Dr. Manfred Puls

Fuel Material

Manfred Puls obtained a Bachelor of Applied Science degree in Engineering Physics (1964) and a Masters of Applied Science degree in Physics (1965) both from the University of British Columbia, Vancouver, Canada.  Subsequently Puls obtained a PhD degree in Physics (1970) from McMaster University, Hamilton, Ontario, Canada.  Both post-graduate degrees involved experimental studies.  Taking a five month break after completion of his PhD studies, Puls worked with J.S. Kirkaldy (his PhD supervisor) in the Department of Metallurgy and Materials Engineering at McMaster University from 1970 September to 1971 August as a post-doctoral fellow.  The focus of Puls’ studies during this period was theoretical models of the pearlite reaction in steels.

In 1971 September Puls obtained a position as a research scientist in Pinawa, Manitoba at the newly created Whiteshell Nuclear Research Establishment (WNRE) of Atomic Energy of Canada Limited (AECL).  The job entailed setting up a program for determining the effects of neutron irradiation on the mechanical properties of pressure tubes.  One aspect of this involved determining the types and behaviour of point defects produced by high energy neutron irradiation.  This program required fast neutron irradiation of the material at very low (liquid helium and/or liquid air) temperatures and tracking the annealing of the defects produced during subsequent heat up of the sample.

A study was carried out to determine what facility would be best suitable for such work and to determine the feasibility of such a facility being funded and built at the WNRE site.  For theoretical support of such experimental studies it was thought that atomistic calculations of the configurations and energies of point defects, dislocations and their interactions would be needed.  Atomistic modelling was a relatively new field of study that had come into vogue internationally at that time, made practical by the advent of powerful mainframe computers.  The perception amongst some scientists, however, was that the validity of the results of such calculations was compromised for metals because of the difficulty of constructing realistic interatomic potentials for such materials.  This was deemed not to be the case for ionic (ceramic) materials.

An opportunity arose for Puls to spend approximately five months in the summer of 1973 at the Theoretical Physics Divisions of AERE Harwell, Didcot, UK to assist in the development of such programs for ionic crystals.  The Theoretical Physics Division was at that time a hotbed of some of the most talented and knowledgeable theoretical scientists in the world involved in the study of nuclear materials.  The collaboration with this group resulted in the successful production of two very powerful, state-of-the-art computer programs for computation at an atomistic level of the configurations and interaction energies between point defects and dislocations in ionic crystals.  The theoretical predictions made with these programs were within a short few years internationally recognized as being among the best of their kind in this field and led to numerous invitations for Puls for presentations at international conferences.  In addition, invitations were received over a period of time from various research centres for collaborations entailing extended stays at these centres.  These invitations led to the following extended visits: (i) a follow up five-week stay in 1976 August to September at the Theoretical Physics Division in Harwell, (ii) a 10-month stay from 1981 September to 1982 July at the Laboratoire de Métallurgie Physique at the Université de Poitiers, France; and (iii) a two-months stay from 1982 August to September at the Applied Physics Division of the University of Groningen, Netherland.

During the time that Puls was investigating the feasibility of constructing a low-temperature fast-neutron irradiation facility at WNRE, he also became involved in theoretical studies of creep crack growth.  These studies were being pursued because of the initial focus at WNRE on the development of ceramic pressure tubes for the Organic Cooled Reactor (OCR), a test reactor that formed the initial focus of WNRE.  When delayed hydride cracking (DHC) was discovered by the nuclear reactor industry in Canada in 1974 as a cracking mechanism that could occur under certain abnormal conditions in zirconium alloy pressure tubes, a theoretical model for DHC propagation was quickly (within a month) derived by Dutton and Puls.  This DHC propagation model was seminal in providing, for the first time, an analytical expression for DHC rate formulated on the basis of universally applicable thermodynamic principles.  A subsequent important enhancement of the model by Puls involved the derivation of theoretical solvus relationships (the solvus is generally referred to in the industry as terminal solid solubility (TSS)) accounting for the experimentally observed difference between the TSS for hydride precipitation and dissolution.  The incorporation of this theory into the model for DHC rate made it possible to account theoretically for the experimentally observed effect on DHC rate and arrest temperature of direction of approach to the test temperature.  The importance of the model was in providing a rationalization of these experimental results, whilst also serving as a guide for the establishment of test conditions for studying DHC.  Complementing these foregoing studies by Puls on the theory of DHC and TSS was a theoretical model for the effect of stress on hydride orientation.

In 1983 an abnormal service condition in one of the reactors of the Pickering NGS resulted in some of the horizontally oriented pressure tubes contacting their respective surrounding calandria tubes. The contact between these two types of tubes (an out-of-design condition) produced the formation of a row of hydride blisters (lens-shaped regions consisting of a collection of zirconium hydride precipitates of varying densities) on the outside of a number of zirconium alloy pressure tubes in one of the reactors at Pickering NGS. This led to the rupture of one of these tubes during reactor operation. Failure of the tube was subsequently diagnosed as having been caused by the initiation of a crack in at least one of a row of blisters formed on the outside surface of this tube and the subsequent propagation by DHC of the crack in this blister to critical length. Data was required to understand the conditions and the extent to which these blisters could grow under a temperature gradient as well as the stress required to fracture them. Puls – in conjunction with researchers in other laboratories – set up an extensive experimental research program to obtain this information. The data obtained, combined with those from the other researchers, was subsequently incorporated into the physical basis document supporting the first version of the CSA standard N285.8 providing the procedures for the assessment of the results of periodic, in-service inspections of pressure tubes. Other data provided by Puls for the physical basis document supporting this CSA Standard were van’t Hoff type equations derived from fits of TSS data obtained from various experimental studies.

In 1991 Puls became manager of the Materials and Mechanics branch at WNRE (at which time it had been renamed Whiteshell Laboratories (WL)). During this period a theoretical model was derived by Shi and Puls that, for the first time, provided an expression for the threshold stress intensity for DHC initiation (K_IH).  An accompanying model dealt with DHC initiation from volumetric flaws (flaws of know bluntness).  These models relied on data giving the threshold stress to fracture individual hydride precipitate clusters in zirconium materials.  The stresses to fracture such hydride clusters were obtained by Puls and co-workers from the results of a series of experiments in which tensile specimens containing such hydrides were subjected to a rising tensile load.  The hydrides in these tests had been previously grown and were radially oriented.  The fracture stresses were determined for hydrides in different zirconium materials as a function of macroscopic hydride cluster lengths (in the mm-size scale range) and over a range of test temperatures and stress states.  Supporting these experimental/theoretical studies were various internal friction and dynamic elastic modulus studies of Ritchie and Pan and Pan and Puls of hydride formation and dissolution.  From some of these types of tests, data was obtained suitable for deriving TSS relationships.  Most noteworthy with respect to the latter was the ground-breaking study of Pan, Ritchie and Puls showing how maximum temperature in a thermal cycle just prior to cooling, hold time at the maximum temperature, cooling rate and the presence of pre-precipitated hydrides could affect the TSS for hydride precipitation (TSSP).

Further details of Puls’ research activities and publications can be found under his ResearchGate profile.

In 1997 Puls re-located from WL to AECL’s Engineering Company, located at Sheridan Park in Mississauga, Ontario where he was manager of the Fuel Channel Engineering (later Fuel Channel Engineering and Materials) branch.  The Fuel Channel Engineering and Materials branch was a functional branch consisting of the company’s experts knowledgeable in the design, build support, development and service of all aspects of fuel channel technology in CANDU reactors.

Puls was, at one time or another, a member of the following groups:

Puls retired from AECL in 2006 after completing 35 years of service with the company.  Since his retirement from AECL, Puls has carried out consulting work for the Canadian nuclear industry through Kinectrics Inc., under funding provided by the CANDU Owners Group (COG).  A noteworthy achievement during this time – not directly connected with Puls’ consulting work – was the completion by Puls as sole author of a book on DHC entitled The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components: Delayed Hydride Cracking published in 2012 August by Springer Verlag, U.K.  A follow-up to this book, entitled “The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components: Hydride Reorientation, has been completed for publication by ANT International

Aside from his continuing interest in scientific studies involving the field of DHC and fracture of zirconium alloys containing hydride precipitates, Puls enjoys going on daily 5-km-long walks and the occasional bike trip. In addition, living on his own, Puls is kept busy looking after house and garden. Puls also enjoys going to some of the many cultural offerings provided by the nearby city of Toronto such as concerts of the Toronto Symphony Orchestra, Esprit Orchestra (specializing in classical music of contemporary composers), Jazz concerts, the occasional performances of the Canadian Opera Company, the National Ballet and the occasional theatre production. In addition Puls makes full use of the extensive catalogue of concerts available for streaming from the Digital Concert Hall of the Berliner Philarmoniker and keeps in touch with what is going on in and around his birth and childhood city of Hamburg, Germany through free streaming of newscasts provided by the NDR (Norddeutscher Rundfunk) from Hamburg and the surrounding states of Schleswig-Holstein, Niedersachsen and Mecklenburg-Vorpommern.