Bocksteins and the nilpotent filtration on the cohomology of spaces

N Kuhn has given several conjectures on the special features satisfied by the singular cohomology of topological spaces with coefficients in a finite prime field, as modules over the Steenrod algebra. The so-called realization conjecture was solved in special cases in [Ann. of Math. 141 (1995) 321-347] and in complete generality by L Schwartz [Invent. Math. 134 (1998) 211-227]. The more general strong realization conjecture has been settled at the prime 2, as a consequence of the work of L Schwartz [Algebr. Geom. Topol. 1 (2001) 519-548] and the subsequent work of F-X Dehon and the author [Algebr. Geom. Topol. 3 (2003) 399-433]. We are here interested in the even more general unbounded strong realization conjecture. We prove that it holds at the prime 2 for the class of spaces whose cohomology has a trivial Bockstein action in high degrees.