L-R: C Till, C Whittier and J. Hilborn
On June 25 Canadian Nuclear Laboratories (CNL) held a highly-successful Open House in celebration of the 60th anniversary of the Nuclear Power Demonstration (NPD) reactor start-up, at the NPD reactor site. During the celebration John Hilborn, who played a crucial role in the calculations to determine the fuel loading at start-up, visited the Nuclear Heritage exhibit and related an interesting, previously-unrecorded anecdote about the frantic days before criticality in April 1962.
Three reactor physicists, C. Till (Ontario Hydro) C. Whittier (Canadian General Electric) and J. Hilborn (AECL) supervised the step-wise approach to critical in April 1962, by observing the rising neutron level as heavy water was added to the reactor vessel. Calculations done with a “state-of-the-art” Monroe mechanical calculator (no digital computers were available) indicated that for a start-up with fresh natural uranium fuel, the neutron chain reaction would have exceeded the normal design range of neutron power control by raising and lowering the heavy water level in the reactor vessel. Consequently, the plan was to replace a number of natural uranium fuel channels with depleted uranium fuel channels, so the heavy water level could control the “neutron power” over its normal design range (depleted uranium is natural uranium processed to remove fissionable U-235, thereby absorbing, instead of producing neutrons).
However, a few days before start-up, it was discovered that the heavy water was slightly down-graded by light water, to the extent that the depleted uranium would not be needed. So, the start-up was completed in April as scheduled, followed by first electric power to the grid in June. And for the next six months, the relatively small heavy water purification system operated 24/7 to upgrade the moderator to the design purity.
The Society for the Preservation of Canada’s Nuclear Heritage Inc. (SPCNHI) welcomes previously unrecorded stories and anecdotes about the history of Canada’s rich nuclear heritage. We invite oral contributions as well as written ones at all times. Please contact any member of the Board or send your contributions to info@nuclearheritage.com
