Wednesday, November 17, 1999

Effects of Tokai Accident

As already written in an earlier story of Femto-Essays, the accident that happened at a nuclear-fuel processing plant in Tokai, Japan, on 30 September 1999 is the worst in recent years. On 4 November 1999, the Science and Technology Agency of the Japanese government announced the estimated exposure dose. During about 20 hours of overcriticality, a person could have been exposed to the dose of 150 mSv at the boundary of the plant, which was about 80 m from the chain-reaction site. An evacuation order had been given to the residents within the distance of 350 m from the site, but the results of estimation indicated that the persons outside the evacuation area might have been exposed to the dose above the annual dose limit of 1 mSv (Asahi-Shimbun).

An article in the "Opinion" column of Nature took up this accident [1]. The author of the editorial writes that the responsibility lies squarely on the shoulders of the government. This is the same opinion as I wrote in the earlier essay. The author says further that the problem of the effectiveness of safety regulation in Japan is not confined to nuclear power, and refers to deficiencies in Japan's regulation of the pharmaceutical industry, commenting on the inability of the Japanese government to set up competent regulatory bodies and the possible continuation of the problem in the future. This is a keen observation similar to the one that might be made by some of Japan's nongovernment parties.

In the concluding paragraph of the editorial, it is written that this is bad news for the world's nuclear industry. The reason given is that despite calls in some circles for its greater use to curb carbon dioxide emissions, the nuclear power generation, expected to expand significantly only in Asia, would meet with more fierce opposition for many years to come. Why does the author (as well as the people of "some circles" mentioned above, possibly) consider that the use of nuclear power should expand only in Asia? The reasons might be: The movement of opposition to nuclear power is weaker in Asia than other areas of the world, and presently the ratio of electricity supplied by nuclear power reactors to the total power generated is rather low in Asia.

In the mother country of Nature, England, electricity supplied by nuclear power reactors in 1998 is 27% of the total power, and no reactors are under construction. This situation falls much behind (or, from the viewpoint of opponents of nuclear power, is much advanced than) that of Japan, where the fractional power of 36% is already generated by nuclear reactors, and two more reactors are under construction [2]. Therefore, people of England also have to make a great effort to reduce carbon dioxide emissions by some method.
  1. "Perils of inadequacies in safety regulation," Nature, Vol. 401, p. 513 (1999).
  2. "Table of Reactors" IAEA Press Release, 29 April (1999).
Further Reading
  • "Report on the preliminary fact finding mission following the accident at the nuclear fuel processing facility in Tokaimura, Japan," IAEA (1999) 35 pp.
Notes Added Later:
  1. I have learnt that England has the advantage of having much natural gas resource in suppressing nuclear power.
  2. On 11 December 1999, the Ministry of Science and Technology announced the results of re-evaluation of the doses the persons around the site of the JCO accident might have been exposed. The revised doses were lower by about 40% than the original estimates.
  3. Hisashi Ouchi, the worker of JCO who was exposed to the highest dose of radiation, died on 21 Dec 1999, the 83rd day since the accident. The dose he was exposed to was estimated to be from 16 to 20 Sv by the National Institute of Radiological Sciences (Asahi-shimbun, 22 Dec 1999).

Sunday, November 07, 1999

Assessment of Producing Mini Black Holes

The construction of a machine for the physics experiment was completed at Brookhaven National Laboratory (BNL) at the beginning of November 1999. The machine is called the Relativistic Heavy Ion Collider (RHIC, pronounced "Rick"), and its purpose is to create the stuff that has not existed since the early universe (quark-gluon plasmas). An article on this machine and related physics has been published in the March 1999 issue of Scientific American [1]. Sending letters to the editors of this journal, some readers expressed worries about the possibility of catastrophic results by the production of unknown matter and miniature black holes. Two of the letters were printed in the July 1999 issue together with the reply from the physicist Frank Wilczek of the Institute for Advanced Study in Princeton, N. J. His conclusion was that a doomsday scenario was not plausible [2].

A committee of distinguished physicists convened by BNL Director John Marburger gave a more complete answer to this Sci-Fi like problem recently. The speculative disaster scenarios considered were:
  • Creation of a black hole that would "eat" ordinary matter.
  • Initiation of a transition to a new, more stable universe.
  • Formation of a "strangelet" that would convert ordinary matter to a new form.
The committee concluded that there were no credible mechanisms for catastrophic scenarios at RHIC. A summary of the committee report can be viewed at a website [3]. BNL Director Marburger said [4], "Nature has been creating collisions of energies comparable to those at RHIC for billions of years, and there is no evidence of any kind of disaster related to those collisions. RHIC does not take us beyond the limits of natural phenomena. It brings a rare phenomenon into the view of our instruments so we can puzzle out its inner workings."

The fact that a comprehensive assessment has been made of the very speculative "disaster" is to be welcomed. However, we should worry about that the assessment of more probable danger is sometimes incomplete in a certain country.
  1. M. Mukerjee, Sci. Amer. 280 (3), 42 (1999).
  2. F. Wilczek, Sci. Amer. 281 (1), 5 (1999).
  3. Brookhaven Natl. Lab., Committee Report on Speculative "Disaster Scenarios" at RHIC (1999).
  4. Brookhaven Natl. Lab. News Release (Oct. 6, 1999).