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and the moving of casks is limited to this area.

  1. Refueling machine

The refueling machine is used to load fresh fuel assemblies into the reactor core, retrieve spent fuel assemblies from there and shuffle the loaded fuel therein.

There are two types of refueling machines. One is operated by an operator seated in a cab on the machine who controls the machine directly, while looking at the fuel in the pool water. The other type is operated automatically and remotely. The latter type is described here and is shown in Figure 2.8.12. The body of the refueling machine consists of a bridge running on a rail on the top floor of the reactor building, a trolley moving on the bridge, a grabble head and a mast to handle fuel rods, and a driving control system.. The control panel and computers to operate the driving control system are located in a remote control room.

Figure 2.8.12 Outline of refueling machine

  1. Radioactive Waste Treatment Systems

The various radioactive waste treatment systems properly process radioactive wastes generated during nuclear power plant operations while ensuring that safety of the environment is kept and normal plant operations are maintained.

The main sources of radioactive wastes in a BWR plant are the reactor coolant system and the spent fuel pool clean-up system. Radioactive materials in those wastes are primarily radioactive corrosion products which are dissolved in the reactor coolant If small pinholes are generated in fuel cladding, the fission products will leak into the reactor coolant

The discharged radioactive wastes include gaseous, liquid and solid wastes and those wastes are treated accordingly.

  1. Gaseous Waste Treatment System

The main sources of gaseous wastes are:

  1. non-condensable off-gas extracted from the turbine condenser;

  2. off-gas from the turbine gland seal released by blowers; and

  3. vacuum pump off-gas generated at reactor start-up.

A flow sheet of a typical gaseous waste treatment system is shown in Figure 2.9.1. Since the non­condensable gas from the turbine condenser contains air leaked to the condenser, and hydrogen and oxygen generated by water radiolysis, to prevent hydrogen explosions, the hydrogen content is diluted to below 4 vol % by using driving steam of the air ejector. Hydrogen and oxygen are converted to water vapor by a recombiner using a catalytic recombining reaction and the off­gas volume is reduced by the dehumidifier. After radioactivity of short half-life nuclides is reduced by decay in the decay pipe, the off-gas is introduced to the activated charcoal bed noble gas hold­up system. Radioactive krypton and xenon are selectively absorbed by activated charcoal. Example absorption times for krypton and xenon are 40 hours and 30 days, respectively, resulting in an efficient reduction in radioactivity.

Plants without decay pipes have recently become popular and, in addition, noble gas absorption time has been shortened due to improved fuel performances (no pinholes). In order to maintain

NSRA, Japan

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