April 25th, 2011 – Reactor 1 Seeming Stop of DW Water Level Increase

Author: 1 Comment Share:

From: Salay, Michael
Sent: Monday, April 25, 2011 7:09 PM
To: Marksberry, Don; Lee, Richard; Esmaili, Hossein; Gauntt, Randall 0
Subject: U1 seeming stop of DW water level increase


Based on this handout (4/23 RPV and PCV level determinations):

It seems that the water level in U1 PCV stopped increasing on the afternoon of 4/18 at -16400mm above reference level.

This is probably why they made the calculations for the two lower water level injection rates 2 and 1 mA3/hr. Their initial calculation was -3 mA3/hr (6 mA3/hr injected – 3 mA3/hr evaporated with the remaining 3 being assumed to contribute to the U1 PCV water level increase.

The pressure trends for both DW sensors seemed to track the 3mA3/hr curve until the time mentioned above.

It seems that the sensors used for this plot are different from those listed in the daily plots for SC and DW pressures – which both seem to read identical pressure (table on 4/21 7:00 Plant Data handout).

The data seems to suggest that the water level reached the DW pressure tap 15150mm above OP (just under RPV bottom head (15200mm above OP)) but then stopped rising soon after, because:

-the pressure difference between the SC tap and this tap stopped increasing.
-the pressure difference between the SC tap and this upper DW tap ([email protected] 28650mm above OP) also stopped increasing.
-the pressure difference between this tap and another in the upper DW 28650mm above OP started increasing but then seemed to have stopped soon after
-the absolute pressure in the (assumed to be) submerged tap (PNL925) started trending upwards.

Note that the level readings don’t always seem to exactly coincide with pressure readings even thought the same pressure data are being used – I’m guessing that this is due to water and steam density assumptions made in the level calculation.

If water level were continuing to rise after reaching the DW PNL925 pressure tap, the level as indicated by the SC:PNL999 – DW:PNL925 pressure trace would have stabilized whereas the level as indicated by SC:PNL999  – DW:PNL999 would have continued to rise.

I don’t know what the leveling off is attributed to – perhaps the water level reached the vessel (hot spots not measured by the reported detector thermocouples) or perhaps the water level reached a leak from the DW.

If it reached a leak it would be expected that the absolute pressure from the lower tap would rise somewhat, faster if the covered leak were a significant amount of the total DW leakage.

A hot spot on vessel being reached by the water would also increase DW pressure from increased steaming.

Also coincident with this leveling off: a small perturbation in the FW nozzle temperature provided in the daily status plots I don’t know why the absolute DW pressure (DW:PNL925) didn’t level off after N2 injection.

If they are leaking at 30%/day (calculated before nitrogen injection and recalculated based on pressure increase following loss of N2 injection following the LOOP of 4/11 (or 12 -can’t tell from plot)).

The pressure seemed to level off about 4/12 – the rate seemed coincident with a 30% per day exchange rate – i.e. – 1.5 to 2 day gas composition stabilization half time but the change was perturbed by the earthquake so it could have been affected by that.

After the switch to higher purity N2 on April 14, the pressure also started to drop until this level change event.

After more thought about curves:

Why didn’t SC:PNL999 – DW:PNL925 curve level off after water level reached the level of DW:PNL925 tap (i.e. 15150 mm above OP)???

Is the elevation of this tap higher or am I incorrectly understanding how it should work (i.e. once water level exceeds that of a tap, the difference in pressure between two submerged taps should be rho-g-dz and should thus remain constant except for changes in water density)?

I am basing this on the assumption that they are determining the level by subtracting the pressure from the different DW taps from the one SC tap to get both curves.

The labels for the curves seem to indicate this (I can’t make out second line other than the words “pressure” and “water level” – I’m guessing it says something to the effect of “pressure difference converted to water level”).

Do you think I am doing this wrong? Do any of you interpret this differently? If I am interpreting it correctly, the P tap that they are indicating as DW:PNL925 cannot be at the level indicated.

Do you have any other ideas about what the data are showing – have you heard anything about this?

– Mike

From: Salay, Michael
Sent: Monday, April 25, 2011 2:58 PM
To: Marksberry, Don
Cc: Lee, Richard; Esmaili, Hossein
Subject: RE: RST assessment rev 2


Attached is another document related to today’s and Thursdays industry discussions.

I think this is TEPCO‘s document as they have been using the change in pressure upon nitrogen injection to estimate water levels.

This has already been added to Sharepoint.

Another document of interest in the “interesting docs” directory on sharepoint today is the (JNES or JAEA) assessment of plant conditions.

This seems to be the document that industry was referring to about the high water levels in the pedestal region.

At the time I saw this document (or a very similar one) they wanted to keep their assessment restricted – even from TEPCO or US industry perhaps. pre-decisional, not verified.

It seemed that only one individual was putting forth this assessment.

Other Japanese expressed disagreement with this.

It was partially based on the fact that temperatures on the lower heads were showing low.

The pressure differences don’t seem to agree with the level indications shown (1 atm is about 10 meters of water).


From: Salay, Michael
Sent: Monday, April 25, 2011 1:18 PM
To: Marksberry, Don
Subject: RST assessment rev 2

Richard does think that we should look at this. The attached looks like latest version (obtained from Japan RST drive).

I have added this and about 15 other documents to Fukushima working group sharepoint / interesting docs. (I noticed at least one duplicate – will have to go through and remove other duplicates later)

Tomorrow will go over to the Chernobyl seminar or will have a meeting on steam generator tube ruptures (if that can’t be moved earlier) so won’t be able to meet/listen in on call.

BTW: Just put some drawings from site team/RST in G:\DSA\FSTB\Fukushima updates\drawings.

I don’t have time to check/upload to Sharepoint but it seems that some drawings there are not already in Sharepoint.

If you find the time to check and upload any additional ones, let me know.


[toggle_simple title=”Related articles” width=”600″]


Previous Article

April 25th, 2011 -Unit 3 100% Leak rate – Updating Source Term – MELCOR analysis

Next Article

Noteworthy LOCA Events and Reactor Meltdowns