The Canadian Nuclear Society tribute to the NRU research reactor on its 40th anniversary featured a panel of scientists and engineers that had been involved at the conception and start-up of the reactor. The capacity audience included many more originals as well as later associates of this most durable and reliable reactor, which still produces some 85% of the worlds medical radioisotopes.

Dave Thompson, Director, Reactors Division, introduced the seven member panel along with a photo of the November 3, 1947 start-up, with panel member John Inglis at the controls, and the others in the background.

Thompson briefly described the reactor and the changing history of commitment to it over the years. He characterised the first eight years as ones of euphoria, where NRU was the crown jewel of research reactors. The next twenty years concentrated on production, followed by a period of budget cuts and dwindling resources. In 1990 some renewal began and then the heavy water leak of 1991 raised the question of upgrading the old machine or letting it go to pasture. It was finally decided to keep it operating long enough to fill the gap until the construction of the planned new IRF (Irradiation Research Facility) in 2005.

Given the state of technology when NRU was designed and built, Thompson said that the reliability had been nothing short of astonishing. There was a rod failure in 1958 which caused a 4 month shutdown. In 1963 the core was converted to run on enriched uranium to increase the neutron flux available for research. This was done in 6 months. Extensive repairs to the vessel took 3 months in 1971 and the vessel was actually replaced in 1974 over a 27 month period. In 1984 a failed fast neutron rod caused a 2 month shutdown. A year later a leaking through tube cost 7 months of down-time and the heavy water leak of 1991 shut the unit down for 11 months. Over its lifetime Thompson stated that the reactor has been available nearly 88% of the time.

Thompson credited this performance to the excellent original construction and to the redundancy built in to the reactor systems. Although the resource requirements are high, the maintainability of the reactor has paid off. Thompson noted that the reactor carries an operation and maintenance staff of 220.

Don Hurst led off the panel presentations with a review of the original considerations that went into the choice of reactor design. He noted that they had hoped for 5 years out of NRX (which finally ran for 40) and reviewed many alternative designs. It was decided to stay with the heavy water concept and a development panel was set up which narrowed the selection down to six types. Dr. W.B. Lewis chose the name National Research Universal and the designation NRU was born. Hurst said that "the British and Americans were interested in plutonium and were approached as possible buyers" but that "plutonium production was not initially of much interest". The USA provided a major source of funding in the early years by buying the spent NRU fuel elements. This also meant that Canada had no need to build a problematical reprocessing plant. Hurst pointed out that on-power fuelling was at first rejected as being too difficult but as design progressed better than expected it was reinstated. Final design was contracted to the C.D. Howe company in Montreal with the National Research Council overseeing the operation.

The next speaker, Harry Collins, stated that the key to NRU's success was people, many of them no longer alive. Once in operation NRU was a major training ground for nuclear operators and professionals, providing Ontario Hydro and Hydro Quebec with the initial personnel for their nuclear industries. Many of the original Atomic Energy Control Board staff also came up through NRX and NRU. Collins noted that the Foundation Co. and Canadian Comstock were on site when the 1952 NRX leak forced evacuation of the site and that many of them would not return. This accident resulted in major modifications to the safety systems that went into NRU and resulted in marked improvement in reliability.

Collins remarked that many commissioning problems stemmed from secrecy surrounding the project, which left manufacturers in the dark about what they were building. Pumps with steel on steel bearings and no lubrication seized up. Rats ate the insulation on electrical motors and shaft seals for heavy water leaked. Collins gave credit to J.L. Gray for finally "lowering the boom" and forcing construction to completion on November 3, 1957.

Collins also noted three important NRU firsts; First reactor contaminated before start-up (someone sawed into a radioactive source and the building had to be decontaminated); first successful on-power fuelling; first female shift supervisor.

John Hilborn went over the wartime origins of the project. NRX was built to enhance the heavy-water reactor system as a backup in case the graphite production-reactor system failed. NRU was built as an engineering test reactor but sale of its spent fuel for plutonium recovery was a major source of funding. (Neither reactor was large enough to be called plutonium production reactors in the military sense of the word). Hilborn related the difficulty of agreeing with the Americans on the analysis of the spent fuel. The Canadian calculations finally proved correct which resulted in a large monetary settlement in favour of Canada.

On the subject of computation, Hilborn explained that there were no computers at the time but that they developed a system of punch cards, using knitting needles to sort the many fuel positions and burn up times in order to calculate accurately at what time to withdraw fuel from the reactor, the exact burnup being critical to the quality of the plutonium.
Hilborn also noted that NRX experience with safety instrumentation was critical to the triplicated design of the NRU systems which has resulted in such remarkable reliability. He closed by noting that the NRU console had no chair. The control system was automatic and did not require an operator to sit at the console for the entire shift.

John Inglis explained that every shift was trained for start-up and that his shift happened to be on duty when the time came at ten after six on a Sunday morning. Because of the lucrative plutonium contracts, Inglis said that the name NRU was magic in the early days. Mention NRU and all the best resources in men and materials were immediately at your disposal. For this reason many early problems were quickly overcome, which led to the reactors remarkable performance.

Turning to the scientific aspects of NRU, Gerald Dolling related the advent of neutron scattering work at CRNL (now CRL). For the first ten years NRU had the strongest neutron source available in the world. This permitted Don Hurst to attract Bertram Brockhouse, who recently received the Nobel Prize for his early work at NRU. Brockhouse in turn brought Dolling over from the UK. Neutron scattering at CRL is still, according to Dolling, at the forefront of world capability. He noted the contribution of Tom Holden in 1983, to the application of neutron scattering to industrial problems.

Phil Ross: Ross provided a slightly different slant on NRU operation. When he came in 1959 to work on pressure tube development, he said that the attitude at the reactor was hard to accept. The loops which had been installed were superb facilities for pressure and fuel tube irradiation work but the reactor was being run for plutonium production first, everything else second. His team had to work graveyard shifts to get any time on the reactor. In the middle of the night they discovered the phenomenon of creep which has been critical to the development of the Candu power reactor.

Ross MacEwan represented the fuel development side of the evening's coverage. He said that under the leadership of W.B. Lewis and Ara Mooradian, some 650 man years of professional effort and $180 million went into the troubleshooting of Candu fuel. Mac Ewan recounted the Douglas Point and Pickering fuel failures of 1970 which required operating rule changes as a crutch for operators until the problem was solved. It had been necessary to limit power ramp on fuel at various burnups to avoid failures, a time consuming and expensive proposition. MacEwan stated that 50 design changes were studied and tested in special NRU bundles designed to simulate power reactor conditions in NRU. They finally discovered that a thin graphite coating on fuel pellets solved the problem but the reasoning was in fact wrong. It finally turned out that graphite lubrication was not preventing the failures but rather protection of the sheath from iodine absorption, which the graphite also provided.

Gerald Dolling summed up the review by stating that the criteria essential to the NRU success story were; the ability of the powers that be to make fast decisions involving huge expenditures; the availability of a vast array of expertise; the plutonium production incentive; the inspired philosophy of triplication of control instrumentation.

These among many other attributes allowed the NRU reactor to play such a critical role in the pressure tube and fuel development for Candu power reactors, to remain one of the worlds primary research tools and to provide nearly 85% of the worlds medical radioisotopes.