Basic Mechanics:

If you pass Y level=50 you get Radiation unless you have a form of radioactive protection
(Anti-Rad, Anti-Rad Gum or a Gas Mask)
Zombies are Buffed, they are much faster now, and once they spot you, they will follow you for ≈200 blocks.
Respawning grants you 1 and a half minutes of Anti-Rad.

Loot Pool Changes:

Oak Leaves will have a 10% chance of dropping Radioactive Leafs when destroyed.
Lapis Ore now has a 30% chance of dropping Plutonium Ore when mined.
Chickens now have a 10% chance of dropping Leather when killed.
Zombies now have a 25% chance of dropping a Potato and a 5% chance of dropping Flint when killed.
Fully grown Grass now has a 1% chance of dropping a Carrot when cut.
Spiders now have a 10% chance of dropping an Egg when killed.
Creepers have a 2% chance of dropping a Special Music Disk when killed.

It also adds multiple new structures to the world like cities, new villages, 2 new types of mineshaft, new temples and even a city metro!

This ModPack Includes:

Mods:

-JEI

-Adventure Plus Structures

-After War Mod

-Better Mineshafts

-Creative Core

-Enchanced Visuals

-Lost Cities

-Music Player

-Optifine

-Repurpused Structures

-Sound Filters

-TumbleWeed

-U Team Core

The Texture Packs:

-Apocalyptic Skies

-Modified Fallout Pack

-Tissou's Zombie Pack

Nuclear Fallout Pack