April 18, 2011

Apr 18, 2011 | Fukushima Accident Updates

  • Temperatures and pressures in reactor pressure vessels 1, 2 & 3 continue to decrease. The feedwater nozzle temperatures are 179 degrees C for #1, 141 C for 32, and 92 C for #3. Pressures for # 2 & 3 indicate atmospheric, while #1 pressure is down to ~60 psi.
  • Containment pressures for #2 and #3 remain at atmospheric while #1 is above atmospheric (~24 psi abs.) due to the nitrogen injection.
  • Western news reports on Saturday that the sea contamination at Fukushima has sharply increased seem to be, once again, misleading. The increases detected have been from samples taken inside the containment fences and silt dams put in place last week to minimize releases to the open sea. (KYODO News) The factor of six increase indicates that the fences and dams are restricting the outflow of radioactive isotopes to the open sea, and as such the levels inside the dams are going up. This was hoped to be the case when TEPCO installed the barriers, and it seems to be working.
  • All Japanese news media today report that robots have been used inside reactor buildings 1 & 3 in order to inspect damage and measure radiation exposure levels. The highest reading so far are inside the access doors of Unit #3 on the first floor (ground level?) and vary between 28 and 57 millisieverts per hour (2.8-5.7 REM/hr.) These are very high, but not really unexpected for the severity of the situation. A worker in these fields would reach the emergency dose limit of 25 REM (250 millisievert) in 4-7 hours. Reactor building No. 1 levels were from 10 to 49 millisieverts/hr (1-4.9 REM/hr). In both cases, the amount of recovery work any individual could perform would be severely limited. Remote control robots will be used to do as much as possible, but sending workers into these areas do do some work is inevitable. The robots can do only so much. There is no word on plans to reduce dose levels, at this point. Measures to reduce dose levels and increase worker stay times will unquestionably happen, but how these things will occur needs considerable planning time.
  • All Japanese media also report that new, externally-located pumps and “coolers” will be installed to speed up the process of dropping reactor temperatures below the 95 degree C cold shutdown level. The coolers are actually portable heat exchangers that will use sea water to cool the waters circulated to and from the reactor pressure vessels. Kyodo News reports TEPCO has ordered “dozens” of “gasketed plate heat exchangers” for the job. They measure 3 meters high, on meter wide, and two meters long. TEPCO plans using “five or six” heat exchangers for each reactor’s cooling.TEPCO told the Press that merely pumping water into the fuel pools and reactors is not cooling them down quickly enough. The fuel pool levels drop due to evaporation caused by decay heat production, and the waters pumped and/ or sprayed into them recover the levels. The reactors, however, are a different story. TEPCO reports indicate that the waters being pumped into the reactors is ending up as raised water levels in the turbine buildings. This writer has mentioned several times that the flow paths have not been reported, and it would be helpful to everyone if this was done.
  • TEPCO reports it could take at least 3 months to stop all leaks from the stricken reactor plants, and up to 9 months to bring all three reactors into a cold shutdown condition. Details are necessarily sketchy. However, JAIF summarizes as follows…
    1. Cool reactors 1 and 3 by circulating water through them, through coolers, and then purify the water for re-use. It sounds like a closed loop, of some sort
    2. TEPCO will have to stop the continued leakage from the #2 reactor system by “patching the damaged section” before applying the cooling process planned for the other 2 units.
    3. Because Unit #2 will take the longest to bring to a cold shutdown condition, its time-line will be essentially the “critical path” toward completion. The “critical path” is that part of a process that will take the longest time to accomplish.
    4. Water purification systems will be used to remove radioactive materials from all waste waters so they can be re-used in the cool-down process.
    5. TEPCO plans to put giant covers over the reactor buildings and use the tested resin sprays to prevent additional airborne releases.
    6. TEPCO will increase the monitoring and sampling points in the surrounding evacuation areas during the first 3-6 months, and the results will determine decontamination measures needed to allow people to return home.
  • TEPCO also reports water level in the underground tunnel from Unit #2 continues to increase, but the concentration of radioactive contamination in the water seems to be decreasing. This seems to be a combination of the relatively rapid decay of iodine 131, and the reduction of radioactive materials leaking out of the plant system. In fact, all tunnel activity levels at Fukushima seem to be dropping.
  • The seawater contamination levels off shore also seem to be dropping, with the exception of the one location 30 km due west of the power plant complex. The sea sampling points 15 km off-shore have not seemed to change since last week.
  • TEPCO has announced that recovery of some of their “thermal” power plants, damaged by the quake/tsunami, has allowed them to no longer have rolling blackouts. The reserve power margin is small, so occasional losses of power to some locations might occur.