Ionising radiation dose calculations for the release of I¹³¹ during accident conditions for materials test reactor

The doses and dose rates following a Loss of Coolant Accident (LOCA) in Material Test Reactor MTR reactor have been studied. MTR reactor is an open water pool reactor type. The water pool serves as a shield from radioactive radiations. The most serious accident in this type of reactor is the Loss of Coolant Accident (LOCA) due to rupture either of a primary coolant pipe or of any experimental beam tube. In the present work it has been assumed that pool water drains out due to double ended rupture of the tangential irradiation beam tube (TIC) which has a diameter 150 mm. For an operating power level of 22 MW, the equilibrium core would enter into melting conditions if the pool drain time is less than one hour. It was also assumed that Emergency Core Cooling System (chimney water injection system and siphon effect breaker) were not working. Therefore conservatively a severe damage (⁓80%) is expected to occur to the core, either by a core uncover situation following extended boiling operation, or by a core covered situation with extended boiling. The reactor interiors have been modeled using the Monte Carlo N-Particle Transport code MCNPX 2.7.0. The source term has been determined using the ORIGEN-S code. The doses and dose rates calculations in different places of operator (as phantom of Tissue-Equivalent Material) inside of the reactor building were determined by using Monte Carlo N-Particle Transport (MCNPX).The results show that the dose rate in the control room would be 5.24 SV/h, the dose rate in the reactor hall above the pools on the gate would be 7.20 SV/h and the dose rate in the Emergency control room would be 2.68 SV/h. Those dose rates are extremely high and would lead to fatal doses in short time