The second experiment series included four SBLOCA tests with break in one cold leg of PACTEL. Two break sizes (2 and 4 mm or 0.5 and 2%, respectively) were used. The tests also included studies of primary system depressurization and reproducibility of the phenomena (one test was repeated twice with the same initial and boundary conditions). The PACTEL operators depressurized the primary system by opening a pressurizer relief valve. The core power in the tests was 80 kW corresponding to about 1.8% of the scaled thermal power of the reference reactor. In all tests, only the CMT provided ECC water to the primary loop.

The primary pressure used in the tests was again lower than the nominal operation pressure of PACTEL. The maximum operation pressure of the passive accumulator limited the maximum experiment pressure to 3.8 MPa. The experiment loop geometry in the second series have been described in reference [3]. Munther [4] and Munther et al. [7, 8, 9] have published the results of these experiments. Since one loop of PACTEL was equipped with a different steam generator model the tests run with only two loops in operation. The main results of the second test series can be summarised as the following:

• only a limited period of single phase natural circulation through the cold leg pressure balancing line to the CMT was observed,

• the CMT level started to drop immediately after the opening of the break,

• the saturated water layer formed to the CMT remained thin,

• the ECC water injection was stopped totally during injection, due to rapid vapour condensation in the CMT,

• two types of mixing in the CMT during condensation was observed: complete mixing or only the mixing of the uppermost water layer in the tank.

There was still water in the CMT when the tests were terminated after about 2000 seconds from the opening of the break. During the rapid condensation period water level in the core simulator dropped close to the top of the core. However, also in these test no core heat-up occurred.

In 1996, a new project for the investigation of passive safety injection systems of ALWR’s begun. The project, entitled "Investigation of Passive Safety Injection Systems of Advanced Light Water Reactors", was a part of the INNO cluster of the European Commission Nuclear Fission Safety (NFS-2) Programme. The project received funding from the European Commission. The project had four partners: VTT Energy and Lappeenranta University of Technology from Finland, AEA Technology from the UK and the University of Pisa from Italy. VTT and LTKK were responsible for the experiments in PACTEL and for the APROS simulations of selected experiments. AEA Technology and University of Pisa were responsible for simulation of selected experiments with RELAP5 and CATHARE codes. The general objectives of the new project were:

• to provide new and independent information about passive safety injection system performance,

• to contribute to a public data base for the users and developers of thermal-hydraulic computer codes on the phenomenological behaviour of PSIS’s in LOCA conditions, and

• to identify the accuracy, uncertainties and limitations of thermal-hydraulic computer codes in the modelling of passive safety injection system behaviour.

The next sections summarise the main results of the three series (called here the third, fourth and fifth Passive Safety Injection experiment series) of the EC funded programme.