Loss of cooling

IF reverse 1. Failure of water source resulting in 1. Loss of cooling, possible runaway 1. See 1A.2 ... 

Runaway Reactions Runaway temperature and pressure in process vessels can occur as a resiilt of many fac tors, including loss of cooling, feed or quench failure, excessive feed rates or temperatures, contaminants, catalyst problems, and agitation failure. Of major concern is the high rate of energy release and/or formation of gaseous produc ts, whiai may cause a rapid pressure rise in the equipment. In order to properly assess these effec ts, the reaction kinetics must either be known or obtained experimentally. 

Perform functional test of cooling system prior to batch reaction addition Ensure automatic isolation of feed on detection of loss of cooling... 

Because these trips are disabled by a loss nf cooling signal, they should be disregarded in calculating the diesel reliability in a loss of cooling sequence. If liic trip were bypassed the diesel would have failed, and it is counted as a failure. 

Nuclear power plant systems may be classified as "Frontline" and "Support. . iccurding to their. service in an accident. Frontline systems are the engineered safety systems that deal directly with an accident. Support systems support the frontline systems. Accident initiators are broadly grouped as loss of cooling accidents (LOCAs) or transients. In a LOCA, water cooling the reactor is lost by failure of the cooling envelope. These are typically classified as small-small (SSLOCA), smalt (SLOCA), medium (MLOCA) and large (LLOCA). 

The large water inventory above the core provides a long time to respond to a feedwater flow interruption or a loss-of-cool accident. 

Loss of cooling pump Loss of cooling Cooling system Pump redundancy, opcr.Hor LiLtiGii. reduce power me... 

Core damage can result most likely from heat imbalance. Figure 6.3-3 is an example from the Indian Point PRA that uses heat imbalance to approach completeness. This diagram shows that cote damage may result from either a loss of cooling or excess power (or both). The direct causes of insufficient heat removal may be loss of flow, makeup water, steam flow, or heat extraction by the turbine. Indirect causes are reactor trip or steam line break inside or outside of containment. Cau.ses of excess power production are rod withdrawal, boron removal, and cold water injection. 

Loss of cooling to irradiated fuel in fueling machine 2.0E-3... 

Loss of river water supply to the cooling water reservoir and in sequence 2 was dominated by failure of operating personnel to respond to the alarm for loss of cooling water to the cooling water reservoir. Values estimated from one minute to several hours, and for various stress levels were estimated. 

Typical pressure versus time curves for runaway reactions are illustrated in Figure 8-2. Assume that an exothermic reaction is occurring within a reactor. If cooling is lost because of a loss of cooling water supply, failure of a valve, or other scenario, then the reactor temperature will rise. As the temperature rises, the reaction rate increases, leading to an increase in heat production. This self-accelerating mechanism results in a runaway reaction. 

What happens with loss of cooling, heating, or agitation ... 

Loss of cooling can be detected by measuring the temperature within the reactor and sounding an alarm. Frequently, by the time the alarm sounds, it is too late. Design a better instrumentation and alarm configuration to detect loss of cooling more directly. Draw the instrumentation diagram. 

The event tree can be used quantitatively if data are available on the failure rates of the safety functions and the occurrence rate of the initiation event. For this example assume that a loss-of-cooling event occurs once a year. Let us also assume that the hardware safety functions fail 1% of the time they are placed in demand. This is a failure rate of 0.01 failure/demand. Also assume that the operator will notice the high reactor temperature 3 out of 4 times and that 3 out of 4 times the operator will be successful at reestablishing the coolant flow. Both of these cases represent a failure rate of 1 time out of 4, or 0.25 failure/demand. Finally, it is estimated that the operator successfully shuts down the system 9 out of 10 times. This is a failure rate of 0.10 failure/demand. 

In practice, large-scale reactors operate close to adiabatic conditions on loss of cooling which causes maximum increases in temperature. In smaller reactors, the temperature increase depends on the heating of coolant and reactor, and the heat loss to the reactor frame and confined coolant as well. 

Cooling water failure The loss of cooling water is one of the more commonly encountered causes of overpressurization. Different scenarios should be considered for this event, depending on whether the failure affects a single piece of equipment (or process unit) or is plantwide. 

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