BIAPWS Award 2011

Outturn Report from David Docherty

Through co-sponsorship by BIAPWS and EDF Energy I worked at EDF's Barnwood office in Gloucester on a project that concerned improving access time for the properties of water and steam when running computer simulations of plant performance. I also spent some time shadowing various engineers and getting a general feel for what it is like to work in the industry. I have now entered my final year at Imperial College, London, studying for MEng in Chemical with Nuclear Engineering.

EDF Energy operates 8 nuclear reactors in the UK, seven AGRs (Advanced Gas Cooled Reactor) and one PWR (Pressurised Water Reactor). Several older AGR stations have now been operating for over 30 years, hence, much work is being done to extend their design lifetime. As part of this work, a very precise understanding of the operational conditions within the Nuclear Plant is required.

A nuclear reactor contains two coolant circuits; the primary and secondary. The fluid in the primary circuit is in direct contact with the fuel and therefore becomes slightly radioactive. To minimise radioactive dose to the environment, the primary circuit fluid is used as a heat source to generate steam within the boilers in the non-radioactive secondary circuit. The steam then passes to turbines which drive generators to produce electricity. In various parts of the circuit, for example within the boilers, there is often limited instrumentation coverage partly due to the original symmetric design assumptions, but often due to instrument failure from prolonged operation in hostile conditions. As boilers age, therefore, temperature asymmetries can increase and so computer models are used along with the limited instrumentation to predict operating conditions within plant both in steady state performance and transients. Such models require the use of accurate thermodynamic property functions within their constitutive conservation equations.

IAPWS (International Association for the Properties of Water and Steam) has published several significant versions of thermodynamic properties formulations over the years. The latest release IAPWS95 (scientific formulation), is generally regarded as the most accurate formulation available. When running computer simulations these properties may be required to be re-evaluated millions of times which makes their use, in their original form, impractical in terms of computing time.

The aim of my project was to use the IAPWS95 codes to produce a set of 'look-up' tables that contained all relevant properties of water and steam and a routine that used interpolation to return a required property from the table. Initially the option of resurrecting a legacy look-up table package was examined, however due to obsolete features of this package it proved unfeasible and the option of generating fresh code from scratch was explored.

Tables were generated for the properties of water that had both a variable and regular 'mesh size' (spacing between points in the table). A routine was written that interpolated within this table to return a desired property at specified conditions. This was shown to be up to 8 times faster than accessing the original IAPWS95 polynomials to determine the same property. Overall the project was relatively successful, however several areas were identified that required further work. The findings from the project are now being taken on as a starting point for implementation of look-up table routines in place of outdated codes.

I also spent my time at EDF Energy talking to and shadowing various people, which gave me a real appreciation for what it is like to work in the nuclear and energy industry as a whole. I was treated in a professional manner and given much independence to develop the direction of the project, which helped improve my confidence and decision-making skills to a new level. Being a Chemical Engineer, I have limited experience of computing and found working in an area outside of my comfort zone was very beneficial for both my technical skills and ability to solve problems. The responsibility I was given was a great experience which I feel stands me in good stead for my future career.

I would like to thank both BIAPWS and EDF Energy for this opportunity and the colleagues that I worked with at EDF for their help and guidance throughout the placement.

 

David Docherty, Imperial College.