var radiusSelectInteraction = new ol.interaction.Draw({
    source: circleLayer.getSource(),
    type: 'Circle',
    features: circleFeatures
});

radiusSelectInteraction.on('drawend', function () {
    circleFeatures.forEach(function(feature) {
        ....
    });
});

radiusSelectInteraction.on('drawstart', function () {
    circleLayer.getSource().once('addFeature', handleAddFeature);
});

function handleAddFeature(evt) {
    var feature = evt.feature;
    ....
}