Single channel events

Single channel event e.g., end-Etting failure w. fuel ejection to vault 2. ii -t... 

The main problem has been a methodological one. The patch clamp analysis of single channels views the world of channels through a very small analytical window [10]. A single channel event (opening) needs to be sufficiently long-lived and sufficiently large to be picked up within the current noise band under optimized conditions, and with the low-pass filter set to say 2 kHz. The open time needs to be close to a millisecond and the current amplitude close to 0.5 pA to permit detection. 

Burt JM, Spray DC Single channel events and gating behaviour of the cardiac gap junctional channel. Proc Natl Acad Sci USA 1988b 85 3431-3434. 

Patch clamping requires that an electrode, housed within a micropipette, is attached to the cell to make an almost perfect seal with the cell membrane. This generates a very high resistance between the cell and the pipette wall, typically 10 CA2. The resulting transmembrane currents, measured between microelectrodes inside and outside the cell, generate extremely low noise so single channel events can be... 

From these experiments it appears that the inward current that drives the neuronal bursts that underlie the ictal activity is a persistent Na current. We were not able to get large numbers of experiments in which whole cell activity could be correlated with single channel events from the same neuron. Therefore it is not clear whether the endogenous bursting in t he neurons with ictal activity is due to an increase in overall persistent Na current, a specific increase in burst openings, or a decrease in countervailing K currents. 

For LOCAs with break size smaller than, and up to, the largest feeder break, there shall be adequate cooling of the core to prevent gross fuel sheath failures. (However, in single channel events, failure of fuel in the affected channel may not... 

LOCA and single channel events) Containment System thermal hydraulics Containment thermal hydraulics Fuel and fuel channel thermal-mechanical behavior Fission product release and transport... 

A severe flow blockage >90% of the channel flow area is required to cause pressure tube failure due to overheating. A single channel event leading to channel failure also requires analysis of the pressure transient within the calandria, to show that the calandria vessel itself remains intact, that the SDS devices within it can still perform their fimction, and the break does not propagate by causing failures of other reactor channels. 

The patch-clamp data consist in records of single-channel current or on macroscopic current records. The single-channel data is obtained, and properties of current amplitude, duration distributions and probability of single channel events are studied. Macroscopic currents are fitted according to kinetic models, or the noise of current records is analyzed to obtain the microscopoic properties of single-channel events that underlie the macroscopic currents. The analysis methods will not be discussed here. Some criteria and methods are discussed in several articles and reviews, as for example [5, 8, 10, 17-23]. 

The utlimate proof of the validity of the above picture can only derive from direct observations of single channel events. 

With the present degree uf mastery of the experimental techniques it is possible that much more accurate data can be collected in the near future, providing more information on detailed channel kinetics. However, major advances in our understanding of the physics of ionic channels in nerve membranes are more likely to be obtained from the analysis of single channel events. This promises to be the most fruitful approach of the forthcoming years. 

The instrumentation designed used two photomultipliers to measure two single-channel events the laser wavelength and its power along with the Raman signal of the species of interest. As has been noted, the instrumentation used to conduct this analysis is now considered primitive. A modern multi-sampling-point multichannel Raman analyzer offers real potential for this measurement. 

Single channel events are a particular subset of small LOCAs affecting only one reactor fuel channel. They consist of ... 

Single channel events are also combined with the impairments of containment, ECC and Class IV power. Safety aspects and acceptance criteria are the same as the small LOCA combined event cases, with the exception that there is no requirement on the integrity of the affected channel or its fuel. For in-core breaks, particular attention is paid to moderator temperature, which will initially rise due to the discharge of coolant into the moderator. If an in-core break is combined with an impairment in ECC, some of the other channels may sag or strain (eventually) into contact with their calandria tubes. Thus, the moderator temperature must be kept low enough to prevent prolonged dryout of the calandria tube. 

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