Fukushima Daiichi NPS Prompt Report 2013

This is follow-up information on the suspension of the system C of the multi-nuclide removal equipment (ALPS) due to the activation of "process error alarm" at around 6:43 AM today (on October 4).

We activated the system C of the multi-nuclide removal equipment (ALPS) at 6:31 PM today, as we finished performing the temporal countermeasure after the investigation and examination of the recurrence prevention measure.
We have found no error so far since the activation.
We will also examine a permanent countermeasure.

As for the details of the investigation and recurrence prevention measure, please refer to the following.
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/index-e.html

<Investigation results>
- The multi-nuclide removal equipment (ALPS) is supposed to open the inlet valve of the batch treatment tank, when the water level is above the automatic water ejection level, and when the treatment level of the batch treatment tank is not "H" (high level) at the same time.

- When "process error alarm" was activated, the backwash of the adsorption tower (7C) was performed, since the differential pressure of that adsorption tower was high. The water after the backwash was sent to the waste water tank, and the water level reached the automatic water ejection level. After the waste water tank, the water was to be transferred to "the batch treatment tank (2C)" as a waste saving tank for the waste water tank.

- In the process of accepting RO waste water into the batch treatment tank 2C, the transfer was suspended and the chemical grouting was undertaken, based on the activation of the detection (Level H) calling for the acceptance suspension, due to the higher water level caused by having accepted RO waste water.

- As the batch tank stirring machine was activated after the chemical grouting was undertaken, the liquid surface was upside down, and it led to a temporal resetting of the level of H signal (a signal calling for acceptance suspension) of the batch treatment tank.

- As water level was above the automatic water ejection level, and the signal of the batch treatment tank 2C (which was chosen as a waste saving tank), the inlet valve connecting to the batch treatment tank was opened. Therefore, "process error alarm" was activated because the inlet valve was "opened", regardless of no capacity in the batch treatment tank. The system was automatically suspended. The inlet valve was automatically closed when the alarm was activated.

- We learned that such an alarm is activated when 1)we choose the batch treatment tank of the system C under continuous treatment as a waste saving tank, 2)the water level was above the automatic water ejection level, and 3)the signal calling for suspending the acceptance at the batch treatment as a waste saving tank has been reset.

<Recurrence prevention countermeasures>
Based on the investigation, we will perform the following recurrence prevention measures.
- As a temporal countermeasure, we will choose the batch treatment tank (1B) in suspension as a waste saving tank. In addition, we will "switch off" the power source of the transfer pump, and "close" the outlet valve (manual valve).
- We will perform the followings as a permanent countermeasure, due to the high probability that the same situation would be caused when resuming a hot test for the system B under the temporal countermeasures.

1. We make it a regular rule to automatically choose a batch treatment tank as a waste saving tank (referred as "multi-nuclide inlet"). We will make an alteration, so that some guidance will be displayed, if the "multi-nuclide inlet" is not chosen.

2. We will make an alteration, so that no water will be accepted into the waste water tank while the tank is in the process of treatment (under continuous treatment process), if we choose "each batch treatment tank" as a waste saving tank.