Cooling event

Items 1 and 2 are experimentally measurable, but it should be borne in mind that highly heat-resistant seals may come at, or near, their glass transition temperature (Tg) during a cooling event, and the coefficient of thermal expansion changes in this region. 

Fig. 3.5. Variation.s in rates of production of back-arc basin crust. Thickness of each bar shows crust production rate the scale is the same for all plots. Area of each rectangle shows area of spreading. Warming and cooling events are also shown (Kaiho and Saito, 1994).

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. 

Figure 7. A and B. Map and topographic cross-sectional view of sample locations from Shuster et al. s (2005) study of incision of the Kliniklini valley, Coast Mountains, British Columbia. C. Model thermal histories for each sample, derived from 4He/3He evolution of step-heating experiments on proton-irradiated samples, and bulk grain (U-Th)/He dates. Samples from the valley bottom require rapid cooling, from 80 °C to surface temperatures, at 1.8 0.2 Ma, and samples from higher elevations require thermal histories with progressively smaller extents of cooling (beginning at 1.8 Ma) with elevation. The highest sample (TEKI-23) was at surface temperature before the 1.8 Ma cooling event experienced by the other samples. Collectively, these data are interpreted to be the result of -2 km incision at 1.8 Ma. After Shuster et al. (2005).

Fig. 1.22.2a. Typical electrical resistance plot of 1 % NaCI solution with 1 °C/min cooling event A at-24.5 °C during cooling, event B at 21.8 °C during warming...

In 1999 a band of maximum annual mean positive SAT anomalies stretched from the North American continent eastward across the Atlantic Ocean and the Eurasian continent toward the equatorial western sector of the Pacific Ocean. Minimum SAT anomalies were observed in a broad band of the central and northeastern region of the Pacific Ocean (including a decrease of SAT). Analysis of the observational data revealed the prevalence of positive temperature anomalies in many regions of the globe. The most vivid anomalous situations include both warming and cooling events (Scafetta et al., 2004). Here are some aspects of temperature variations in 1999 ... 

Although marble migration is only mentioned as an example, this process is not far removed from the crystallization process. In the formation of single crystals, individual ions/atoms/molecules slowly come into contact with one another, and nucleate from thermodynamically favored positions. Sometimes metastable phases may be obtained if one does not allow such preferential migration to occur, through rapid cooling events, for instance. 

Fig. 9. lon-nucleation rates as calculated by Arnold (see [39]) for winter [1], summer [2], and stratospheric winter warming-cooling events [3, 4, 5]. 

House M. A. and Hodges K. V. (1994) Limits on the tectonic signihcance of rapid cooling events in extensional settings insights from the Bitterroot metamorphic core complex, Idaho-Montana. Geology 22, 1007-1010. 

Samthein, M. and Tiedemann, R., 1990, Younger Dryas-style cooling events at Glacial Terminations I-VI at ODP Site 658 associated benthic 6 C anomalies constrain meltwater hypothesis. Paleoceanography 5, 1041-1055. 

Moreira ALN, Carvalho J, Panao MRO (2007) An experimental methodology to quantify the spray cooling event at intermittent spray impact. International Journal of Heat and Fluid Flow 28 191-202. 

For the loss of flow/loss of cooling event without scram, the increased core and bulk sodium temperatures would result in negahve reachvity feedbacks from the thermal expansion of the above-core load pad (ACLP), the radial thermal expansion of the core support grid plate, and core assembly bowing, resulting in a power reduchon to near zero fission power. Decay heaf is removed by fhe passive air natural circulation heat removal... 

To remove all decay and residual heat generated in the reactor cavity during a pressurized and depressurized loss of forced core cooling event. 

It is not a primary function of the RCCS to ensure that the fuel does not exceed its maximum allowable temperature, but together with the design of the heat transfer path from the fuel to the outer surface of the reactor pressure vessel (RPV), the RCCS is providing a heat sink for continuous removal of heat transferred from the RPV during normal operation, and in a postulated loss of forced cooling event [XIV-4],... 

The decision to provide that there be no core melt for any and all loss-of-cooling events has led to the SCWR-PT concept having thermal radiation as the only cooling mechanism that ensures that clad and fuel melting is not possible (Yetisir et al., 2015). In the NuScale AR concept, the requirement to maintain cooling indefinitely has led to a series of natural-circulation paths. 

Loss of cooling events represent a group of events which result in loss of heat removal from the core. When the core is cooled by the RHR System, it s failure is the main initiator in that group. Since loss of off-site power (LOOP) can also cause loss of RHR system, it is sometimes grouped within Loss of Cooling events. 

Loss of cooling events are the initiators with the highest frequency in shutdown. Administrative limitations relevant for loss of cooling are primarily focused to assuring the full availability of RHR system when entering the RHR cooling mode. 

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