4.1 Use of this standard practice yields an equivalent boron content (EBC) that can be used to characterize the neutron-absorbing properties of a nuclear material. The elements included in the calculation are typically chosen so that the EBC represents either the entire material (for example, for a moderator) or the impurities in the material (for example, for a nuclear fuel). This practice is typically used for materials in which thermal neutron absorption is undesirable. The EBC is not intended for use as an input to any neutronic calculation. The EBC factors in Table 1 were selected to represent neutron absorption in water reactors under normal operating conditions. It is the responsibility of the user to evaluate their suitability for other purposes.

(A) Neutron Cross Sections , Vol 1, Parts A and B, Academic Press, New York, 1981 and 1984, respectively.(B) Holden, N. E., and Martin, R. L., Pure and Applied Chemistry, Vol 56, p. 653, 1984.(C) When present in small concentrations, this element should be excluded from determinations of the total EBC.(D) In the absence of other data, the neutron capture cross section for a Maxwellian flux is used.(E) Cross section is primarily due to a single isotope, whose isotopic abundance is variable in nature. The value can vary between 733 and 779 barns depending upon the source. See Holden, N. E., Neutron Capture Cross Section Standards for BNL-325, Fourth Ed., BNL-NCS-51388, January 1981.(F) Cross section is primarily due to a single isotope, whose isotopic abundance is variable in nature. The value can vary between 69 and 72 barns depending upon the source. See Holden, N. E., Neutron Capture Cross Section Standards for BNL-325, Fourth Ed., BNL-NCS-51388, January 1981.

This practice details the recommended method for calculating the equivalent boron content (EBC) values of nuclear elements and materials that are of potential significance as thermal neutron poisons. EBC factors are determined from the atomic weight of elements and the thermal neutron absorption cross section in barns. These may be used depending upon the actual neutron energy characteristics of the applicable reactor system. The elements aluminum, fluorine, rubidium, barium, lead, silicon, beryllium, neon, tin, bismuth, oxygen, zirconium, carbon, magnesium, cerium, and phosphorus are not required to be included in the EBC calculations as their contribution to the total poison effect is not considerably significant.