Fukushima Daiichi Intended To Increase MOX Use In Unit 3

Editors note: Documentation TEPCO #1 Documentation TEPCO #2

Preliminary Analysis of Tepco Documentation 3-2
“Tokyo Electric Power Co., Inc. Fukushima Daiichi Nuclear Power Station Unit 3
According to the results confirm the soundness of the new MOX fuel in the long-term storage”
July 31, 2010
Nuclear and Industrial Safety Agency

Introduction: Analysis of this document began under the premise that MOX fuel could in no possible terms be viable and intact after spending a period of 10-11 years in the spent fuel pool.  Documents show that 32 Mixed Oxide Fuel Assemblies were manufactured and sent to Fukushima-I in 1999.  These fuel assemblies were then stored in the Spent Fuel Pool of Reactor 3 pending local government approval.  This approval did not come until late summer of 2010, at which point arrangements were made and the fuel assemblies were loaded into Fukushima I-3 in September 2010.

Shift of Focus (as it pertains to analysis of Tepco document): Upon periphery work in translating this document, it soon became evident that Tepco was not just seeking approval to install 32 MOX fuel assemblies into the core of Reactor 3 at Fukushima – I.  It appears that they were intentional about taking it a step further and in fact seeking approval for a quick transition to a 1/3 MOX core at the NPP in question.

Below is an excerpt from pages 5-6 of the translated document for consideration:

4.1.2Nuclear reactor core design


Taking into account the impact on the reactivity of the fuel and the characteristics associated with changes in fuel composition will be required to meet the following criteria characteristic of the core nucleus.

  1. Even if one is completely pulled out with a control rod reactivity worth up to be able to subcritical reactor core.
  2. Moderator void coefficient is negative and the Doppler factor.
  3. For boric acid water injection system can be less than the critical core of the reactor rated power operation state, and can be maintained.


(2)Rated by TEPCO

①Evaluation criteria

a. Operating cycle

Is planned core was loaded with MOX fuel in 25 cycles in a cycle following the Unit 3 nuclear power plant Fukushima Daiichi, and MOX fuel since it is expected that the use of three cycles from 25 to 27 cycles of have been evaluated for the core.

The number of MOX fuel loading body

As shown in Table 4.1-2     25 cycles first body 32 in the long-term storage, 26 cycle, the second body 32 of the pending inspection bodies imported fuel, to 27 cycles first new fuel MOX body 80 of the number of body replacement is assumed in the equilibrium core has been evaluated as being loaded with the new.

4.1-2 MOX fuel loading per cycle, the body count

Number of operating cycles*1
for fuel loadingNumber of MOX fuel loading body*2 

New fuel







All the fuel in the furnace


Setting a new basis for fuel loading


25 cycles of
32 body
32 body
MOX fuel in the spent fuel storage pool in Fukushima Daiichi Unit 3
26 cycles of



32 body



64 body




Body examination pending imported fuel (November 14, 2000), MOX fuel


27 cycles of
80 body


144 bodies


MOX fuel per replacement permit a change in the equilibrium core of the analysis established



*1:Operation period of each cycle, the rating is adjusted for duration of operation, including about one month to 13 months
*1:Concerning the operational period of each cycle, in regard to appraisal has included the adjustment operational period of approximately 1 months in 13 months.


(Babel Fish Translation for comparison)
*2:The number of bodies of all fuel assemblies in the core is the body 548.

Talking Point 1:
When looking over this rough translation and table 4.1-2 in particular, the supposition that Tepco was indeed looking at a short term goal of a 1/3 MOX core loaded in Reactor 3 is reinforced.  Taking careful note that there remains to be imported MOX fuel (Nov. 14, 2000) in water cooled storage somewhere pending import inspection.

Talking Point 2:
Information with regard to the operational period of each cycle is given (via google translate) in ambiguous terms.  We can, however, begin with the idea that every 18 months 1/3 of the MOX fuel loaded has to be replaced because it has lost efficiency.  http://dcbureau.org/201103141303/Natural-Resources-News-Service/fission-criticality-in-cooling-ponds-threaten-explosion-at-fukushima.html

If it was indeed Tepco’s intention to rapidly move Reactor-3 to a 1/3 MOX in 3 operating cycles, then we have to assume that this would have to be accomplished prior to the 1st Fuel Assemblies losing their efficiency.  Therefore, I would like to put forth the supposition that Tepco was planning to load the 2nd 32 MOX Fuel Assemblies within a time frame of less than 6 months after the 1st 32 MOX Fuel Assemblies were loaded in the reactor core.  Extrapolating, this leaves the conclusion that March 2011 would have initiated the 26th operating cycle and therefore an additional 32 MOX Fuel Assemblies would have on site at Fukushima I – 3.

Conclusion:  The author of this analysis concedes that “google tranlate” does not offer the best when considering technical documents.

Submitted by:  smoss




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