Reactor Water Chemistry DOE-HDBK-1015/2-93 EFFECTS OF RADIATION ON WATER CHEMISTRY (SYNTHESIS) Rev. 0 CH-03 Page 9 In the preceding discussion, the reactions possible after the addition of air to reactor coolant containing hydrogen were described.  These are Reactions (3-13), (3-14), and (3-16).  The relative rates of these reactions are of considerable importance.  Briefly, Reaction (3-13) is much more rapid than either of the others, and Reaction (3-16) is faster than Reaction (3-14).  Thus, the sequence of reactions is as described in the preceding sections.  H   and O   react to form 2 2 water.  If hydrogen remains, it undergoes an incomplete reaction with N   to form small amounts 2 of NH .  If O   remains after all the H   has been consumed, the O   - N   reaction produces nitric 3 2 2 2 2 acid. The flux of neutrons and protons in a nuclear reactor core region leads to several important nuclear reactions with the constituent atoms of water.  Most of these reactions involve oxygen isotopes and fast neutrons or protons. In many cases, the absorption of a fast neutron by a nucleus is immediately followed by ejection of  a  proton.  These reactions are called neutron-proton or n-p reactions and are commonly written (using the    O reaction to illustrate) in the following manner. 16 O (n, p)    N (t = 7.13 seconds) (3-17) 16 16 8 7 1/2 In this notation, the original isotope that undergoes the reaction is written first, the product isotope is last, and the two are separated by, in order, the particle absorbed and the particle emitted.  The isotope    N decays to    O with a 7.13-second half-life by emitting a beta particle 16 16 7 8 ( ) and a high-energy gamma ray (6 Mev predominantly). - N        O + + 16 16 7 8 Oxygen-17 undergoes a similar reaction. O (n, p)    N (t = 4.1 seconds) (3-18) 17 17 8 7 1/2 The isotope     N decays by emission of a beta particle, a neutron, and a gamma ray. 17 7 N        O + +   n + 17 16 1 7 8 0 Reactions (3-17) and (3-18) have no significant chemical effect on reactor coolant because of the relatively small number of atoms that undergo these reactions.  They are of considerable importance, however, because the radioactive species    N and    N are carried outside the core 16 17 7 7 region by the flow of reactor coolant.  The neutrons and high-energy gamma rays emitted by these  isotopes  easily  penetrate  the  piping  and  components  that  contain  the  coolant  and  are important considerations in the design of shielding for nuclear facilities.  Because the half-lives of these isotopes are very short, they decay to low levels very rapidly after shutdown and are, therefore, of little concern during such periods.