Cold-leg break

Figure 4.28 Semiscale Mod-1 system cold-leg break configuration—isometric diagram. (From Coz-zuol et al., 1978. Reprinted with permission of U.S. Nuclear Regulatory Commission, subject to the disclaimer of liability for inaccuracy and lack of usefulness printed in the cited reference.)...

No external primary loop piping. The use of a natural circulation driven integrated reactor vessel eliminates the potential for hot and cold leg breaks, pressurizer surge line nozzle cracking and breaks, reactor coolant pump suction line breaks, and reactor coolant pump seal breaks. 

The analyses performed demonstrate that the LOCA acceptance criteria are met in the case of the small-break LOCA. The 254 mm cold leg break exhibits the limiting minimum inventory condition that occurs during the initial blowdown period and is terminated by accumulator injection. The APIOOO design is such that the minimiun inventory occurs just prior to IRWST injection for all breaks except the 254 mm cold leg break. All breaks simulated in the break spectrum produce results that demonstrate significant margin to peak cladding temperature acceptance criteria limits. 

Break occurs in system such that some of 1. For postulated PWR cold leg breaks... 

Fig. 1.46 Influence of submergence of quencher in suppression pool on reflooding phase of 100% cold-leg break LOCA...

The SCRELA blowdown module was validated by comparing with REFLA-TRAC, a best estimation code developed by the Japan Atomic Energy Agency (IAEA) [20, 21]. The modified SPRAT-DOWN-DP is also compared with these two codes. The calculations of SPRAT-DOWN-DP and SCRELA start at 25 MPa while the REFLA-TRAC calculation starts at 17 MPa because REFLA-TRAC cannot calculate at the supercritical pressure condition. However, the influence of this difference is small because the period in which supercritical pressure exists is within Is. Figure 6.17 compares the pressures at the 100% cold-leg break. The SPRAT-DOWN-DP code with the water rod model gives a different result from other codes [6]. It cannot be directly compared with other codes especially... 

Fig. 6.17 Comparison of pressure tirmds in cold-leg break blowdown...

Sensitivity analyses for the blowdown phase of the cold-leg break large LOCAs are summarized in Table 6.20. The peak temperature is not sensitive to the break area, which means that the peak temperature is not sensitive to the break flow rate. It is sensitive to the ADS parameters such as the delay from the signal and the number... 

Table 6.20 Sensitivity analysis for blowdown phase of cold-leg break large LOCAs...

In contrast to the cold-leg break, a hot-leg break is less important for the Super LWR. This is because the core coolant flow rate naturally increases during blowdown (cf. Fig. 6.7 [1]), and because forced flooding by the LPCIs is expected after the blowdown. 

The analysis results of the blowdown phase after the 100% hot-leg break are shown in Fig. 7.108 [37]. The cladding temperatures are kept lower than those in the cold-leg break because all the coolant flows to the break point or the ADS through the core, which is the same tendency as that of the Super LWR. 

Fig. 7.110 Coolant flow in momentum conservation calculation at the reflooding phase (for the cold-leg break as an example). (Taken from [37] and used with permission from Atomic Energy...

The small LOCA of the Super FR is distinguished from the large LOCA in the same manner as that of the Super LWR (see Sect. 6.7). As the severest case, 12% cold-leg break is introduced here. The analysis results are shown in Fig. 7.114. AU the conditions for actuating the reactor scram and ADS are assumed not to be reached in the small LOCA, so that the reactor power decreases by only the reactivity feedback and the pressure is kept supercritical. Due to the small heat... 

Fig. 7.114 Calculated results for 12% cold-leg break LOCA (EOEC) without depressurization...

Flow of cold water from downcomer to cold leg of the broken loop occurred in both hot and cold leg break experiments. The cold water did not, however, flow to the CMT through the PEL. So, no condensation problems occurred in the CMT due to flow of cold water to the tank. 

GDE-41 3,5mm cold leg break close to DC, CMT position increased driving force for CMT... 

Passive Safety Injection Test GDE-43 (1 mm cold leg break)... 

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