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  1. Reactor Core Isolation Cooling (rcic) System

  1. System functions and configuration

The functions of the RCIC system are to provide the coolant to the reactor and to cool fuel during a transient, even when the reactor is isolated.

These can be explained in detail as follows. When the reactor is isolated from the turbine system, which is the main heat sink, and the feed water function is lost, the reactor decay heat generates steam which is released from the SRVs to the S/P If this condition is left to continue, the amount of reactor coolant decreases and eventually fuel rods would experience failures. In order to prevent such an occurrence, the RCIC is automatically actuated at low reactor water level conditions, and carries the condensate storage tank (CST) water to make

NSRA, Japan

2~94

Chapter 2 Systems of BWR Nuclear Power Plants

up the reactor coolant Since this system is driven by the steam from the RPV, it must be operable under such conditions as a station blackout (This satisfies the Japanese safety design regulatory guideline 27 *6.)

In the ABWR, the RCIC system is an ECCS and it cools the fuel rods together with other ECCS lines in a LOCA

Figure 2.8.4 shows the RCIC basic system configuration.

The RCIC pumps are driven by the RCIC turbine with the steam which is generated by the decay heat in the RPV. When the reactor pressure changes, the RCIC flow rate is automatically controlled to remain constant by the turbine speed control. Turbine exhaust steam is released into the S/P and condensed. The water source of this turbine driven pump is the CST, and the reactor coolant is provided to the RPV through the feed water sparger or the head spray nozzle. In the ABWR, the coolant is provided to the RPV through the feed water sparger. Since it is not desirable to supply cold water to the RPV in surveillance tests during plant normal operations, when the RCIC is on standby, recirculation lines are provided for testing purposes. These recirculation lines and their pumps are

Figure 2.8.4 Basic system configuration of RCIC for 1,100 MWe BWR

installed on the CST in the 1100 MWe BWR, and on the S/P in the ABWR.

  1. Key components and features

Key component specifications are listed in Table 2.8.2.

Table 2.8.2 Basic specifications of the main components of the RCIC system

Example of a 1,100 MWe BWR

Pump

unit

rated flow/head

type

1

about 140m3/h @ about 190m- 880 m horizontal multi stage type

Turbine

unit type power

1

back-pressure impulse type

about 100-540kw

Example of an ABWR

Pump

unit

rated flow/head

type

1

about 180m3/h @ about 190m- 900 in

multi stage type (horizontal)

Turbine

unit

1

type

back-pressure impulse type

power

about 130 —670kw

  1. Turbine

This turbine is in the standby mode at normal temperatures, and it must be able to reach the rated speed within .30 seconds upon the auto startup signal. Therefore, the RCIC turbine must withstand fast startup and sudden high moisture steam conditions. To meet these requirements, a special turbine is used. Its basic configuration is shown in Figure 2.8.5. The seal function for the RCIC turbine shaft, the stop valve, and the control valve are maintained by a barometric condenser cooled by the RCIC pump discharge water.

(* 6) [Translator’s note] NSCRG: L-DS-I.O Regulatory Guide for Reviewing Safety Design of Light Water Nuclear Power Reactor Facilities. Guideline 27 reads “The nuclear reactor facilities shall be so designed that safe shutdown and proper cooling of the reactor after shutting down can be ensured in case of a short-term total AC power loss.”

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NSRA, Japan