March 15th 2011 – Unclear Fires At Reactor 4 SFP

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Fukushima One Reactor Status

Bottom Line:

Based on an interview with a NISA engineer this morning, the NRC team incorrectly concluded that Unit 2, three fissions barriers were compromised and core cooling was lost. As a result of further discussions with NISA engineers and review of additional radiological data, it is currently believed that this is not the case and the reactor core is being cooled.

Based on an interview with Japanese this morning, the NRC team incorrectly concluded that the Unit 4 spent fuel pool was not being adequately cooled and had experienced a fire. Upon further review throughout the day,

NISA’s position is that the fire was not a fuel fire. Based on this new information, and the information provided by the DOE/NRC dose protections, the team has concluded that the protected actions recommended by the Japanese around the Fukushima are appropriate for American citizens at this time.


Unit 2 – Over the course of the day seawater injection has been reinstated at Unit 2.

Upon further discussions, it is now believed that the reported explosion in Unit 2 may have occurred at Unit 4.

By re-establishing core cooling and by providing additional information regarding the source of the explosion, the teams’ initial assumption that the cause was potentially a breach of the vessel was no longer valid.

The clarification on the explosion location and the conflicting drywell pressure and wet-well pressure indications are still a discrepancy of concern but are not a clear indication of a loss of containment integrity.

Furthermore, there is a possibility that SRV could malfunction.

Unit 4 SFP – Regarding the spent fuel pool fire, this was later explained to us to be an oil fire in the Unit 4 reactor building.

This information was not clearly understood by the team (or NISA at the time of the briefing).

We were told that the level in the SFP is low (exact level undetermined).

NISA indicated that the SFP pool is not being adequately cooled.

They told us that the 40 R/nr reading was taken in the radiation fields between the Unit 3/4 reactors building.

The fields near the SFP would be high. NISA believes there was a hydrogen explosion at Unit 4.

JimTrapp/Tony Ulses – United States Nuclear Regulatory Commission

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