The 2011 Fukushima Daiichi nuclear accident should serve as a wake-up call to nuclear plant operators and regulators on the critical importance of measuring, maintaining, and restoring cooling in spent fuel pools during severe accidents and terrorist attacks, says a new report from the National Academies of Sciences, Engineering, and Medicine.
This report is the second and final phase of a congressionally mandated study on what lessons can be learned from the Fukushima Daiichi nuclear accident.
The report from Phase 1 of this study was released in July 2014. The Phase 2 report provides findings and recommendations for improving U.S. nuclear plant security and spent fuel storage as well as re-evaluates conclusions from previous Academies studies on spent fuel storage safety and security.
The committee that carried out the study and authored the Phase 2 report found that spent fuel storage facilities — both spent fuel pools used to store fuel under water and casks used to dry-store fuel — at the Fukushima Daiichi nuclear plant maintained their containment functions during and after the March 11, 2011, Great East Japan Earthquake and tsunami.
But one of the two gates separating the Unit 3 spent fuel pool from the adjacent reactor well was damaged during the accident. Also, water appeared to have leaked around the gate seals in the Unit 4 spent fuel pool, allowing water to flow into the pool from the reactor well.
This water leak was accidental but also fortuitous, because it replenished water lost from the Unit 4 pool by evaporation, likely preventing water levels from dropping to the tops of the racks where the spent fuel was being stored.
The committee recommended that the U.S. nuclear industry and the U.S. Nuclear Regulatory Commission (NRC) improve the ability of plant operators to measure real-time conditions in spent fuel pools and maintain adequate cooling of stored spent fuel during severe accidents and terrorist attacks.
These improvements should go beyond the current, post-Fukushima response to include hardened and redundant physical surveillance systems such as cameras, radiation monitors, pool temperature and water-level monitors, and means to deliver makeup water or sprays to the pools, even when physical access is limited by facility damage or high radiation levels.
The committee determined that the NRC has implemented most of the recommendations from previous Academies reports on spent fuel safety and security.
However, two recommendations from those reports have not yet been implemented, the committee found. The first was to analyze the vulnerabilities of spent fuel pools to specific terrorist attack scenarios described in the 2004 Academies report, and the second was to carry out an independent examination of surveillance and security measures for protecting stored spent fuel.