BWR containment is a complex system that includes many elements which affect each other’s operation. There is a number of safety important scenarios, where containment pressure suppression function operation can be affected by (i) stratification and mixing phenomena, (ii) interactions with emergency core cooling system (ECCS), spray, residual heat removal (RHR) system, filtered containment venting system (FCVS), and (iii) overall water distribution between containment compartments. Such scenarios include (i) interplay between pool behaviour, diagnostics and operator procedures that can affect activation and performance of ECCS and containment spray systems; (ii) small LOCA; (iii) station blackout; (iv) leaking safety relief valve; (v) LOCA with broken blowdown pipe; (vi) severe accidents; and (vii) steam line breaks inside the radiation shield.
The main aim of the project is to design a spray test facility, start development work of spray calculation models and run pre-test simulations. In addition, behaviour of SRV spargers and RHR nozzles will be studied both experimentally in the PPOOLEX facility and computationally with the help of GOTHIC code.
Summary of the experimental work at LUT:
In 2015, LUT will design spray systems to be installed in the drywell and wetwell compartments of the PPOOLEX facility. Facility modifications and spray installations are started in the second half of the year. A single spray nozzle of the selected design will be tested in a separate effect test facility and its main characteristics will be determined, for example, with the help of Wire Mesh Sensor and Particle Image Velocimetry measurements and high speed cameras. Also experiments with SRV spargers and RHR nozzles will be carried out in the PPOOLEX facility. Data on mixing of a thermally stratified water volume in a pressure suppression pool at different conditions of steam injection through a sparger and water injection through a RHR nozzle will be provided to KTH. The experiments will be done according to a detailed test plan written by KTH on the basis of pre-test calculations.
Summary of the modelling work at VTT:
In 2015, KTH will contribute to selection of spray nozzle designs to be used in the PPOOLEX facility. KTH will also perform pre-test analysis and simulations for selection of operational regimes and test procedures. Finally, post-test analysis and validation with GOTHIC code will be carried out. Further development of EHS/EMS models for spargers and RHR nozzles will be pursued to simulate dynamics of the pool mixing and stratification. The models will be validated against respective separate effect tests.
Summary of the modelling work at KTH:
In 2015, the single spray nozzle experiments performed at LUT are modelled with CFD calculations. The spray droplets are described by using the Discrete Particle Model of the ANSYS Fluent code. Suitable model for the spatial distribution of the droplets is chosen and the size distributions and initial velocities are determined by using results of the experiment. Sub-model for the evaporation and condensation of water droplets is tested and improved. The spray model is validated by performing calculations of the single spray nozzle experiments of LUT. The results are used for the modelling of the PPOOLEX spray experiments. New detailed CFD model is constructed for the PPOOLEX facility with spray systems in the dry and wet well. Two preliminary test cases are chosen for CFD simulation in co-operation with LUT and KTH.