ABSTRACT
Reaction rate distribution in concrete with/without boron dopant up to a thickness of 60 cm was measured using Yayoi fast reactor located at University of Tokyo. The 7 reaction rates such as (197)Au(n,gamma), (59)Co(n,gamma), (115)In(n,n'), (55)Mn(n,gamma), (23)Na(n,gamma), (94)Zr(n,gamma) and (96)Zr(n,gamma) were measured at 12 different depths, and the reduction of the reaction rate as a result of boron doping was quantitatively analysed. These reaction rates were also used to determine epithermal neutron spectrum shape parameter. Monte Carlo simulations of the experimental setup were performed using the MCNP-5 code. Simulated depth profiles of reaction rates and the epithermal neutron spectrum shape parameter agreed with the experimental results with fair accuracy. This experimental results provide useful data to benchmark the accuracy of neutron transport codes in the prediction of transmission and neutron spectrum distortion in boron-doped concrete.
Subject(s)
Boron/chemistry , Construction Materials , Neutrons , Computer Simulation , Monte Carlo MethodABSTRACT
We measured the depth distribution of residual long-lived radioactivity in the inner concrete wall of a cyclotron vault by assaying concrete cores and we estimated the neutron flux distribution in the inner concrete wall by means of activation detectors. Nine long-lived radioactive nuclides (46Sc, 59Fe, 60Co, 65Zn, 134Cs, 152Eu, 154Eu, 22Na, and 54Mn) were identified from the gamma-ray spectra measured in the concrete samples. It was confirmed that the radionuclides induced by thermal neutrons through the (n, gamma) reaction are dominant, and that the induced activity by thermal neutrons is greatest at a depth of 5 to 10 cm rather than at the surface of the concrete and decreases exponentially beyond a depth of about 20 cm. By comparing the radioactivity and neutron flux distributions, we can estimate the induced long-lived radioactivity in concrete after a long period of operation from the short-term activation measurement.
