Fukushima Update: erratic temperature, radiation increase

Fukushima Update #76, January 23, 2012

by Nelle Maxey

Unit 2

First I will address the CRD Housing temperature sensor which became erratic last week.

It would appear that the sensor is indeed broken and has now been taken offline.
After peaking at +149 degrees on Jan 16, the temperatures began dropping until it bottomed -197 degrees on Jan 19.
See Ex-SKF for the TEPCO temperature chart here.
Some discussion on Physics Forum which again suggested that the sensor had become wet caught my eye:
________________________________________
#12207
So first it measures rising temperatures at the CRD. And then suddenly it's giving us readings from Pluto. Or some other planets where it's as cold as -200°C.
I guess there are two likely answers for such a behaviour:
1) Something heats up the sensor until it fails
2) The sensor was broken all along

So what are the implications of the first case? Corium flowing out of the RPV, first heating the sensor up and then killing it? But why ten months after the shutdown?
#12208
sounds like wet extension wires to me.
thermocouple effect, dissimilar metals in contact with each other, gives you tens of MICRO-volts per degree.
battery effect, dissimilar metals in contact with electrolyte, gives tens or hundreds of MILLI-volts, usually overwhelming the theromcouple.
negative temperature is pretty good clue.
have they changed water injection recently?

Picking up on this comment, I went the JAIF reports I have downloaded and extracted all the data for water injection rates into Unit 2 since they began the core spray in September.
Here is the graph I produced.
Click for larger image Water injection rates
As you can see, the water injection rates indeed changed beginning in December. But during the first week of January a large deviation occurred.

While the total injection rate in January remained steady at 10 m3/hr, 90% of this total injection was through the Core Spray system and only 10% was through the Feed Water line into the RPV.
There is no explanation for this in the reports.
Since there was no rise in temperature within the RPV according to the JANTI parameter reports or the daily temperature reports from TEPCO, one can only speculate on the reasons for this. Perhaps it was just an experiment in adjusting the levels.
I do note that in TEPCO's parameter report today they have returned to the 7 m3/hr core spray and 3 m3/hr feed water line injection rates which prevailed throughout October, November and most of December.
At any rate, the increased core spray rate could have affected the CRD temperature sensor which is attached below the RPV.
TEPCO needs to explain why they did this and if it affected the sensor.
Another problem at Unit 2?
Of note today in the Unit 2 report is the significant increase in radiation in S/C B.
This is in the torus portion of the reactor where the explosion occurred back in March.
On Jan 17 at 5:00am the reading was 1.33E Sv/hr.
This slowly increased until yesterday when a reading at 11am showed 1.61E Sv/hr.
Then by 5pm the reading had increase over 5 times to:
1/22 17:00 8.92E
1/22 23:00 7.58E
1/23 5:00 6.97E
1/23 11:00 6.92E+00
It is slowly falling now as you can see. An explanation from TEPCO is in order however.

5 Issues/yr — $25 print; $15 digital