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Koyama, Tomozo; ; Omori, Eiichi; ; ; Shibata, Atsuhiro; Shigetome, Yoshiaki
JNC TN8410 99-027, 423 Pages, 1999/12
The bituminization demonstration facility of Tokai Reprocessig Plant had a fire and explosion incident. The cause of the incident was investigated. Also, the facility condition and release of radioactive materials were evaluated. The cause of the fire and subsequent explosion was determined in a two year investigation. The main cause of the fire was that the temperature of the bituminized product rose to an unusually high temperature by a physical heating phenomena inside the extruder, which was caused by the lowering the feed rate of liquid waste. A moderate chemical reaction in the bituminized product continued and consequently the bituminized product overheated and ignited. The cause of the explosion was the accumulation of flammable gases generated from insufficiently extinguished bituminized product in the filling room in which the ventilation system had been shut down. The flammable gas was ignited by another bituminized product that overheated to the flash point temperature. This report details the condition of the facility before and after the incident, cause of the incident, and an evaluated amount of released radioactive materials.
Miura, Akihiko;
JNC TN8410 99-046, 35 Pages, 1999/10
Judging from several evidences which are operators' testimony, observation result, and so on, the "Committee for an Investigation into the Fire and Explosion Incident at the BDF of the Reprocessing plant of Tokai Works" concluded another fire incident occurred in the filling room (R152) after the explosion (hereafter called second fire incident). This report explains the simulation result of second fire incident. Calculated air temperature and radiation intensity are used another calculations that indicate the thermal influence from the fire name to the extruder or neighboring drums. About second fire incident, calculated result indicates first fire occurred from the No.30104 drum that was produced in 30B or several drums including No.30104 drum. It is estimated that temperature and thermal runaway reaction was not due to fire of neighboring drum because the drum doesn't receive large influence thermally by radiation from the neighboring fire name. Each result suggests the all burnt 29B and 30B drums were filled at higher temperature than usual.
Miura, Akihiko;
JNC TN8410 99-044, 189 Pages, 1999/10
This report includes several results that were made by calculation with several methods to clarify the cause of the fire and explosion incident. In the early times, we didn't have exact information of chemicaI property, reaction rate and any physical constants that we needed. But because the only data that indicate the cooling process of bituminized product was reported, we made heat-transporting calculation with taking this data. Based on the theory of the thermal hazard evaluation that was called Semenov theory or Frank-Kamenetskii theory, the amount of heat generation was estimated using the heat transporting calculation. Common theories were introduced in first section. In the second section, several results of heat transporting calculation were indicated. Calculations were made as follows. First, the model of bituminized product that was filled in the drum was created with the data of cooling process. Second, when the heat was generated in the drum, time-dependent temperature distribution was calculated. And last, judging from the balance of heat generation and heat radiation the critical heat rate was estimated.
; Miura, Akihiko; ;
JNC TN8410 99-043, 135 Pages, 1999/10
All result of chemical analysis and operators observation suggest non-chemical mechanism raised the filling temperature of the bituminized product at the incident. We, Tokai reprocessing plant safety evaluation and analysis team, performed the experiment using laboratory scale extruder and viscosity measurement to explain the high temperature of mixture. The result of the experiment using laboratory scale extruder showed that the phenomena of salt enrichment and salt accumulation oceured and they raised mixture temperature at the decreased feeed rate. These phenomena depend on the feed rate and they have large contribution of heat transportation and rise of operational torque due to the friction between screw and mixture. Based on the experiment result and all information, we investigated the operation procedure, operational records and machine arrangement to try to explain the behavior of the mixture in the extruder. Judging from each torque and temperature behavior, we succeeded in explaining a sequential behavior in the incident. It is estimated that mixture temperature was raised by physical heat generation in the extruder and this report explains each operation, investigated result and estimated event sequences.
