> Does anyone knows if using microwaves might possibly affect the nutritional value of the food?

Cooking in general affects the nutritional value of food—some nutrients are easier to absorb when cooked, so cooking effectively increases their amount, while other nutrients are destroyed [0] [1]. But given that you're probably cooking your food anyways, there's nothing specific to microwaves here.

Microwaves might actually be slightly better than other cooking methods here, since they produce a lower heat that's less likely to destroy nutrients, but the cooking method has such a minor effect that I wouldn't really worry about it either way.

> Or if radiation can leak and affect you body if you stand very close to it while it’s running.

Microwaves are classified as non-ionizing radiation [2], so their main effect is just heating things up. So if you're standing near a microwave and your body starts heating up, then something bad is happening; otherwise, you're probably fine.

The only health risk from microwaves (aside from a hypothetical accident involving someone being cooked inside one like a rotisserie chicken) is cataracts [3]. But this usually only affects radio technicians, who put their heads beside much bigger and much more powerful microwave emitters than a domestic microwave oven. And even cataracts are only due to the heating effect.

[0]: https://en.wikipedia.org/wiki/Cooking#Effects_on_nutritional...

[1]: https://www.healthline.com/nutrition/cooking-nutrient-conten...

[2]: https://en.wikipedia.org/wiki/Non-ionizing_radiation

[3]: https://en.wikipedia.org/wiki/Cataract#Radiation