Intermediate 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. 

To achieve competitive construction costs with a LWR, rationalization of the intermediate heat transport system is required. Considering the direct effect of a sodium-water reaction on the core, even if it is BDBA (Beyond Design Base Accident), it is difficult to secure general acceptance of eliminating the secondary heat transport system at an early stage of FBR practical application. 

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. 

An exception is the BN GT-300 (17) sodium cooled reactor concept of 300 MW(e), which couples a sodimn-cooled reactor with gas-turbine Brayton cycle for electricity generation it also ehminates intermediate heat transport system (ANNEX XVIll). 

The BN GT-300 (ANNEX XVIII) is a transportable modular nuclear cogeneration plant of 300 MW(e) based on a small sodium cooled reactor with fast spectrum of neutrons and a gas turbine cycle for energy conversion. The refuelling interval is designed to be 4.5-6 years. The concept provides the possibility of having several modules of the reactor mounted in railway cars and has no intermediate heat transport system. The modules are delivered to the site by railway and fixed and connected to each other under a shelter. 

The secondary sodium loop acts as an intermediate heat transport system and consists of the MX, piping, dump tank, EM pump, and SG. Secondary sodium coolant heated in the MX flows inside the piping to the SG where heat is transferred to water/steam of the power circuit to be supplied to the steam turbine generator. 

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. 

A three-circuit NPP layout with intermediate heat transport system (MTS) ... 

Different from many sodium cooled reactor designs, the BN GT-300 employs a two circuit scheme with no intermediate heat transport 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). 

This is a small sized tank-type reactor without an intermediate heat transport system. Steam generator is located inside the reactor vessel. The intermediate heat transport system is eliminated because there is no essential chemical interaction between lead-bismuth and steam. 

The PBWFR is designed to generate electricity. The cycle type is direct and the system pressure is the same as in conventional boiling water reactors (BWRs), see Fig. XXVII-2. Steam is generated in the chimneys in direct contact with hot Pb-Bi coolant above the core. There are no steam generators and intermediate heat transport systems. 

Capital cost of the MSR could be almost the same as that of the LWR. There are many pros and contras for choosing between these two reactors. The MSR has 3 circuits with an intermediate heat transport system similar to fast breeder reactors. On the other hand, the thermal efficiency is -30% higher than that in a pressurized water reactor, the core pressure is very low, and the safety system is simplified. 

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 ... 

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. 

Roy, P., and Licina, G.J., Carbon Activity Determinations in a Bimetallic Sodium Loop Mock-up of the Intermediate Heat Transport System of a Liquid Metal Fast Breeder Reactor. Proceedings of the Third International Conference on Liquid Metal Engineering and Technology in Energy Production, Oxford, USA, April 1984,3,207. 

There are two 420 MWt IHXs in the reactor to transfer heat from the primary sodium to the intermediate heat transport system. These are located above the reactor core in an annular region between the support cylinder and the reactor vessel wall. The IHX is designed to withstand, without breaching, the 7 MPa (1000 psi) steam pressure that could possibly be approached in the highly unlikely event of a severe sodium/water reaction. 

Reactor style Pool type intermediate heat transport system Modular type intermediate heat transport system... 

Of the six liquid metal cooled SMRs, three are sodium cooled fast reactors (KALIMER, BMN-170 and MDP), and 3 are lead-bismuth cooled fast reactors (RBEC-M, PEACER-300/550, and Medium Scale Lead-bismuth Cooled Reactor). All designs implement indirect thermodynamic cycles. All sodium cooled SMRs incorporate intermediate heat transport systems (secondary sodium circuits to transport heat to a steam turbine circuit and to prevent the possibility of a contact of water with the primary sodium). All lead-bismuth cooled SMRs have no intermediate heat transport system. All designs use steam turbine power circuit. 

Sodium cooled SMRs need an intermediate heat transport system (IHTS) to prevent contacts of the power circuit water and steam with the primary sodium. Presence of an intermediate circuit generally increases the plant costs. To minimize this increase, the designs of the MDP and the BMN-170 use an adjacent configuration of the primary and intermediate circuits, with the space between main (primary) and safeguard (secondary) reactor vessels being filled with sodium and acting as an intermediate heat transport system. Different from sodium cooled reactors, lead-bismuth cooled SMRs incorporate no intermediate circuit. 

All sodium cooled reactor designs incorporate sodium based intermediate heat transport systems to prevent potential contacts of the power circuit water with the primary sodium, and to exclude the contamination of the primary circuit with sodium-water reaction products. The designs based on heavy lead-bismuth or lead coolants, which are chemically inert with water, incorporate no intermediate heat transport system but require a reliable system of primary coolant chemistry control to prevent the erosion and corrosion of claddings and other structural materials. 

As it was already mentioned, the AHTR concept (Annex XXVI) brings together the technologies of HTGRs (high temperature fuel, gas turbine Brayton power cycle), molten salt reactors (liquid salt coolant that, in the AHTR case, contains no fuel) and fast sodium cooled reactors (no excess pressure in the primary circuit intermediate heat transport system). The AHTR uses forced circulation of the primary liquid salt coolant and its intermediate heat transport system is also based on liquid salt. 

The modular double pool fast breeder reactor (MDP), a sodium cooled fast reactor of 325 MW(e) per module output, has been designed to reduce the construction costs and improve the reliability by factory production of most the components, see Annex XXII, Specifically, the MDP is proposed for use within a 4-module plant of 1300 MW(e).The development of the MDP concept has been performed and funded by the CRIEPI. The double pool design is intended to reduce the distances in the intermediate heat transport system by installing steam generators and secondary pumps in the sodium filled annular space formed between the primary and secondary vessel. The preliminary conceptual design has been completed but, at the moment, there is no financial support for further R D. 

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