Reactor water recirculation system

High-performance jet pumps located within the reactor vessel are used in the recirculation system. The jet pumps, which have no moving parts, provide a continuous internal circulation path for a major portion of the core coolant flow. 

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Nuclear Boiler Assembly. This assembly consists of the equipment and instrumentation necessary to produce, contain, and control the steam required by the turbine-generator. The principal components of the nuclear boiler are (1) reactor vessel and internals—reactor pressure vessel, jet pumps for reactor water circulation, steam separators and dryers, and core support structure (2) reactor water recirculation system—pumps, valves, and piping used in providing and controlling core flow (3) main steam lines—main steam safety and relief valves, piping, and pipe supports from reactor pressure vessel up to and including the isolation valves outside of the primary containment barrier (4) control rod drive system—control rods, control rod drive mechanisms and hydraulic system for insertion and withdrawal of the control rods and (5) nuclear fuel and in-core instrumentation,... 

Reactor water recirculation system Pumps control and equipment isolation valves piping and its suspension devices, restraints, and suppressors used in providing and controlling core flow... 

The function of the reactor water recirculation system (Figure 3.8) is to circulate the required coolant through the reactor core. The system consists of two loops external to the reactor vessel, each containing a pump with a directly coupled water-cooled (air-water) motor, a flow control valve, and two shutoff valves. 

The integration of the turbine pressure regulator and control system with the reactor water recirculation flow control system permits automated... 

Emergency water injection system for reactor flooding under LOCAs is designed as active one because of certain size limitations in the FNPP. It includes 3 high pressure and 2 low pressure pumps Water recirculation system for long term decay heat removal is also provided It is essential that even in case of all emergency heat removal and water injection systems failure under LOCA the reactor core uncovery starts only after 3 hours of the accident initiation... 

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. 

The BWR operates at constant pressure and maintains constant steam pressure similar to most fossil boilers. The integration of the turbine pressure regulator and control system in conjunction with the reactor water recirculation flow control system permits automated changes in steam flow to accommodate varying load demands on the turbine. Power changes of up to 25% of rated power can be accomplished automatically by recirculation... 

The reactor feedwater control system provides the signal for the reduction of reactor water recirculation flow to accommodate reduced feedwater flow caused by failure of a single feedwater pump. 

In both PWRs and BWRs, corrosion of the primary circuit materials is an essential factor in the buildup of contamination layers on the surfaces of the pipes and the components. The materials used in BWRs which are in contact with the reactor water and, therefore, are potential sources of radionuclides are mainly stainless steels wear-resistant hardfacing alloys such as Stellite are also present in most of the plants. Zircaloy as the material of fuel rod claddings, spacers and fuel assembly casks need not be considered in this context, because of the extremely small release of activated constituents from this material. Due to differences in temperature and environment, the mechanisms of the corrosion process and the resulting metal release rates, which contribute to the input of corrosion products into the region of the reactor core, may show differences in different regions of the plant. Thus, corrosion of materials in the water-steam cycle exhibiting H2O phase transformations and considerable temperature differences will proceed differently than in the recirculation lines and the reactor water cleanup system, which are in contact with liquid water exclusively and show comparatively small variations in operating temperature. 

In the BWR plants, the out-of-RPV surfaces which are subject to contamination during steady-state operation are mainly those wetted by high-temperature reactor water. These are, in the main, the pipes leading to the reactor water cleanup system and the recirculation lines (as far as the plant is equipped with an external recirculation system). In addition to these surfaces, the main steam lines and the turbine, as well as part of the feedwater system, may be contaminated by radionuclides carried with the steam. In the course of a shutdown of the plant, certain regions of the main steam lines and of the feedwater lines are also in contact with low-temperature reactor water containing radionuclides. 

As an example of the decontamination of subsystems, the treatment of a BWR recirculation loop and, in addition, parts of the residual heat removal system and the reactor water cleanup system, by using the Cord process in parallel to the... 

Flow proceeds from the lower plenum, through the core. The steam and water are separated the steam is then dried and passed to the turbine. Other flow (see above) returns to the recirculation system. Feedwater is introduced to the annulus between the core shroud and reactor vessel (Fig. 4). The recirculation system piping is a primary pressure boundary for the high-pressure, high-temperature reactor coolant. Type 304 stainless steel was selected for recirculation system piping and numerous other auxiliary systems (such as the reactor water cleanup system, residual heat removal system, core spray, and other emergency core cooling systems) for its corrosion resistance and adequate mechanical properties. Failures of weld heat affected zones... 

Many instances of intergranular stress corrosion cracking (IGSCC) of stainless steel and nickel-based alloys have occurred in the reactor water systems of BWRs. IGSCC, first observed in the recirculation piping systems (21) and later in reactor vessel internal components, has been observed primarily in the weld heat-affected zone of Type 304 stainless steel. 

Many techniques have been developed to accomplish this, for example, the use of a cooled recirculating system in which the chlorine is dissolved in one part and the allyl chloride is dissolved and suspended in another (61). The streams are brought together in the main reaction zone and thence to a separator to remove water-insoluble products. Another method involves maintaining any organic phase present in the reaction zone in a highly dispersed condition (62). A continuous reactor consists of a recycle system in which make-up water and allyl chloride in a volume ratio of 10—50 1 are added... 

The presence of water, or water vapour, affects the chemistry of thermal modification and heat transfer within the wood (Burmester, 1981). Under dry treatment conditions, the wood is dried prior to thermal modification, or water is removed by the use of an open system, or a recirculating system equipped with a condenser. In closed systems, water evaporated from the wood remains as high-pressure steam during the process. Steam can also be injected into the reactor to act as a heat-transfer medium, and can additionally act as an inert blanket to limit oxidative processes. Such steam treatment processes are referred to as hygrothermal treatments. Where the wood is heated in water, this is known as a hydrothermal process. Hydrothermal treatments have been extensively studied as a... 

Fig. 1 Reactor system for continuous mns I Feed flask, 2 pump, 3 bath 4, 5, 6 reactors 1, 2, and 3, 7 effluent, 8, 9 security flasks, 10 water/CuS04 column. A reactor detail II thermometer, 12 stainless steel screen, 13 jacket. Water recirculation dashed line), substrate (line)...

Emergency core cooling system consists of two trains. Each train meets the single failure principle. System includes high and low pressure sub-system. High-pressxue subsystem includes passive (hydro-accumulators) and active pumps and water storage tanks) features for water injection in reactor. Low-pressure sub-system ensures returning a condense accumulated in containment, into the reactor by recirculation pumps. 

Steam is produced in the reactor vessel in a manner similar to that of current BWRs. The forced recirculation system of large BWRs is replaced with natural circulation. The steam-water mixture exiting the core is directed to separators and dryers which are positioned above and around the core periphery to allow entry of control rod drives to the top of the core. Control rod drives are mounted on the top head to reduce vessel and building size, to simplify the shutdown system, and to minimize penetrations below the core. 

Alder, H. R Corrosion products, activity transport and deposition in boiling water reactor recirculation systems. Review of the state of the art. May 1990. Report lAEA-TECDOC-667 Coolant Technology of Water Cooled Reactors. Vol. 3 Activity Transport Mechanisms in Water Cooled Reactors, Vienna, 1992, p. 124—132 Alder, H. R, Buckley, D., Grauer, R., Wiedemann, K. H. Corrosion products, activity transport and deposition in boiling water reactor recirculation systems. Report lAEA-TEC-... 

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