FRANKFURT, March 12 (Reuters) - Switzerland's Beznau 1 nuclear reactor will shut for 120 days from March 13 for a long maintenance outage with fuel rod exchanges, operator Axpo said on Thursday.
It said that during the shutdown, which was previously planned, it would invest 700 million Swiss francs ($698.74 million) to carry out checks and tests and work on three projects during the standstill.
These would be new emergency power supply, a new plant information system, and the exchange of a lid at the reactor pressure vessel.
The measures are meant to make the plant fit for running well beyond the year 2020. "They will raise the high safety levels of the plant and improve its availability," Axpo said.
The 365 megawatts (MW) plant last shut between April 1-14 of 2014.
Axpo also said that Block 2 at Beznau, another 365 MW unit, would close in August to undergo similar measures.
The emergency power sets would offer supply independently, in case of flooding or earthquakes, replacing current emergency provisions secured by a hydroelectric plant, and would be housed in a building that could withstand plane crashes.
The exchange of the lid was not made necessary by any problems but because experiences with the same equipment in similar reactors had shown that maintenance costs over time outstripped the cost of replacements.
Germany and Switzerland are about to begin the spring and summer maintenance season for nuclear stations, which can take big chunks of supply out of the wholesale market.
In Germany, RWE's Gundremmingen B will go offline from March 21 for a three-week outage.
$1 = 1.0018 Swiss francs Reporting by Vera Eckert; Editing by Mark Heinrich