Wednesday, March 30, 2011

Is A Recriticality Accident Possible?

A commenter on one of my articles about the possibility of a recriticality accident said such an accident was not possible. Well actually, a study of the type of reactor now having problems in Japan (BWR) shows that a recriticality accident is possible:

ftp://ftp.cordis.europa.eu/pub/fp5-euratom/docs/09-sara.pdf

From the summary of the document:

Recriticality in a BWR during reflooding of an overheated partly degraded core, i.e. with relocated control rods, has been studied for a total loss of electric power accident scenario. In order to assess the impact of recriticality on reactor safety, including accident management strategies, the following issues have been investigated in the SARA project: (1) the energy deposition in the fuel during super-promt power burst, (2) the quasi steady-state reactor power following the initial power burst and (3) containment response to elevated quasi steady-state reactor power. The approach was to use three computer codes and to further develop and adapt them for the task. The codes were SIMULATE-3K, APROS and RECRIT. Recriticality analyses were carried out for a number of selected reflooding transients for the Oskarshamn 3 plant in Sweden with SIMULATE-3K and for the Olkiluoto 1 plant in Finland with all three codes. The core initial and boundary conditions prior to recriticality have been studied with the severe accident codes SCDAP/RELAP5, MELCOR and MAAP4.

The results of the analyses show that all three codes predict recriticality – both super-promt power bursts and quasi steady-state power generation - for the range of parameters studied, i.e. with core uncovering and heat-up to maximum core temperatures of around 1800 K, and water flow rates of 45 kg/s to 2000 kg/s injected into the downcomer. Since recriticality takes place in a small fraction of the core, the power densities are high, which results in large energy deposition in the fuel during power burst in some accident scenarios
So does that mean such an accident has happened at Fukushima? Well we can't be certain and we may never be certain but the evidence points in that direction.

One must also add that without the evidence (neutrons, Iodine 134) computer codes are not definitive. When the "experiment" matches the code you may actually have something.

Cross Posted at Classical Values

2 comments:

Toney said...

Amazing, is it not, that containing the truth has become as important, if not more important, than containing the radiation at Fukushima.

Regarding re-criticality: We have the smoking guns, so to speak.

Neutrons - http://ti.me/hQCycR

I-134 - http://bit.ly/fqIY0v

Also, your own timeline calculations re I-131 v. I-134 half lives.

Therefore, at least one re-criticality event has occurred. I'm not convinced the sticky-glue solution will be anymore effective than the various hose downs given these grave circumstances.

The point of this exercise in reality is simple. Measures can and should be taken to ameliorate the horrendous human health consequences of continued sang-froid if but two things were to happen: 1) forget about the Nikkei; 2) release the truth, Mr. Kan.

M. Simon said...

I have more news and confirmation. The post will be up in a few minutes.

Here it is:

A Random Source Of Neutrons