What really happened to the Fukushima Daiichi reactors when workers from owner Tokyo Electric Power Company added ocean saltwater to cool them?Fairewinds recently received this question and important technical comments from several viewers and engineers regarding utility owner TEPCO’s use of saltwater to cool the Fukushima Daiichi atomic reactors during their triple meltdowns. As we continue looking at aging operating atomic reactors around the world, it is important to understand this issue and know what may go wrong at other sites.Listen as Fairewinds’ Chief Engineer Arnie Gundersen explains why TEPCO’s workers injected saltwater into Fukushima’s failing reactors, what happens when salt water meets steel, and what forces come into play after saltwater is used to cool down an atomic reactor in this Fairewinds Audio Update.
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MG: Thank you for tuning in to Fairewinds Energy Education’s Audio Update with our Chief Engineer Arnie Gundersen. I’m Maggie Gundersen, President and Founder of Fairewinds. I’d like to take a quick moment to express my appreciation to all of you for your continuous support and viewership. Your donations are vital as we continue to speak truth to power and expose the nuclear industry’s hidden safety risks. So, once again, thank you and enjoy.
AG: Hi I’m Arnie Gundersen, Chief Engineer for Fairewinds Energy Education.
AG: What really happened to the Fukushima Daiichi reactors when TEPCO added ocean saltwater to cool them? Fairewinds recently received this question and important technical comments from several viewers and engineers regarding utility owner Tokyo Electric Power Company’s use of saltwater to cool the Fukushima Daiichi atomic reactors during their triple meltdowns.
AG:As we continue looking at aging operating atomic reactors around the world, it is important to understand this issue and know what may go wrong at other sites.
AG: First, let’s start at the beginning. Because all the cooling pumps were immediately destroyed by the tsunami, when the meltdowns began there was no clean water available to cool the nuclear reactor cores.
AG: Personnel at the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi atomic site realized that in this dire emergency, the only way to cool its atomic reactors was with saltwater from the nearby ocean. While TEPCO’s Tokyo-based engineers opposed the use of saltwater, the only alternative tool available to onsite personnel was to inject saltwater into the core of the atomic reactor as a last ditch effort to slow the meltdowns.
AG: Why were engineers in TEPCO’s home office so opposed to the use of saltwater to cool the atomic reactors? As anyone who has ever lived by the sea or been on an oceangoing boat knows, saltwater makes steel rust. Atomic reactor vessels are made of steel, and hot atomic steel in saltwater can equal catastrophe. This phenomenon is called intergranular stress corrosion cracking or IGSCC.
AG: If you took chemistry, you might remember that salt is made up of sodium and chloride. It is the chloride ion that is very aggressive and viciously attacks steel.
AG: When I was a new engineer back in 1972, I worked on Connecticut’s Millstone Unit 1 atomic reactor, which is a BWR or boiling water reactor, just like the reactors at Fukushima Daiichi.
AG: Millstone Unit 1 had blown a pipe in its condenser allowing salt water to enter the atomic reactor. In less than 15 seconds, the chloride concentration reached 15 parts per million (ppm) inside the reactor causing all of the stainless steel neutron monitors to crack and fail and leaving the plant staff with absolutely no idea what power level the reactor was operating at. The subsequent shut down, which the nuke industry calls an outage, lasted for almost 1-year during which much of the stainless steel piping associated with the atomic reactor had to be replaced.
AG: During this serious reactor event, in which vital reactor safety systems were compromised in only 15 seconds, I received my first lesson about nuke speak and industry efforts to massage the messages delivered to both federal nuclear regulators and the public. In my report, I called this major mishap a “serious saltwater leak”, but my boss changed my wording to call this condenser mishap a “saltwater intrusion”!
AG: Japan’s Hamaoka Plant, also a BWR like Fukushima Daiichi, had saltwater cause irreversible damage when it leaked into the atomic reactor in 2011.
AG: At both the Hamaoka and Millstone atomic powered reactors, only a very small amount of the chloride ion reached the atomic reactor core, and yet it caused enormous damage. TEPCO engineers knew that the chloride ion in salt is fundamentally incompatible with stainless steel and that the nuclear reactor would crack. However, with the manmade crisis and subsequent meltdowns in process, a crack already in the atomic reactor, and no other alternative available, TEPCO employees at Fukushima Daiichi injected saltwater directly into the rector’s nuclear core.
AG: After the saltwater was injected, four forces were at play: First, the saltwater immediately helped to cool the atomic meltdown. And while, cooling down the meltdown was critical, the other three results were terrible: When the saltwater was injected, the chloride ion from the salt viciously attacked the nuclear fuel, the internal structures inside the reactor, and the walls of the reactor. So, if the meltdown itself did not destroy the atomic reactor, then the saltwater exacerbated that process causing the reactor to crack anyway. Additionally, so much saltwater was injected that the cooling channels began to plug as the water boiled off leaving only salt behind. And finally, hot saltwater and the atomic core, which had melted through the reactor, aggressively attacked the concrete underneath the atomic reactor. This means that the containment failed entirely and that the reactor core (often called corium) destroyed the containment system in its molten lava-like state.
AG: I’d like to be clear that the workers at TEPCO’s Fukushima Daiichi atomic reactor took the only action they could take with the only tools available in their attempt to mitigate this tragic situation. But in solving one problem, three other problems were created. Using saltwater compared to the use of pure water to cool the reactor, the staff increased the magnitude of the destruction inside the reactor, increased how quickly the atomic reactor melted down, and created a chemical attack on the concrete containment outside the reactor vessel.
AG: Perhaps one hundred years from now, when the Fukushima Daiichi atomic reactors are finally able to be fully dismantled, we will understand exactly how severe the saltwater attack was on each stainless steel reactor and the concrete barriers that were designed to prevent radioactivity from leaking into the atmosphere and groundwater.
AG:What the Fukushima Daiichi meltdowns make clear is that these aging atomic reactors are not designed to survive what the nuclear industry calls a “maximum credible” catastrophe.