Fuel fragments from Fukushima explosions

US Nuclear Officials: Fuel fragments were likely ejected from cladding at the 3 Fukushima reactors

Particles of fuel resemble highly radioactive ‘mystery black substance’ often seen in Japan since 3/11

ENENews,

10 December, 2013

Interview with energy and nuclear policy analyst Mycle Schneider, Dec. 9, 2013 (Emphasis Added): Record radiation levels have been detected at the Fukushima nuclear power plant [...] Mycle Schneider, an independent analyst on energy and nuclear policy, talked in detail about the situation. [...] the latest cases were an indication that “there are many places where there could be very high levels of radiation.” This case, according to Mr Scheider, also indicates that “other places might have received fractions of highly radioactive spent fuel pieces.” [...] “it is obvious that we are facing the situation that is completely unprecedented, unprecedented in scope and unprecedented in complexity.” [...]

NRC: NUREG-2121 “Fuel Fragmentation, Relocation, and Dispersal During the Loss-of-Coolant Accident”, Published March 2012: In light of recent results from the U.S. Nuclear Regulatory Commission loss-of-coolant accident (LOCA) research program [...]  a comprehensive review of past research programs for observations related to the phenomena of fuel fragmentation, relocation, and dispersal [was conducted]. […] Fuel dispersal is the ejection of fuel fragments or particles through a rupture or opening in the cladding. […] Fuel fragmentation—that is, fracture of the fuel pellet into large fragments—appears to occur as soon as any meaningful amount of burnup is accumulated, as low as a few megawatt days per metric ton uranium. Fragmentation in irradiated fuel occurred in all but one case for which it was assessed. The only case in which it did not occur was in an unirradiated fuel rod. […] The review of existing data confirms that fragmentation appears to almost always occur, regardless of burnup and other variables […] Said in another way, the review of existing data confirms that fuel fragmentation and subsequent relocation are real physical phenomena expected under LOCA conditions. Therefore, given that these physical phenomena are expected and with the move to best-estimate methodologies, accounting for the impact of fuel relocation is appropriate. […]

NRC: Generic Issue Proposal — Fuel Dispersal During a LOCA, Oct. 7, 2011: Fuel particles can be expelled from ballooned and ruptured fuel rods during a LOCA. […] the phenomenon can occur well below the regulatory limits […] Potential damages include (but are not limited to) increased radiological activity levels in the coolant and containment, displaced heat load potentially causing flashing of coolant (particularly at pump inlets), erosion of pump components due to entrained fuel particles […] Fuel dispersal is expected to occur in almost every instance where a LOCA results in failed fuel rods […] Fuel dispersal occurred in the TMI-2 accident, and likely occurred in the Fukushima Dai-Ichi accident (based on indications of severe core damage). […] The phenomenon of fuel dispersal is important because of its potential consequences, described above, and because it is currently not taken into account in safety analyses. We believe that fuel dispersal could have a significant impact on debris load, as well as temperature of the coolant, during the reflood and recirculation phases of a LOCA. […]

Could this be why Tepco was required to report that “nuclear fuel material” was in the leaks from the tank farm:

Tepco on August 19, 2013 after a storage tank leaked 100s of tons of water with 80,000,000 Bq/L of strontium-90: “We determined that this incident corresponds to “a case when nuclear fuel material (not in the form of gas) or the like has leaked [...] due to an unpredictable event [...] per Article 18, item 12 of the regulations concerning the operational safety and the protection of specified nuclear fuel material” (A similar event was reported on October 3, 2013)

Also, the dispersed fuel resembles the mysterious black substance observed in the Tohoku and Kanto regions after the explosions.

Video of Boston Chemical Data’s principal investigator Marco Kaltofen discussing his findings after analyzing the mystery substance.