Direct reactor cooling

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... 

The potential that the sodium cooled reactOT has for the removal of residual core heat by passive means, i.e., without the need for emergency power supplies, has been confirmed by extensive water modelling and analysis of the primary circuit and by tests of a direct reactor cooling loop in sodium. Tlus not only validated the concept, but demonstrated the sodium/air heat exchanger design by large scale prototype testing. 

In the EUROPEAN FAST REACTOR (EFR) the decay heat is rejected from the primary sodium via a safety graded Direct Reactor Cooling (DRC) System [5.28-5.30] in the case of failure of the normal steam plant (Figs.5.10, 5.11). 

There are two Direct Reactor Cooling Systems (DRC 1 and 2) of three loops each. All loops extract heat from the hot pool of the primary sodium by immersed sodium/sodium heat exchangers (DHX) and reject the heat to the environment by sodium/air heat exchangers (AHX) arranged above the DHXs [5.31]. 

Diiweke, M., et al., The Direct Reactor Cooling System of EFR, Overview and R D Activities, Proc. of the Intern. Fast Reactor Safety Meeting, Snow-bird, USA, 12-16 August 1990. 

Each secondary sodium purification loop is associated with one m n secondary loop and one direct reactor cooling loop. All associated loops are arranged in the same Steam Generator Building compartment and are supplied from the same electrical division. Each of the six parallel and independent purification loops consists of a cold trap with recuperative heat exchanger, a plugging meter unit, an EM pump and the pipework with valves. 

The reaction is exothermic, and multitubular reactors are employed with direct cooling of the reactor via a heat transfer medium. A number of heat transfer media have been proposed to carry out the reactor cooling such as hot oil circuits, water, sulfur, mercury, and so on. However, the favored heat transfer medium is usually a molten heat transfer salt, which is a eutectic mixture sodium-potassium nitrate-nitrite. 

Step 3. The open-loop instability of the reactor acts somewhat like a constraint, since closed-loop control of reactor temperature is required. By design, the exothermic reactor heat is removed via cooling water in the reactor and product condenser. We choose to control reactor temperature with reactor cooling water flow because of its direct effect. There are no process-to-process heat exchangers and no heat integration in this process. Disturbances can then be rejected to the plant utility system via cooling water or steam. 

One feasible network would correspond to the cold streams Cl, C8, and C9 diverted to suitable jacketed reactor compartments, as the simple network in Fig. 14 shows. The hot streams not shown in this network are matched directly with cooling water (CW), and the amount of steam used here is very small. Note that this network would require the same minimum utility consumption predicted by the solution of (PIO). It can be inferred that the network in Fig. 14 is equally suitable for both the simultaneous and sequential solutions. In fact, Balakrishna and Biegler (1993) showed that, for exothermic systems in which the reactor temperature is the highest process temperature, the pinch point is known a priori as the highest reactor temperature (in this case, the feed temperature) and the inequality constraints in (PIO), Qh 2h () ). F G P. can be replaced by a simple energy balance constraint. This greatly reduces the computational effort to solve (PIO). 

In the Texaco process, if the desired product is hydrogen, the raw syngas leaving the reactor is cooled with a direct-water-quench system. In this way, the steam necessary for the downstream shift reaction is produced in situ. A simplified flow diagram depicting the process flow scheme with the direct-quench cooling system is shown in Figure 13 [17). 

The site area is divided into two general areas. A "limited or "clean" area containing most of the nonradioactive operations and service functions is separated by a fence from an "exclusion" or "hot" area containing the reactor and its closely related radioactive auxiliaries. The exclusion area is approximately the south half of the plot< Since the subterranean and deep water flows are to the southeast, this location decreases the possibility that escaping radioactive water may flow toward the wells located in the north portion of the limited area. The most prominent wind direction at the site is from the southwest, and the direction of secondary frequency is from the northeast. Therefore the stack for the exhaust of reactor-cooling air is near the southeast corner of the site. 

DRAGS direct reactor auxiliary cooling system... 

Fig. 2.1. Schematic of the LS-VHTR. (DRAGS = direct reactor auxiliary cooling system PRACS = pool reactor auxiliary cooling system.)...

To meet the passive safety requirements of the NGNP, the AHTR uses a reactor vessel auxiliary cooling system (RVACS) similar to that of S-PRISM. It may also use a direct reactor auxiliary cooling system (DRAGS) similar to what was used in the Experimental Breeder Reactor II to supplement the RVACS and reduce the reactor vessel temperature. 

It is also possible to supplement the RVACS heat removal capacity using a direct reactor auxiliary cooling system (DRAGS) based on natural circulation of an intermediate coolant from bayonet heat exchangers in the reactor vessel to air-cooled heat exchangers. This type of DRAGS system was used in the Experimental Breeder Reactor II (EBR-II) with sodium-potasium as the intermediate coolant. There are a variety of potential intermediate coolants, several of which have been used extensively in industry for similar heat transfer applications. 

Chlorobenzene and dichlorobenzenes are obtained by direct catalytic chlorination of benzene with chlorine. In the production process, gaseous chlorine is bubbled through a solution of the iron(III) catalyst FeCla in benzene. All chlorination reactions at the aromatic core are highly exothermic (e.g., AH= —131.5 kj mol for chlorobenzene formation from benzene and AH = —124.4 kJ mol for dichlorobenzene formation from chlorobenzene) and therefore appropriate reactor cooling (e.g., by internal coohng coils in the reactor) is required. Keeping the reaction temperature at a certain value is important to adjust the product distribution obtained from the process. For a high selectivity to monochlorobenzene the reaction temperature should be adjusted between 40 and 50 °C. Temperatures below 40 °C are unsuitable due to unfavorably low reaction rates. Temperatures above 50 °C, however, favor the formation of di- and even trichlorobenzenes. To maximize mono-chlorobenzene production it is, moreover, important to work with excess benzene such that the benzene conversion is limited to 65% at the desired full chlorine conversion. 

The assessment method that is reviewed in this publication is directly applicable to existing light water and heavy water reactors, and to spent fuel transported or stored in the pools outside the nuclear reactor coolant system on the site of these reactors. With some minor modifications, the method can also be used for other types of reactor such as reactors cooled with gas or with liquid... 

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