Thursday, May 17, 2012

TECPO's triage at Unit 4

My prior post debunking some of the more outrageous myths circulating the internet as to the state of the Fukushima Daiichi Unit 4 spent fuel pools generated some considerable amount of heat, particularly over at its syndicated location at The Energy Collective. Much of this discussion has focused upon the physical state of the Unit 4 reactor building itself (at the top of which the Unit 4 spent fuel pool resides). Yet contrary to popular belief in particular circles, TEPCO has certainly not left the spent fuel pool at Unit 4 to the vagaries of nature, nor have they failed to produce a credible, long-term plan for stabilizing and containing the remaining spent fuel at the reactor units.

Before getting too far into the topic, it's useful to point to a comprehensive companion piece to the prior discussion by Will Davis (of Atomic Power Review) over at the ANS Nuclear Cafe, entitled "Spent Fuel at Fukushima Daiichi Safer than Asserted." (Along with several other nuclear bloggers, I offered a moderate amount of technical consultation for this topic.)

TEPCO's remediation strategy for the Fukushima Daiichi site (original)
Given the concern over the structural state of the reactor building, it is thus useful to look at what TEPCO is actually doing to address the issue. Much of TEPCO's strategy is oriented around immediately stabilizing the site with a focus upon long-term remediation; in a word, triage.

In order to stabilize the earthquake-damaged reactor building, TEPCO has already conducted an evaluation of the structural integrity of the Unit 4 reactor building, deciding to reinforce the foundation of the building with a steel-beamed outer support structure, work which was completed last summer. In this sense then, the immediate concern over the stability of the reactor building (and spent fuel pool) has already been addressed.

However, there remains the issue of the fuel itself in the Unit 4 spent fuel pool. TEPCO has already put measures into place to ensure adequate cooling in the event of a sudden loss of water (i.e., from another large earthquake), including the deployment of concrete pumper trucks (referred to as "giraffes," which were used to originally restore the water levels at the Unit 4 pools). To emphasize - the concern here is not from a loss of water due to evaporation (again, spent fuel pools are kept at atmospheric temperature and pressure under normal conditions; meanwhile, the youngest fuel within the pool is now well over a year old, meaning it is cool enough where sudden evaporation is not a concern). Rather, the planning is again one of being able to respond to issues such as future earthquakes.

Despite the fact that the situation is as stable as can be expected presently at Unit 4, there is a legitimate concern about the impact of future earthquakes. Again, to emphasize - the chief concern over a (rather unlikely) collapse of the spent fuel pool is not the global catastrophe flogged by certain activists lacking in technical credentials (both my prior post and Will Davis' post adequately address why this is so), but rather a mechanical failure of the fuel (which would release local contamination - in particular, radioactive cesium and strontium) and force a local evacuation from the site, thus greatly complicating the cleanup response. (Thus, while far from catastrophic, such a collapse would greatly hinder the ability of TEPCO to clean up the site and add considerable expense to an already vastly expensive project.)

Thus, the medium-term strategy is to relocate the fuel out of the Unit 4 spent fuel pool into the common pool, thus obviating the risk from further damage to the Unit 4 reactor building; current plans call for the fuel from Unit 4 to be fully removed by mid-2013 (and from Unit 3 by the end of 2014). Again, in contrast to the opinions of certain press-seeking political office-holders and activists, this is not a process accomplished with the wave of a wand.

According to TEPCO's mid-to-long term roadmap, this will roughly consist of the following:

  • Clear debris from the spent fuel pool which was dropped into the pool due to the hydrogen explosion
  • Install a cover over the damaged building to shield heavy equipment from the environment (e.g., wind and rain). Following this, heavy fuel handling equipment (e.g., heavy cranes) will be installed in the reactor buildings in order to begin the process of moving undamaged fuel rods.
  • Relocate undamaged, older fuel from the common fuel pool into dry cask storage to make room for newer, hotter fuel from the spent fuel pools at each reactor building. 
  • Begin removing spent fuel from the reactor buildings; this will involve placing the fuel from the reactor buildings in temporary transportation canisters and lowering the canisters to ground level, where they can then be relocated to the common fuel pool.
Ultimately, this is not a quick process; nor is it clear how, despite the best intentions of "concerned outsiders" how this could reasonably be expedited beyond the current schedule, as several tasks are contingent upon one another. (i.e., spent fuel pools must be cleared of debris and a temporary cover must be installed before heavy equipment can be installed, and subsequently fuel can be relocated). Yet it is also clear from both current triage efforts as well as long-term recovery plans that the situation is far the looming disaster it is being sold as.

Update: Via TEPCO's English-language Twitter feed comes this presentation specifically addressing their analysis of the structural soundness of the Unit 4 reactor building.