Two on-going questions have remained in the background concerning the Fukushima emergency. First, how did hydrogen find its way into the upper refueling deck of Unit #4 to cause an explosion? There is no evidence of a massive hydrogen release from the pool’s stored fuel bundles, so where did the hydrogen come from? Second, why was there no hydrogen explosion on the refueling deck of Unit #2? The progression of events, including considerable fuel damage inside #2 reactor pressure vessel (RPV), parallels the sequence of circumstances in Units #1 and #3, so why didn’t a hydrogen explosion occur as with the other three buildings? It seems we can now answer the first question, but the second remains open to possibilities.
- Japan’s Atomic Industrial Forum (JAIF) and NHK News have reported that the source of the hydrogen which exploded in the #4 refueling deck came from Unit #3. This web site, as well as French government and American University sources, have previously rejected speculations that the hydrogen explosion in Unit #4 was due to the spent fuel in pool (SPF) #4 having been completely or partially uncovered at some point prior to the onset of spraying operations on March 17. Remote portable camera inspection of the SPF show little or no damage to the fuel bundles, and any damage that may be the case came from hydrogen explosion debris. It now seems the hydrogen came from pathways that interconnect Units #3 and #4, especially the ducting common to both units for the venting of pressure from the containment suppression pool (torus). Unit’s 3&4 were built together, providing common auxiliary systems and interconnections for use by both power plants. These interconnections allowed the hydrogen generated from #3 RPV to cause the unit #4 explosion. The indirect hydrogen pathway between Unit’s 3 & 4 probably delayed the build-up on Unit #4 deck, resulting in the explosion occurring a day after Unit #3 detonated. Plus, it is probable that the Unit #3 explosion occurred nearly 2 days after Unit #1 because the hydrogen from Unit #3 RPV had to fill two refueling decks before detonating, rather than the single deck of Unit #1.This revelation also adds evidence to this web site’s contention that the worst fuel damage is in RPV #3. We can now safely assume that #3’s volume of hydrogen produced from the fuel core was probably the greatest of the three RPVs, sufficient to generate two violent hydrogen explosions. This, combined with the ongoing inversion of temperature gradients above and below the Unit #3 fuel cell, strongly suggests the fuel damage in Unit #3 is worse than that now assumed for Unit #1. If Unit #1 experienced a meltdown, it seems Unit #3 has had a worse one.
- Nuclear and Industrial Safety Agency (NISA) records show some interesting differences between the event sequence at Unit #2 and the other two units. For example, operator’s began injecting seawater into RPV#2 on March 14, but similar seawater injections began with #1 RPV on March 12 (after the #1 explosion) and RPV #3 on March 13 (10 hours before its explosion). In addition, Unit #2 began its venting several hours after Unit#3 venting began, and nearly two days after Unit #1 venting. Both of the above sequential differences indicate that, for some reason not yet possible to ascertain, the operators of Unit #2 must have had indication(s) telling them that the rate at which conditions were deteriorating was much less than Unit #1, and somewhat less than Unit #3. It is unlikely that parametric instruments (e.g. temperatures, pressures, water levels) were functioning reasonably well until after any venting started, when RPV temperatures increased enough to overheat them. It will be most interesting to find out what caused the operators to delay #2 water injection and venting for so long.It will also be interesting to find out where the #2 unit was vented to. Reviewing the last two months of information out of Japan, it seems Units #1&3 were vented internal to the secondary containment, releasing the hydrogen from the RPVs and suppression chambers, resulting in the three hydrogen explosions. Assuming Unit #2 RPV core damage is somewhat similar to the other two, there ought to have been roughly the same amount of hydrogen generated as with RPVs #1 and #3. Thus, venting ought to have resulted in a fourth refueling deck explosion. But, that did not happen. Four possibilities emerge…
- The degree of fuel damage in Unit #2 core is considerably less than anyone (including this writer) have assumed.
- Flying debris from the explosions in refueling decks #1 and #3 penetrated the walls of unit #2 refueling deck, allowing the hydrogen to escape sufficiently to prevent an 8% concentration to build up, thus avoiding an explosive reaction with atmospheric oxygen.
- The reported explosion in the area of #2 suppression pool torus on March 15, soon after venting began, may have been due to hydrogen buildup around the torus, but inside the primary containment (PC). The PC is many times stronger in its construction than the outer containment, so it may well have survived the detonation. If this is the case, much of the core-generated hydrogen may have been removed by the PC explosion, keeping the buildup in the outer containment refueling deck below explosive concentration.
- Or, the operators for Unit #2 realized that a venting like Unit #1 might cause another hydrogen explosion. Instead, they may have vented through the tall external exhaust stack, directly to the atmosphere. If this is the case, we must ask why the operators of Unit #3 did not do the same.
All we know for sure is that Unit #2 experienced no refueling deck hydrogen explosion, and finding out why could be extremely important.
Now, a few other update items…
- TEPCO has told JAIF they are making plans to have workers enter Units #2 and #3 reactor buildings to recalibrate the RPV water level instruments, similar to what was done last week in Unit #1. They will follow the same sequence of preparatory events (e.g. cleaning the air of contaminants, etc.) before sending the workers in.
- TEPCO also informed JAIF and NHK News that the attempt to raise the water levels in RPV #1 and PC #1 to above what they feel is now the top of the remaining fuel cell, has failed. A reactor building basement area was filling up with water almost as fast as the rate of water injections into the RPV and PC, indicating there is yet another leak from the system into the building. It is unlikely that the thick RPV walls are leaking, so it is likely coming either from piping attached to the RPV or leaking instrumentation penetrations. TEPCO says their goal is still to make a temporary “water entombment” surrounding RPV #1.
- Prime Minister Kan reports that the “road map” for complete safe shutdown of the four stricken Fukushima Daiichi power plants is still valid. However, NISA also reports TEPCO is re-thinking the road map based on the new information generated out of the Unit #1 reactor building entries last week. This dichotomy might be due to Kan’s order for all TEPCO press releases to be approved by his office, made two days after the earthquake/tsunami hit. In other words, the road map was approved by Kan, and his controlling nature wants that map followed to the letter. TEPCO doesn’t seem to agree.
- Temperatures in the three stricken RPV’s continue to slowly decrease. The problem, last week, of getting cooling water into RPV #3 seems to have been solved since the temperature readings have decreased this weekend. However, as temperatures decrease, the pressure instrument readings remain unchanged. TEPCO ought to recalibrate them, while they’re at it!
- NHK News reports some of the companies in east-central Japan want TEPCO to scrap all Fukushima Daiichi power plants as soon as possible, even entombing the four stricken units similar to Chernobyl. Why? Because the reports of radiation leaks, broadcast around the world, have hurt their international business. Has their business been hurt because of Fukushima, or is it because of the world-wide infection of the Hiroshima Syndrome? You know what this web site would say.
- Saturday, Asahi Shimbun headlined “TEPCO concealed radiation data before explosion at #3 reactor”. Asahi says TEPCO had radiation readings inside reactor building #3 in the 300 millisievert range (30 REM) on March 13, which was not relayed to workers trying to bring the deteriorating condition of Unit #3 under control. Further, Asahi implies that seven workers injured in the March 14 hydrogen explosion chould have been avoided (which may well be the case). However, two “experts” in Japan, Keiji Miyazaki of Osaka University and “another nuclear expert” Kiyoshi Sakuri, believe that public protective actions would have happened sooner if the information was made immediately available, which makes little or no sense. Public announcements of the emergency at Daiichi came but a few hours after the quake/tsunami, and evacuations out to 3 kilometers began at 10:20 at night on March 11. The government declared a state of emergency an hour later. The announcement for a 10 kilometer “stay indoors” precaution came a few hours after that, early in the morning of March 12. By following the public protection factor sequence of events there-after, we find that all reasonable actions were taken well-before the above “concealment” began on March 13. On the other hand, TEPCO maintains that “severe radiation levels inside the plant” were reported as quickly as possible to the Press, but releasing the actual data before it had been internally scrutinized and verified was not possible. Could TEPCO mean this happened after Kan’s “all information goes through my office” dictum was issued? Is there a connection?