Grey rods can be inserted in the core for most of the cycle to control the radial power distribution in the core, or they may reside out of the core and only inserted and withdrawn to make quick small changes to the power level. The Russians have used Dy in the form of Dysprosium titanate as a control rod material.
A rhetorical question is a device used to persuade or subtly influence the audience. It's a question asked not for the answer, but for the effect. Oftentimes, a rhetorical question is used to emphasize a point or just to get the audience thinking. Sometimes, a rhetorical question is asked with the asker already knowing the answer, such as the weather example.
rhetorical device. A rhetorical device is a use of language that is intended to have an effect on its audience. Repetition, figurative language, and even rhetorical questions are all examples of rhetorical devices.