Source Link: https://www.nap.edu/read/21874/chapter/1
LESSONS LEARNED FROM THE
Fukushima Nuclear Accident
FOR IMPROVING SAFETY AND SECURITY OF
U.S. Nuclear Plants
Committee on Lessons Learned from the Fukushima Nuclear Accident
for Improving Safety and Security of U.S. Nuclear Plants
Nuclear and Radiation Studies Board
Division on Earth and Life Studies
THE NATIONAL ACADEMIES PRESS
International Standard Book Number-13: 978-0-309-38888-7
International Standard Book Number-10: 0-309-38888-0
Digital Object Identifier: 10.17226/21874
The following is extracted from the Summary of Findings:
“TASK 2: LESSONS LEARNED FOR SPENT FUEL STORAGE5
“Spent fuel was stored in eight locations at the Fukushima Daiichi plant on March 11, 2011: in spent fuel pools in each of the six reactor units (Units 1-6), in a common spent fuel pool, and in a dry cask storage facility. The present report focuses on spent fuel storage in the Unit 1-4 pools because these units sustained severe damage as a result of the March 11, 2011, earthquake and tsunami.
The committee finds (Finding 2.1) that the spent fuel storage facilities (pools and dry casks) at the Fukushima Daiichi plant maintained their containment functions during and after the March 11, 2011, earthquake and tsunami. However, the loss of power, spent fuel pool cooling systems, and water level- and temperature-monitoring instrumentation in Units 1-4 and hydrogen explosions in Units 1, 3, and 4 hindered efforts by plant operators to monitor conditions in the pools and restore critical pool-cooling functions. Plant operators had not planned for or been trained to respond to the conditions that existed in the Unit 1-4 spent fuel pools after the earthquake and tsunami. Nevertheless, they successfully improvised ways to monitor and cool the pools using helicopters, fire trucks, water cannons, concrete pump trucks, and ad hoc connections to installed cooling systems. These improvised actions were essential for preventing damage to the stored spent fuel and the consequent release of radioactive materials to the environment. The committee recommends (Recommendation 2.1) that the U.S. nuclear industry and its regulator give additional attention (described in Chapter 2) to improving the ability of plant operators to monitor real-time conditions in spent fuel pools and maintain adequate cooling of stored spent fuel during severe accidents and terrorist attacks.
The spent fuel pool in Unit 4 was of particular concern because it had a high decay-heat load. The committee used a steady-state energy-balance model to provide insights on water levels in the Unit 4 pool during the first 2 months of the accident (i.e., between March 11 and May 12, 2011). This model suggests that water levels in the Unit 4 pool declined to less than 2 m (about 6 ft) above the tops of the spent fuel racks by mid-April 2011. The model also suggests that pool water levels would have dropped below the top of active fuel6 had there not been leakage of water into the pool from the reactor well and dryer/separator pit through the separating gates. This water leakage was accidental; it was also fortuitous because it likely prevented pool water levels from reaching the tops of the fuel racks. The events in the Unit 4 pool show that gate leakage can be an important pathway for water addition or loss from some spent fuel pools and that reactor outage configuration can affect pool storage risks.
The events in Unit 4 pool have important implications for accident response actions. As water levels decrease below about 1 m above the top of the fuel racks, radiation levels on the refueling deck and surrounding areas will increase substantially, limiting personnel access. Moreover, once water levels reach approximately 50 percent of the fuel assembly height, the tops of the rods will begin to degrade, changing the fuel geometry and increasing the potential for large radioactive material releases into the environment.
end quote. emphasis added.
Other than that, there was absolutely nothing to worry about and anyone who disagrees is a radiophobe. For the nuclear industry and nuclear authorities have always known precisely what it has been doing and no one is able, in its view, to question those authorities rationally. They say.
Key words and terms:
Comparison with press and other technical records of the state of SFP 4:
Pivotal events occurred on 14, 15 March 2011 and the Japanese government, the IAEA and disaster response measure changes on those days all confirm that these pivotal events did indeed occur. These events are recorded by the following official, qualified and press sources:
Questions to be put to Mr Shepherd, author, Caltech: