LOBI/A1-66, Loop for Blowdown Investigation, PWR Double-Ended 2A Cold-Leg Break

1 - Description of test facility: The LOBI facility is a 1/700 scale model of a four loop PWR and has two primary loops, the intact loop representing three loops and the broken loop representing one loop of a four-loop PWR. The reactor pressure vessel model contains an electrically heated rod-bundle with 64 rods and a heated length of 3.9 m. The nominal heating power is 5.3 MW. The downcomer is of annular shape. An upper head simulator is connected to the vessel. Each of the two primary loops contains a pump and a steam generator. The different mass flows in the loops are established by the pump speeds, since the two pumps are identical. Heat is removed from the steam generators by a secondary system. ECC water can be supplied from two accumulators, one for each loop. Cold or hot leg as well as combined injection can be simulated. The LOBI test facility is the only high pressure integral test facility within the European Communities (1982), built and operated in the Joint Research Centre, Ispra, Italy. In the LOBI experiments the thermal-hydraulic behavior of the facility during a transient, caused by a simulated loss of coolant accident (LOCA), is investigated to provide an experimental basis for analytical model development and code verification. 2 - Description of test: The Test A1-66 is one of a series of three LOBI tests in which the ECC injection mode was studied. In all experiments, a double-ended 2A break in the cold leg was simulated. The downcomer gap width was 12 mm. In test A1-66, ECC water was injected from the intact loop accumulator into the cold leg only. The pressurizer was connected to the intact loop. After blowdown initiation, the intact loop pump speed decreased to 72% after about 8 seconds and remained constant. The broken loop pump speed diminished to 10% after 3.0 seconds and reached zero speed after about 27 seconds. 3 - Experimental limitations or shortcomings: LOBI experiments cover only the blowdown phase of a transient. The available downcomer gaps result in either unrealistic core flows or too large a hot-wall effect and unrealistic ECC delivery