Cladding temperatures

It is thus clearly demonstrated that the accurate predictions of CHF (or dryout) delay and the existence of transition boiling are very important in the evaluation of a maximum clad temperature in this type of accident. The test results of Tong et al. (1965, 1967a) and of Cermak et al. (1970) indicate the validity of using the steady-state CHF correlation to predict the CHF during a PWR transient cooling or blowdown. 

Since 1984 SFAs have been stored at storage facilities of ESVs in dry shrouds placed into filled-with-water cooling ponds. Thus if such shrouds are intact, SEAs are stored in virtually dry medium. There is an excess of cladding temperatures above that of the environment throughout the storage period due to decay heat in fuel elements, and thus no water condensation on such claddings occurs. 

To minimize these effects on power plant operation, limits are established on the power level rate of change and the maximum cladding temperature (1200°C) allowable during a loss of coolant accident. 

LMFR core orificing is important because fuel lifetime strongly depends on maximum cladding temperature, which is determined primarily by the core coolant temperature rise (AT) and inlet temperature. 

During the transient, the fuel cladding temperatures are not higher than the initial value of the steady state and the core is flooded, so that the minimum DNBR never falls down from the initial value. This leads to a greater contribution for demonstration of MRX s outstanding feature of safety. As a result, core flooding and decay heat removal are revealed to be done appropriately by the engineered passive safely system. 

The Chernobyl accident, as well as that at Three Mile Island, therefore suggests that the circumstances under which a rapid rise in cladding temperature can occur should receive special study, both experimentally and analytically, for water-cooled reactor systems. 

In the transient described, the maximum fuel clad temperature is of the order of 843 K (570°C), well below the limit of 1477 K (1204°C) specified by the US regulations (US Code of Federal Regulations, 2004) universally followed in other countries. 

Figures 4-12-4-17 depict the important phenomena of the transient and show the critical parameters. The difficulty of keeping a high mixture level in the core is evident. The presence of a second clad temperature peak is a consequence of this fact. See Table 3-1 in Chapter 3 for a list of typical external releases in this type of accident.

Acceptance criteria should be clearly defined (see Section 8.2.1). An accident may generate more than one unwanted consequences (e.g. excessive system pressure and excessive clad temperatures) and this situation may require different sets of conservative... 

Multilayer submerged arc strip cladding temperature control, post-weld heat treatment in order to eliminate hydrogen (imder-cladding cracks). 

Calculations show that, if HPIS injection is not available, early start of secondary bleed is very important to avoid core damage in FR-C.l, especially in case without HA injection. If so, the secondary side depressurisation initiated at 370°C core outlet temperature can avoid extended core damage, although short term violation of cladding temperature limit could occur. 

Such kind of changes also will impact the peak clad temperature, and consequently thermal limits will be modified, if such is the case. 

Clad temperatures are estimated in case the sodium filled pot carrying subassembly gets struck. It is found that the nominal central pin clad temperature exceeds the limit (923 K) when the pot is stmck in roof slab region, rotating shield, secondary ramp and ex-vessel transfer position. Hence cooling is required. However, it remains to be seen whether temperature limits can be raised from the considerations of economy and avoidance of complex cooling arrangement. 

Fig 8 Clad temperature evolution during 5 kW spent fuel handling... 

In order to study the effect of heat transfer surface condition on the fuel element cladding temperature, one fuel element mock-up with polished cladding surface and the others with the rough surface were used. 

Cladding Outside Diameter/Thickness Permissible Cladding Temperature (middle of thickness)... 

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