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Atomic Energy of Canada Limited National Research Universal Reactor Safety System Upgrades and the Canadian Nuclear Safety Commission's Licensing and Oversight Process

II. Background

The NRU reactor is a 135 MWt heavy water reactor operated by AECL at the Chalk River Laboratories (CRL) site. The NRU reactor has multiple purposes, which include the production of medical isotopes, testing of various fuel types, and other irradiation services. It began operation in 1957, and is currently continuing operation with a licence renewed by the CNSC in July 2006, and which expires in October 2011. The licence was issued by the CNSC Commission with the understanding that seven safety upgrades had been installed and were fully functional. The seven safety system upgrades, which had been declared fully operational, were the following:

  • an independent second reactor trip system,
  • a qualified emergency response center,
  • a new emergency core cooling system,
  • a qualified emergency water system,
  • main pump flood protection,
  • liquid and gaseous confinement boundary, and
  • a new emergency power system.

The main issue in this report is related to the new Emergency Power System, which provided a hazard-qualified power supply to the six other upgraded safety systems, while also intended to provide a hazard-qualified power supply to two MHWPs, P-104 and P-105. These latter connections were not made at the time of licence renewal. A general description of the NRU reactor and the safety upgrades is provided in Appendix F.

On November 5, 2007, the CNSC CRL site inspector discovered a statement in an operating manual that the EPS was not connected to the MHWPs. AECL confirmed that to be the case in writing, on November 7, 2007 [1]. CNSC expressed concern that the NRU physical plant was not consistent with the licensing and safety basis. On November 14, 2007, NRU completed a technical operability evaluation (TOE) which concluded that there was no loss of function and that there was reasonable assurance of adequate margins of safety. CNSC was informed of the results of the TOE on November 16, 2007. The NRU reactor was shut down for a four-day scheduled maintenance outage on November 18, 2007. CNSC informed AECL of its concerns regarding the depth and conclusions of the TOE, advised AECL that it was working on a letter stating its concerns, and recommended that AECL not restart the reactor, but no such letter was ever sent.

After much discussion with the CNSC staff, centred on the concern that restarting the reactor was outside of the licensing basis, on November 22, 2007 [2], AECL informed the CNSC that the NRU reactor would not be restarted that day (as originally planned), in order to complete installation and testing of new seismically-qualified direct current (DC) Motor Starters and EPS supplied power for MHWPs P-104 and P-105.

NRU management believed that they had two paths available to resolve the issue. One was to complete the EPS connection to both pumps; the other was to submit and obtain approval of a safety case for one-pump operation. From mid-November to mid-December, the projected end dates for these paths were changing, as progress was made and understanding was gained. NRU shifted its primary success path according to the way in which one path's end date moved ahead of the other.

On November 29, 2007 [3], AECL formally submitted a safety case to support restart with the upgraded EPS connected to one pump (P-105). Both AECL and CNSC staffs recognized that it was unlikely that a prompt resolution would be reached. AECL notified the CNSC on December 2, 2007 [4], that it was not continuing with that option, and that the reactor would only be restarted after both DC motor starters for MHWPs P-104 and P-105 were connected to the EPS. On December 7, 2007 [5], AECL requested regulatory approval for a modification to the Facility Authorization (FA), in order to permit the “one pump” operation for a limited period of time,. CNSC staff informed AECL, in letters dated December 7, 2007 [6], and December 10, 2007 [7], that a complete safety case and request for licence amendment was required of AECL before the matter could be referred to the CNSC Commission. Subsequently, the Minister of Natural Resources Canada and the Minister of Health Canada wrote to the Presidents of the CNSC and AECL on December 10, 2007 [8, 9], and urged them to work together to restart the reactor safely with due regard for those reliant on the medical isotopes produced by NRU. The reactor remained shut down. On December 11 and 12, 2007, the House of Commons and the Senate respectively passed a law [10] which gave AECL the authorization for operation of the NRU reactor for 120 days, with certain conditions. The reactor was restarted on December 16, 2007, and medical isotope production resumed within days.

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