The JCO Criticality Accident Assessment Committee, organized by CNIC together with the Japan Congress Against A- and H- Bombs and established in Dec. 1999, recently compiled and released an interim report which criticizes the government's safety review of the JCO facility and emphasizes the responsibility of those who commissioned that review. Following is a brief summary of the report.
The amount of uranium nitrate put into the precipitation tank was said to be 16.6 kg, but examination of the contract between JCO and Japan Nuclear Cycle Development Institute (JNC) for the order of the uranium solution, and other documents, indicates that only about 15 kg was supposed to have been manufactured. Clarifying this point is of the utmost importance in relation to the amount that led to criticality, but the most basic of facts such as this are not examined by the Nuclear Safety Commission (NSC)'s investigation at all. The commission finished its accident inquiry in December and has already disbanded, despite not having tracked down the accident's cause.
The main cause of worker's exposure was neutron emissions. On two occasions the government investigation reviewed the workers' exposure assessments, both times lowering their exposure dose. The government's assessment of exposure dose from the accident is grossly under-estimated and will have to be reviewed because the recommendations of the International Commission on Radiological Protection Publication 60, which will be legally adopted in Japan from 2001, assess the impact of neutrons on the human body (quality factor) at double than the quality factor that was used for the current government estimation.
In addition, it has become clear from our survey of local residents that there were many who experienced during the accident, or who are still experiencing, various physical symptoms and illnesses. There needs to be a thorough investigation into the relationship between the accident and these symptoms. An important part of such research would be an investigation into the effects of internal and external exposure from radioactive iodine and rare gases, which have short half-lives.
It was pointed out during the government's safety review of the JCO plant's license application that the precipitation tank was not designed with geometrical control. However, the Science and Technology Agency (STA) avoided dealing with this problem by double-checking the mass control of the tank. Their conclusion was that since the workers would never violate the mass control, criticality was an 'impossibility.' This clear fault in the reviewing process was never brought up in the government's Investigation Committee, but it is obvious that the STA and the NSC, which are in charge of safety reviews, carry grave responsibility for letting the matter slide.
In addition, the NSC's Investigation Committee deliberately avoided pursuing the responsibility of JNC, which placed the order for the particular uranium solution. JNC (formerly PNC) made an order for uranium solution which had a very high concentration of 370 g per liter and demanded procedural specifications for the homogenization process which were difficult for JCO to carry out at its plant. It is written in the contract between JNC and JCO that JCO must provide JNC with the conversion process manual and the conversion process summary (outline) before preparation of the particular uranium solution. Obviously JNC was aware of the illegal procedures that were adobted at the JCO plant. And of course the company was aware from the very beginning that the conversion building of the JCO plant was not installed with sufficient equipment to prepare uranium nitrate solution and was thus unsuitable for preparing high-enriched, high-concentrated uranium solution. The responsibility of JNC is actually the heart of the cause of this accident. Our investigation has gone into depth in this matter. We plan to release the final report of our investigation this fall. By Hideyuki Ban
Radioactive scrap metal was found in Japan on a number of occasions recently. On 28 April 2000, a radiation detector at the gate of Sumitomo Metal Industries in Wakayama Prefecture alerted workers to the presence of radioactive material in a container holding scrap metal imported from the Philippines. The container was opened on 24 May, and a pipe containing the source of radiation was removed. The pipe seemed to be part of a moisture density gauge. Two hundred and thirty MBq of cesium 137 and 1,800 MBq of americium 241-beryllium were detected.
Shortly after that, on 9 May, radiation was detected from scrap metal passing through the gate of the Kobe Steel plant in Kakogawa city, Hyogo Prefecture. The scrap was returned to the scrap-iron dealer. Staff of the Japan Radioisotope Association opened a lead container recovered from the returned scrap metal, and found four cylindrical containers with radium 226 for medical use. It is highly probable that the scrap was disposed of in this way with full knowledge that it is illegal, since the warning label on the lead container had been concealed with adhesive tape.
Incidents in which radioactivity has been traced to scrap metal or discarded medical materials have become common. In recent years there have been a number of incidents in Egypt, Thailand, Taiwan, Spain, and in many more countries. Following such incidents overseas, the Japanese steel industry began setting up radiation detectors at the gates of factories. In contrast, the Science and Technology Agency only began to prepare a manual for treating scrap metal after the two recent incidents in Japan.
Possible improvements in inspection standards at steelworks following the two incidents may well have enabled two recent discoveries. A fragment of depleted uranium was found in a pile of scrap metal at a steelworks in Tamano-city, Okayama Prefecture on 19 June 2000, and two days later, radiation was detected from scrap metal at the gate of a steelworks in Kurashiki city, Okayama Prefecture. The transport routes and the origins of the contaminated materials in Kobe, Wakayama, and Okayama must be carefully investigated in order to prevent any further intrusion of radioactive materials into the public domain.
In early June, envelopes containing monazite (thorium ore) were sent to ten governmental agencies. The letters included in the envelopes gave information on a certain foundation, and from further investigation it was found that the director of this foundation had secretly stored 40 tons of monazite in Saitama, Nagano, and other prefectures across Japan. Only 17 tons of the stored monazite have so far been discovered. The Science and Technology Agency has known of the secret cache of monazite since last November, but did not respond to the matter in any way. This raises the possibility that there are many other places in which radioactive materials are being stored without public knowledge.
Nor can we afford to ignore the debate within the Nuclear Safety Commission's Radioactive Waste Safety Standards Special Committee about the concept of 'clearance level.' (See NIT 69, 'News Watch' and NIT 76, 'Decommissioning'.) The assumption underlying the idea of 'clearance level' is that radioactivity from the huge quantities of scrap metal produced by decommissioning nuclear power plants is of a sufficiently low level to allow such scrap to enter the public domain. However, the recent discoveries of radioactive materials in public spaces show that the concept of 'clearance level,' if legalized, would only increase citizens' vulnerability to unknown sources of radioactivity. Radioactive materials are already creeping into the public domain far too often; introduction of the 'clearance level' would ensure that there were many more such incidents.