Vessel failure prevention

Directly cools the vessel metal wall by spray impingement and rundown and, in sufficient quantity, can prevent vessel failure by reducing excessively high metal wall temperatures even in an empty, or nearly empty, vessel. 

PRD Pressure relief device—used on pressure vessels to prevent failure due to over-pressure. 

Abbreviations CDK, cyclin-dependent kinase CREST, cilostazol for restenosis trial MACE, major adverse cardiac events ORAR, oral rapamycin to prevent restenosis ORBIT, oral rapamune to inhibit restenosis REAR, peroxisome proliferator-activated receptor PRESTO, prevention of restenosis with tranilast and its outcomes SMC. smooth muscle cell ThR, target lesion revascularization tREAT, Tranilast restenosis following angioplasty trials TVR, target vessel failure. ... 

Line spectra were first observed by J. von Fraunhofer, D. Brewster, and J. F. W. Herschel in the 1820s.180 In the ensuing decades a considerable amount of work was done on spectral phenomena prior to the demonstration by Bunsen and Kirchhoff in 1859 that line spectra could be used for qualitative chemical analysis. Accounts have appeared of the development of the spectroscope both prior and post Bunsen and Kirchhoff.181-183 Significant observations were undoubtedly made prior to 1860 by Stokes, Stewart, Fox Talbot, and others. The priority claims of Stokes, who recorded his ideas in some private letters to William Thomson, have been examined.184 The work of Bunsen and Kirchhoff did not owe a great deal to that of their predecessors, with the exception of the demonstration by W. Swan in 1856 that the almost omnipresent yellow line that coincided with Fraunhofer s dark solar D line was due to contamination by minute quantities of sodium salts.185 186 Platinum played an important role in the early development of spectroscopy. The metal was widely used to support the material in the flame, since it did not colour the flame itself. Bunsen ensured the purity of all his samples for spectrum analysis by recrystallization (sometimes up to fourteen times) in platinum vessels, thereby preventing contamination by minute quantities of salts that could be leached from glass vessels.187 Sharply contrasting views have been expressed about the failure of chemists prior to Bunsen to exploit spectroscopy.188-190... 

This chapter also does not consider the analysis of stresses around piping, connections, supports, attachments, and so on. While the experienced engineer can design a vessel to prevent failure at these locations, accurate analysis requires elaborate techniques such as the Finite Element Method. This method has been applied with great success to analyze complex vessels such as nuclear reaction vessels. The reader should consult appropriate references if he wishes to pursue this area. References 2 and 3 are basic textbooks in the field of finite element analysis. 

Containment (guard vessel) X Prevent core from uncovery under failure of coolant pressure boundary... 

The reactor vessel lower head has no vessel penetrations, thus eliminating penetration failure as a potential vessel failure mode. Preventing the relocation of molten core debris to the containment eliminates the occurrence of several severe accident phenomena, such as exvessel fuel-coolant interactions and core-concrete interaction, which may threaten the containment integrity. Therefore, AP 1000, through the prevention of core debris relocation to the containment, significantly reduces the likelihood of contaimnent feilure. 

The capability to flood the reactor cavity prevents the failure of the reactor vessel given a severe accident. The vessel and its insulation are designed so that the water in the cavity is able to cool the vessel and prevent it from failing that is, in-vessel retention (IVR). By maintaining die vessel integrity, the core debris in the vessel eliminates the potential of a large release due to ex-vessel phenomena and its potential to fail the containment. 

Engineers and scientists may now understand the mechanisms of pressure vessel failures, and have the tools and techniques for monitoring for cracks and preventing corrosion, but it still requires a great deal of vigilance to ensure that their integrity is maintained. 

The calandria vessel pressure transient does not cause vessel failure or loss of moderator (other than through the relief pipes), and any vessel deformation does not prevent operation of the shutdown systems. 

For the AB sequence, FP revolatilization from the RCS surfaces seems to have a minor effect. The high temperatures of the carrier gas prevent FP vapors conversion into the aerosol phase, therefore condensation onto surfaces controls their retention within the RCS during the whole accident. Tab. 4.3.3.1 shows the material distribution in the plant just before vessel failure, time 2h 11 whereas time evolution of the vapor and aerosol deposits on the vessel structures and on the whole RCS surfaces, can be seen in Figs. 4.3.3.1 to 4.3.3.4. 

Careflil material selection is required to prevent brittle failure of tanks at low temperatures. In addition, for tanks where the service temperatures are reduced, it is essential that an engineering analysis be performed to ensure that the tanks are not subject to brittle failure at the house temperature. The tank and vessel codes usually specify allowable materials based on design temperature. Further information about selection of metals for low temperature is available (8). 

Protection from Fire Exposure and Pressure Relief Considerations - Pressure relief valves cannot protect a vessel that becomes locally overheated on an unwetted surface, although they do prevent the pressure from rising beyond the accumulation pressure of the valve. However, in such a case the vessel may be effectively protected against failure by either one of two methods for mitigating the effect of fire ... 

Typical events that are considered are fire, explosion, ship collision, and the failure of pressurized storage vessels for which historical data established the failure frequencies. Assessment of consequences was based partly on conservative treatment of past experience. For example ilic assessment of the number of casualties from the release of a toxic material was based on past histoiy conditioned by knowledge of the toxicology and the prevailing weather conditions. An altemati. e used fault trees to estimate probabilities and identify the consequences. Credit is taken in this process for preventative measures in design, operation, and maintenance procedures. Historical data provide reliability expected from plant components and humans. 

Note When rupture disk devices are used, it is recommended that the design pressure of the vessel be sufficiently above the intended operating pressure to provide sufficient margin between operating pressure and rupture disk bursting pressure to prevent premature failure of the rupture disk due to fatigue or creep. 

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