Table 1: Unit 1 Reactor: Fukushima Daiichi Nuclear Power Plant - 18 May 2011
TABLE 1. UNIT 1 REACTOR: 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 Observation Evaluation of safe state TEPCO Roadmap countermeasures and conditions Reactor is subcritical and - No power spike or power increase ACHIEVED No additional countermeasures sub-criticality is - No significant neutron flux measured and reported Caution: reportedControl of demonstrated and - Short lived fission products (e.g. La-140) are not reported at - Continue detection of The need for boric acid injection isreactivity maintained present neutrons and short- being investigated by TEPCO lived isotopes Stable cooling shall be - The rate of water injection into the reactor pressure vessel of Unit NOT ACHIEVED Nos 1, 3, 4, 7, 8, 9, 13, 14, 16 and 17 assured: 1 was changed from 8 m3/h to 10 m3/h at 20:28 UTC 15 May and Establishment of a long - Keep the coolant was still 10m3/h at 20:00 UTC 16 May. term closed-loop heat Actions aimed to establish closed- temperature sufficiently - Based on available measurements (at 21:00 UTC on 16 May): removal circuit is loop cooling are in progress: below the boiling point • Reactor vessel temperatures are: 92.8 °C at feedwater nozzle advised 1. Installation of primary and at atmospheric pressure and 80.7 °C at the lower head secondary closed-loop cooling - Cover the damaged core • Reactor pressure: (A) 5.96 atm / (B) 14.59 atm) based on systems (planned for 31 May) 2. Flooding of the containment Residual heal removal adequately with water available measurements - Off-site and back-up - In accordance with TEPCO information, after calibration of the to provide water supply for the power supply shall be reactor water level gauges, the actual water level in Unit 1 primary system available reactor pressure vessel has been lower than was indicated. The - Achievement of long results of provisional analysis show that fuel pellets melted and term closed-loop heat fell to the bottom of the reactor pressure vessel. TEPCO also removal capability reported that leakage of cooling water from the reactor pressure vessel is likely to have occurred. TEPCO considers that the actual damage to the reactor pressure vessel is limited, on the basis of the temperatures at present measured around the reactor pressure vessel. - 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[Type text]
Necessary safety function Observation Evaluation of safe state TEPCO Roadmap countermeasures and conditions - Containment pressure - Pressure in the primary containment vessel is maintained at about ACHIEVED Nos 2, 6, 11 and 15 maintained below design 1.0 atm which is well below the design operating pressure of 4.85 Caution:Containment integrity limits atm - Pressure and H2 - Hydrogen explosion to - Nitrogen injection is maintained concentration of the be prevented containment to be further monitored - Reactor pressure vessel - Reactor pressure vessel is assumed to be leaking most probably PARTIALLY Nos 5, 10, 29–46, 50, 54 and 55 Confining radioactive (including connected through connected recirculation system (pump seal loss of coolant ACHIEVED TEPCO has on 13 May commenced systems) should not leak; accident) Caution: the preparatory work for the material or if so the leakage shall - Exiting gap in pressure containment vessel is assumed (ongoing - radioactive releases installation of a cover for the reactor be confined injection of nitrogen has not led to increase of pressure in including venting building of Unit 1. - Leakages from the pressure containment vessel) operations should be containment should be limited, controlled and prevented or controlled, monitored or shall be confined - No additional releases - Intermittent releases have been observed PARTIALLY Nos 12, 47–49, 51–53, 55–63 Limiting effects of shall be anticipated - Radiation monitors are available ACHIEVED - Radiation monitoring - Reactor pressure vessel and pressure containment vessel are Caution: In order to reduce air radiation levels releases measurements shall be assumed to be leaking. - radioactive releases inside the reactor building, a filtered available - Opening of the airlock in the reactor building did not lead to including venting air circulation system and system measurable increase in the releases to the environment operations should be circulating outside air through the limited, controlled and building have been installed monitored
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