Loss of Electrical Power

Appendix III contains failure rate estimates for various genetic types of mechanical and electrical equipment. Included ate listings of failure rates with range estimates for specified component failure modes, demand probabilities, and times to maintain repair. It also contains some discussion on such special topics as human errors, aircraft crash probabilities, loss of electric power, and pipe breaks. Appendix III contains a great deal of general information of use to analysts on the methodology of data assessment for PRA. 

None No flow -chlorination loop Pump failure. Loss of electric power to pump. No chlorine flow to tower basin. Low chlorine concentration in tower basin. Chlorination pump malfunction alarm. 1 ... 

Occasionally an incident occurs that results in a common mode failure. This is a single event that affects a number of pieces of hardware simultaneously. For example, consider several flow control loops similar to Figure 11-4. A common mode failure is the loss of electrical power or a loss of instrument air. A utility failure of this type can cause all the control loops to fail at the same time. The utility is connected to these systems via OR gates. This increases the failure rate substantially. When working with control systems, one needs to deliberately design the systems to minimize common cause failures. 

Good practice guidelines illustrate how these parameters are typically examined for both normal and postulated abnormal conditions, such as variations in reactant quantity, concentration, agitation, sequence, time, failure of utilities, and instrumentation. Qualitative hazard evaluation protocols are not well suited for such complex chemical phenomena (e.g., the severity of an uncontrolled reaction under a loss of electrical power may not be apparent without sufficient test data). 

It is important to perform a data capture operation for electronic data as soon as possible to maximize the quantity and quality of such information. For example, one investigator had to download the data within the preset file purge time of eight hours. The programmer was on vacation and there was no documentation available on the program. Even when computer specialists are available, this may be a difficult task because computer specialists do not frequently encounter the questions asked by investigators, f f there is a of loss of electric power, information may be accessible for a limited period due to battery backup for volatile memory. (Email should also be considered as electronic evidence.)... 

An extremely important operating requirement for the MPF is the safe shutdown and restarting of the unit if there is a loss of the air supply for combustion, loss of exhaust fan capacity, or both. A loss of electrical power is the usual cause of such an occurrence. If this happens, there is a significant probability that the munitions in the MPF will still be vaporizing uncombusted agent when the furnace temperature drops below 1,200°F. At JACADS, the solution was to cool the furnace to 400°F with water sprays, then to back the trays into a buffer storage zone upstream of the MPF (MR E, 1996). Once the furnace was restarted, the trays were processed normally. 

Recommendation 3-6. A modified baseline process at Pueblo should include a four-zone (rather than three-zone) metal parts furnace with design provisions to ensure safe shutdown and restarting in the event of operational upsets, such as a loss of electrical power, combustion air supply, or exhaust gas capability. 

On January 7, 1998, an ice storm struck the northeastern United States and southeastern Canada. In Maine, 3 consecutive days of rain combined with ground temperatures consistently below freezing resulted in heavy accumulations of ice on trees and electric power lines. Falling trees and branches and breaking utility poles resulted in the loss of electrical power to an estimated 600,000 persons. Although the rain had stopped by January 11, temperatures declined to less than 10 °F (-12 °C) over most of the state, exacerbating the danger. On January 16, an estimated 50,000 households, primarily in the interior portion of the state, remained without power. 

In evaluating relief scenarios, the design engineer should consider sequential events that result from the same root cause event, particularly when these can increase the relief load. For example, the loss of electric power in a plant that carries out a liquid phase exothermic reaction could have the following impacts ... 

Loss of electric power. This is another failure that frequently sets the column relief requirements. A common practice (9) is to study the installation to determine the effect of power failures and to set the required relief capacity for the worst condition that can occur. All electrically driven equipment, such as pumps, compressors, and fans (including those in the site cooling water system or steam supply system), may fail, and so will electronic controllers and computer control equipment. 

IDENTIFICATION OF PROTECTION. Protection reduces the probability of the consequence occurring given that the cause has occurred. There are two key questions to ask when reviewing the protection portion of a PrHA. First, is the protection capable of preventing the consequence if it functions correctly Second, will the protection function, given the cause For example, a normally open electric solenoid valve will not close after loss of electrical power and, therefore, cannot function as protection under that circumstance. A motor-operated valve also will not operate after loss of electrical power. However, a normally closed electric solenoid valve will automatically close upon loss of power. 

Fault trees and event trees can be combined. The gates in the event tree are treated as top events of multiple fault trees. So, for example, one of the event tree gates could be Loss of Electrical Power. That term then becomes the top event of a Loss of Electrical Power fault tree. When using fault trees as subsets of event trees it is important to identify the common cause or interdependent events and to enter them separately into the tree s structure. 

Annex 8. Behaviour of the PAMELA Plant in Case of Loss of Electrical Power Annex 9. Container Handling... 

The heat loss from the secondary side occurs by steam dump to the atmosphere as the turbine-generator combination stops on the scram signal. The condenser is lost if there is a total loss of electric power. The safety and steam dump valves open within seconds of the start of the accident. 

As far as modelling the decrease of flow rate with time after the loss of electric power is concerned, the codes used balance the momentum in each cooling circuit and in the core. This momentum balance is combined with the continuity equations, with the momentum balance of the pumps and with the pump characteristic curves. In these calculations the head losses are overestimated for sake of conservatism. 

TE = transient - -loss of electric power SE = small LOCA - -loss of electric power V = interfacing systems LOCA... 

Loss of electric power with LOCA from the pump seals (SE= small LOCA + loss of electric power)... 

The assumption here is that, as a consequence of the total loss of electric power and with a delay of about 45 minutes, the pumps seals are damaged beeause of the loss of the cooling system. This sequenee of events and the consequences are very similar to the preceding scenario (Section 5-5-1). In this case no safety valve opening takes place because the pressure is kept low by the efflux through the pumps seals. 

Transient for loss of outside lines Transients not caused by the loss of the electric power generation system Transients caused by loss of electric power generation system Spurious opening of relief valve... 

T is the transient of main feed-water loss due to loss of electric power supply. M, B indicate the lack of recovery of the outside lines and the non-operation of the station diesels for at least three hours (in the Rasmussen report, the probability of non-recovery of the outside lines in one hour is assumed equal to 2x 10" and the probability, to be combined with the preceding one, of nonrecovery for the other two hours of the same lines, is assumed equal to 5 x 10 ). L indicates the malfunction of the auxiliary feed-water system and therefore also of the turbine-driven pump. 

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