Etydhv

God's in this universe inhabit a higher plane of existence. Their spirits inhabit large, humanoid forms upwards of 30ft, and watch over humanity by protecting it from outside threats. On occassion, a god must enter the mortal plane for various reasons. However, there are certain conditions that must be met. A god cannot simply possess a human, for their divine essence would destroy it not long after. Therefore, special human bodies must be constructed from scratch to contain the godly essence within and allow gods to walk among mortals. These bodies are made using Godtech, highly advanced technology that only gods have access to.

These bodies are 8ft tall and look human on the outside, but inward they are heavily modified, possessing advanced organs that humans do not. Inside these bodies is an organ called the core, which contains the soul of a god. These cores operate similar to a miniature nuclear reactor that powers the body and contains the divine essence inside it, preventing it from leaking out into the environment. These bodies are powerful and highly durable, and provide for almost instant regeneration. However, gods can still be killed if they have taken enough damage, which leads to a problem.

When a god dies, the core containing it's spirit ceases to function and becomes unstable, causing a rupture. The explosion alone would destroy a significant part of the surrounding environment. The true danger, however, is the divine radiation which would spread to a larger area due to factors such as wind currents. This radiation would spread further and further, causing damage to lesser creatures unable to withstand the power, killing hundreds or even thousands of people. Lesser still would be the rampant mutations of those touched by divine power, which can lead to disastrous consequences for them.

I need a way to limit the effects of a failed nuclear reactor from blowing up a huge area so that only the body is destroyed, while prevent the spread of divine radiation from turning the surrounding environment from becoming holy cherobyl. How can I make this happen?

So this is difficult to answer, because these are your nuclear reactors and your rules so you may handwave as you see fit.

That out of the way, you're effectively talking about a nuclear bomb, not a nuclear reactor:

The explosion alone would destroy a significant part of the surrounding environment.

This more or less implies that any attempts to confine or limit the spread of, uh, "theoactive" debris are doomed to failure because shielding and confinement devices in the original reactor will likely be shattered and flung far and wide.

In a civil nuclear disaster, major explosions are pretty rare... even the chernobyl explosion wasn't really destructive to the surroundings (and it was a steam explosion, not a nuclear one), but rather was a problem because it damaged the containment structure. The issue is radioactive dust and ash and smoke caused by fires, minor explosions and structural collapses in and around the failing reactor being lofted high into the altiude and forming a fallout plume. There are all sorts of theories about how you might make civil reactors safer, many of them dubious, most of them probably won't get field-tested, but none of them apply here because you're following the classic sci-fi trope of nuclear-reactor-go-boom.

So, to answer:

I need a way to limit the effects of a failed nuclear reactor from blowing up a huge area

A reactor won't. A bomb will. You need to choose which one you're dealing with here.

Edit: I can think of one radiation-releasing nuclear reactor which might go bang when it failed: an antimatter reactor. That, however, will cause almost no fallout because the radiation it releases is prompt EM and light unstable particles that rapidly decay.

Make the core a divine power receiver, like a radio receiver but receiving the energy needed for the god-tech bodies. Tesla was working on something like this at the Wardenclyffe Tower. Such a core would allow you to keep the divine soul (and the majority of its power) at a safe distance, in a heavenly or on an infernal plane.

When the body falls, only the power that it is currently receiving gets unleashed. This is enough to incinerate the body, but is not enough to decimate/contaminate the area or mutate the indigenous life.

For a fission reactor, you can mitigate their damage by cooling them, moderate or absorb the neutron flow, and reducing their mass below criticality.

Cooling: Pour water or chemical salts to conduct heat away from the critical mass. Water keeps the temperature ~100 C on the surface in contact with water. But, Water boils to steam, but as long as the water is replaced this prevents a full-blown meltdown from burning its way down in the Earth.

Moderating the Neutron Flow: Flood reactor with neutron absorbers like boron, water(again), titanium, molybdenum, or other more rare elements that absorb neutrons. This can starve the reactor and shut down the chain reaction. This works best while the nuclear core is still intact. If the fuel rods have melted down and are a puddle at the bottom of the reactor vessel this is harder to deal with. But, since you are likely cooling it, adding boric acid to the cooling water can reduce neutron flow.

Reducing their mass: Separate the fissionable material into small pieces below its critical mass and the reaction will shut down.

For a fusion reactor: Conceptually, adding iron or high atomic number atoms to the reactor would squelch the reactor, if one existed. Atoms like Iron and above are endothermic when they fuse, requiring more energy to fuse then they produce. Atoms below Iron on the periodic table are exothermic, producing more energy than required to fuse them.

So the way I see things is that you could basically have some Godtech that prevents the spreading of the radiation after the body explodes. Let's say for instance that when the body is created, some tech is included in the body such that when it is destroyed, molecules in the body, maybe an extra organ that contains a substance, binds to the God particles and renders them dormant. This could add a few extra layers to your world where non-God creatures could try to harness God particles in dormant form and make themselves Gods, etc.

Another option could be a celestial force that is specialized and tasked with recapturing the God particles. You could make it such that the particles are more like large gems that a creature could consume to mutate and each God "body" releases X number of them upon explosion that must be tracked down.

Really the world is your oyster here because there is no limit to how things can work for you. I personally like the idea of there being crystal like objects that are expelled on release because it introduces the chance for a black market that trades them, a task force to recover them, even a limit to the amount that exist that makes it so there are a finite number of God "bodies" that can be created at any one time.