Summary of Reactor Status (2 June 2011)
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1) The reactor at Fukushima Daiichi Nuclear Power Plant is subcritical and stable, with no significant neutron flux or power increase detected. However, boric acid injection is still being considered to ensure subcriticality is maintained. 2) Residual heat removal is not fully achieved, as a long-term closed-loop cooling system has not been established. Actions are ongoing to install primary and secondary closed-loop cooling systems. 3) Containment integrity is also not fully achieved, as pressure and hydrogen levels continue to be monitored for risks of explosions. The condition of the reactor pressure vessel is unknown.
Summary of Reactor Status (2 June 2011)
- 1. Technical Briefing Summary of Reactor Unit Status Based on IEC report of May 31st 2011 Javier Yllera IAEA International Atomic Energy Agency
- 2. UNIT 1 - REACTOR: FUKUSHIMA DAIICHI NUCLEAR POWER PLANT: ASSESSMENT OF STATUS IN TERMS OF FUNDAMENTAL SAFETY FUNCTIONS FOR ACHIEVING A SAFE STATE May 31st 2011 Necessary safety function TEPCO Roadmap Observation Evaluation of safe state and conditions countermeasures Reactor is subcritical and sub- • No power spike or power increase No additional ACHIEVED Control of Reactivity criticality is demonstrated and • No significant neutron flux measured and reported countermeasures reported Caution: maintained • Short lived fission products (e.g. La-140) are not reported at present Boric acid injection is being Continue detection of neutrons and considered by TEPCO short-lived isotopes. Continue the evaluation of need for Boron injection. Stable cooling shall be assured: • The rate of water injection into the reactor pressure vessel of Unit 1 was changed NOT ACHIEVED Nos 1, 3, 4, 7, 8, 9, 13, 14, • Keep the coolant temperature from 6 m3/h to 6,2 m3/h at 21:00 UTC 29 May. 16 and 17 Residual heat removal Establishment of a long term closed- sufficiently below the boiling • Reactor vessel temperatures are: 112 oC at feedwater nozzle and 95.4 oC at the Actions aimed to establish loop heat removal circuit is advised point at atmospheric pressure lower head. closed-loop cooling are in • Cover the damaged core • Reactor pressure: (A) 6,66 atm / (B) 16.24 atm based on available measurements. progress: adequately with water • Changes in temperature and pressure are not significant. • Off-site and back-up power • In accordance with TEPCO information, after calibration of the reactor water level 1.Installation of primary and supply shall be available gauges, the actual water level in Unit 1 reactor pressure vessel has been lower than secondary closed-loop • Achievement of long term was indicated. The results of provisional analysis show that fuel pellets melted and fell cooling systems (planned closed-loop heat removal to the bottom of the reactor pressure vessel. TEPCO also reported that leakage of for 31 May). No completion capability cooling water from the reactor pressure vessel is likely to have occurred reported • Off-site power supply and backup power from portable diesel generators are available 2.Flooding of the • Fresh water injection is provided; however, closed-loop heat removal is not yet containment to provide established water supply for the primary system • Containment is leak-tight • Pressure in the primary containment vessel stabilized at about 1.29 atm which is well NOT ACHIEVED Nos 2, 6, 11 and 15 Containment • Containment pressure below the design operating pressure of 4.85 atm. Caution: integrity maintained below design limits • Nitrogen injection is maintained • Pressure and H2 concentration • Hydrogen explosion to be of the containment to be further prevented monitored • if the RPV is melted through, the containment integrity could be endangered Confining radioactive • Reactor pressure vessel • Reactor pressure vessel is assumed to be leaking. The location of the leak is not clear PARTIALLY ACHIEVED Nos 5, 10, 29–46, 50, 54 (including connected systems) as the level in the reactor is not known. It might be either the possible damaged and 55 Caution: should not leak; or if so the bottom of the reactor or through the connected recirculation system TEPCO has on 13 May • Radioactive releases including leakage shall be confined • Exiting gap in pressure containment vessel is assumed (ongoing injection of nitrogen commenced the material venting operations should be • Leakages from the containment has not led to increase of pressure in pressure containment vessel) preparatory work for the limited, controlled and monitored should be prevented or • TEPCO has reported on 15 May that leakage of cooling water from the reactor installation of a cover for Among other parameters, indications controlled, or shall be confined pressure vessel due to fuel pellets melted and fell down to the bottom of RPV is likely the reactor building of Unit of radiation monitoring system in the to have occurred and TEPCO considers that the actual damage to the reactor 1. drywell should be followed to identify pressure vessel is limited, on the basis of the temperatures at present measured increase in the radioactivity level if around the reactor pressure vessel. the reactor is damaged at the bottom. • No additional releases shall be • Intermittent releases have been observed PARTIALLY ACHIEVED Nos 12, 47–49, 51–53, 55– Limiting effects anticipated • Radiation monitors are available 63 of releases Caution: • Radiation monitoring • Reactor pressure vessel and pressure containment vessel are assumed to be leaking. In order to reduce air • Radioactive releases including measurements shall be available • Opening of the airlock in the reactor building did not lead to measurable increase in radiation levels inside the venting operations should be the releases to the environment reactor building, a filtered IAEA limited, controlled and monitored air circulation system and system circulating outside air through the building have been installed
- 3. IAEA
- 4. Spent fuel pool of Unit 1 • Total of about 150 t of fresh water were sprayed over the spent fuel pool of Unit 1 using a concrete pump truck on May 20 and May 22. • Following a leak test of the fuel pool cooling and clean-up system performed on May 29, this system was used to inject about 168t of fresh water into the spent fuel pool. • Periodical fresh water injection serves to reduce the SFP temperature. However cooling through a closed loop circulation must be pursued. IAEA
- 5. UNIT 2 - REACTOR: FUKUSHIMA DAIICHI NUCLEAR POWER PLANT: ASSESSMENT OF STATUS IN TERMS OF FUNDAMENTAL SAFETY FUNCTIONS FOR ACHIEVING A SAFE STATE May 31st 2011 Necessary safety function and TEPCO Roadmap Observation Evaluation of safe state conditions countermeasures Reactor is subcritical and sub-criticality is • No power spike or power increase No additional countermeasures ACHIEVED Control of Reactivity demonstrated and maintained • No significant neutron flux measured and reported reported • Short lived fission products are not reported at the Caution: moment (e.g. La-140) • Continue detection of neutrons and Boric acid injection is being short-lived isotopes considered by TEPCO • Continue the evaluation of need for Boron injection Stable cooling shall be assured • Injection of fresh water into the RPV was changed from NOT ACHIEVED Nos 1, 3, 4, 7, 8, 9, 13, 14, 16 and Residual heat removal • Keep the coolant temperature sufficiently below 7.0 m3/h to 5.0 m3/h at 21:00 UTC on 29 May. 17 the boiling point at atmospheric pressure • Reactor vessel temperature is: (110.7 oC at feedwater Establishment of a long term closed-loop • Cover the damaged core adequately with water nozzle, reactor pressure vessel pressure is around heat removal circuit is advised • Off-site and back-up power supply shall be atmospheric based on available measurements) available • Changes in temperature and pressure are not • Achievement of long term closed-loop heat significant. removal capability • Water level of reactor core is below about -1500 mm (A) and -2100 mm (B) from the top of active core • Off-site power supply and backup power from portable diesel generators are available • Fresh water injection is provided; however, closed-loop heat removal is not yet established • Containment is leak-tightness • Containment is believed to be damaged: latest NOT ACHIEVED Nos 2, 6, 11 and 15 • Containment pressure is maintained below design measurements show the containment pressure to be Containment limits around atmospheric • Measures to make the containment integrity • Hydrogen explosion to be prevented. • Containment probably damaged following hydrogen leak-tight should be pursued explosion at this unit at 21:14 UTC on 14 March 2011 • Pressure and H2 concentration of the containment to be further monitored • if the RPV is melted through, the containment integrity could be endangered • Reactor pressure vessel (including connected • Reactor pressure vessel is assumed to be leaking. The NOT ACHIEVED Nos 5, 10, 29–46, 50, 54 and 55 systems) should not leak; or if so the leakage shall location of the leak is not clear as the level in the radioactive be confined within allowable limits reactor is not known. It might be either the possible Confining Construction of a cover above the reactor material • Leakages from the containment should be damaged bottom of the reactor or through the building has to be pursued prevented or controlled, or shall be confined connected recirculation system Among other parameters, indications of • Containment is believed to be damaged: latest radiation monitoring system in the drywell measurements show the containment pressure and should be followed to identify increase in reactor pressure vessel pressure to be around the radioactivity level if the rector is atmospheric damaged at the bottom. • No additional releases shall be anticipated • Intermittent releases have been observed PARTIALLY ACHIEVED Nos 12, 47–49, 51–53, 55–63 Limiting effects of • Radiation monitoring measurements shall be • Radiation monitors are available available • White smoke has been observed but is no longer Measures to prevent radioactive releases The transfer of stagnant water from releases reported Samples of water in the turbine building floor and leaking of water with high level the turbine building to the area show high radioactivity releases from the reactor radioactivity to the environment should be radioactive waste treatment and the containment to the environment further pursued facilities is continuing Work to block the trench pit to IAEA prevent release of water with high level radioactivity to the environment is continuing
- 6. Spent fuel pool of Unit 2 • A preliminary walk-down survey by TEPCO employees was conducted inside the Unit 2 reactor building to check the environmental condition from on May 18th. • About 53t of fresh water were injected into the Spent Fuel Pool of Unit 2 via the Fuel Pool Cooling and Clean-up line on May 26 (hydrazine was also added during the injection). • Periodical fresh water injection serves to reduce the SFP temperature. However cooling through a closed loop circulation must be pursued. IAEA
- 7. UNIT 3 - REACTOR: FUKUSHIMA DAIICHI NUCLEAR POWER PLANT: ASSESSMENT OF STATUS IN TERMS OF FUNDAMENTAL SAFETY FUNCTIONS FOR ACHIEVING A SAFE STATE May 31st 2011 Necessary safety TEPCO Roadmap Observation Evaluation of safe state function and conditions countermeasures Reactor is subcritical and sub- • No power spike or power increase ACHIEVED Boric acid was injected on May Control of Reactivity criticality is demonstrated and • No significant neutron flux measured and reported 15 as a precautionary measure to Caution: maintained • Short lived fission products (e.g. La-140) are not reported at present preclude criticality a condition • Continue detection of neutrons and short-lived isotopes • Continue the evaluation of need for boron injection Stable cooling shall be assured: • Stopped injection of fresh water through fire extinguishing lines on May 28, NOT ACHIEVED Nos 1, 3, 4, 7, 8, 9, 13, 14, 16 Residual heat removal • Keep the coolant temperature and injection through feedwater system at a rate of 13.5 m3/h (from May 30) and 17 Establishment of a long term closed-loop sufficiently below the boiling • Increase in temperature have been measured: 122.4 °C on May 29 at the heat removal circuit is advised. point at atmospheric pressure feedwater nozzle (104.6 °C on 22 May); 128 °C at the lower head on May 29 Preparation for injection of water • Cover the damaged core (114.6 °C on 18 May) through the feedwater system is adequately with water continuing: • Reactor pressure vessel pressure and containment pressure reported are • Off-site and back-up power • The water from the about atmospheric; however, the pressure measured on 29 May in the wet supply shall be available condenser was transferred to well is 1.84 atm, showing a slight decrease since May 22. • Achievement of long term the basement of the turbine • Off-site power supply and backup power from portable diesel generators are closed-loop heat removal building on 9 May available capability • Fresh water injection is provided; however, closed-loop heat removal is not yet established • Containment is leak-tight • The latest measurements show the reactor pressure vessel pressure and NOT ACHIEVED Nos 2, 6, 11 and 15 • Containment pressure is containment pressure to be around atmospheric pressure Containment • Measures to make the containment maintained below design limits • On 20 March a sudden significant drop in pressure in the reactor pressure leak-tight should be pursued integrity • Hydrogen explosion must be vessel and a decrease in the containment pressure occurred. The reasons for • Pressure and H2 concentration of prevented this are unknown. One possible explanation is a loss of containment integrity; the containment to be further however, the pressure in the containment was decreasing slowly and at monitored present remains stable at around atmospheric. In addition water on the turbine • If the RPV is melted through, the building floor of Unit 3 does not show high level radioactivity containment integrity could be • Images of Unit 3 showed a crack in the primary containment and steam being endangered. released from the reactor building • Reactor pressure vessel • Reactor pressure vessel is assumed to be leaking. The location of the leak is NOT ACHIEVED Nos 5, 10, 29–46, 50, 54 and 55 (including connected systems) not clear as the level in the reactor is not known. radioactive Construction of a cover above the Confining material should not leak; or if so the • Containment is believed to be damaged; latest measurements show the reactor building should be pursued leakage shall be confined containment pressure is about atmospheric pressure Among other parameters, indications of • Leakages from the radiation monitoring system in the containment should be drywell should be followed to identify prevented, controlled or shall increase in the radioactivity level if the be confined rector is damaged at the bottom • No additional releases shall be • Intermittent releases have been observed PARTIALLY ACHIEVED Nos 12, 47–49, 51–53, 55–63 effects of anticipated • Radiation monitors are available releases Limiting Measures to prevent radioactive • Radiation monitoring • Reactor pressure vessel and pressure containment vessel are assumed to be releases should be further pursued measurements shall be leaking available • White smoke has been observed but is no longer reported • Highly contaminated water flew out into the sea from a pit near the intake channel of Unit 3 (NISA report of May 23) IAEA
- 8. Spent fuel pool of Unit 3 • About 50t of water and about 0.38m3 of hydrazine were injected into the Spent Fuel Pool via the Fuel Pool Cooling and Clean-up System on May 28. • Periodical fresh water injection serves to reduce the SFP temperature. However cooling through a closed loop circulation must be pursued. IAEA
- 9. Spent fuel pool of Unit 4 • Total of about 160t of fresh water was sprayed again over the Spent Fuel Pool using a Concrete Pump Truck on May 27 and 28 (method shown the fig. below). Total of about 0.7 m3 of hydrazine was also injected during those days. • Periodical fresh water injection serves to reduce the SFP temperature. However cooling through a closed loop circulation must be pursued. IAEA