18. Any refund of contributions to be issued as a result of a death must be reduced by the sums awarded to the spouse with interest compounded annually at a rate determined for each period under the Regulation respecting interest applicable under the general retirement plan for the mayors and councillors of municipalities (chapter R-16, r. 1) and accrued from 1 July of the year of assessment to the first day of the month during which the refund is issued, except for the period during which a pension is paid.