Keeping Proper Track of Spent Fuel Pool Conditions
by Moderator
Lauren Gibson
Project Manager
Japan Lessons-Learned Directorate
Knowing
the water level is important because if the pool had boiled dry, it
would have damaged the fuel and added to the accident’s radiation
release. The Japanese plant’s staff did the right thing in assuming the
worst and making many attempts to add water to the pool. They even
dropped water from helicopters. If they had known the pools were OK,
however, they would have been able to focus on addressing the real
problem: the damaged reactors.
While
“spent fuel pool #4” at Fukushima Daiichi did keep its contents safe
during the March 2011 accident, no one could confirm that during the
accident. The plant’s staff and other experts, including the NRC, simply
didn’t have enough information to know what was going on in the pool.
Why not? There was no reliable way to measure the pool’s water level.
Knowing
the water level is important because if the pool had boiled dry, it
would have damaged the fuel and added to the accident’s radiation
release. The Japanese plant’s staff did the right thing in assuming the
worst and making many attempts to add water to the pool. They even
dropped water from helicopters. If they had known the pools were OK,
however, they would have been able to focus on addressing the real
problem: the damaged reactors.
This
experience led the NRC to order U.S. nuclear power plants to add
instrumentation to their spent fuel pools. That way, if an accident
occurs at a U.S. reactor, plant staff will be able to tell when the
spent fuel pool needed attention. Spent fuel pool instrumentation will
help plant staff properly prioritize their accident response and keep
the public safe.
U.S.
reactors already monitor a small fraction of the water level in the
spent fuel pool. However, this system may not work if power is lost, as
it was at Fukushima, and can’t provide advance warning of low water
levels.
The
NRC’s order requires U.S. reactors to be able to tell whether water is
at or above certain important levels. The highest level means enough
water is available for the normal cooling system to work. The second
level marks the level of water needed to protect someone standing next
to the pool from the fuel’s radiation. The lowest level is still enough
to cover the fuel, but the plant staff should begin adding more water to
the pool.
Of
course, water may be added—and most likely would be—prior to reaching
this point. The order also requires that plant staff must be able to
read these levels from somewhere away from the pool, such as in the
control room.
U.S.
reactors must install the new instruments no later than two refueling
cycles after they submit their plan to the NRC or by the end of 2016,
whichever comes first. All U.S. plants submitted their instrumentation
plans in February 2013. We’ve been reviewing the plans and we recently
issued interim staff evaluations. These documents give the plants
feedback so they can continue on the right track for implementing the
order.
The
evaluations also ask plants for additional information we need to
complete our review. While the agency’s final approval is yet to come,
the interim evaluations give plants the confidence to order equipment
and move forward with installing the instruments. We’ll provide the
plants a final staff evaluation when we can conclude that they’ll comply
with the order by the deadline by following their plan. We’ll continue
inspecting plants to confirm they’ve finished complying with the order.
Our website’s Japan Lessons Learned section has a page with more information about the order and related guidance.
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