reactor process instrumentation system includes the reactor pressure vessel instrumentation, the primary loop recirculation system instrumentation, the reactor feedwater system instrumentation, the main steam system instrumentation, the control rod drive system instrumentation, and others. Main parameters are indicated and recorded in the MCR.

Major instrumentation systems of the reactor process instrumentation system are described below.

1. Reactor pressure vessel (RPV) instrumentation The RPV instrumentation measures the

RPV process conditions and its inside process conditions. This instrumentation is used for monitoring of normal operation and for initiating and monitoring the reactor shutdown system and the ESFs.

Main items measured are water levels and pressures inside the RPV, temperatures of the RPV body, and seal leakage at the flange. An example of water level and pressure measurements inside the RPV is shown in Figure 2.6.14. To measure the water level, two types of

Primary containment vessel

To reactor safety protection system

PS

[PT1

Excess flow check, valvQ

Condensing

chamber

Isolation

valve

Reactor pressure vessel

Differential pressure transmitter in the local area

Water level switch in the MCR

JI

Water level indicator in the MCR

Instrumentation

line

Steam dryer

LS

iPT

Pressure transmitter in the local area

JI

Pressure switch in the MCR

FT

Pressure indicator in the MCR

Figure 2.6.14 Reactor water level and pressure instrumentation

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water level detectors are installed, i.e. narrow range and wide range water level detectors. The narrow range water level detector measures water level, which is for use by control systems and initiation of the reactor shutdown system, within the narrow range that covers the water level change anticipated during normal operation and in transient conditions. The wide range water level detector measures water level in the wide range that covers the water level change anticipated in accident conditions. Appropriate redundancy and independency are required of water level detectors related to the RPS to meet the single failure criterion. While the RPS is electrically separated from other instrumentation and control systems, only instrumentation lines may be used in common.

Water levels are continuously measured with local differential pressure transmitters as differential pressure between the condensing chamber which provides a reference water head and the lower nozzle water. These water level signals are sent to the MCR for indication and recording as well as for alarm annunciation at low water level or high water level. The reactor shutdown system is initiated at a low water level to protect the reactor, and the ESFs are initiated at an even lower water level to cool the reactor core. These initiations are made in conjunction with other instrumentation as described in section 2.6.1 (2). In the case of a higher water level, a turbine trip is actuated to protect the turbine.

Reactor pressures are continuously measured with local pressure transmitters connected via the instrumentation line to the condensing chamber for water level measurement. These pressure signals are indicated and recorded in the MCR. High reactor pressure is annunciated. The reactor shutdown system and the SRVs are actuated at the higher reactor pressure to protect the reactor pressure boundary. Appropriate redundancy and independency are required of pressure detectors related to the RPS to meet the single failure criterion. While the RPS is electrically separated from other instrumentation and control systems, only instrumentation lines may be used in common.

Temperatures of the RPV body are measured

with thermocouples at the upper, middle and lower parts, and recorded as supporting information for reactor operation. The seal leakage at the flange at the vessel head is detected via the drain lines connected to the flange face between two O-rings. Leakage from the inside O-ring is detected by the pressure detectors in the drain line, and high pressure is annunciated.

2. Primary loop recirculation systeminstrumentation Main measured items of the primary loop

recirculation system are recirculation flows, coolant temperatures, differential pressures between the pump inlet and outlet, and generator speeds of the recirculation pump M-G sets. They are continuously measured, indicated and recorded. Core flow is measured from the differential pressures of the jet pump diffusers, and also indicated and recorded. For the primary loop recirculation pumps, seal leakage rates, coolant flow rates and temperatures, shaft vibrations and temperatures are measured. Alarm annunciation is actuated for high seal leakage rate, low flow rate or high temperature of the coolant, and excessive vibration or high temperature of the shaft

In an ABWR plant, since there are reactor internal pumps, core flow is measured from the differential pressures at the pumps and the differential pressure at the core plate. Ulis signal is indicated and recorded, and also used for reactor core monitoring and recirculation flow control. The speed of each pump is measured with an eddy current detector, and indicated as well.

3. Reactor feedwater system and main steam system instrumentation

Reactor feedwater flow and main steam flow are continuously measured, indicated, recorded, and used as inputs to the reactor water level control system. The nozzles for measuring the main steam flow are designed also to function as a flow limiter, in the event of a main steam pipe rupture, to limit main steam discharge flow to less than 200% of rated main steam flow as critical flow.

In an ABWR plant, the RPV nozzles in the main steam pipes have the flow limiter function. Main steam flow is measured by detecting differential pressures between the nozzles.

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