Energy · day by day, 2015–2026

For eleven years Romania never had a full day without nuclear power. In 2026 it has had 93

Cernavodă, on the Danube about 150 km east of Bucharest, is Romania’s only nuclear plant. Its two Canadian-designed CANDU reactors usually make about a fifth of the country’s electricity. Each band below is a year and each stripe a day: bright blue when both reactors ran, dim blue for one, black for none. The data runs to 26 October 2026.

both reactorsone reactorno reactorno reactor, from the balanceno data

0full days without nuclear power, 2015–2025 (4,004 days with data)

93whole days with no reactor running in 2026, to 26 October

1,170 MWcame in from abroad at 3–5 a.m. on average, since 14 August

#At night, the power came from across the border

By day, solar power makes the gap smaller. At night there is no sun, and the plant used to give the same power at every hour. That is why the gap shows most clearly between midnight and morning.

From 14 August to 26 October, at 3–5 a.m., an average 1,170 MW flowed into Romania from its neighbours: nearly what the plant gave with both reactors (1,240 MW, the 2025 median). In the same weeks of 2023, at the same hour, Romania was sending power out (498 MW). In 2024 and 2025 the exchange was close to balanced (21 and 204 MW in).

Power flowing into Romania across all borders, by hour, 14 August – 26 October, MW (below zero: power sent out)

Where it came in

At 3–5 a.m. the balance moved towards imports on every border. Across Bulgaria and Moldova, the flow that used to leave Romania turned around; towards Serbia, Romania almost stopped sending power. These are measured physical flows, not purchases: grids are linked, and power bought from Hungary can arrive across another border.

Power flowing in at 3–5 a.m., by border, MW, average 14 August – 26 October2025 2026

On 29 July, acting prime minister Ilie Bolojan asked Romanians to use less electricity between 8 and 11 p.m., when the sun sets and imports reach their daily peak.

#Why the plant stopped, twice

The first gap has nothing to do with the Danube. On the evening of 4 May, reactor 2 disconnected automatically after a fault in an insulator on the transformer that carries the plant’s power out. The transformer had to be replaced with a spare. On 10 May at 11 a.m., reactor 1 began its planned maintenance outage, prepared two years ahead. From 11 May, the first full day, neither ran. Reactor 2 returned to the grid on the evening of 30 May and reactor 1 on 5 July.

What ran in 2026: each reactor, from Nuclearelectrica’s reports and the daily output

The second gap comes from the drought. Reactor 1 was shut down in a controlled way on 28 July “due to the very low, unprecedented water level of the Danube”, as Nuclearelectrica, the state-controlled operator, told the Bucharest Stock Exchange. Reactor 2 followed on 13 August. The plant takes its cooling water from the river; the operator does not publish the exact level at which it must stop.

On 11 October, Nuclearelectrica said both reactors would stay in a safe shutdown state until the Danube’s level allows a restart. By 26 October 2026 it had announced no reconnection.

#The closest call before: two days in 2017

In the data for the eleven years before, nuclear output fell under 50 MW for hours on end only twice: on 13 May 2017 (7 hours) and on 1 June 2017 (15 hours, from 4 a.m. into the afternoon). On the day with the lowest average, 1 June 2017, the plant gave 197 MW. A few isolated zero readings in 2024 and 2025, between normal values, look like reporting errors. Data is missing for 14 days.

#What next

A restart depends on how fast the Danube rises and how long it stays up. When a reactor comes back, the picture above will change: the data is rebuilt from the same sources, and the count stops at the last day with no reactor running.

For the river itself, and how rare the 2026 low is against 183 years of measurements, see “The Danube at low water”. For the price of power hour by hour (in Romanian), see “Electricity is no longer cheap at night”.

#How it was counted

Nuclear output comes from the European grid operators’ public data (ENTSO-E), as served by Energy-Charts: hourly to 2021, every quarter-hour after. Each day, in Romanian time, is averaged. A whole day with no reactor means at least 90% of the day’s readings are under 50 MW; otherwise an average under 1,000 MW means one reactor or part of the day, and over 1,000 MW, both. The thresholds were fixed before counting: one reactor gives roughly 600–700 MW, both 1,200–1,400 MW.

Nuclear output is missing for September 2026, though every other source is present. For those days the grid was balanced: consumption, minus everything the other plants made, minus net imports. With the reactors running, typically 1,522 MW is left (the median); in September between 177 and 295 MW was left, the same as on days when reported nuclear output is zero. Nuclearelectrica’s reports of 24 August and 11 October confirm both reactors were off. These 30 days are counted and marked separately.

Data is also missing for 14 days in 2015–2025 (the first four days of 2015 and a few days in 2015, 2018 and 2021); the days around them show both reactors running. They are not counted either way.

The cross-border power in the night section is the physical flow measured on each line, 2023–2026, years in which all five borders are reported (in August 2022 the Ukrainian border is missing). For the day you pick, the 3–5 a.m. figure comes from scheduled exchanges, the only series reported for every year; in the 2026 weeks the two give almost the same number (1,169 and 1,170 MW).

From December 2024, reported output with both reactors running fell from about 1,380 to about 1,230 MW, and the sources consulted do not explain it. The page therefore does not compare the plant’s output between years; the share of consumption for your day is the one reported that day.