Whoever RESOLVED this lied they linked it to a similar but not exactly the same issue. Mine only involves 2 tnt carts and are not activated with an activator rail they hit a wall and explode, in multiplayer the pitch also increases until the boom.
It can be done in both creative and survival
If you place 3 regular rails in a straight line, and then place a detector rail facing a different direction so that it connects to the 3rd rail and turns. Then 4 powered rails, but not powered, then another dectector, than another 4 powered rails but not powered and then a 3 by 3 wall of obsidian stopping the end of the rails. Do this on a flat map preferably and warning it crashes or severely lags out your game. Then go to where the track turns on the regular rail. Place a minecart with TNT in it and then look at the rail on the bottom and place another. This should place 2 but only look like 1 minecart with tnt in it. Then push both of them with your player and when they hit the obsidian it may take a few seconds but it will create a Massive nuke affect that doesn't destroy any blocks and looks like a square with patterns in it similar to other nuke mods out there. This is a fresh vanilla minecraft. there are some videos on youtube about it. THIS BELOW IS THE CRASH ERROR I GOT, IM RUNNING WINDOWS 8 ON A NEWER COMPUTER. DELL.

Minecraft has crashed!
----------------------

Minecraft has stopped running because it encountered a problem; Ticking entity

A full error report has been saved to C:\Users\Matthew\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-12_14.23.58-client.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT 70a51cd5 --------
Full report at:
C:\Users\Matthew\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-12_14.23.58-client.txt
Please show that file to Mojang, NOT just this screen!

Generated 1/12/13 2:23 PM

– Head –
Stacktrace:
at java.util.Arrays.copyOf(Unknown Source)
at java.util.ArrayList.grow(Unknown Source)
at java.util.ArrayList.ensureCapacityInternal(Unknown Source)
at java.util.ArrayList.add(Unknown Source)
at aph.a(SourceFile:24)
at apf.b(SourceFile:74)
at lv.J(SourceFile:760)
at lv.y(SourceFile:349)
at lv.l_(SourceFile:272)
at qd.l_(SourceFile:64)
at yn.a(SourceFile:1312)
at yn.g(SourceFile:1290)

– Entity being ticked –
Details:
Entity Type: Item (qd)
Entity ID: 37855
Name: item.tile.quartzBlock.default
Exact location: 345.56, 46.13, -83.87
Block location: World: (345,46,-84), Chunk: (at 9,2,12 in 21,-6; contains blocks 336,0,-96 to 351,255,-81), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
Momentum: -0.01, -0.00, 0.01
Stacktrace:
at yn.h(SourceFile:1197)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [azu['BVGamer'/20216, l='MpServer', x=297.43, y=93.52, z=-38.05]]
Chunk stats: MultiplayerChunkCache: 441
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: World: (203,4,157), Chunk: (at 11,0,13 in 12,9; contains blocks 192,0,144 to 207,255,159), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 36460 game time, 5995 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: ~_ERROR~ OutOfMemoryError: Java heap space
Retry entities: 0 total; []
Stacktrace:
at azr.a(SourceFile:281)
at net.minecraft.client.Minecraft.b(SourceFile:1865)
at net.minecraft.client.Minecraft.run(SourceFile:534)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 13w02b
Operating System: Windows 8 (amd64) version 6.2
Java Version: 1.7.0_10, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 120037488 bytes (114 MB) / 954466304 bytes (910 MB) up to 954466304 bytes (910 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 1823230 (102100880 bytes; 97 MB) allocated, 1823230 (102100880 bytes; 97 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
LWJGL: 2.4.2
OpenGL: GeForce GT 620/PCIe/SSE2 GL version 4.2.0, NVIDIA Corporation
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: 205271 (11495176 bytes; 10 MB) allocated, 205271 (11495176 bytes; 10 MB) used

java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Unknown Source)
at java.util.ArrayList.grow(Unknown Source)
at java.util.ArrayList.ensureCapacityInternal(Unknown Source)
at java.util.ArrayList.add(Unknown Source)
at aph.a(SourceFile:24)
at apf.b(SourceFile:74)
at lv.J(SourceFile:760)
at lv.y(SourceFile:349)
at lv.l_(SourceFile:272)
at qd.l_(SourceFile:64)
at yn.a(SourceFile:1312)
at yn.g(SourceFile:1290)
at yn.h(SourceFile:1197)
at net.minecraft.client.Minecraft.l(SourceFile:1318)
at net.minecraft.client.Minecraft.K(SourceFile:573)
at net.minecraft.client.Minecraft.run(SourceFile:525)
at java.lang.Thread.run(Unknown Source)
— END ERROR REPORT 9c88a779 ----------