Blackout

Blackout problem if the instrument does not properly work, it is difficult to observe intermediate states. Very sophisticated instmmentation is needed to measure voltages, currents or logical levels on the boards of the instrument. 

The situation may have a cascading effect until all the machines fall out, resulting in a total blackout. 

Key features of the 1,300 MWe System 80+ (Bagnal, 1992) are 15% improvement in thermal margin, slower response to upset conditions, no fuel damage up to a 6-in. break, and the ability to withstand an 8-hour station blackout. System 80+ integrates the nuclear island, turbine island, and balance of plant. 

The accident resulted from a routine safety test of some electrical control equipment at the start of a normal reactor shutdown for routine maintenance. The test was to determine the ability to continue to draw electrical power from a turbine generator during the first minute of coast-down following a station blackout. In a blackout, the reactor automatically scrams and diesel generators start to assume load (about 1 minute required). 

Select 1 and type a title for the problem the default title is "Siation Blackout from l ss of Offsite Power, unless you want to use this enter your title. 

A,-i-,DG-A,DG-A-M B,-t-,DG-B,DG-B-M C,-i-,DG-C,DG-C-M where the semicolon designates enter. Notice these equations are linked with BLACKOUT being the top event. This completes the preparation of FTAP input selection 6 exits FTAPlus to return to the FTAPSUn menu (Figure 6.4-3). Figure 6.4-2 shows file FN.Fl was created. This is an ASCII file which can be edited, if needed, with a text editor. 

After selecting the MEX command (selection 5) the comma delimited input consists of groups of basic events that are pairwise mutually exclusive. To extend the group to the next and subsequent lines, the first field must be blank. Up to 100 names per group are allowed with a new group starting when a non-blank character is encountered in the first field. The number of pairs that are mutually exclusive is n /[(n-2) 2 ], where n is the number of basic events in the group. An example for the plant blackout fault tree is DG-A-M,DG-B-M,DG-C-M (where means enter). 

Refinements have been made on the source term calculational methods since WASH-1400. The general trend has been toward source term reduction (e.g., the iodine release for the large LOCA) as compared with the RSS results. In cases such as Station Blackout, the RSS underestimated the tellurium and barium compared with results from the BMI-2104 suite. 

A long evolving use of PSA was for Anticipated Transients without Scram (ATWS) which extended over 15 years to culminate in NUREG-0460 which was upset by the Salem failure-to-scram incident and the subsequent SECY Letter 83-28. Other special studies have been (a) value-impact analysis (VIA.) studies of alternative containment concepts (e.g., vented containment, NUREG/CR-0165), (b) auxiliary feedwater studies, (c) analysis of DC power requirements, (d) station blackout (NUREG/CR-3220), and (e) precursors to potential core-damage accident.s (NUREG/CR-2497), to name a few of the NRC sponsored studies. 

Two studies resolved the Unresolved Safety Issue A-44, "Station Blackout." The first siudy, The Reliability of Emergency AC Power Systems in Nuclear Power Plants," when combined uh die lelevant loss-oToffsite-power frequency, provides estimates of station-blackout frequencies lor 18 nuclear power plants and 10 generic designs. The study also identified the design and operational features most important to the reliability of AC power systems. The second study, "Station Blackout Accident Analysis" (NUREG/CR-3226), focused on the relative importance to risk of laiion blackout events and the plant design and operational features that would reduce this risk. 

IPE results genrally are consistent with the results of previous NRC and industry risk studies in indicating that the CDF is often determined by many accident sequence combinations, rather than a failure. The largest contributors to CDF vary among the plants (e.g., LOCAs dominate some IPE while station blackout [SBO] dominates others). Support systems, whose design varies considerably with plant, are important to all plants because they can cause multiple front-line system failures. This may account for much of the variability in the IPE results. 

RCP Seal LOCAS -Evaluate or replace RCP seal materMl [b.pj -Independent seal injection or chari. irie ]"iinp for station blackout (p) -Operator training on tripping pumps on o-.s of cixiling ) -Review HPSI dependency on CCW (p)... 

Emrit, R. et al., A Prioritization of Generic Safety Issues, NUREG-0933 suppliment. Reassessment of the Technical Bases for Estimating Source Terms, Draft, May 1985. Baranowsky, P.W., Evaluation of Station Blackout Accidents at Nuclear Power Plants, May 1985. 

The bulk of the information in the report is included in a 317-page appendix that contains systems descriptions, station blackout fault trees, diesel generator historical data, and diesel generator common cause failure analysis results for 18 different nuclear power plants. Tables and graphs are well organized and present data correlated to each plant studied. The study also contains conclusions and recommendations for improving reliability. 

Appliances began to attract serious analytic interest toward the end of this era. The Northeast blackout of... 

By the 1990s, after decades of extremely reliable service, most customers have come to expect electricity to be available when they want it and how they want it, and feel the utility has the obligation to supply the power. If the customer s preference is to keep the air conditioning on all day, it is the obligation of the utility to supply the power for this preference. Customers have become so accustomed and reliant on electricity that the 1990s consumer felt service without interruption was a right. This was far different than a few decades earlier. New York City residents tolerated the major blackout of 1965 and the inconveniences it caused, yet the minor blackout of 1999 was widely believed to be inexcusable and that Con Edison (the local utility) should compensate its customers for damages, and it did. 

During prolonged heat waves which can cause blackouts and brownouts, electric utilities always request that customers limit energy consumption by raising thermostats and turning off the air conditioning when not home. It is uncertain if these requests are heeded, and if they arc, it is uncertain whether conformity is out of altruism (help the utilities) or self-interest (save money). 

The bulk system has long been seen as a vital element in the maintenance of an economic and reliable supply of electrical energy in North America, and a high degree of redundancy has been incorporated to achieve this objective. The North American Electric Reliability Council (NERC) was formed in 1968, following the November 9-10, 1965, blackout that affected the northeastern United States and Ontario,... 

A map at Los Angeles s energy troubleshooting facility in 1987. Circuit 72-4, the source of an earlier blackout, is marked in the upper right. (Corbis-Bettmann)... 

First major blackout occurs in northeast United States and Canada. 

---