NUREG/BR-0523

April 2015

REGIO

RESPO

CENT

PORTABLE MITIGATION STRATEGIES

LOSS OF 

OFFSITE 

POWER

REGIONAL 

RESPONSE 

CENTERS

MITIGATING STRATEGIES 

RESOURCES

You can find more information on mitigating 

strategies and related guidance at the NRC 

website (www.nrc.gov) in the Japan Lessons 

Learned section.

www.nrc.gov/reactors/operating/

ops-experience/japan-dashboard/

mitigating-strategies.html

REGIONAL 

RESPONSE 

CENTERS

INSTALLED MITIGATION STRATEGIES

LOSS OF 

OFFSITE 

POWER

OVERVIEW

The March 2011 Fukushima accident 

underscored how important prior planning is 

when it comes to safely handling extreme events 

at a nuclear reactor. The NRC continues to 

conclude U.S. plants can survive many scenarios, 

such as loss of offsite power or flooding. After 

Fukushima, however, the NRC ordered every 

U.S. commercial reactor to have strategies for 

dealing with the long-term loss of normal safety 

systems. Instead of figuring out which events 

might happen, the order focused on significantly 

improving the plants’ flexibility and diversity in 

responding to extreme natural phenomena, such 

as severe flooding and earthquakes.

The plants’ strategies must protect or restore 

key safety functions indefinitely in the case of an 

accident. The strategies focus on keeping the 

reactor core cool, preserving the containment’s 

barrier that prevents or controls radiation 

releases, and cooling the spent fuel pool. Plants 

with more than one reactor must be able to do 

this for every reactor on the site at the same time.

The strategies must protect the plant 

indefinitely, so plants may need to bring in 

additional equipment or resources. The order 

reflects this by having three phases with 

different requirements.

The plants have all submitted a plan for what 

they intend to do and use in each of these 

phases. The plans must also explain how the 

plants will have everything in place by the end 

of 2016. The NRC reviewed those plans and 

has issued interim staff evaluations, which 

let the licensee know whether the NRC thinks 

the plants are on the right track. The NRC will 

inspect the plants throughout this process to 

ensure the strategies will get the job done. 

The agency website’s Japan Lessons Learned 

section has more information about the 

mitigating strategy requirements and related 

guidance.

Mitigating Strategies: 

Safely Responding to 

Extreme Events

PHASE 1

PHASE 2

PHASE 3
REGIONAL 

RESPONSE 

CENTERS

MITIGATING STRATEGIES OVERVIEW

LOSS OF 

OFFSITE 

POWER

REGIONAL 

RESPONSE 

SUPPLIES FROM 

OFFSITE AND 

REGIONAL 

RESPONSE 

CENTERS

PORTABLE

BACKUP PUMPS, 

HOSES AND DIESEL 

GENERATORS

INSTALLED 

BATTERY BANKS

AND PUMPS

PHASE 1: 

This begins with the accident or event. 

At this point, the plants will use installed 

equipment, such as steam-driven pumps 

or battery-powered systems, to protect or 

restore safety functions. The plants must 

be able to shift to the second phase before 

the installed equipment is exhausted. 

PHASE 2: 

The strategies’ second phase uses portable 

equipment that’s stored onsite, such as additional 

pumps or generators. This equipment is stored 

near the reactors and reasonably protected 

from severe weather or earthquakes. The Phase 2 

resources are brought to the reactors and 

connected to maintain the safety functions. During 

this phase, plants would also be able to transfer 

diesel fuel from onsite tanks to the places where 

it’s needed to run generators and other equipment. 

Plants have to ensure the third phase can take over 

before the portable equipment runs out of supplies.

PHASE 3: 

The final phase starts 

when outside support 

arrives. The nuclear 

energy industry has two 

response centers to provide 

additional equipment and 

other resources to any U.S. 

reactor within 24 hours. 

One center is in Memphis 

and the other is in Phoenix.