* Rainfall boosts hydro output along Tennessee River
* Nuclear reactors shut after losing outside power (Updates power status at nuclear plant)
HOUSTON, April 27 (Reuters) - Severe storms and tornadoes moving through the U.S. Southeast dealt a severe blow to the Tennessee Valley Authority on Wednesday, causing three nuclear reactors in Alabama to shut and knocking out 11 high-voltage power lines, the utility and regulators said.
Governors in Alabama, Arkansas and Tennessee each declared a state of emergency as more than 20 deaths were blamed on a recurring round of severe storms this week moving eastward across the southern United States. [ID:nN27120833]
All three units at TVA's 3,274-megawatt Browns Ferry nuclear plant in Alabama tripped about 5:30 EDT (2230 GMT) after losing outside power to the plant, a spokesman for the U.S. Nuclear Regulatory Commission said.