Reactor cooling system failure

Cooling system failure could occur due to failure of pumps or controls supplying cooling media to the reactor vessel jacket, coils, or overhead reflux condensers. Piping to or from the condensers could become plugged or any of the heat exchange surfaces could become excessively fouled. 

In the event of a cooling system failure it can be assumed that the reactor operates adiabatically. The adiabatic temperature rise can be found from... 

As long as the final temperature is less than some critical onset temperature where a secondary decomposition reaction occurs, then the process can safely handle a cooling system failure. If a batch reactor temperature cannot be assured to remain less than the onset temperature after a cooling system failure, then a semibatch operation should be used. As noted in Section 3.1.3.5, it is necessary to assure that reactant concentration is not increasing above an onset concentration where a similar decomposition could occur with a cooling system failure. 

Third core heat removal system is a passive heat removal system (PHRS). The heat is removed from the monoblock to the water storage tank located around the monoblock vessel. This system ensures the reactor core cooling in case of postulated maximal accident with all secondary equipment failed, reactor protection system failure and total de-energizing of the NPP. 

There is a minor requirement for the auxiliary steam system after a turbine trip, when the main condenser is a desirable component of the defence in depth capability identified within the fault schedule for cooling down the steam generators and the reactor coolant system. Failure of the auxiliary steam system during such fault transients could result in the main condenser becoming unavailable if no gland sealing steam were available. A reliable auxiliary steam system is thus desirable but not essential, because defence in depth capability is not claimed by the safety case. 

Passive safety systems based on natural circulation are intended to provide the ultimate heat sink in cases of failure of the normal operation of the reactor cooling system. Because of its critical importance, fundamental understanding of the properties and characteristics of namral-circulation hydrodynamics, thermal responses, and thermodynamics in the complex engineering equipment of nuclear reactor power systems is essential. For the Gen IV systems that are based on natural circulation at normal operating states the properties and characteristics under steady-state conditions must also be well understood. 

Meltdown of a nuclear reactor. This involves overheating and melting of the nuclear fuel rods with the subsequent, possible explosive release of radioactive material. It should be noted that the explosion in this case is not nuclear but related to the reactor cooling system. The reactor failures in Chernobyl in the Ukraine and at Fukushima in Japan are examples. Both produced the release of high concentrations of radioactive isotopes. 

LOCA, is presented in Table 3.4.5-1. In preparing the event tree, reference to the reactor s design determines the effect of the failure of the various systems. Following the pipe break, the system should scram (Figure 3.4.5-2, node 1). If scram is successful, the line following the node goes up. Successful initial steam condensation (node 2 up) protects the containment from initial overpressure. Continuing success in these events traverses the upper line of the event tree to state 1 core cooled. Any failures cause a traversal of other paths in the evL-nl tree. 

Excess sulfur dioxide feed to a chlorine dioxide reactor, leading to excessive exothermic reaction, combined witli failure of the cooling system... 

Successive failures of a chemical reactor s cooling system in days is ... 

The water flow to a chemical reactor cooling coil is controlled by the system shown in Figure 11-4. The flow is measured by a differential pressure (DP) device, the controller decides on an appropriate control strategy, and the control valve manipulates the flow of coolant. Determine the overall failure rate, the unreliability, the reliability, and the MTBF for this system. Assume a 1-yr period of operation. 

An actuator fault can be generated by a malfunction of the cooling system, such as electric-power failures, pomp failures, valves failures, and leaking pipes. Without loss of generality, actuator faults may be modeled as an unknown additive term affecting the state equation in (6.5), due to unexpected variations of the input u with respect to its nominal value, i.e., the value computed by the reactor control system. 

Excess sulfur dioxide feed to a chlorine dioxide reactor, leading to excessive c.xothennic reaction, combined witli failure of the cooling system Backflow of process reactants to a sulfur dioxide feed tank, resulting in the formation of corrosive sulfurous acid or explosive reactions witli incompatible materials... 

The safety concept considers two nuclear shutdown systems, a set of six reflector rods for reactor scram and power control and a KLAK system of small absorber balls for cold and long-term shutdown. Decay heat removal is made via the heat exchanger, an auxiliary cooling system, and the panel cooling system inside the concrete cavern, or, in case of a failure of these systems, passively by heat transfer via the surface of the reactor vessel. 

If only half the solvent quantity D is used, Texo remains unchanged at 180°C, but the adiabatic temperature increase rises because of the reduced quantity of D, and therefore the changed total heat capacity of the reaction mixture, to ATadiab = 112 K. At the same time, the reaction power increases. However, through reactor cooling it can still be reliably removed (ATfaiiure = approx. 17 K). Even with this failure, the system still remains below Texo-... 

The heatup and cooldown of the reactor vessel and the addition of makeup water to the reactor coolant system can cause significant temperature changes and thereby induce sizable thermal stresses. Slow controlled heating and cooling of the reactor system and controlled makeup water addition rates are necessary to minimize cyclic thermal stress, thus decreasing the potential for fatigue failure of reactor system components. 

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