Simulation Study on the Cold Neutron Guides in China Advanced Research Reactor

The designs of the two cold neutron guides, CNG1 adn CNG2, to be built in China advanced research reactor (CARR) are studied with MonteCarlo simulation technique. The neutron flux density at the exit of the both guides can reach above 1×109 cm-2·s-1 under the assumed flux spectrum of the cold neutron source. The transmission efficiency is 50% and 42%, and the maximum divergence is about 2.2° and 1.9°, respectively for CNG1 and CNG2. Neutron distribution along horizontal direction is quite uniformal for both guides, with maximum fluctuation of less than 3%. Gravity can affect neutron distribution along vertical direction considerably.