Core damage better in unit 1, slightly worse in 2&3, according to TEPCO reanalysis

28 April 2011

TEPCO has revised its estimates of the extent of fuel damage in units 1, 2 and 3 of the Fukushima Daiichi nuclear power plant.

Reactor-by-reactor, system-by-system summary from JAIF as of 28 April
Reactor-by-reactor, system-by-system summary from JAIF as of 28 April; yellow indicates abnormal/unstable; red means damaged/nonfunctional

It said that mistakes made in data measured by the gamma detector-based Containment Atmospheric Monitoring System (CAMS) in each unit's drywell and wetwell has thrown off the estimates.

As a result of the correction, its estimates of the unit 1 core damage ratio have decreased from 70% to 55%. The change is due to a corrected CAMS radiation measurement in the unit 1 wetwell that was one-third of the original value.

Its estimates of the unit 2 core damage ratio have increased from 30% to 35%. The change is due to a reinterpretation of a prior CAMS radiation wet well measurement, which has not changed. Core damage measurements are estimated based on a radiation-versus-time logarithmic chart. Contour lines on the chart mark 5%, 10%, 25%, 50%, 75% and 100% damage. TEPCO estimates the extent of core damage by plotting the measurements and interpolating the distance between contour lines. It has reassessed its earlier estimation.

Its estimates of the unit 3 core damage ratio have also increased, from 25% to 30%. The change is due to plotting different data on the graph. TEPCO used radiation measurements from 62 hours after reactor scram for the unit 3 drywell, but did not plot 62-hour data for the wetwell, for reasons that are unexplained. The data has now been plotted.

FilesReactor-by-reactor, system-by-system Fukushima Daiichi summary from JAIF as of 3 May 2011
Fukushima-Daiichi plant parameters as of 1 May 2011

Privacy Policy
We have updated our privacy policy. In the latest update it explains what cookies are and how we use them on our site. To learn more about cookies and their benefits, please view our privacy policy. Please be aware that parts of this site will not function correctly if you disable cookies. By continuing to use this site, you consent to our use of cookies in accordance with our privacy policy unless you have disabled them.