Conference Proceedings Paper
Sticking of the AL-CAN Containing Irradiated TeO2 Target to the Bottom of the Dry Irradiation Channel of the 3MW TRIGA MK-II Research Reactor of Bangladesh Atomic Energy Commission
NURETH-14 - 2011 September 25-30
Md. Shafiqul Islam (Director)
Iodine-131 is one of the most important medical radioisotopes (RI) that are being used at fourteen (14) nuclear medicine centers of the country. It is routinely produced by irradiating TeO2 powder loaded into a heat sealed quartz vial called “target” in the Dry Central Thimble (Dry CT tube) of the 3 MWth TRIGA MK-II nuclear research reactor of Bangladesh. The target is to keep inside the standard irradiation canister/can made of aluminum, called “Al-can”. A few reportable thermal incidents occurred during the irradiation of the TeO2 powder at full power due to lack of proper evaluation of safety of in-core irradiations. Of them, sticking of the Al-can containing 40g irradiated TeO2 target to the bottom of the Dry CT tube at full power (3 MWth) operation of the reactor was one of the major thermal incidents in November 2008. The stuck Al-can with the Dry CT tube in the reactor core was lifted up using an innovative handling tool designed and developed by the author. The physical and visual investigations have identified several weaknesses related to the thermal incident. The thermal problem of the incident has been addressed elaborately and then attempts have been made to solve it using experiments as well as numerical analyses. Two cases (Case-1; Dry CT tube and Case-2; Wet CT tube) have been analyzed both numerically and experimentally. It has found from the numerical analyses and experiments that temperature assessment considering 50g TeO2 power at 3MWth full power operation of the reactor over the walls of the quartz vial and Al-can are about 86 and 700C, respectively which is far below the melting point of these materials for the case of Wet CT tube. On the other hand, temperature over the walls of the quartz vial and Al-can are about 520 and 3700C, respectively for the case of Dry CT tube. The shape and size of the quartz vial and the area of its contact point with Al-can plays a very vital role in rising the temperature of the target material. Target irradiation with 50g TeO2 at full power operation of the reactor under dry condition of the CT tube may cause vial failure due to excessive temperature rise that cause melting of the TeO2/Al-can. It is thus recommended to use a Wet CT tube replacing the existing Dry CT tube for irradiation of more target materials for routine production of RIs in the research reactors to avoid repeating the thermal incident.
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