Electricity from existing reactors
Beznau 1, Beznau 2, Gösgen and Leibstadt supply electricity that a replacement plan would need to provide. Their operating record includes both routine maintenance and extended outages.
Historical data and methodsOur assessment: a credible replacement plan must account for when electricity is available, as well as its annual total. This is a reason to examine continued operation carefully. It is not an argument to relax safety requirements.
Capacity factor across three periods
A capacity factor compares actual output with output at full nominal capacity throughout the period. It is not the share of time available.
On a small screen, scroll the table to see all columns.
| Reactor | 2016–2025 Ten years | 2021–2025 Five years | 2025 |
|---|---|---|---|
| Beznau 1 | 68.0% | 86.0% | 91.0% |
| Beznau 2 | 89.2% | 87.8% | 77.7% |
| Gösgen | 85.3% | 79.2% | 38.8% |
| Leibstadt | 75.4% | 80.8% | 88.5% |
Generation and capacity: BFE table 15 and footnotes · Period calculations
How much electricity per year?
| Reactor | 2016–2025 Annual mean | 2021–2025 Annual mean | 2025 |
|---|---|---|---|
| Beznau 1 | 2'177 | 2'751 | 2'909 |
| Beznau 2 | 2'855 | 2'807 | 2'483 |
| Gösgen | 7'552 | 7'012 | 3'429 |
| Leibstadt | 8'094 | 8'697 | 9'558 |
BFE table 15 · Inputs and arithmetic means . The same four reactors are compared throughout. Mühleberg is excluded, including before its closure.
Gösgen: operating history and the 2025–2026 shutdown
Gösgen stopped for planned maintenance on 24 May 2025. A potential design weakness in the feedwater system delayed restart.
The plant replaced check valves and submitted safety evidence. ENSI approved restart on 23 March 2026, after about ten months offline. ENSI: findings and restart approval
The operator confirms that electricity delivery resumed that day. Gösgen: return to the grid
Gösgen’s capacity factor was 90.4% across 2016–2024, before the extended outage. Across the full 2016–2025 period, including the outage, it was 85.3%. Historical calculations
Calculated capacity factor. Each bar uses the same 0–100% scale.
- 201692.1%
- 201791.4%
- 201892.4%
- 201987.7%
- 202093.0%
- 202188.5%
- 202289.2%
- 202390.2%
- 202489.4%
- 202538.8%
2025 includes the extended shutdown. BFE table 15 · Data and calculation
Annual data and calculation method
| Year | Beznau 1 | Beznau 2 | Gösgen | Leibstadt |
|---|---|---|---|---|
| 2016 | 0 GWh 0.0% | 2'994 GWh 93.4% | 8'174 GWh 92.1% | 6'108 GWh 57.0% |
| 2017 | 0 GWh 0.0% | 2'768 GWh 86.6% | 8'091 GWh 91.4% | 5'649 GWh 52.9% |
| 2018 | 2'452 GWh 76.7% | 3'022 GWh 94.5% | 8'178 GWh 92.4% | 7'813 GWh 73.1% |
| 2019 | 2'815 GWh 88.0% | 2'803 GWh 87.7% | 7'757 GWh 87.7% | 8'820 GWh 82.5% |
| 2020 | 2'747 GWh 85.7% | 2'930 GWh 91.4% | 8'254 GWh 93.0% | 9'059 GWh 84.5% |
| 2021 | 3'026 GWh 94.6% | 2'824 GWh 88.3% | 7'828 GWh 88.5% | 4'852 GWh 45.4% |
| 2022 | 2'521 GWh 78.8% | 2'944 GWh 92.1% | 7'895 GWh 89.2% | 9'753 GWh 91.3% |
| 2023 | 2'892 GWh 90.4% | 2'780 GWh 86.9% | 7'980 GWh 90.2% | 9'682 GWh 89.6% |
| 2024 | 2'406 GWh 75.0% | 3'006 GWh 93.8% | 7'929 GWh 89.4% | 9'642 GWh 89.0% |
| 2025 | 2'909 GWh 91.0% | 2'483 GWh 77.7% | 3'429 GWh 38.8% | 9'558 GWh 88.5% |
Annual capacity factor = generation in GWh × 1,000 ÷ (net capacity in MW × calendar hours) × 100.
For several years, divide total generation by the sum of each year’s capacity × hours. Do not average rounded annual percentages. Leap years have 8,784 hours; other years have 8,760.
Beznau uses 365 MW per reactor and Gösgen uses 1,010 MW. Leibstadt uses 1,220 MW through 2022, then 1,233 MW. These are BFE’s dated nominal net capacities. Table 15, footnotes 1, 4 and 6
BFE’s published utilization rates include heat for Beznau and Gösgen. Our calculations use its generation rows and do not copy those utilization rates. This annual record does not establish hourly or winter reliability.
Gösgen’s 2025 total differs between BFE and the operator. Source definitions and difference.
Source definitions and the Gösgen 2025 difference
BFE lists 3,429 GWh for Gösgen in 2025. The operator reports 3,397 GWh of electricity and 31 GWh of process steam in electrical-equivalent units. BFE table 15 · Operator report, page 9
The tables use BFE’s series throughout. The difference from the operator’s figures remains unresolved. Using the operator’s electricity-only figure gives a calculated capacity factor of 38.4%. Calculation and boundaries
Download the data, methods and source notes (JSON) · Download annual rows (CSV)
Continued operation has conditions
ENSI’s national report describes the system for safety assessments and oversight. Our support for existing plants depends on meeting the applicable safety requirements and on a viable operating plan.
ENSI: safety assessment and oversightOur position: compare the cost and reliability of continued operation with the cost and reliability of replacing its output. Keep the maintenance, outage and waste obligations in that comparison.
Requirements for new nuclear
We support developing a credible option for new nuclear in Switzerland. Support for an option is not approval of any reactor, vendor, price or subsidy.
Our decision test asks for:
- A design and site that can meet Swiss safety requirements.
- A delivery schedule with allowances for delay.
- A cost estimate that states its currency, price year and financing terms.
- A plan for fuel, maintenance, waste and final dismantling.
- A clear allocation of construction, operating and financial risk.
- A comparison with other ways to provide the same level of reliable supply.
These criteria require a project-specific price and construction schedule before a new-build decision.
Costs, waste and supply dependence
A strong case for nuclear must address outages, waste, insurance, construction risk and the cost of capital. It must also test dependence on foreign suppliers. We do not use the word “sovereignty” to mean that every input is domestic.
No conclusion that new nuclear is the cheapest option follows from the output of existing plants alone.
References
- Swiss Electricity Statistics 2025
Swiss Federal Office of Energy (BFE) · 2025 - Convention on Nuclear Safety: tenth Swiss report
Swiss Federal Nuclear Safety Inspectorate (ENSI) · Tenth report - Nuclear generation and capacity factors, 2016–2025
WattInfo / Niko Storni · Historical comparison v1 - Gösgen restart permission after the extended shutdown
Swiss Federal Nuclear Safety Inspectorate (ENSI) · Restart decision of 23 March 2026 - Return to grid after extended outage, 23 March 2026
Kernkraftwerk Gösgen · 2026-03-23 - Gösgen annual report 2025
Kernkraftwerk Gösgen-Däniken AG · 2025 annual report
Find definitions, calculations and model inputs in the source register.