Design, construction and facility enhancement for digital neutron radiography at Reactor Triga Puspati

Abstract

Neutron radiography (NR) is an important application in non-destructive testing which has been used especially in industrial, nuclear material, medical and agriculture. Reactor TRIGA PUSPATI (RTP) is the only research reactor in Malaysia which located at the Malaysian Nuclear Agency, with total capacity of 1MW operation. Its main applications are neutron activation analysis, small angle neutron scattering, and neutron radiography. The first NR facility system in RTP was ready for use in 1985. However, this neutron radiography facility known as NUR-2 was disassembled in 2014 due to several factors such as low collimation ratio, low thermal neutron flux, high gamma dose, and inadequate radiation shielding. Thus, there is a need to upgrade the capabilities of existing neutron radiography facility to meet current users’ needs. Monte Carlo simulation code of MCNPX was used to simulate the important parameters and instrument design of the new neutron radiography facility. This simulation code of the neutron beam helps to design experiments before placing any sample objects in the neutron beam. The new collimator, beam shutter, and shielding were fabricated based on the results from Monte Carlo simulations while the concrete mixture of the new exposure room shielding was formulated using Department of Environmental’s design method. The concrete samples were tested in terms of radiation shielding capability and strength. The best mix design was chosen to be fabricated as new exposure room shielding for NR facility at RTP. Furthermore, results obtained from the experimental works were used to verify the simulation modelling. Based on the simulation results, the new NR facility has a thermal neutron flux of 3.86×103 ncm-2s-1 at the sample position. The new collimated beam has been characterized using beam purity indicator and sensitivity indicator from American Society for Testing and Materials. Radiographs of a sensitivity indicator taken using both digital and conventional direct film radiographic method provide one example of the radiographic capabilities of the new facility. The neutron radiograph which was taken by charged-coupled device camera and film showed that digital neutron radiography is not currently capable of producing good quality radiographs but it is mainly due to the limitations of the digital detector itself.