Boiling water reactors systems components

Herein reactors are described in their most prominent appHcation, that of electric power. Eive distinctly different reactors, ie, pressurized water reactors, boiling water reactors, heavy water reactors, graphite reactors, and fast breeder reactors, are emphasized. A variety of other appHcations and types of reactors also exist. Whereas space does not permit identification of all of the reactors that have been built over the years, each contributed experience of processes and knowledge about the performance of materials, components, and systems. 

Except for the fact that the mode of reactor cooling has been changed from forced circulation to natural circulation (reactor water recirculation pumps have been eliminated), all other sterns and components employed for plant operation are based on the extensive upeiating expel leiice gained fiom the boiling water reactor plants currently in service in Germany as well as on the proven system and component designs implemented in these plants. 

In India, nuclear power stations of the Pressurised Heavy Water Reactor type are in operation in different parts of the country. Two boiling water reactors are in operation at Tarapur. Some of these reactors have completed more than a decade of operating life. Need has been felt to decontaminate the reactor systems and components in order to reduce radiation exposure to operating personnel. A Research and Development programme was therefore undertaken to develop dilute chemical formulations suitable for decontamination of our reactor systems. 

If the water tank of a passive heat removal system (PHRS) is included as the reactor installation component, it is possible to remove heat from the core via the wall of the reactor mono-block vessel. In the failure of all reactor systems, the PHRS tank offers passive heat removal from the mono-block vessel through the evaporation of water from the tank (by boiling) and steam disposal via the air tubes to the atmosphere. The quantity of water stored in the tank is sufficient to remove heat from the reactor over a 5-day period without any damage to the reactor core. 

The potential applications of SiC SiC composites currently considered are core components, especially the control rod sheath and cladding of the VHTR, GFR, SFR, MSR, and LFR. Because the scope of this chapter is restricted to the Generation IV system, only part of the nuclear applications of SiCf/SiC was described. However, SiC SiC composites are also considered as the in-vessel components of magnetic confinement fusion devices including blanket structures, flow channel inserts (FCI) for the liquid metal (LM) blankets, and plasma-facing components (PFCs) [88—91]. In addition, they are candidates for an advanced fuel cladding for LWRs as an ATF (accident tolerance fuel) concept [72,92—97] and a channel box for the BWRs (boiling water-cooled reactors) [96,98,99]. 

Flow instabilities are undesirable in boiling, condensing, and other two-phase flow processes for several reasons. Sustained flow oscillations may cause forced mechanical vibration of components or system control problems. Flow oscillations affect the local heat transfer characteristics and may induce boiling crisis (see Sec. 5.4.8). Flow stability becomes of particular importance in water-cooled and watermoderated nuclear reactors and steam generators. It can disturb control systems, or cause mechanical damage. Thus, the designer of such equipment must be able to predict the threshold of flow instability in order to design around it or compensate for it. 

In most industrially relevant reacting systems, one main reaction typically makes the desired products and several side reactions make byproducts. The specific rate of production or consumption of a particular component in such a reaction set depends upon the stoichiometry and the rates. For example, assume that the main reaction for making vinyl acetate, Eq. (4.4.1, proceeds with a rate r< (mol/L s) and that the side reaction, Eq. (4.8), proceeds with rate r2 (mol/L s). Then the net consumption of ethylene is (-l)r1 - (-1 )r2 (mol/L s). Similarly, the net consumption of oxygen is (-0.5)fi + (— 3)r2, and the net production of water is (l)r-, + (2)ra. For a given chemistry (stoichiometry), our ability to control the production or consumption of any one component in the reactor is thus limited to how well we can influence the various rates. This boils down to manipulating the reactor temperature and/ or the concentrations of the dominant components. Occasionally, the reaction volume for liquid-phase reactions or the pressure for gas-phase reactions can also be manipulated for overall production control. These are the fundamentals of reactor control. 

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