Following the mid-July scram at Sweden’s Forsmark 1 reactor, when a switchyard short-circuit revealed a common cause failure of diesel backup generators, the Swedish Nuclear Inspectorate (SKI) has disclosed the measures required before allowing the station and its sister unit to restart.

The investigation by two SKI teams led the regulator to insist the operators eliminate any risk of failures outside the plant affecting safety system functions within the facility, specifically:

• The battery secured net will be made more durable to high-voltage transients.

• The electrical supply from the diesel generators shall be secured

• Displays in the control room in the event of loss of electricity must be secured

• The gas turbine must be possible to control from the control room.

• Instructions in the control room shall be set by the board.

Oskarshamns Kraftgrupp (OKG), which voluntarily shut down the similarly designed Oskarshamn units 1 and 2, has not submitted any application to restart Unit 1 although SKI’s assessment allows Oskarshamn 2 to restart after its annual revision which is due to conclude within the next week. Unit 1 is expected to restart around the turn of the year after changes in its back-up power system.

Other Swedish reactors do not have any restrictions on operations.

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