LITTLETON, Colo., Feb 1 (Reuters) - A steep drop in France's nuclear power output in 2022 exacerbated Europe's power crisis by forcing French utilities to flip from net power exporters to importers just as Russia's invasion of Ukraine snarled energy markets across the continent.

A combination of planned maintenance shutdowns along with unplanned shortages of reactor cooling water forced French nuclear power operators to cut electricity generation by 23% in 2022 from the year before to record lows, data from think tank Ember shows.

As France historically relies on nuclear for more than 70% of total electricity supplies, this shortfall in reactor output forced French utilities to drastically adjust their power fuel mix by increasing imports and the use of natural gas by nearly 30% to record levels.

In turn, France's higher gas consumption tightened regional natural gas markets at the worst possible time, just as other major European gas consumers scrambled for alternatives to Russian pipelined supplies that were being curtailed amid the fallout from Moscow's so-called special operation in Ukraine.

Going forward, a sustained recovery in French nuclear output would help cut France's appetite for power and gas imports, and potentially help utilities export surplus power to other European nations that are still struggling with tight and expensive energy markets.

ROLE REVERSAL

From 2019 through 2021, France's average annual power exports were roughly 54 Terawatt hours (TWh), or as much as Greece's total electricity generation in 2021, according to data Ember and energy technology firm EnAppSys.

In 2022, however, due to reduced nuclear output as well as a drop in hydropower generation because of dry conditions, France slashed power exports to less than 8 TWh, and lifted power imports to a record 26.84 TWh, EnAppSys data shows.

This flip in French power flows not only tightened Europe's power markets, but also made a major dent in France's trade balance: The nearly 10 billion euro cost of 2022's power imports surpassed France's total earnings from power exports from the previous three years, EnAppSys data shows.

POWERING UP

So far in 2023, France's nuclear power output remains 17.5% below the average from 2020 and 2021, Refinitiv data shows, due in part to strikes against planned pension reforms for unionised workers.

However, utilities have previously stated that nuclear output will climb once maintenance work is completed, although the ailing system may struggle to reach previous annual output levels of around 400 TWh as much-needed repairs and upgrades drag on.

Even if average output remains below that previous target, any sustained increase in nuclear production from 2022 totals stands to have an impact on local power prices, as well as France's overall power import needs.

For example, in December, some previously curtailed reactors resumed operations and that boosted national nuclear output by 40% from the average of the previous eight months, Refinitiv data shows.

In January, average output was higher still, and even if production rates over the remainder of the year only match the average from the past three years - which includes 2022's record low sum - cumulative output by year end would still be roughly 14% above 2022's total.

In turn, because a majority of France's electricity comes from nuclear stations, that potentially higher nuclear output total could help utilities curb generation from other sources, such as natural gas, freeing up those fuels for other users.

Higher nuclear output in 2023 could also help France resume its status as a net exporter of power, with an ability to charge the prevailing record high market rates that could help the country recoup some of its expenses from 2022 while alleviating pressure on other power consumers.

So after a tumultuous 2022 that saw power markets upended by Russia's actions in Ukraine, Europe's power consumers may look to France in 2023 in the hopes that the country gets its nuclear shop in order and helps free up surplus power for other users in the months ahead.

(Reporting By Gavin Maguire; Editing by Christian Schmollinger)