Kansai Electric reported a manual shutdown of its Mihama Nuclear Power Plant Unit 3 on September 17, 2026. The utility confirmed water dripping from feedwater heater piping during equipment checks but stated the issue does not impede operational safety.
The incident occurred on September 17, 2026, during the 29th regular inspection at Mihama Unit 3. Around 15:45, employees observed water dripping at a rate of three drops per second near the air vent valve on the normal water level control valve outlet piping of the No. 6A high-pressure feedwater heater. The company attributes this to steam condensing and leaking as it returns to the feedwater system, noting it is not a critical fault requiring immediate emergency shutdown. However, because the affected section cannot be isolated from the system, Kansai Electric decided to manually stop the reactor at 17:45 to ensure safety. Load reduction began at 20:30, and operations will remain suspended for the foreseeable future.
Kansai Electric stated that there is no radiological environmental impact from this event. The leak occurred in the secondary feedwater system, which circulates between the steam generator, turbine, and condenser, indicating a low risk of external release. The company will now conduct precise inspections of the piping and valves around the insulation to identify parts requiring repair or replacement. While Kansai Electric pledged to disclose any material financial impacts promptly, potential effects include increased equipment maintenance costs and reduced supply capacity. Financial implications will likely be detailed in a subsequent regulatory filing.
The unplanned stoppage during a regular inspection adds to supply constraints in the Kansai region, where Kansai Electric is headquartered. While safety-based decisions necessitate such actions, the closure of Mihama Unit 3 may further pressure peak-hour supply reserves in the area. Although other utilities face similar risks due to aging infrastructure, this incident temporarily reduces operational flexibility. Analysts suggest that while the overall short-term impact on power supply balance remains limited due to the company's diverse reactor portfolio, the situation remains sensitive for investors. The timeline for repairs and the resulting reduction in operating profit will be key drivers of future stock performance.
Analyst take
Decision to comply with safety standards. The manual shutdown highlights the company's priority on isolation capabilities despite the minor leak rate of three drops per second. Attention now shifts to whether repair duration and costs will compress profits. It is more appropriate to view this as a sign of long-term capital investment in equipment renewal rather than a concern over short-term power shortages.
