The document summarizes the status of fundamental safety functions for Unit 2 at the Fukushima Daiichi nuclear power plant on 18 May 2011. It finds that stable cooling and containment integrity had not been achieved, and that radioactive releases were not fully contained. Water levels in the reactor core were low and the containment was likely damaged. Off-site power and backup generators provided electricity but a long-term closed-loop cooling system had not been established. TEPCO's roadmap included pursuing additional countermeasures to cool the reactor, prevent further releases, and monitor radiation levels.

1. TABLE 2. UNIT 2 REACTOR: FUKUSHIMA DAIICHI NUCLEAR POWER PLANT: 18 MAY 2011
ASSESSMENT OF STATUS IN TERMS OF FUNDAMENTAL SAFETY FUNCTIONS FOR ACHIEVING A SAFE STATE
TEPCO Roadmap
Necessary safety function and conditions Observation Evaluation of safe state
countermeasures
Reactor is subcritical and sub-criticality is - No power spike or power increase ACHIEVED No additional
Control of
Reactivity
demonstrated and maintained - No significant neutron flux measured and reported Caution: countermeasures reported
- Short lived fission products are not reported at the - Continue detection of neutrons The need for boric
moment (e.g. La-140) and short-lived isotopes injection is investigated by
TEPCO
Stable cooling shall be assured - Reactor vessel temperature is: (115.1 °C at NOT ACHIEVED Nos 1, 3, 4, 7, 8, 9, 13, 14,
- Keep the coolant temperature feedwater nozzle, reactor pressure vessel Establishment of a long term closed- 16 and 17
Residual heat removal
sufficiently below the boiling point at pressure ≤ 1.0 atm based on available loop heat removal circuit is advised
atmospheric pressure measurements)
- Cover the damaged core adequately - Water level of reactor core is below about
with water −1500 mm (A) and −2100 mm (B) from the top
- Off-site and back-up power supply of active core
shall be available - Off-site power supply and backup power from
- Achievement of long term closed-loop portable diesel generators are available
heat removal capability - Fresh water injection is provided; however,
closed-loop heat removal is not yet established
- Containment is leak-tight - Containment is believed to be damaged: latest NOT ACHIEVED Nos 2, 6, 11 and 15
- Containment pressure is maintained measurements show the containment pressure to - Measures to make the
Containment
below design limits be around atmospheric
integrity
containment leak-tight should
- Hydrogen explosion to be prevented. - Containment probably damaged following be pursued
hydrogen explosion at this unit at 21:14 UTC on - Pressure and H2 concentration of
14 March 2011 the containment to be further
monitored
- Reactor pressure vessel (including - Reactor pressure vessel is assumed to be NOT ACHIEVED Nos 5, 10, 29–46, 50, 54
radioactive material
connected systems) should not leak; or leaking, most probably through connected Construction of a cover above the and 55
if so the leakage shall be confined recirculation system (pump seal loss of coolant reactor building has to be pursued
Confining
within allowable limits accident)
- Leakages from the containment should - Containment is believed to be damaged: latest
be prevented or controlled, or shall be measurements show the containment pressure
confined and reactor pressure vessel pressure to be
around atmospheric
[Type text]

2. TEPCO Roadmap
Necessary safety function and conditions Observation Evaluation of safe state
countermeasures
- No additional releases shall be - Intermittent releases have been observed NOT ACHIEVED Nos 12, 47–49, 51–53, 55–
anticipated - Radiation monitors are available Measures to prevent radioactive 63
Limiting effects of releases
- Radiation monitoring measurements - White smoke is observed emanating releases and leaking of water with The transfer of stagnant
shall be available continuously from the reactor building high level radioactivity to the water from the turbine
- Samples of water in the turbine building floor environment should be further building to the radioactive
area show high radioactivity releases from the pursued waste treatment facilities is
reactor and the containment to the environment continuing
Work to block the trench
pit to prevent release of
water with high level
radioactivity to the
environment is continuing
Spent fuel pool of Unit 2
About 56 tonnes of fresh water was injected into the spent fuel pool of Unit 2 via the fuel pool cooling and clean-up line from 04:09 until 05:45
UTC on 10 May.
Hydrazine was injected from 04:19 UTC until 05:35 UTC on 10 May.
The temperature of the pool was 47 °C at 20:00 UTC on 16 May.