Development of Blow Down Model for the LEAP Code; Validation by Data of Sodium-Water Reaction Tests

Jitsu, Koji; Ono, Isao*; Kawada, Koji; Kurihara, Akikazu ; Yatabe, Toshio

It is one of the important matters to select the design base leak (DBL) of the steam generator (SG) of a fast breeder reactor (FBR) in sodium-water reaction. The selection of the DBL has an influence on safety, economical efficiency, etc. of the plant.It is necessary to develop the computational model to estimate the sodium-water reaction phenomenon with high accuracy and rationality for selecting the DBL of large SGs. The blow down evaluation on overheating tube failure phenomenon is pointed out as part of the necessary improvements, since the behavior of overheating tube failure is largely affected by the steam conditions inside of the tube.This document shows the validation of blow down model for the LEAP code, which is developed as analysis code for failure propagation of the SG tubes, by test's data in Sodium-Water Reaction Test Rig No.1 (SWAT-1R). The following results have been obtained through the validation.(1) Within the mass flow rate ranging from 160 to 540 g/s in SWAT-1R, it has been confirmed that calculated internal pressure shows good agreement with the test's one. The pressure in tests becomes close to the calculation by Ogasawara model in critical flow models.(2) Mass flow rate is appropriately calculated of the test after about 10 seconds in the beginning of test. Calculated mass flow rate by Ogasawara model is closer to the test than that by Moody model.(3) On both Moody model and Ogasawara model in critical flow models, internal pressure in calculation shows the underestimation of HT-3 test. It will be necessary to investigate this reason.(4) Mass flow rate at the pipe near water heater tank shows the large overshoot in the beginning of test. Also, the small overshoot that supposed to be moved from upper stream appears at the nozzle about 2 seconds. Since these overshoots are estimated too large, these phenomena should require to be examined.(5) As calculated mass flow rate at the nozzle in both critical models have a tendency to be evaluated l