LACEY TOWNSHIP - The nation's oldest operating nuclear plant is back online following a month-long outage for refueling and maintenance.

The Oyster Creek nuclear plant in Lacey Township returned to service at 7:18 Thursday morning.

Workers replaced both of the plant's main power transformers, refueled the reactor and did maintenance that can only be performed while the unit is offline.

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The transformer replacement cost $33 million.

Another $13.3 million is being spent on underground piping work to deal with a tritium leak on plant grounds.

The day before the plant was back online, officials reported an "unusual event," after an equipment malfunction during warmup procedures.

An unusual event is the lowest emergency level in the Nuclear Regulatory Commission's emergency classification system.

The incident happened at 2:55 p.m. Wednesday and was under control half an hour later.

Oyster Creek produces 636 megawatts of electricity an hour, enough to power 600,000 homes.

The Associated Press contributed to this report.

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