Primary heat transport system

PHTS Primary Heat Transport System SHTS Secondary Hert Transport System... 

Another ongoing item on the steam generator safety is a leak detection system development for the double wall tube that is being developed for the steam generator installed in a primary heat transport system of a future FBR plant. Basic performance data was obtained for an outer tube leak detection system to detect helium leak into sodium. An inner tube leak detection system using infrared rays is also under developing to quickly detect humidity at gas plenums. 

Small reactors oHitain less stcxed energy and often cerate at a lower pressure in the primary heat transport system than typical large pow reactors. In addition, they have lower core power density and passive systems or features instead of active (Hies for heat tran xat and control. These characteristics are basically conducive to operation without fully lic ised operat(HS on-site. Some of the prerequisites for such operation are ... 

Primary heat transport system - designed and maintained to achieve very low leakages ... 

The containment is basically an envelope around the reactor and other nuclear systems. In normal condition, it acts as a housing. In case of an accident involving a break in the primary heat transport system, it acts as a barrier (fourth and final) against the release of fission products to the environment. This is a safety system comprising of many subsystems which are briefly outlined below. 

Primary containment is designed to withstand the overpressure and higher temperature caused by release of hot fluid from the primary heat transport system under LOCA condition. It is coated on both sides with epoxy paints to further restrict the release of radioactive fission products during the period of pressurised state. 

Nuclear heat is removed from the reactor core by the primary heat transport system (PHTS). The PHTS is entirely contained within the reactor vessel and is composed of the... 

The rated thermal output of MONJU [5.63, 5.64] is transported through the primary heat transport system (PHTS) and intermediate heat transport system (IHTS) loops to the steam generators. Shutdown heat removal is normally by forced circulation (FC) provided by pony motors associated with each of the loop pumps. Heat is rejected to air at the air blast heat exchanger of the intermediate reactor auxiliary cooling system (ACS) which branches off from each IHTS loop. Thus the auxiliary cooling system (ACS) of the Monju reactor is coupled with the secondary system which also has the role as decay heat removal system. 

Reactor Protective System Reactor Regulation System Primary Heat Transport System Moderator System... 

PHTS stands for primary heat transport system... 

The KALIMER heat transport system is composed of a primary heat transport system (PHTS), an intermediate heat transport system (MTS) and a steam generation system (SGS). The PHTS is a pool type system and this feature provides a large thermal inertia of the primary system, which enhances the plant safety. The function of the PHTS is to deliver core heat to... 

ATOMIC ENERGY CONTROL BOARD, Overpressure Protection Requirements for Primary Heat Transport Systems in CANDU Power Reactors Fitted with Two Shutdown Systems, AECB Regulatory Policy Statement R-77, AECB, Ottawa (1987). 

The fuel is contained in a large number of pressure tubes that form the pressure boundary of the primary heat transport system [73]. This concept avoids the use of a large pressure vessel, and makes it possible to use a separate moderator around the fuel channels that does not have to operate at the same conditions as the primary coolant. Detailed considerations on the fuel channel design can be found in reference [75]. The role of the moderator as a passive heat sink can be significantly enhanced by optimizing the heat transfer characteristics of the fuel channel [76]. 

The primary components of each RS (core, reflectors, and associated supports, restraints, and controls) are contained in the reactor vessel. The nuclear heat is generated in the reactor core. Removal of the heat energy is provided by the Heat Transport System (HTS) with the main circulator providing the driving force to supply helium coolant into an upper core inlet plenum and to draw heated coolant from a bottom core outlet plenum. The primary coolant is distributed to numerous coolant channels running vertically through the core. The outlet plenum directs the flow to the central portion of the coaxial cross duct which channels the helium flow to the steam generator vessel (see Chapter 5). 

On Etecember 8, 1995, a leakage of sodium occurred in the piping room (C) of the Secondary Heat Transport System (SHTS) while the output of the reactor was being raised for a plant trip test at 40% output as part of a series of performance tests. The nuclear reactor was shut down manually after the accident, and sodium was drained from the SHTS in which the accident occurred and also from the Loop C of the Primary Heat Transfer System (PHTS). The plant is currently in a low-temperature shutdown state. The plant conditions of Monju at the time of the sodium leak occurrence are shown in Fig. 3.1. 

From thermodynamic point of view, the higher enthalpy will give higher efiBciency and to do so, normally the thermodynamic conditions of the working fluid is translated directly to the op>erating condition of the primary loop of heat transport system. 

The Double Pool concept has been driven by an objective to reduce fast reactor construction costs to the same level as those of an LWR. A major contribution has been to reduce the overall size of the intermediate heat transport system by installing the steam generators in the sodium filled annular space between the primary vessel and the guard vessel. These two examples serve to show some of the ways in which the basic modular concept can be modified to meet different objectives. 

This is one of the engineered safety features provided to mitigate the consequences of Loss of Coolant Accident (LOCA) in the event of a break in Primary Heat Transport (PHT) system boundary. The ECCS is designed to provide enough coolant to the PHT system and to transport heat from the core to the ultimate heat sink in such a way as to ensure adequate core cooling during all phases of LOCA. 

LOCA (primary) Leak before break concept and lifetime monitoring of pressure tubes and heat transport system piping and components (L) Division into two loops (L) Reactor coolant pumps with multiple mechanical seals (R) Valveless system (S)... 

The intermediate heat transport system (IHTS) is located within the reactor vessel. The IHTS consists of piping and components required to transport the reactor heat from the primary system, through the IHX, to the SG system (SGS). The IHTS is shown schematically in Figure 6.10. The IHTS is a closed loop system with an expansion plenum in the SG top head and an argon cover gas space to accommodate thermally induced system volume changes. 

MAIN COMPONENTS OF HEAT TRANSPORT SYSTEM (cont.) 7.1. Reactor vessel (primary tank)... 

The primary coolant flow path is shown in Fig. I-15(a). A simplified schematic of heat transport system in normal operation is given in the body of the previous part of the design description, in Fig. 1-13. 

The 4S is sodium-cooled reactor therefore, an intermediate heat transport system is employed to avoid a reaction between the primary (radioactive) sodium and water/steam of the power circuit. The 4S has three heat transport systems the primary sodium system located inside the RV, the secondary sodium system in which sodium is sufficiently non-radioactive to define it as an uncontrolled area , and the water/steam turbine system. 

The use of a two circuit scheme instead of a 3-circuit one (elimination of intermediate heat transport system) and the absence of on-site refuelling facilitate simplification of the primary circuit design. The absence of steam generators, steam condensers, water chemistry and purification units and others significantly simplifies the design of the turbine circuit. As a result, the relative weight of the BN GT main equipment is about 5 t/MW(e) while serial PWRs have 15-20 t/MW(e) and some APWR designs over 25 t/MW(e). 

A decay heat removal path is provided through the heat transport system through the balance of plant and ultimately to a seawater ultimate heat sink. Additionally, a passive decay heat removal channel operates continuously carrying 1 % of full power from the pin lattice to the ambient air, using passive natural circulation, conduction, and radiation heat transport links. This passive path may be periodically tested in situ to assure its operability. The thermal inertia of the primary circuit coolant is sufficient to safely absorb the initial decay heat transient, which exceeds the 1% capacity of the passive heat removal channel. 

There is no possibility for pressure increase in the primary circuit because the boiling point of the fuel salt is very high (about 1800 K) compared with the operating temperature (about 1000 K). In addition to this, the containment has no water inside because FUJI adopts a molten-salt based intermediate heat transport system, which altogether eliminates the accidents with pressure increase in the primary system due to water evaporation or steam ingress ... 

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