiation monitor |
Scintillation counter |
Iff1 to 106 cps |
SGTS exhaust radiation monitor
Radioactive gases in the exhaust from the SGTS are monitored during
normal operation and in accident conditions. Ion chambers and
scintillation (Nal)
counters are used for detectors. Iodine filters and particle filters
are installed to capture, collect and measure radioactive iodine and
particulate radioactive
materials.
Liquid waste treatment system drainage radiation monitor
Radioactivity is monitored in the drainage released from the liquid
waste treatment system. Scintillation (Nal)
counters are used for detectors.
Reactor component cooling water system radiation monitor
Radioactivity leakage to the cooling water is monitored for
safety-related and non-safety-related reactor system components and
the radwaste treatment system. Scintillation (Nal)
counters are used for detectors.
Area radiation monitoring systems
The area radiation monitoring systems are installed inside the
associated buildings to monitor external radiation dose rate. Solid
state detectors are used. The area radiation monitoring systems are
mainly installed in the MCR, the
radwaste treatment system control room, the refueling platform and
the turbine generator operating floor. Table 2.6.5 shows typical
area radiation monitors.
Environmental monitoring systems
The following radiation monitoring systems are provided to perform
environmental monitoring around the plant site.
Fixed radiation monitoring system
Monitoring posts are installed around the site boundary to monitor
external radiation dose rate continuously.
Environmental samples measuring system
Dust samplers are installed around the site boundary to continuously
catch radioactive materials in the air. Measuring systems are also
installed to measure the radioactive material concentration of
environmental samples such as water, food and soil around the plant
Radioactivity monitoring vehicles
Radioactivity monitoring vehicles, which carry gamma ray survey
meters, dust samplers and iodine monitors, are available to measure
external radiation dose rate around the site and radioactive
material concentration in the air.
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Chapter
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Table
2.6.5 Area radiation monitors (example) |
Detector Type |
Measuring Range |
Reactor building radiation monitor |
Solid state |
104 to 1 mSv/h |
103 to 10 mSv/h |
||
102 to 102 mSv/h |
||
1 to 104 mSv/h |
||
Turbine building radiation monitor |
Solid state |
10’ to 1 mSv/h |
10"3 to 10 mSv/h |
||
Monitor building radiation monitor |
Solid state |
104 to 1 mSv/h |