Water cracking

Alternative approaches, termed indentation thermal shock tests , with pre-cracks of known sizes have been used by several authors to assess thermal shock damage in monolithic ceramics. Knoop (Hasselmann et al., 1978 Faber etal, 1981) or Vickers (Gong etal., 1992 Osterstock, 1993 Andersson and Rowcliffe, 1996 Tancret and Osterstock, 1997 Collin and Rowcliffe, 1999, 2000 Lee et al., 2002) indentations were made on rectangular bars, which were then heated to pre-determined temperatures and quenched into water. Crack extensions from the indentations were measured as a function of quench temperature differential, and the critical temperature for spontaneous crack growth (failure) was determined for the material. Fracture mechanics analyses, which took into account measured resistance-curve (7 -curve) functions, were then used to account for the data trends. 

It should be mentioned that recent investigations indicate the possibihty of cold water breakdown in nanosecond pulsed discharges. The effect can be provided in particular by electrostatic water cracking. ... 

Figure 2.8 Scanning electron micrograph of unidirectional glass epoxy laminate containing residual dicyandiamide curing agent. After prolonged exposure to hot water, cracks propagated from where the particles had been before they dissolved in the water...

Most of these concepts require development and demonstration of currently undeveloped high temperature structural materials, high temperature heat transport components, new combinations of coolant/fuel/cladding and, in some cases, the development and optimization of process heat application cycles, such as thermo-chemical water cracking. 

XXIII-16] WADE, D., MOISSEYTSEV, A. SIENICKI, J. STAR-H2 Passive load follow/passive safety coupling to water cracking balance of plant, MIT Symposium on Nuclear Energy and The Hydrogen Economy (Paper presented at Int. Conf., Cambridge, MA, USA, September 23-24, 2003). 

Cycle type Indirect cycle intermediate loop of forced circulation molten salt. Ca-Br thermochemical water cracking cycle/ supercritical CO2 Bra54on cycle with a feed-forward multi-effect distillation bottoming cycle... 

See Fig. XXIV-4) water cracking cycle and a supercritical CO2 Brayton cycle (sized for on site needs). 

Since the Ca-Br water splitting chemical reaction requires a heat source at 725 C to cause the CaBr2 + H2O CaO + 2HBr reaction to take place, that temperature must be maintained even if the water cracking plant is operating at only partial load. Therefore, for STAR-H2, another design constraint was imposed - the core outlet temperature of 800X at full load must also be maintained at all levels of partial load. 

Flibe return temperature dismptions Lowest temperature encountered in the three heat exchangers in BOP Reagent steam super-heater Water cracking heat exchanger CO2 heat exchanger. Pb temperature in reactor heat exchanger (HX)... 

Given that the asymptotic states in response to ATWS initiators are safe, it remains to show that the dynamic transition to the asymptotic state will not engender damaging conditions on the in-core structures. A plant dynamic code, which can model the STAR-H2 balance of plant, was not available at the time when this report was prepared. Such a code is being developed first for the STAR-LM, which has a simpler (SC-C02 Bra)hon cycle) balance of plant. In the future, after further refinement of the Ca-Br water cracking cycle, that dynamics code will be modified for applicability to the STAR-H2. 

The STAR-H2 balance of plant (BOP) is comprised of three cascaded cycles (water cracking Brayton cycle and desalination) operating at successively lower temperatures - and with the heat rejected from each cycle used to drive the succeeding cycle, see Fig. XXIV-4. The reactor supplies 400 MW(th) of heat between 800 and 650°C. The strategy for BOP plant design is to use that heat as follows ... 

FIG. XXIV-22. Process heat cascade water cracking —> Bray ton cycle — desalination. 

Crack rates, da/dN, spread over the crack depths, increase in the range 10 to 1000 pm from 10 up to 10 and 10 pm/cyde and most pronounced in high oxygen containing water. Crack rates as a function of stress intensity, determined for steel A 533-B (c.f. 1.5403, 1.6310) for various oxygen contents lie higher than the values of the ASME Section XI reference curve. A test method used to determine the potential at the crack tip of steel (here pressure vessel steel A 533-(B) (UNS K12539, c.f. ... 

FIG. 6. STAR-H2plant configuration at 100% load water cracking Brayton cycle... 

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