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TABLE 4. UNIT 4 REACTOR, SPENT FUEL POOL: FUKUSHIMA DAIICHI NUCLEAR POWER PLANT: 18 MAY 2011
                                    ASSESSMENT OF STATUS IN TERMS OF FUNDAMENTAL SAFETY FUNCTIONS FOR ACHIEVING A SAFE STATE

                                 Necessary safety function and                                                                                                               TEPCO Roadmap
                                                                                        Observation                                 Evaluation of state
                                            conditions                                                                                                                        countermeasures
                              Spent fuel pool shall be subcritical   - According to TEPCO statement and to its            PARTIALLY ACHIEVED:                       Maintaining the geometry of spent
                              Keff < 0.95 (design value), and sub-     assessment from the water sampling of the spent    CAUTION                                   fuel pool (including aftershocks)
                              criticality shall be demonstrated        fuel pool, TEPCO assumes that the fuel             - Risk of criticality a priori excluded   reinforce by countermeasure 20,
      Control of reactivity




                              and maintained                           assemblies are ‘intact’ (sampling 26 April 2011)     by TEPCO (provided that                 21, 26
                                                                     - New sampling performed (280 mL on 7 May).            geometrically safe configuration is     Make-up/cooling of spent fuel pool
                                                                       The activity concentrations (Cs-134/Cs-137) are      maintained, etc.)                       by external water injection
                                                                       increasing compared with previous                  - Further assessment needed               (countermeasures 18, 22, 28)
                                                                       measurements. Analysis by TEPCO is                 - In order to avoid any potential         No borated water injected
                                                                       continuing                                           problem due to further aftershocks,     No countermeasure explicitly
                                                                     - Only fresh (non-borated) water is being sprayed      make-up with borated water to avoid     mentioned
                                                                       into the spent fuel pool (120 tonnes on 11 May)      any risk of criticality is advised
                                                                     - Hydrazine is being continuously injected           - Monitoring of neutrons and short
                                                                     - No neutron flux measured reported                    lived isotopes to be considered
                              Stable cooling shall be assured        Latest temperature reported: 81 °C after spraying    PARTIALLY ACHIEVED:                       Cooling of spent fuel pool by
                              - Spent fuel pool temperature          on 9 May (no updated data available)                 CAUTION                                   external water injection
                                  should be similar to the spent                                                                                                    (countermeasures 18, 22, 28)
                                  fuel pond design values                                                                                                           Sampling of steam/pool water and
      Residual heal removal




                                                                                                                          Make-up (with borated water) to be
                                  (approx. 30 °C)                                                                         continued                                 measurement of radioactive
                              - To recover the spent fuel pool                                                            Spent fuel pool temperature is not        materials (countermeasure 19)
                                  water level adequately with                                                             reported on May 16                        Circulation cooling of spent fuel
                                  (borated) water to about 7 m                                                                                                      pool
                                  above the top of active fuel.                                                                                                     (countermeasures 23, 24, 25, 27)
                              - To restore spent fuel cooling




[Type text]
Necessary safety function and                                                                                                            TEPCO Roadmap
                                                                                          Observation                               Evaluation of state
                                             conditions                                                                                                                      countermeasures
                                 - To recover the spent fuel pool      -   Fuel assemblies are covered by water           ACHIEVED:                                -   Cooling of spent fuel pool by
Confining radioactive material



                                    water level adequately to                                                             CAUTION                                      external water injection
                                    ensure some form of shielding                                                         -   to continue spraying and/or make         (countermeasures 18, 22, 28)
                                    above the top of active fuel.                                                             up                                   -   Circulation cooling of spent
                                                                                                                          -   to continue monitoring of major          fuel pool (countermeasures 23,
                                                                                                                              spent fuel pool parameters               24, 25, 27)
                                                                                                                              (temperature, water level)           -   Sampling of steam/pool water
                                                                                                                          -   to improve radiation protection          and measurement of radioactive
                                                                                                                                                                       materials (countermeasure 19)
                                                                                                                                                                   -    Reactor building cover
                                                                                                                                                                        (countermeasures 5, 50, 54,
                                                                                                                                                                        55)
                                 -   Releases shall be only within     -   Uncontrolled release are not expected so far   PARTIALLY ACHIEVED:                      -   Nos 10, 12, 29–46 cooling of
                                     the agreed allowed legal limits   -   Radiation monitoring positions are available   CAUTION                                      spent fuel pool by external
                                 -   Radiation monitoring              -   According to a TEPCO statement, fuel           - Radioactive releases to be prevented       water injection
Limiting effects of releases




                                     measurements shall be                 assemblies are assumed to be ‘intact’.           by sufficient water make-up                (countermeasures 18, 22, 28)
                                     available                             However, further assessment by TEPCO of        - Reactor building cover to be pursued   -   Circulation cooling of spent
                                 -   Leakages from the spent fuel          the latest sampling should confirm this                                                     fuel pool (countermeasures 23,
                                     pool should prevented or              statement                                                                                   24, 25, 27)
                                     controlled, or if not shall be                                                                                                -   Sampling of steam/pool water
                                     confined                                                                                                                          and measurement of radioactive
                                                                                                                                                                       material (countermeasure 19)
                                                                                                                                                                   -   Reactor building cover
                                                                                                                                                                       (countermeasures 5, 50, 54, 55)

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Table 4: Unit 4 Reactor: Fukushima Daiichi Nuclear Power Plant - 18 May 2011

  • 1. TABLE 4. UNIT 4 REACTOR, SPENT FUEL POOL: FUKUSHIMA DAIICHI NUCLEAR POWER PLANT: 18 MAY 2011 ASSESSMENT OF STATUS IN TERMS OF FUNDAMENTAL SAFETY FUNCTIONS FOR ACHIEVING A SAFE STATE Necessary safety function and TEPCO Roadmap Observation Evaluation of state conditions countermeasures Spent fuel pool shall be subcritical - According to TEPCO statement and to its PARTIALLY ACHIEVED: Maintaining the geometry of spent Keff < 0.95 (design value), and sub- assessment from the water sampling of the spent CAUTION fuel pool (including aftershocks) criticality shall be demonstrated fuel pool, TEPCO assumes that the fuel - Risk of criticality a priori excluded reinforce by countermeasure 20, Control of reactivity and maintained assemblies are ‘intact’ (sampling 26 April 2011) by TEPCO (provided that 21, 26 - New sampling performed (280 mL on 7 May). geometrically safe configuration is Make-up/cooling of spent fuel pool The activity concentrations (Cs-134/Cs-137) are maintained, etc.) by external water injection increasing compared with previous - Further assessment needed (countermeasures 18, 22, 28) measurements. Analysis by TEPCO is - In order to avoid any potential No borated water injected continuing problem due to further aftershocks, No countermeasure explicitly - Only fresh (non-borated) water is being sprayed make-up with borated water to avoid mentioned into the spent fuel pool (120 tonnes on 11 May) any risk of criticality is advised - Hydrazine is being continuously injected - Monitoring of neutrons and short - No neutron flux measured reported lived isotopes to be considered Stable cooling shall be assured Latest temperature reported: 81 °C after spraying PARTIALLY ACHIEVED: Cooling of spent fuel pool by - Spent fuel pool temperature on 9 May (no updated data available) CAUTION external water injection should be similar to the spent (countermeasures 18, 22, 28) fuel pond design values Sampling of steam/pool water and Residual heal removal Make-up (with borated water) to be (approx. 30 °C) continued measurement of radioactive - To recover the spent fuel pool Spent fuel pool temperature is not materials (countermeasure 19) water level adequately with reported on May 16 Circulation cooling of spent fuel (borated) water to about 7 m pool above the top of active fuel. (countermeasures 23, 24, 25, 27) - To restore spent fuel cooling [Type text]
  • 2. Necessary safety function and TEPCO Roadmap Observation Evaluation of state conditions countermeasures - To recover the spent fuel pool - Fuel assemblies are covered by water ACHIEVED: - Cooling of spent fuel pool by Confining radioactive material water level adequately to CAUTION external water injection ensure some form of shielding - to continue spraying and/or make (countermeasures 18, 22, 28) above the top of active fuel. up - Circulation cooling of spent - to continue monitoring of major fuel pool (countermeasures 23, spent fuel pool parameters 24, 25, 27) (temperature, water level) - Sampling of steam/pool water - to improve radiation protection and measurement of radioactive materials (countermeasure 19) - Reactor building cover (countermeasures 5, 50, 54, 55) - Releases shall be only within - Uncontrolled release are not expected so far PARTIALLY ACHIEVED: - Nos 10, 12, 29–46 cooling of the agreed allowed legal limits - Radiation monitoring positions are available CAUTION spent fuel pool by external - Radiation monitoring - According to a TEPCO statement, fuel - Radioactive releases to be prevented water injection Limiting effects of releases measurements shall be assemblies are assumed to be ‘intact’. by sufficient water make-up (countermeasures 18, 22, 28) available However, further assessment by TEPCO of - Reactor building cover to be pursued - Circulation cooling of spent - Leakages from the spent fuel the latest sampling should confirm this fuel pool (countermeasures 23, pool should prevented or statement 24, 25, 27) controlled, or if not shall be - Sampling of steam/pool water confined and measurement of radioactive material (countermeasure 19) - Reactor building cover (countermeasures 5, 50, 54, 55)