97.07×10^15 Bq of plutonium is ready to be released

97.07×10^15 Bq = 97,070,000,000,000,000 Bq = 97.07 quadrillion Bq

Xenon 133 and 135 were measured at reactor 2. We reported earlier that Tepco explained it is from “spontaneous fission” of Curium.

Curium-244 decays into Plutonium 240 by emission of an alpha particle, but it also absorbs neutrons resulting in a small amount of heavier curium isotopes.

Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 20 grams of curium. The discovery of curium, as well as americium, in 1944 was closely related to the Manhattan Project, the results were confidential and declassified only in 1945. The most commonly used curium isotopes are 242Cm and 244Cm with the half-lives of 162.8 days and 18.1 years, respectively. All isotopes between 242Cm and 248Cm, as well as 250Cm, undergo a self-sustaining nuclear chain reaction. The mixed-oxide (MOX) fuel, which is to be used in power reactors, should contain little or no curium because the neutron activation of 248-Cm will create californium. Currently, curium is not used as a nuclear fuel owing to its low availability and high price. 245-Cm and 247-Cm have a very small critical mass and therefore could be used in portable nuclear weapons, but none have been reported thus far. Curium-243 is not suitable for this purpose because of its short half-life and strong α emission which would result in excessive heat. Curium-247 would be highly suitable, having a half-life 647 times that of Plutonium 239. The longest-lived isotope of curium, 247Cm, has a half-life of 15.6 million years. Therefore, all primordial curium, that is curium present on the Earth during its formation, should have decayed by now. Curium is produced artificially, in small quantities for research purposes. Furthermore, it occurs in spent nuclear fuel.

Curium is produced in small quantities in nuclear reactors, and by now only kilograms of it have been accumulated for the 242-Cm and 244-Cm and grams or even milligrams for heavier isotopes. In nuclear reactors, curium is formed from 238U in a series of nuclear reactions. In the first chain, 238-U captures a neutron and converts into 239-U, which via β–decay transforms into 239-Np and 239-Pu. Further neutron capture followed by β–decay produces the 241-Am isotope of americium which further converts into 242-Cm SOURCE

However, the possibility that curium decays to Xenon is extremely low.

The possibility of the spontaneous fission of 242-Cm = 6.2×10^-6% = 0.0000062%

The possibility of the spontaneous fission of 244-Cm = 1.4×10^-4% = 0.00014%

This means in reality that the rest of the curium is decaying to plutonium at the following percentages:

Cm-242 decays to Pu238 at 0.9999938%

Cm-244 decays to Pu240 fat 0.99986%

(Curium decays to plutonium after the period of the curium half life time)

According to Tepco’s release data, the inventory of Curium just after 311 was:

  • 242-Cm: 9.32×10^16 Bq
  • 244-Cm: 3.87×10^15 Bq
  • Total: 97.07×10^15 Bq

This is why they “managed to” catch Xenon even though it’s only 0.0000062% and 0.00014% likely to happen. It seems that their inventory of curium is massive.

Also, more than 99% of 97.07×10^15 Bq of Curium will decay to plutonium 238 and 240.

The half life time of 242-Cm is only 162.8 days. (about 5 months)

Thus, we can think most part of 97.07×10^15 Bq of curium is already becoming plutonium-238.

From the press release material of tepco, out of the gas controlling system, 0.6 cubic meters of evaporated water comes out of the container vessel per hour.

Its possible that a considerable amount of plutonium may have leaked already.

(Source)

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