Emergency cooling

For emergency cooling, it is critical that the temperature does not fall below the solidification point of the reaction mass. Otherwise a crust would form, resulting in reduced heat transfer, which again may favor a runaway situation. The remediation may then have worse effects than the initial failure. 

Agitation of the reaction mass may also be critical in such a situation without agitation, cooling being provided by natural convection only, leads to a considerable reduction of the heat transfer coefficients (see Section 9.3.5). Generally, by natural convection, the heat transfer coefficient is reduced to 10% of its value with stirring [14], Nevertheless, this is only valid when natural convection is established, that is, for smaller vessels and contents with moderate viscosity (see Section 

Large reaction masses behave almost adiabatically, even if cooled from the outside. Here the injection of nitrogen into the bottom of the reaction mass has proved helpful for emergency mixing. However, this method must be tested under practical conditions. 

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The General Electric simplified boiling-water reactor (SBWR) of lower (600 MWe) power features natural ckculation of the coolant rather than the usual forced ckculation. Use is made of a water reservok and pools for emergency cooling of the reactor and the containment building ak. 

The development of computer capabiUties in hardware and software, related instmmentation and control, and telecommunication technology represent an opportunity for improvement in safety (see COMPUTER TECHNOLOGY). Plant operators can be provided with a variety of user-friendly diagnostic aids to assist in plant operations and incipient failure detection. Communications can be more rapid and dependable. The safety control systems can be made even more rehable and maintenance-free. Moreover, passive safety features to provide emergency cooling for both the reactor system and the containment building are being developed. 

Insufficient diluent due Provide automatic control of diluent to under feed or exces- addition sive evaporation result-, Select diluent less susceptible to evaporation ing in insufficient heat sink. Possibility of run- automatic/manual isolation based on away reaction due to detection of unexpected reaction rate high temperature excur- Provide emergency cooling Sion or high concentra-. adequately designed relief device tion of reacting species Monitor liquid level CCPS G-11 CCPS G-23... 

Eliminate sources of fuel Blank unused lines at switching station Provide emergency cooling activated by external fire (e.g., fusible link, plastic tubing)... 

Interlock agitator power consumption to cutoff feed of reactants or catalyst or activate emergency cooling... 

Install high temperature interlock on discharge of condenser to shutdown reactor and initiate emergency cooling... 

Charging ther- Install local indication and alarm on high mally unstable temperature material to warm. emergency cooling reactor results in decomposition. CCPS G-23... 

Never Exceed lOCf C, start emergency cooling at 95 C, trip reactor at97°C... 

Figure 3.4.4-6 presents a flow diagram of a simplified emergency cooling injection system. It is activated by a safety injection signal (SIS) which... 

Loss of Heat Sink Failure of heat transfer between the primary and secondary cooling systems requiring emergency cooling. 

Provision of emergency cooling systems for reactors, where heat continues to be generated after shut-down for instance, in some polymerisation systems. 

The process unit has many loss control features. The plant has a diesel emergency power generator with an emergency cooling system. The plant is also under computer control with emergency shutdown based on redundant inputs. Vacuum is always broken with nitrogen. The process has complete, written, and up-to-date operating instructions. A reactive chemicals review was completed recently. The process has several interlocks to prevent polymerization. 

Process Restabilize Controls i Emergency Cooling Inhibitor i Quenching (add water)... 

In an early stage of warning for a runaway reaction, emergency cooling should be applied in an attempt to control the situation. This often is not sufficient to be a fully preventive measure, particularly if the runaway initiation was not identified quickly. Quenching of the reaction is the usual next step to take. The reaction can be quenched by using one or more of the following procedures ... 

The reactor vessel is on top of a 20 foot concrete slab with a leaktight core catcher. In the event of a meltdown the molten core would collect there and cool down. Four safeguard buildings are also used with independent pressurizers and steam generators. Each of these buildings is able to provide emergency cooling for the reactor core. 

Can reactors be modified to eliminate auxiliary equipment (e.g., by creating a self-regulatory mechanism by using natural convection rather than forced convection for emergency cooling) ... 

The TNR is an important feature if an emergency cooling system has to cope with an imminent runaway reaction it must become efficient in a time shorter than TNR. 

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