Can you find a possible way to MAKE a fusion reactor melt down or explode?

The simplest way with 20th/21st century technology is to sabotage the dampening rods, aka fuel rods. If they will not go into place to check or halt the reaction, nothing will prevent a meltdown.

Since 'containment fields', first designed for Star Trek to keep the antimatter away from solid objects, were created for that particular purpose, you would first have to determine what kind of energy system you are using and WHY it needs Containment Fields.

Containment Fields do not actually exist but are designed in fiction based upon what you want to contain and why. Therefore you must first have the what and why, and what problems you want to prevent before you can decide what will go wrong.

First find out how to make a fusion reactor.What is for sure is that the working fluid will be a form of matter needing containment with ultra strong magnetic fields so the field would be the thing to bust'

Now you be careful or you will get your collar felt.

EDIT' re your remarks about tritium etc.

When I was in the nuclear business I used to travel from our place in Berkshire to London each week and usually with a fellow in fusion researc: me to study metallurgy and him to do Math's to do with fusion research.His tales just about the maths involved turned my hair several colour shades paler.So far as I know the only contiuous fusion reactors are inside stars and the like.(all in 1960's)

So what this means is that you can write your story without fear that someone can take the Mickey.

Get on with it and god luck.

Take a nap while 10kg of Uranium undergoes fission.