(a) Any member may redeposit in the retirement fund, prior to filing an application for retirement, by lump sum payment or by installment payments over a period of one year or for a longer time upon approval of the board, an amount equal to all of the accumulated normal contributions which he has withdrawn, plus regular interest thereon from the date of separation from the retirement system, and his membership is the same as if unbroken by such termination. Except as provided in this section his rate of contribution shall be based on age at the nearest birthday at time of reentrance into the system. If he does not redeposit all of the accumulated normal contributions previously withdrawn he shall be considered as a new member without credit for any previous service.

“Regular interest” as used in this section shall mean that amount of interest which would have been credited to the account of the member on the amount to be deposited at the interest rates established for the system if the contributions required by this section had been on deposit from the date of separation from the retirement system until the amount required to be deposited has been paid.