Study of corrosion product activity due to non-linearly rising corrosion rates coupled with pH effects for long-term operating cycles in pressurized water reactors

Abstract

This work is a study of changes in coolant activity due to corrosion products of extended burn-up cycles of 18-24 months duration, in a typical pressurized water reactor, under pH and boric acid variations. It deals with non-linearly changing corrosion rates coupled with pH effects. The CPAIR-P computer program was modified to accommodate for time-dependent rising corrosion and effects of coolant chemistry. These simulations suggest that the effect of an increase in pH value for an extended 24-month cycle on a specific activity, in the form of a decrease in the said activity, is smeared by the rising corrosion. The new saturation values for activity at the end-of-cycle are lower than with a reactor operated at constant low pH/natural boric acid in the coolant. For a non-linear rise in the corrosion rate coupled with a pH rise from 6.9 to 7.4 and the use of enriched boric acid (30%-40%), coolant activity first rises to a peak value during the cycle and then approaches a much smaller saturation value at the end of the cycle, when compared with the activity for the system having a constant low pH value (6.9) in the coolant. In this work, we have shown that the use of enriched boric acid as a chemical shim actually lowers primary coolant activity when higher pH values, rather than natural boric acid, are employed in the coolant. For multiple long-term operating cycles, the saturation value of corrosion product activity increases in the first two cycles and becomes constant in subsequent ones, due to the high operational pH value for enriched boric acid (40%) as a chemical shim

Immobilization of 60Co and 90Sr ions using red mud from aluminum industry

“…60 Co is one of the cor ro sion prod ucts gen er ated by neu tron ac ti va tion of struc tural ma te ri als in nu clear re ac tors. Nearly all of the long-lived ac tiv ity in the cool ant is due to 59 Fe, 99 Mo, and 60 Co, fur ther more, ac tiv ity of the 60 Co predom i nates in the post-shut down pe riod [2]. On the other hand, 90 Sr is com monly pro duced as a fis sion byprod uct of ura nium and plu to nium in nu clear power plants and re search re ac tors [3].…”