---
title: "When the River Stopped Cooling the Reactor: Summer 2026 Exposed the Climate Vulnerability of Nuclear Power"
description: "The summer of 2026 exposed the vulnerability of nuclear generation: drought and the shallowing of the Danube forced nuclear plants in Hungary, Romania, and Bulgaria to reduce output. For Ukraine, where nuclear supplies over 60% of electricity, this is a direct climate risk."
date: 2026-09-14T08:40:00.000Z
lang: en
url: https://xab.info/en/posts/when-the-river-stopped-cooling-the-reactor-climate-vulnerability-of-nuclear-power
tags: [nuclear-energy, climate-change, water-shortage, ukraine-energy, danube]
publisher: "XAB.info"
---

# When the River Stopped Cooling the Reactor: Summer 2026 Exposed the Climate Vulnerability of Nuclear Power

![Когда река перестала охлаждать реактор: лето 2026-го обнажило климатическую уязвимость атомной энергетики](https://xab.info/media/2026/09/14/klimat-ugroza-atomnoj-energetike/klimat-ugroza-atomnoj-energetike-1.webp)

## 🎯 Key Points

- In the summer of 2026, nuclear plants in France, Switzerland, Hungary, Romania, and Bulgaria cut output due to drought and low water levels, particularly in the Danube.
- A single reactor requires between 1,514 and 2,725 liters of water per MWh, making water a critical resource for nuclear generation.
- Hungary was preparing to reduce Paks' output for the first time in 44 years and decided to build a dam on the Danube; Romania shut down two Cernavodă units and used controlled explosions; Kozloduy cut output for the first time in 52 years.
- For Ukraine, where nuclear generation supplied more than 60% of electricity in certain periods, the key climate risk is the South Ukrainian Nuclear Plant in the Southern Bug basin.

Nuclear energy has traditionally been presented as a reliable, cheap, and low-carbon source of electricity. However, the summer of 2026 revealed another side of this technology and raised the question of how resilient nuclear generation is in a changing climate and whether it is wise to increase dependence on it without diversifying the energy system. This was explained in a column for RBC-Ukraine by Anastasia Yahniuk, project coordinator at the EcoClub NGO. According to her, this year nuclear power plants in France, Switzerland, Hungary, Romania, and Bulgaria were forced to cut output: some units were moved to reduced power, while individual reactors were shut down entirely. The cause was extreme drought and record-low water levels, primarily in the Danube — one of Europe's largest rivers, along which the Paks (Hungary), Cernavodă (Romania), and Kozloduy (Bulgaria) nuclear plants are located.

### Why Water Is a Critical Resource for a Nuclear Plant

The vulnerability of nuclear energy to such conditions is explained by the physics of the process itself. A reactor produces not only electricity but also a huge amount of heat, about two-thirds of which must be continuously removed into the environment. This is precisely why water becomes one of the key resources for the operation of a nuclear plant. According to data from the Institute of Nuclear Power, a single reactor may require between 1,514 and 2,725 liters of water per MWh of generation — that is hundreds of billions of liters over the course of a year. Under climate change, prolonged droughts, declining river levels, and rising water temperatures can limit the capacity of cooling systems and create a direct risk to electricity production.

### Paks, Cernavodă, Kozloduy, and Beznau: How Operators Responded

A striking example was Hungary's only nuclear plant — Paks. In August, due to unfavorable cooling conditions, it was preparing to reduce the output of its units; according to Reuters, in 44 years of operation the plant had never faced such critical conditions for its cooling system. After a brief rise in water levels, a full shutdown of the units was averted. To prevent a recurrence, Hungarian authorities decided to build a dam on the Danube — a particularly sensitive issue for the country, since nuclear generation supplies 42% of its electricity. However, intervening in the Danube's water regime may have consequences for downstream countries: at Romania's Cernavodă plant, two units had already been shut down due to low water levels, and to increase the inflow of water to the plant, Romanian authorities even resorted to controlled explosions in a Danube channel. Due to the river's shallowing, Bulgaria's Kozloduy plant was also forced to cut output for the first time in 52 years.

### Water Temperature: The Second, Hidden Limit

For the operation of a nuclear plant, not only the volume of available water matters, but also its temperature. Technical regulations limit the discharge of return water by plants if it leads to a significant rise in the water body's temperature. When river water becomes too warm, it loses its ability to efficiently remove heat from a unit, and even with sufficient water levels an operator may be forced to reduce power or temporarily stop operations. This risk has already manifested in Europe: in early June, due to the high water temperature in the Aare River in Switzerland, the Beznau nuclear plant was shut down.

### Ukraine: More Than Half of Generation and New Climate Risks

For Ukraine, this topic is of particular significance. Before the full-scale invasion, nuclear generation supplied more than half of the country's electricity production, and after the start of hostilities its role became even more important, since part of the thermal and hydro generation was damaged or ended up in occupied territories. In certain periods, nuclear plants supplied more than 60% of generation, while the state declares its intention to increase the share of nuclear generation, including through the construction of new units. All four operating Ukrainian nuclear plants belong to a single operator — JSC NAEK "Energoatom" — but they operate in different river basins and have different dependencies on water resources. The South Ukrainian Nuclear Plant in the Southern Bug basin is especially sensitive to climate change: climate forecasts for it already anticipate growing risks of low water and longer summer low-water periods.

### Conclusion: Diversification or Deepening Dependence

The combination of these factors shows that the climate resilience of nuclear generation is not unconditional and depends directly on the water regime of specific rivers and water bodies. For an energy system in which nuclear generation holds a dominant share, this means that planning the development of nuclear energy must account for future climate change — from assessing the water resources of each river basin to the need to diversify generation sources in order to avoid concentrating risks in a single technological and natural loop.

## 🔍 Fact-Check Verification

- [When Water Runs Short: A Climate Challenge for Nuclear Energy](https://www.rbc.ua/ukr/news/koli-vistachae-vodi-klimatichniy-viklik-atomnoyi-1789375011.html) - Первичный источник: колонка А. Яхнюк с фактами о снижении мощности АЭС в Европе летом 2026, данными IAEA по расходу воды, случаями «Пакш», «Чернаводэ», «Козлодуй», «Бецнау» и контекстом по Украине.
- [Scientists Find a Way to More Accurately Calculate Cooling of Liquid-Fueled Reactors](https://www.ferra.ru/news/v-rossii/uchenye-nashli-sposob-tochnee-rasschityvat-okhlazhdenie-reaktorov-na-zhidkom-toplive-09-07-2026.htm) - Техническая новость о расчетах охлаждения реакторов на жидком топливе; не связана с фактами колонки и в статью не включалась.
- [Climate Change Threatens to Derail Europe's Plan for Wider Use of Nuclear ...](https://rus.postimees.ee/8538278/klimaticheskie-izmeneniya-ugrozhayut-sorvat-plan-evropy-po-bolee-shirokomu-ispolzovaniyu-atomnoy-energii) - Коррелирует с общей тезой о климатической уязвимости европейского плана расширения атомной энергетики.

## ❓ FAQ

### Q: Why does drought affect the operation of nuclear power plants?
**A:** A reactor produces a lot of heat, about two-thirds of which must be removed into the environment through water. When water levels are low or temperatures are high, the cooling system works inefficiently, and the operator is forced to reduce power or shut down the unit.

### Q: How much water does a nuclear reactor require?
**A:** According to data from the Institute of Nuclear Power, a single reactor needs between 1,514 and 2,725 liters of water per MWh, which adds up to hundreds of billions of liters per year.

### Q: Which plants were affected in the summer of 2026?
**A:** Nuclear plants in France, Switzerland, Hungary, Romania, and Bulgaria. In particular, Paks (Hungary), Cernavodă (Romania), Kozloduy (Bulgaria), and Beznau (Switzerland).

### Q: How important is nuclear to Ukraine's energy sector?
**A:** Before the invasion, nuclear generation supplied more than half of electricity, and in certain periods — more than 60%. All four Ukrainian nuclear plants belong to JSC NAEK "Energoatom", with the South Ukrainian Nuclear Plant in the Southern Bug basin considered the most climate-sensitive.