All death benefit payments shall be charged to the Death Reserve, other than $3,000 death benefits paid after December 31, 1988 upon the death of an annuitant. All contributions for death purposes under Section 7-172(b)4 shall be credited to the same reserve. Whenever the balance in such reserve at the close of a year exceeds 100% of the average annual charges to this account during the 3 preceding calendar years, the basic actuarial assumptions upon which municipality contribution rates for these purposes are based, shall be reviewed and revised in such manner as is deemed necessary to reduce such balance.