Loss of coolant

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

Heat build-up Monitor and alarm temperature due to loss of, coolant flow/temperature sensors or product cooling. temperature sensors. CCPS G-12 CCPS G-23 CCPS G-29... 

Accumulation of Noncondensihles - Noncondensibles do not accumulate under normal conditions since they are released with the process vapor streams. However, with certain piping configurations, it is possible for noncondensibles to accumulate to the point that a condenser is "blocked". Such a condition could occur if an automatic vent control valve failed closed for a period of time. This effect is equal to a total loss of coolant, and thus need not be considered separately. 

Reactor coolant pump (RCP) seal failures that lead to a loss of coolant accident (LOCA)... 

Primary Loss of Coolant AccidenI A leak in (he primary (DZO) cooling system. ... 

Generic Evaluation of Feedwater Transients and Small Break Loss-of-Coolant Accidents in GE-Designed Operating Plants and Near-Term Operating License Applications, January... 

In April 1982, a data workshop was held to evaluate, discuss, and critique data in order to establish a consensus generic data set for the USNRC-RES National Reliability Evaluation Program (NREP). The data set contains component failure rates and probability estimates for loss of coolant accidents, transients, loss of offsite power events, and human errors that could be applied consistently across the nuclear power industry as screening values for initial identification of dominant accident sequences in PRAs. This data set was used in the development of guidance documents for the performance of PRAs. 

In the following sections, the flow patterns, void fraction and slip ratio, and local phase, velocity, and shear distributions in various flow patterns, along with measuring instruments and available flow models, will be discussed. They will be followed by the pressure drop of two-phase flow in tubes, in rod bundles, and in flow restrictions. The final section deals with the critical flow and unsteady two-phase flow that are essential in reactor loss-of-coolant accident analyses. 

Transient two-phase flow in rod bundles. In analyzing transient two-phase flows in rod bundles, such as the case resulting from a postulated loss-of-coolant or flow accident in a nuclear reactor, Ishii and Chawla (1978) developed a multi-... 

Rupture of a large-size pipe, capable of causing complete loss of coolant and depressurization of the primary system... 

Although these equations were developed from steady-state CHF data, they are also suggested for use in flow depressurization during a loss-of-coolant accident (Slifer and Hench, 1971). 

Bauer, E. G., G. R. Houdayer, and H. M. Sureau, 1978, A Nonequilibrium Axial Flow Model and Application to Loss-of-Coolant Accident, in Proc. Transient Two-Phase Flow CSN1 Specialists Meeting, 1976, Atomic Energy of Canada 7 429-437. (3)... 

Edwards, A. R., and D. J. Mather, 1973, Some U.K. Studies Related to the Loss of Coolant Accident, ANS Topical Meeting on Water Reactor Safety, Salt Lake City, UT. (3)... 

Hoppner, G., 1971, Experimental Study of Phenomena Affecting the Loss of Coolant Accident, Ph.D. thesis, University of California, Berkeley, CA. (6)... 

Oberjohn, W. J., and R. H. Wilson, 1966, The Effect of Non-uniform Axial Flux Shape on the Critical Heat Flux, ASME Paper 66-WA/HT-60, Winter Annual Meeting, ASME, New York. (5) Ogasawara, H. et al., 1973, Cooling Mechanism ofthe Low Pressure Coolant-Injection System of BWR and Other Studies on the Loss-of-Coolant-Accident Phenomena, ANS Topical Meeting Water Reactor Safety, p. 351, Salt Lake City, UT. (4)... 

Schraub, F. A., 1969, Spray Cooling Heat Transfer Effectiveness during Simulated Loss-of-Coolant Transients, ASME Paper 69WA/NE-8, ASME, New York. (4)... 

Slifer, B. C., and J. E. Hench, 1971, Loss of Coolant Accident and Emergency Core Cooling Models for General Electric Boiling Water Reactors, NEDO-10329, General Electric Co., San Jose, CA. (5) Smith, A. M., 1969, Oak Ridge National Lab., Personal communication to J. K. Jones, November. (5)... 

Figure 11-9 Event tree for a loss-of-coolant accident for the reactor of Figure 11-8.

Since the overall heat transfer coefficient U depends also on the coolantflow rate, it must be emphasized that loss of coolant flow or fouling of the heat transfer surface on the coolant side has a similar effect as shown for loss of agitation. 

Loss, in lasers, 14 664-666 Loss factor, monitoring, 10 15 Loss-in-weight method, 26 248 Loss-in-weight systems, 26 249 Loss modulus, 20 346 21 722-723 Loss-of-coolant accident (LOCA), 17 577, 582, 595, 596... 

It is highly improbable that a nuclear fission power plant would ever explode like a nuclear bomb, but a loss of coolant accident could result in a melt down condition. In a melt down, a large amount of radiation can be released at ground-level. A nuclear or conventional chemical or steam explosion could disperse much of the radioactive particles into the atmosphere. This is essentially what happened when the Chernobyl gas explosion occurred in the Soviet Union in 1986. 

FIG. 3—Exhaust gas leakage into the cooling system can cause foaming, overflow, loss of coolant, overheating, and shortened inhibitor life with subsequent corrosion and rust clogging. 

FIG. 6—Insufficient antifreeze coolant protection, or incomplete mixing of solution, may result in slush-ice freezeup in the radiator, stoppage of circulation, loss of coolant through the overflow, and serious engine overheating. 

AP600 Passive Safety System Details, These features reduce operator responsibilities and add an extra margin of safety over contemporary PWR designs. See Fig. 37 on p. 1121. Large volumes of water stored in the containment eliminate the need for operator action to assure make-up water, either for small leaks that may occur during normal operation or for a major loss of coolant accident (LOCA). A passive plant is a system llial assures public safety even if the operators fail to act... 

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