Simply Info gives a hint of what burned in sfp4; Tepco’s unknown source.
http://www.fukuleaks.org/web/?p=11668
Quote:It is assumed that most of the radiation releases were from units 1-3 out of the reactor with some potential from the spent fuel pools.
Unit 1 = 20% released (130 Pbq)
Unit 2 = 40% released (360 Pbq)
Unit 3 = 35.5% released (230 Pbq)
*TEPCO considers 110 Pbq of releases to have an unknown source and a total initial release at the plant of 900 Pbq
We saw Unit 4 smoking in the early days, no core in the reactor; it could only be the sfp. Covered over, a fuel removal process started. We saw the CSFP steam up every time a hot load from sfp4 was dropped in. The steaming events and the reported numbers coming out of sfp4 didn’t always match. Reported empty after a year, the CSFP steaming events continued on for another year. The CSFP doesn’t steam up as much now, thus fewer of the webs of radioactive steam sticking to the camera lens. Steam still coming out the side of r4 must be the fuel melt and broken rods still in that leaning, leaky pool. All the Dai-ichi radiation readings we get to see are from ground stations; the emission plumes rising into the air are not measured except maybe by the spark activity on the tepcams. I can hope the reactor melts are being kept cool in basement water but the spent fuel sitting in those pools are the biggest risk of further catastrophic releases. Spent fuel rods should not touch each other. The danger now is fuel rod assemblies coming too close to another and causing a criticality accident.
Fuel Removal from Fukushima Reactor 3 Likely to Be Put Off Again
https://nuclear-news.net/2016/11/19/fuel...off-again/
Quote:It now appears difficult to begin the work in January 2018, as currently targeted by the company, the sources said. The expected postponement is due to a delay in preparations necessary for the removal work.
The fuel removal from the No. 3 reactor pool was initially planned to begin during April-September 2015.
Aug 1, 2015 Unit 3 sfp – The broken fuel removal crane that had fallen into the pool during debris cleaning efforts was removed from the pool. That effort occurred during heavy fogging events and high spark activity. The ENEnews webcam forum had quit functioning making my efforts to document the event more difficult. Damage to the pool and the condition of spent fuel contents aren’t in the public domain. I wonder if the delays are caused by whatever damage there is to the pool/contents.
Search: spent fuel pool zirc fires
Talking Points: Spent Fuel Pool Fires
http://www.nirs.org/wp-content/uploads/r...lfires.pdf
Investigations of Zirconium Fires
during Spent Fuel Pool LOCAs
http://pbadupws.nrc.gov/docs/ML1203/ML120380359.pdf
Quote:After five years, the potential for a zirconium fire is considered to be essentially non-existent due to the low decay heat level of the spent fuel.
ZIRCONIUM FIRES IN POOLS OF SPENT NUCLEAR FUEL:
HIGH-PROBABILITY SCENARIOS AND PHENOMENA
By Mark Leyse, Atomic Safety Organization
A Report Completed for Riverkeeper, December 2013
http://www.riverkeeper.org/wp-content/up...R-FUEL.pdf
Quote:In a SFP LOCA, partial fuel assembly uncovery would be a greater threat to safety than complete uncovery of the fuel assemblies.
Neutron-absorber materials are needed in the SFP storage racks that have densely packed fuel assemblies—high-density storage racks. Neutron-absorber materials are needed to help prevent criticality accidents; in fact, “new rack designs rely heavily on permanently installed neutron absorbers to maintain criticality requirements.”134 High-density storage racks also rely on the particular arrangements of discharged and fresh fuel assemblies that help to control reactivity in the SFP.
Criticality accidents can occur when fuel rods get too close to another. The studies assumed an undamaged pool that had no debris in them. Tepco has to remove the debris without dropping a big chunk into a pool and damaging more fuel assemblies. Another earthquake could cause more structural damage and leave a pile of fuel rods sitting out in the open with no easy way to control the nuclear fires.
"The map is not the territory that it is a map of ... the word is not the thing being referred to."
