So I added some XML script to allow the Exocomp units to scrub the radiation, but in trials, it says it will take over 2 million turns to scrub the radiation. Any Ideas?

<BuildInfo>
<Type>BUILD_SCRUB_FALLOUT</Type>
<Description>TXT_KEY_BUILD_SCRUBIT</Description>
<Help/>
<PrereqTech>NONE</PrereqTech>
<iTime>300</iTime>
<iCost>25</iCost>
<bKill>0</bKill>
<ImprovementType>NONE</ImprovementType>
<RouteType>NONE</RouteType>
<EntityEvent>ENTITY_EVENT_IRRIGATE</EntityEvent>
<FeatureStructs>
<FeatureStruct>
<FeatureType>FEATURE_FALLOUT</FeatureType>
<PrereqTech>NONE</PrereqTech>
<iTime>300</iTime>
<iProduction>0</iProduction>
<bRemove>1</bRemove>
</FeatureStruct>
</FeatureStructs>
<HotKey>KB_S</HotKey>
<bAltDown>0</bAltDown>
<bShiftDown>0</bShiftDown>
<bCtrlDown>0</bCtrlDown>
<iHotKeyPriority>1</iHotKeyPriority>
<Button>,Art/Interface/Buttons/Builds/BuildScrubFallout.dds,Art/Interface/Buttons/Actions_Builds_LeaderHeads_Specialists_Atlas.dds,2 ,8</Button>
</BuildInfo>

I remember there was some bug in BtS that caused builds to give a time very long (I think 2^8 - 1, the size of the largest regular int in 32-bit C++) but I don't remember the details. It also might also relate to the damage caused by radiation; non-combat ships function a little weird in it but if the game thinks the unit will be killed before it completes it may do something like that.

hmm...

I did make the exocomps immune to the radiation, So I doubt it is that. I wonder about that bug. I'll keep looking, thanks.

Please let me know if you get this unit to work, I've been thinking about a similar unit for the B5 mod we are working on.

Have you tried giving the unit a combat value so there is something for the radiation to damage but making the unit -100 % defence against all combat vessels?

Edit:-
I've added my own version of a Radiation Scrubber to the B5 Mod which is basically a construction ship that can enter a radiation feature and can only perform the clean up radiation function. The unit is destroyed before it completes the task but a second unit completes what the first one started in one turn. What I would like to do in our Mod is have a Radiation Shielding Promotion that the Radiation Cleaner can have that reduces the amount of damage done by the feature giving the unit a little more chance of completing the clean up before it is destroyed. Unfortunately none of the Promotions give this function. I could add the always heal function but then it would heal when moving outside of a radiation tile which I wouldn't want it to do. So it's either make the unt immune as you have done or add the Always heal function. If you have any ideas that offer a different approach I'm willing to explore them.

MetaPhasic Shields:

<PromotionInfo>
<Type>PROMOTION_METASHIELD</Type>
<Description>TXT_KEY_PROMOTION_METASHIELD</Description>
<Sound>AS2D_IF_LEVELUP</Sound>
<LayerAnimationPath>NONE</LayerAnimationPath>
<PromotionPrereq>PROMOTION_WOODSMAN3</PromotionPrereq>
<PromotionPrereqOr1>NONE</PromotionPrereqOr1>
<PromotionPrereqOr2>NONE</PromotionPrereqOr2>
<TechPrereq>TECH_EXOCOMP</TechPrereq>
<StateReligionPrereq>NONE</StateReligionPrereq>
<bLeader>0</bLeader>
<bBlitz>0</bBlitz>
<bAmphib>0</bAmphib>
<bRiver>0</bRiver>
<bEnemyRoute>0</bEnemyRoute>
<bAlwaysHeal>0</bAlwaysHeal>
<bHillsDoubleMove>0</bHillsDoubleMove>
<bImmuneToFirstStrikes>0</bImmuneToFirstStrikes>
<iVisibilityChange>0</iVisibilityChange>
<iMovesChange>0</iMovesChange>
<iMoveDiscountChange>0</iMoveDiscountChange>
<iAirRangeChange>0</iAirRangeChange>
<iInterceptChange>0</iInterceptChange>
<iEvasionChange>0</iEvasionChange>
<iWithdrawalChange>0</iWithdrawalChange>
<iCargoChange>0</iCargoChange>
<iCollateralDamageChange>0</iCollateralDamageChange>
<iBombardRateChange>0</iBombardRateChange>
<iFirstStrikesChange>0</iFirstStrikesChange>
<iChanceFirstStrikesChange>0</iChanceFirstStrikesChange>
<iEnemyHealChange>0</iEnemyHealChange>
<iNeutralHealChange>0</iNeutralHealChange>
<iFriendlyHealChange>0</iFriendlyHealChange>
<iSameTileHealChange>0</iSameTileHealChange>
<iAdjacentTileHealChange>0</iAdjacentTileHealChange>
<iCombatPercent>0</iCombatPercent>
<iCityAttack>0</iCityAttack>
<iCityDefense>0</iCityDefense>
<iHillsAttack>0</iHillsAttack>
<iHillsDefense>0</iHillsDefense>
<iKamikazePercent>0</iKamikazePercent>
<iRevoltProtection>0</iRevoltProtection>
<iCollateralDamageProtection>0</iCollateralDamageProtection>
<iPillageChange>0</iPillageChange>
<iUpgradeDiscount>0</iUpgradeDiscount>
<iExperiencePercent>0</iExperiencePercent>
<TerrainAttacks/>
<TerrainDefenses/>
<FeatureAttacks/>
<FeatureDefenses>
<FeatureDefense>
<FeatureType>FEATURE_FALLOUT</FeatureType>
<iFeatureDefense>99</iFeatureDefense>
</FeatureDefense>
<FeatureDefense>
<FeatureType>FEATURE_JUNGLE</FeatureType>
<iFeatureDefense>99</iFeatureDefense>
</FeatureDefense>
</FeatureDefenses>
<UnitCombatMods/>
<DomainMods/>
<TerrainDoubleMoves/>
<FeatureDoubleMoves/>
<UnitCombats>
<UnitCombat>
<UnitCombatType>UNITCOMBAT_RECON</UnitCombatType>
<bUnitCombat>1</bUnitCombat>
</UnitCombat>
<UnitCombat>
<UnitCombatType>UNITCOMBAT_LIGHT</UnitCombatType>
<bUnitCombat>1</bUnitCombat>
</UnitCombat>
<UnitCombat>
<UnitCombatType>UNITCOMBAT_HEAVY</UnitCombatType>
<bUnitCombat>1</bUnitCombat>
</UnitCombat>
</UnitCombats>
<HotKey/>
<bAltDown>0</bAltDown>
<bShiftDown>0</bShiftDown>
<bCtrlDown>0</bCtrlDown>
<iHotKeyPriority>0</iHotKeyPriority>
<Button>,Art/Interface/Buttons/Promotions/Woodsman1.dds,Art/Interface/Buttons/Promotions_Atlas.dds,6,6</Button>
</PromotionInfo>