3. DESCRIPTION
The Jet Impingement Tests (JIT) project at Marviken constitutes the fourth large scale reactor safety experiment conducted at the Marviken Power Station and is referred to as the Marviken-IV-JIT project. It was established in March 1980. The testing started in September 1980, and continued for about one year.
The behaviour of large two-phase, critical flow jets as they exhaust beyond the choking plane is of interest in nuclear power plant design and safety analyses. To prevent the jet resulting from a loss-of-coolant accident (LOCA) from becoming destructive to surrounding equipment, special design features are included to protect against:
- jet impingement on surfaces, components, supports, instrumentation, cables etc, and
- pipe whip due to the reaction forces from the jet acting on the pipe, and
- erosion on surrounding surfaces and equipment.
Various features such as structural supports, restraints, and isolation barriers are analyzed based on conservative predictions of the jet loads.
In the 1970s, a need for more extensive experimental information about two-phase jet behaviour has led to the performance of a number of small scale jet impingement experiments at different places throughout the world. In the beginning of 1980 a group of organizations from different countries agreed to jointly undertake a comprehensive program aimed at increasing their knowledge about jet behaviour. This program provided all participants with information from different small scale jet behaviour experiments. And other related projects performed by the participants (in kind contributions). To quantify the actual loads from large scale jets, and to provide a basis for scaling data from laboratory experiments, the group agreed to jointly perform a complementary series of large scale tests in the Marviken testing facility. The results of these tests are summarized herein.
The principal objective of the JIT project was to provide experimental data from a large scale facility on the behaviour of two phase jets as they exhaust beyond the choking plane into the containment. These data, together with data from small scale experiments, would provide individual participants the information necessary to develop or verify analytical or empirical models used in estimating jet impingement loads in the safety analysis of nuclear power generating stations.
Both jets with a free expansion and jets directed towards instrumented targets were included in the test program. The free expansion tests provided information about the axial and radial pressure distributions in the jet for different flow regimes, and the jet impingement tests focused on the determination of the total target forces and the force distribution on targets in the jet stream. Emphasis was placed on the determination of the quasi-steady behaviour of the jets; in addition, some data were obtained on dynamic aspects of the jet impingement tests.
A total of twelve tests were performed, all with an initial pressure in the reactor vessel of 5 Mpa. Breaks were simulated through nozzles with diameters of 200, 299 and 509 mm. Water line breaks, giving flow regimes from subcooled water through saturated water and steam, as well as steam line breaks were simulated.
Because the JIT tests required an accurate determination of the critical mass flow from the discharge pipe, they were a logical extension of the previous series of critical flow tests at Marviken (Ref 1). In fact, the results of the present JIT experiments may also prove useful to those interested in additional critical flow data from large diameter pipes.
The organizations represented were from Canada, Germany, Finland, France, Italy, Japan, the Netherlands, Sweden and the United States.
The official documentation of the project is given in the reports and appendices, the titles of which are listed on the back cover.
