Radiation Chemistry of Radioactive Nitrogen Species in BWR Reactor Cores

Abstract

Chemical behavior of nitrogen species in intense radiation fields was studied. Simulation models and a N/H/O reaction scheme were developed and verified with a series of experiments. The following results and suggestions were obtained:

1.	Ammonium formation rates in water pressurized with H2 and N2 gases at temperatures of 288~473 K were measured and numerically simulated with the reaction scheme within an error factor of 2.
2.	Chemical behaviors of radioactive nitrogen (13N and 16N) were also theoretically analyzed. Computer simulations demonstrated that the major species of radioactive nitrogen released to the main steam was nitric oxide (NO). This prediction was partly supported by a 13N analysis in the main steam of an actual BWR: About 85% of the 13N was found to be in anionic species whose precursor was supposed to be NO.
3.	Calculated results showed that 13N and 16N in the main steam under hydrogen water chemistry increased similarly but quantitatively not identical with each other: Nitrogen-13 seemed less volatile than 16N.
4.	Numerical simulation showed 16N released to the main steam might be decreased by addition of hydrogen atom scavenger such as nitrous acid in the reactor water.

KEYWORDS:

• BWR type reactors
• radiolysis
• gamma radiation
• nitrogen
• hydrogen
• chemical composition
• reaction scheme
• ammonium
• nitrogen 13
• nitrogen 16
• nitric oxide
• primary cooling system
• steam