Large break

The Primary LOCA sequences. result from expansion joint breaks (51/59) and large break LCXZAs (8/59). Response to LOCAs in the primary system involves shutdown, emergency injection makeup of... 

The Secondary LOCA sequences are related to large breaks (23/24) with small breaks and expansion joint (< 1%). Response to Secondary LOCA involves shutdown, leak control and/or isolation, water removal from the building to avoid flooding of pumps, and direct core cooling in the event of pump flooding. 

The hardest part of engineering risk assessment has turned out to be the prediction of the modes of failure. Serious accidents at nuclear installations, such as those at Three Mile Island or at Chernobyl, have been caused by modes of failure that had not been analysed at all. For example, the report of the Presidents Commission on the Accident at Three Mile Island (Presidents Commission, 1979, p9) highlighted that the concentration of the assessment process on more obvious large break scenarios meant that the eventual mode of failure, which was a result of a chain of a number of more minor events, was not even considered. Despite the use of significant resources in the design process, the risk assessment had been unable to characterize the complex system adequately, a system that was totally human-made and defined. In particular, the risk assessment process had not been able to identify modes of failure caused by humans involved in the operations of the reactor behaving in unexpected ways. 

The voltage change near the equivalence point increases as the difference between 6° of the two redox couples in the titration increases. The larger the difference in 6°, the greater the equilibrium constant for the titration reaction. For Figure 16-2, half-reactions 16-2 and 16-3 differ by 0.93 V, and there is a large break at the equivalence point in the titration curve. For Figure 16-3, the half-reactions differ by 0.47 V, so there is a smaller break at the equivalence point. 

A basic question of whether hierarchical or nonhierarchical cluster analysis is used deals with the correct or best number of groups in a data set. The notion of best relates not only to a criterion value or large break in a dendrogram, but to the research objectives as well. We can not resist quoting from Everitt (48) what is probably the ultimate word regarding the number of groups ... 

Experiments at even higher U indicated another enhancement in few coincident with the onset of wave breaking and the formation of bubbles (Broecker and Siems, 1984). Large breaking waves are known to be associated with high levels of near-surface turbulence and with the injection of bubbles. The magnitude of the enhancement in few was found to depend on the solubility of the gas (Broecker and Siems, 1984 de Leeuw et al., 2002 Merlivat and Memery, 1983). As discussed in Section 6.03.2.1.6, bubble-mediated gas exchange is the most likely explanation for the observations... 

We have shown in Chapter 8 that in acid-base titrations the pH of the solution exhibits a large break at the equivalence point. This pH change can easily be monitored with a glass pH electrode. By plotting the measured pH against volume of titrant, one can obtain titration curves similar to those shown in Chapter 8. The end point is taken as the inflection point of the large pH break occurring at the equivalence point this is the steepest part of the curve. 

In a stretched rubber, the molecules elongate, and the r vectors move towards the tensile axis. Fience the variation of Pi with extension ratio will differ from the pseudo-affine model. For moderate strains the increase of Pi with extension ratio is linear, but at high extensions the approximation used in Eq. (3.12), that both q and q are large, breaks down. Treloar (1975) described models which consider the limited number of links in the network chains. Figure 3.33 shows that the orientation function abruptly approaches 1 as the extension ratio of the rubber exceeds v. Although the model is successful for rubbers, it fails for the amorphous phase in polypropylene (Fig. 3.32), presumably because the crystals deform and reduce the strain in the amorphous phase. 

It is surprising that this issue does not receive much attention in the field of safety studies. Probably, this is due to the fact that a limited overcoming (even 10 times the specifications value) has a small effect on the result of the risk analyses (usually dominated by very unlikely but very catastrophic accident sequences, involving a large break in the containment). 

A flooding system is provided with two systems containing pressurized borated water, which automatically inject water when the pressure goes below a preset value. This system has the objective of protecting the core in cases of intermediate and large breaks in the primary cooling system. 

Excessive rollover in the material prior to fracturing A large break out of the tapered opening in the material Excessive burr on the underside of the material An increase in stripping pressure... 

Dissolve the pellet in a minimum volume of GH. If the size of the pellet is large, break it into several pieces by a brief sonication followed by repeated pipetting. Vortex vigorously in an Eppendorf tube. 

It should be noted that some of the accident initiators that have been treated historically as DBAs may have a frequency that is lower than 10 per year. This may be the case for PIEs such as a large break LOCA for plants designed and built to modem standards. The regulatory mles, however, may still request that such PIEs be... 

Analysis has shown that the peak clad temperature following a large break (LOCA) is about 800 °C which is substantially lower than a PWR plait of current design and well below NRC limit of 1204°C. For small LOCA (s 8 inches) analysis show that core uncovery does not occur. 

During 1988, new data was developed for the RVSS materials at Oak Ridge National Laboratory (ORNL) (References 2 and 3). This data indicated that low neutron flux at low temperatures caused greater embrittlement of the materials used in RVSS than previously anticipated. This increased material embrittlement or "upward shift" in NDTT reduces the fracture toughness of these materials and, under certain specific and conservative transient conditions such as an earthquake or Large-Break Loss-Of-Coolant Accident (LBLOCA), could conceivably result in the failure of the supports thus permitting the reactor vessel to move. 

The Leak-Before-Break methodology in CESSAR-DC, Section 3.6.3, was used to demonstrate that the detection of flaws in pipes can be assured before they cause large break LOCAs and, therefore, the asymmetric loads and the resultant loads on primary system components and supports are no longer significant. Any effects from small-break LOCAs which cannot be eliminated by... 

A very small LOCA (or leak) is defined as having a break discharge flow rate that can be handled by the heavy water makeup system without the need for any safety system intervention. A small break LOCA is defined as a pipe break that carmot be compensated by the heavy water makeup system and extends multiple feeder pipe ruptures such that the reactor regulating system, without credit for stepback action, is capable of limiting any power excursion. A large break LOCA is defined as a pipe break beyond the range of breaks in multiple feeder pipes which give rise to uncompensated coolant void reactivity and a resultant power excursion. 

Because of the total length of feeders and pressure tubes, a small break is about 100 times more probable than a large break. Clearly this range is analyzed for both economic and safety considerations. 

A double-ended guillotine rupture of an inlet header reverses the flow in the downstream core pass. On the other hand, a small break at the inlet header will maintain the flow in the normal flow direction. Therefore, it is possible to select a break size that leads to a period of sustained very low-flow in the downstream core pass. This low-flow arises from a balance between the break flow and the flow delivered by the upstream pump. Such breaks, referred to as critical breaks, tend to more limiting with respect to cooling of the fuel and fuel channels than other large breaks and are therefore analyzed in detail. After a short period of about <30 s of very low-channel flows in the affected pass, voiding at the pump suction degrades the pump head causing channel flows in the downstream pass to reverse toward the break. 

Flows in the long-term are determined by the balance between the break and the pumps (which may be tripped at some point in the accident). At the lower end of the large break spectrum, ECCS refill flows and long-term flows will be in the forward direction. If the break is larger, ECCS refill will be in the reverse direction and this flow direction will persist into the long-term. Flow for intermediate breaks may reverse when the pumps are tripped. 

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