use the timers, that are allready running instead of allocating a new one every tick

technic/machines/HV/nuclear_reactor.lua

@@ -319,7 +319,7 @@ minetest.register_node("technic:hv_nuclear_reactor_core_active", {
 		local meta = minetest.get_meta(pos)
 		
 		-- Connected back?
-		if meta:get_int("HV_EU_timeout") > 0 then return end	
+		if meta:get_int("HV_EU_timeout") > 0 then return false end
 		
 		local burn_time = meta:get_int("burn_time") or 0
 
@@ -329,12 +329,11 @@ minetest.register_node("technic:hv_nuclear_reactor_core_active", {
 			technic.swap_node(pos, "technic:hv_nuclear_reactor_core")
 			meta:set_int("structure_accumulated_badness", 0)
 			siren_clear(pos, meta)
-			return
+			return false
 		end
 		
 		meta:set_int("burn_time", burn_time + 1)
-		local timer = minetest.get_node_timer(pos)
-        	timer:start(1)
+		return true
 	end,
 })
 

technic/machines/register/generator.lua

@@ -135,7 +135,7 @@ function technic.register_generator(data)
 			local meta = minetest.get_meta(pos)
 			
 			-- Connected back?
-			if meta:get_int(tier.."_EU_timeout") > 0 then return end
+			if meta:get_int(tier.."_EU_timeout") > 0 then return false end
 			
 			local burn_time = meta:get_int("burn_time") or 0
 
@@ -143,7 +143,7 @@ function technic.register_generator(data)
 				meta:set_int(tier.."_EU_supply", 0)
 				meta:set_int("burn_time", 0)
 				technic.swap_node(pos, "technic:"..ltier.."_generator")
-				return
+				return false
 			end
 
 			local burn_totaltime = meta:get_int("burn_totaltime") or 0
@@ -158,8 +158,7 @@ function technic.register_generator(data)
 				"image[4, 1;1, 1;default_furnace_fire_bg.png^[lowpart:"..
 				(percent)..":default_furnace_fire_fg.png]"..
 				"list[current_player;main;0, 5;8, 4;]")
-			local timer = minetest.get_node_timer(pos)
-	        	timer:start(1)
+			return true
 		end,
 	})