Posted by: Costin | March 18, 2011


It’s a great news story but I don’t see anybody telling us what really happened there. So it happens that I’m an insider of the nuclear industry so I pretty much I can do more than assume what really happened.

A LOCA accident (loss of coolant agent) is the worst thing that can happen to a nuclear reactor from an economical point of view at least. LOCAs are big and small, while small ones are just leaks, the big ones relate with the impossibility of the active area to be cooled thus leading to the zirconium alloy (zircaloy) tubes that are storing the sintered uranium pellets, to be reaching melting temperature. This is not happening in a sec but it’s a developing situation if not properly following specific procedures for these kind of situations. What are the procedures saying? Well they’re saying to pump at full power water to cool down the reactor if the primary rapid shutdown graphite neutron absorber bars cannot be lowered due to low level of the coolant agent,  altogether with fission inhibitors (gadolinium nitrate for PHWR designs or boric acid for PWR reactors) at the same time putting the unit(s) in a long undetermined outage.

There’s no issue of power failure since all reactors have different power grids called classes, the last one being class I (one), meaning huge UPS battery banks that are powering exclusively critical safety functions (while other diesel backup generators are available and can be switched over to power whatever unit needs the energy).

There is a catch, the decision taking process in flooding a nuclear reactor in a LOCA situation is controversial since it puts one man – the shift superintendent – in the situation of taking out from the commercial operation an entire unit, thus cutting down profit margins, endangering his position (well, it’s nice to think that the guy might be a hero, but the bottom line of it’s actions means a 500,000 euros/day income cut and up to 1000 people fired) and all kinds of factors that will delay the decision to be taken and try to find a workaround to the situation, delay that is not quite compliant with the fission process in the reactor. Sadly, due to the complex nature of this scenario, automatic response cannot be engineered.


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