Power raising phase

The thermal criteria for startup of the Super LWR are summarized in Table 1.9. The maximum cladding temperature during the power raising phase is limited below the same value as the rated power. The moisture content of steam sent to... 

Fig. 1.23 Redesigned curves of sliding pressure startup before the power raising phase...

In the power raising phase, the thermal criteria are not as limiting as stability criteria, because the coolant flow is a single phase one at supercritical pressure operation. If only thermal criteria are considered, the power to flow rate ratio in the power raising phase can be kept as one, and the MCST can be maintained so it does not exceed the rated value. However, if stability considerations are also taken into... 

J. Cai, Y. Ishiwatari, S. Bcejrri and Y. Oka, Thermal and Stability Considerations for a Supercritical Water-cooled Fast Reactor During Power-Raising Phase of Plant Startup, Proc. ICAPP09, Tokyo, Japan, May 10-15, 2009, Paper 9265 (2009)... 

From these two background facts, the purposes of this section are to revise the design of the sliding pressure startup scheme, propose its detailed procedures, and assess their feasibility by a system transient analysis. This section covers just the procedures before the power raising phase because the power raising phase itself... 

Thermal and Stability Considerations During Power Raising Phase of Plant Startup... 

In the Super LWR analyzed in Chap. 5, the coolant channels of all the fuel assemblies are cooled by upward flow, so that only one hot channel is treated in the thermal analysis and thermal hydraulic stability analysis. On the other hand, the coolant flow scheme in the reactor pressure vessel of the Super FR is the so-called two-pass scheme where part of the seed fuel assemblies and all the blanket fuel assemblies are cooled by downward flow as shown in Fig. 7.35. The fractions of the downward flow rate in the seed assemblies, blanket assemblies, and downcomer at the normal operating condition are determined in the core design as shown in Figs. 7.36 and 7.58 [26]. The flow distribution among those downward flow paths would change during the power raising phase so as to balance the pressure drops. 

The plant transient analysis code SPRAT-F, introduced in Sect. 7.9, is used to calculate the flow distribution and the MCST in the three hot channels with respect to the core power and feedwater flow rate. The nodahzation is shown again in Fig. 7.81 [32]. Since the core power and feedwater flow rate are raised very slowly at the power raising phase, the reactor can be practically treated as in a steady state... 

Fig. 7.95 Designed feedwater flow rate for power raising phase of 1,000 MWe class Super FR. (Taken from [32] and used with permission from Atomic Energy Society of Japan)...

Table 7.38 Highest values of MCSTs during power raising phase with various heat transfer correlations at BOEC/EOEC (unit °C)...

Table 7.40 Highest decay ratios of thermal-hydraulic instability during power raising phase with...

The power raising phase in the plant startup was designed in consideration of the thermal and thermal-hydraulic stability criteria. Due to the two-pass flow scheme, the power to flow rate ratio became locally large in the downward flow channels during certain power and flow conditions. Thus, the flow rate required to satisfy those criteria was determined by the MCST and the decay ratio of thermal-hydraulic stability in the downward flow channels. 

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