A nuclear elemental is simply a toxic fire elemental. Fire elementals aren't really that dangerous, neccessarily. However, as soon as that fire elemental gets corrupted (I think that's the metamagic), its Energy Aura, Energy Attack, and Engulf attacks change from (Fire) to (Radiation). Street Magic kinda tells us a little about radiation damage; how it's treated as physical damage and how it ignores armor. That in and of itself is really dangerous.
But it gets worse.
Enter Arsenal, on the bottom of page 167, where it starts refining radiation damage. It remains physical damage that ignores armor, but now it's also treated as a pathogen, as per Augmentation, page 129.
There are 4 forms of radiation listed in Arsenal; Mild, Moderate, Severe, and Deadly. Now all of them have Speeds that also have a timer next to them like pathogens, but unlike pathogens there's no minimum amount of intervals. I'd imagine that means they keep going until actual medical care is given, but that's not the important part.
The important part is how it states
QUOTE (Arsenal, pg 168)
The long-term effects of radiation hazards, contamination, and cumulative irradiation on characters uses the same mechanics given for pathogens...
(emphasis added). This means that even if you reduce the power of the attack down to 0 and take no damage from the attack, since you were subject to said radiation, it starts to accrue. And as soon as you accrue Deadly levels of radiation, even if you took no damage from the radiation, you still enter a state known as the walking ghost phase, which means you have 1-4 days before you enter into QUOTE (Arsenal, pg. 169)
... general organ failure and total metabolic shutdown.
One of the very interesting things about Energy Aura is how, irregardless of the Force of the elemental, it deals a set +4 DV, and if you strike it with a melee attack, you're subject to a 4 DV attack of said element. 4 DV with 0 penetration is exactly like Mild Radiation Poisoning. So when you hit this F1 Nuclear Spirit, you have to save vs. 4 Radiation damage. Even if you reduce the DV to 0, since you were subjected to Mild Radiation Poisoning, you're still mildly irradiated. Additional attacks will accrue the radiation poisoning until, after who knows how many hot sources you're exposed to, you hit Severe Radiation Poisoning, and, even though you haven't taken damage, you have 1-4 days to live.
Now normally it'd be easy to stay away from these things, but we can do mean things like have them on the astral plane, moving their 5 kM/CT to keep up with/catch up to the group, then materialize (in 2 IPs, IIRC) right beside the players. Most people would just smack it, and that would induce radiation poisoning. Or, you could have them posess other creatures, and have said creatures get into melee range.
The point being, it's easy to use an elemental that inflicts radiation damange to induce radiation poisoning in a group.
Let's take a F6 or F8 Nuclear Elemental's Energy Attack (Radiation). A f6 would take 1 or 2 (maybe 3 if you're feeling generous) to reach Deadly Radiation Poisoning, since 6 DV is slightly above Severe Poisoning. And that's ignoring net hits increasing DV. On the other hand, a F8 Nuclear Elemental's base DV is already 8, wich starts us out in Deadly Radiation Poisoning levels.
Considering a magic 1 toxic shaman can summon f1 Nuclear spirits, and it only takes a magic 4 shaman to summon f8 nuclear spirits, I think the world just got a lot more dangerous.
Interesting, no?