Secondary sodium systems

Primary and Secondary sodium systems are in service for the past 14 years at a maximum temperature of 485°C at the outlet of core and 420 C in sodium circuits and tibe performance of the sodium circuit components has been satisfactory/ The sodium purity has been well maintained and there has been no incident of any radioactive sodium leak from the primary circuit. Once-through steam generator (SG) has been in service for about 6600 h and there is no incident of steam generator tube leak. 

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. 

Several problems were identified to be resolved to enhance the feasibility of an earlier realization of the 4S-LMR project, related to the reliability of a reactor shutdown system including a reflector control system, and chemical activity of the secondary sodium systems. The total R D costs, including the construction of a prototype reactor needed to obtain data for licensing of the commercial reactor is estimated at under US 1 billion, under the present design conditions. These costs may depend on the future design conditions and other factors. 

The heat generated in the reactor is removed by a loop-type sodium cooling system composed of three independent loops. It is transferred to a steam/water system through the primary and secondary sodium systems (Fig. 3.6). 

In addition to the main cooling system there is an auxiliary cooling system to remove decay heat from the core when the reactor is shut down for refueling, or in an emergracy. The auxiliary cooling system which is separated from the secondary sodium system, has an air cooler in parallel with the steam generator. When it is operating, the primary and secondary sodium are circulated by the primary and secondary main circulation pumps driven by pony motors. 

Most fast-spectrum reactors operated around the world use liquid sodium metal as a coolant. Future fast-spectrum reactors may use lead or a lead-bismuth alloy, or even helium, as a coolant. One of the attractive properties of metals as coolants is that they offer exceptional heat-transfer properties in addition, some (but not all) metal coolants are much less corrosive than water. However, because sodium is reactive with air and water, fast-spectrum reactors built to date have a secondary sodium system to isolate the sodium coolant in the reactor from the water in the electricity-producing steam system. The need for a secondary system has raised capital costs for fast reactors and has limited thermal efficiencies to the range of 32 to 38 percent. Novel steam-generator designs, direct gas cycles, and different coolants are options that may eliminate the need for this secondary sodium loop and improve the economics of fast reactors (Lake et al 2002). 

Heat transfer is therefore seen to occur in several different links of a thermal transport chain with sensitivity to many parameters. However, emphasis is given here to the heat transfer picture within the core since it has an important bearing on the design of the reactor system. Some attention is given to the primary and secondary sodium system, particularly in problem areas. The steam system and turbine-generator complex are similar to those for fossil fueled plants and are consequently not covered. 

Fabrication of the large size vessels required for the pool-type LMFBR s may be a problem. Field fabrication may be required and strict quality control will be extremely important. The top closure region may prove to be especially difficult as size is increased in that it must serve simultaneously as a shield, gas enclosure, and component support. The loop system appears to offer fewer problems in scaling to large sizes. It will also be much more flexible with respect to possibilities for eventual elimination of the intermediate sodium system. Elimination of the secondary sodium system from a plant containing a pool primary does not appear possible since this would require introduction of water into the reactor vessel. 

Sodium is used as a heat-transfer medium in primary and secondary cooling loops of Hquid-metal fast-breeder power reactors (5,155—157). Low neutron cross section, short half-life of the radioisotopes produced, low corrosiveness, low density, low viscosity, low melting point, high boiling point, high thermal conductivity, and low pressure make sodium systems attractive for this appHcation (40). 

Carbamazepine continues to be studied with regard to its actions on primary and secondary neurotransmitter systems and on sodium and potassium ion channels. It has a limited ability to block norepinephrine reuptake (Hollister 1992) and has been reported to decrease norepinephrine release (Post, Weiss, and Chuang 1992). Dopamine release is enhanced, and reuptake is blocked. As with lithium and valproate, long-term administration causes an increase in GABA receptors (upregula-tion) in the hippocampus, but not in the cortex (Post, Weiss, and Chuang 1992). 

These terms are also used to name salts of ortho-phosphoric acid (H3P04) in which one, two, or three of the hydrogen atoms have been replaced by metal or radicals NaH2P04 is primary sodium phosphate, Na2HPC)4is secondary sodium phosphate. The same system of names is used for salts of other acids containing three replaceable hydrogen atoms. 

Abnormal G protein functioning dysregulates adenylate cyclase activity, phosphoinositide responses, sodium/potassium/calcium channel exchange, and activity of phospholipases. Abnormal cyclic adenosine monophosphate and phosphoinositide secondary messenger system activity. 

It has been suggested (80, 88) that the Aquaclaus or Citrate process might be substituted for the conventional Claus plant to convert all the hydrogen sulfide to elemental sulfur. One major factor determining the practicality of this approach is the problem of separating the sulfate and thionates from the phosphate or citrate. A secondary process system to recover sodium and sulfur from the purged absorbent will be a virtual necessity at any large installation. 

Reactor vessel height / diameter Primary coolant systems Primary coolant sodium mass Inlet / outlet reactor temperature Primary coolant flow rate Primary coolant flow velocity Secondary coolant systems Secondary coolant sodium mass Inlet / outlet IHX temperature Secondary coolant flow rate Secondary coolant flow velocity Water - steam systems Feed water flow rate Steam temperature (turbine inlet) Steam pressure (turbine inlet) Type of steam generator Refueling system... 

FIG. 5 Drain system and Storage system of secondary sodium circuit. 

In case off-site power is available, the decay heat is removed through normal heat transport path of secondary sodium and water/steam circuits. Additionally, an independent safety grade passive direct reactor cooling system consisting of 4 independent circuits of 6 MWt nominal capacity each has been provided. Each of these circuits comprises of one sodium to sodium heat exchanger dipped in reactor hot pool, one sodium to air heat... 

An electro-chemical carbon meter is installed in one of the secondary sodium loops to measure the active carbon level in the system. Its performance is being studied. 

Primary and secondary sodium coolant removed from reactor systems ... 

Main isolations these isolations are designed to separate the residual heat evacuation systems and the primary circuits materially and functionally, and allow secondary sodium draining from the intermediate exchangers. These isolations will also be used to set up the carbonation installations for treatment of the circuits residual sodium. The main operations are as follows ... 

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