Reactor heat removal

Heat transfer. Reactor heat removal preheater, reboiler, and condenser heat transfer areas temperature levels of steam and cooling water... 

The digestion and hydrolysis temperatures are controlled between 110 and 125°F. During hydrolysis, approximately 2 parts of water per 100 parts of reaction product are added to convert acid anhydrides to sulfonic acid. Both the oleum and S03 sulfonation processes are quite exothermic and almost instantaneous. In order to prevent decomposition and maintain optimum product color, an efficient reactor heat removal system is necessary. 

Sulfonation of LAB. The sulfonation of alkylbenzenes leads to sulfonic acid tyre product, which is then neutralized with a base such as sodium hydroxide to produce sodium alkylbenzene sulfonate. The sulfonation reaction is highly exothermic and instantaneous. An efficient reactor heat removal system is used to prevent the decomposition of the resultant sulfonic acid. The sulfonation reaction takes place by using oleum (SO3H2SO4) or sulfur trioxide (SO3). Although, the oleum sulfonation requires relatively inexpensive equipment, the oleum process has major disadvantages compared to sulfur trioxide. The need for spent acid stream disposal and the potential corrosion owing to sulfuric acid generation increased the problems related to oleum process [1]. 

The primary coolant circuit of a PWR is shown in schematic form in Fig. 36. In this particular circuit, there are four loops between the reactor and the steam generators. The pressurizer is also shown, which maintains the pressure in the primary loop at a sufficiently high value (typically 150 bar) such that sustained boiling does not occur and maintains the desired concentration of hydrogen in the coolant. The reactor heat removal system (RHRS) and the reactor water cleanup system are not shown. The general operating conditions in a PWR primary loop are summarized in Table 2. 

Fig. 39 Schematic of the primary coolant circuit of a PWR, showing the three principal loops (1) the main loop (SI -SI 2), (2) the reactor heat removal system (RHRS, SI 7-SI 9), (3) the reactor water cleanup unit (RWCU,...

Comparison of Temperature-control Characteristics of Various Types of Reactors. Several methods of heat removal are used in the various reactors. Heat removal for the most part may be considered to take place either directly, as in the oil- or gas-cooled systems where the catalyst surface is in contact with the cooling medium, or indirectly, as in the fixed or fluid beds where heat must be transferred through the bed to a cooling surface. Admittedly this is an oversimplification, especially in the case of the fixed and fluid beds where some direct heat transfer occurs. 

In the separation of the major systems of control and instrumentation for the reactor and.the reactor heat removal processes, two major control and instrument centers are provided. These major control centers are located in the Reactor Building and in the Process Water Building. The reactor is controlled from the former, while the latter center, which is primarily for the control and instrumentation of process-water flow through the reactor, includes the instrumentation of the locally controlled reactor cooling-air system. A number of the supporting process systems are like the cooling-air system in that they have- locally controlled equipment but have some instrumentation extended to one or both of the major control centers. 

Anticipated operational occurrences are off-normal events, usually plant transients, which can be coped with by the plant protection systems and normal plant systems but which could have the potential to damage the reactor if some additional malfunction should happen. Their typical frequency of occurrence may be more than 10 year Some of the anticipated occurrences (PIEs - postulated initiating events) are due to the increase of reactor heat removal (as might occur for an inadvertent opening of a steam relief valve, malfunctions in control systems, etc.). Some are due to the decrease of reactor heat removal (such as for feed-water pumps tripping, loss of condenser vacuum and control systems malfunctions). Some are due to a decrease in reactor coolant system flow rate, as in the case of a trip of one or more coolant pumps. Some are connected with reactivity and power distribution anomalies, such as for an inadvertent control rod withdrawal or unwanted boron dilution due to a malfunction of the volume control system for a PWR. Events entailing the increase or decrease of the reactor coolant inventory may also happen, due to malfunctions of the volume control system or small leaks. Finally, releases of radioactive substances from components may occur. 

Maintenance re-allocation more maintenance is required on some components, less on others (RHRS on Reactor Heat Removal System more maintenance on some valves, less on others)... 

FIG. 7. Combined Safety Injection System IS/ Reactor Heat Removal System. 

Increase in reactor heat removal inadvertent opening of steam relief valves secondary pressure control malfunctions leading to an increase in steam flow rate feedwater system malfunctions leading to an increase in the heat removal rate. —Decrease in reactor heat removal feedwater pump trips reduction in the steam flow rate for various reasons (control malfunctions, main steam valve closure, turbine trip, loss of external load, loss of power, loss of condenser vacuum). 

Increase in reactor heat removal steam line breaks. 

Decrease in reactor heat removal feedwater Une breaks. 

On positive reactivity addition or loss of reactor heat removal following reactor trip by the electromechanical protection system or the emergency boron injection system, the core residual heat removal is effected by the passive emergency heat removal system. The amount of water in the tanks of the system ensures reactor cooling for at least 72 hours (seven days with two tanks and three days with one tank available). 

Such system is able to cool the primary system down to the cold shutdown state and replace the normal reactor heat removal system. Heat exchangers submerged in a pool constitute the heat sink for half of the modules. Other modules are supposed to employ cooling tower systems (Fig. 8). 

Forced convection is only required when cooling is needed for core refuelling. The twelve RRPs cool the primary system to a cold shutdown state. They replace the conventional reactor heat removal system. 

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