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Saturday, July 16, 2011
Reactor stress tests heavy on redundancies
The Nuclear and Industrial Safety Agency on Friday submitted the outline of a two-stage stress test for the nation's reactors, focusing on four categories, including earthquakes, tsunami, loss of power sources and loss of cooling systems for fuel rods.
According to the outline submitted to the Nuclear Safety Commission, the first stage will target reactors currently out of operation for regular inspections and maintenance.
The government will decide if the reactors are able to endure severe events beyond the current safety standards in terms of the four categories.
For the second stage, tests will be conducted on all reactors, including those covered by the first stage. But there are exceptions — the reactors at the Fukushima No. 1 and No. 2 plants as well as those now being decommissioned and do not have nuclear fuel rods inside.
The second stage will also check the reactors' endurance levels in the four categories.
The tests are aimed at identifying what level of tsunami or earthquake would cause severe damage to fuel rods.
There are numerous redundancies in the tests, according to NISA.
A NISA official explained that the difference between the first and second tests is that the first is designed to make sure "fuel rods will not be damaged if something beyond expectation based on the design standard" were to occur, while the second is to check how much stress a reactor can take and for how long before it breaks down.
The stress test outline will be reviewed by the NSC, which has to approve it.
If the tests go ahead, utilities will check their reactors based on the outline and submit reports to NISA, which will review them.
NISA said once the test plan is approved, utilities can submit the reports for the first stage when they are ready.
The power companies can't fire their halted reactors back up unless they finish the first stage and receive approval.
For the second stage, NISA expects the utilities to submit reports by the end of the year.