The ANSWERS Seminar, 9-11 May 2006

The ANSWERS Seminar was held at the Durley Hall Hotel in Bournemouth, a location near to the superb Dorset coast and in close proximity to the town centre. Over seventy delegates attended all or part of the three-day meeting, with the programme covering the shielding, reactor physics and criticality technical areas. Programme topics included ANSWERS code developments, code applications, related general interest issues and software demonstrations. In addition to the seminar itself, parallel meetings of the UK Shielding Forum and the UK Working Party on Criticality were hosted at the same venue.


The first day of the 2006 ANSWERS Seminar started with Radiation Shielding. There was a variety of application talks and development talks, given by both Serco Assurance personnel and guest presenters.


The morning began with a presentation on the Release of RANKERN 15A. This gave an overview of the New Features within RANKERN 15A – particularly the new FG options, Unified Source and the ANS643 Build-Up factors. The presentation also included an outline of the testing carried out before release. This was followed by an application talk from Ruben Van Parys of Tracebel. Ruben presented the second part of some work he has been carrying out using MCBEND to model the response of detectors used to investigate the effects of material degradation in spent fuel ponds. This was a follow-on from his presentation at the 2005 Seminar. The next talk was a description of JEFF3.1 Decay Data.


After the morning break a presentation was given which described a piece of work carried out for NIREX where RANKERN was used to generate dose-rate data that will be integrated into a Derived Inventory Querying tool ( DIQuest) so as to allow calculation of waste package dose rates for any given waste stream. This was followed by a talk on a new development for independent scoring meshes in MCBEND. Another application talk described MCBEND calculations to investigate the heating and damage in Graphite moderators for Magnox reactors by calculating heating and damage in installed graphite samples. The final talk of the morning was on MCBEND Parallelisation. This started with an overview of the current method used for parallel calculations in MCBEND and went on to describe a number of different available options for parallelisation.


The afternoon started with the ever popular demonstration of the new features in LaunchPad and the Graphics codes and in particular the developments in VISUAL Workshop, which is being aimed as a single replacement for all the various Graphics Products. This was followed by a very interesting presentation on the “Applications of Monte Carlo Simulation in Neutron and Radioactivity Metrology” given by Steven Judge of NPL. This gave a very interesting overview of the work at NPL and how they use Monte Carlo modelling in their work. Next on was a presentation summarising the ANSWERS Customer support which mentioned the helpline, customer web pages, training courses and the Seminar itself. The last applications talk of the day was using MCBEND for a dosimetry study on the topcore of the Wylfa reactor. The day ended with an overview of the current and future developments in the ANSWERS Shielding area. Overall there was a good variety of presentations which gave a very good start to the Seminar.


The second day of the meeting, the Reactor Physics day, started with a presentation on recent work on WIMS9 validation and ‘International Reactor Physics Experiments evaluation project’ IRPhE benchmarks. About half the WIMS validation manual has been re-calculated so far using WIMS9 and it is expected to complete this task in 2007. The IRPhE is a database of evaluated experiments against which validation studies can be performed and benchmarks from this database will be added to the WIMS validation set. The talk also explained that Serco had contributed to 5 benchmarks in the database, two performed on the DIMPLE reactor and 3 on the ZEBRA reactor. The second

presentation was given by Pavel Mikolas of SKODA in which he detailed the results of a series of Gadolinium (Gd) poison studies for the Dukovany VVER 440 plant. The studies examined the use of assemblies with lower Gd content to reduce pin power peaking and increase cycle length. Important improvements resulted although it was considered that these would not be so large in full core calculations, however, the benefits of using the modified assemblies was demonstrated. The final presentation before the mid-morning coffee break was on progress toward production and testing of JEFF3.1 application libraries. Work, in conjunction with the CEA, had been performed on updating the JEFF3.1 production codes and these have been used to generate libraries containing a limited number of JEFF3.1 nuclide evaluations. Test results obtained using the libraries show encouraging results although more work is needed. FISPIN fixed data files for 324 actinides, 1380 fission products and 1913 structural materials have been produced and these will be distributed with FISPIN10. Further testing of the JEFF3.1 libraries is planned leading to their eventual general release.


The first presentation following the coffee break was given by Paul Bryce of British Energy and reviewed work undertaken to consider the use of WIMS9 for PWR calculations rather than the currently used LWRWIMS. The motivations to change are due to the revised resonance treatment in WIMS9, its extensive benchmarking against Monte Carlo calculations as well as the availability of an exact geometry transport theory solution. The studies show it should be relatively easy to move to WIMS9. the next step is to consider whole core calculations which is scheduled for next year. The next presentation considered a study of void coefficients in the RBMK reactor. A physical insight into the main components contributing to the void coefficient was outlined by considering their role in the classic ‘four factor formula’. These studies have identified the need for further method refinement such as the need for super-cell models, improved cell homogenisation and the modelling of variations in coolant density. The final presentation of the morning described the current status of the WIMS CACTUS characteristics module and a proposed method to include ‘hole geometries’ in its modelling capability. Developments to include MONK/MCBEND fractal geometry have been completed as well as the introduction of material dependent fission spectra. All CACTUS2D options are now coded in CACTUS3D as well as some additional symmetry options. The new form of the geometry input allows visualisation of the geometry using the powerful features of the VISAGE package. A short demonstration of this was given immediately following lunch.


The first presentation after lunch gave a review of the Generation IV project and Serco’s contribution within it. Each of the six proposed Generation IV reactor types were described along with an outline of some of their strengths and weaknesses. From the UK perspective most interest is in the VHTR and Gas Cooled Fast Reactor while maintaining a watching brief on the Sodium Cooled Fast Reactor. Serco have participated in pre-conceptual and conceptual studies of both the VHTR and Gas Cooled Fast Reactor which has also entailed the development and validation of computational tools and nuclear data. The next presentation entitled “ Future radiation transport, Fluids and Structural Mechanics Developments for the FETCH Transient Criticality Model” was presented by

Matthew Eaton of Imperial College. It is proposed to develop radiation transport methods using high-order and sub-grid methods, adaptive angular spherical wavelets and hierarchical solutions. Within fluid dynamics interface tracking allows the modelling of multi-fluid and solid-fluid interfaces as well as improving accuracy in representing shock waves, temperature and salinity interfaces etc. The driving force of this work is to identify and highlight deficiencies in current modelling methods. The final presentation before the afternoon tea break was a description of recent developments to the WIMS code. These include the storage of temperatures on the WIMS interface for detailed resonance shielding treatments, enhanced capability for sub-group fitting, the inclusion of the ECCO code in WIMS for the preparation of high energy cross-sections and further development of edits for perturbation theory and breeding gain. Validation calculations for these developments were also presented.


The first presentation in the final session of the day was on the effects of graphite oxidation on AGR reactor physics and was presented by Paul Hutt of British Energy. Graphite weight loss suffered by the AGR reactors affects a range of core parameters. The effect on two significant parameters, shut-down margin and steam ingress worth, are of particular importance. In the assessment of these effects the difficulty of accurately representing both the presence of the water and burnable poisons was stressed. It was recognised that prediction accuracies could best be improved through the development of the MAX module in WIMS and this was proposed for consideration. The next presentation described Serco’s contribution to three international benchmarks for the PBMR reactor, the OECD/NEA PBMR-400 benchmark, the OECD/NEA HTR reactor physics benchmark and the PROTEUS benchmark. The first of these benchmarks gives validation of the calculation of core temperature profiles in the PBMR using the new WIMS PBTRANS modules. Results from the second benchmark are to be presented in a paper at the Physor 2006 conference to be held in Vancouver, Canada in September. The PROTEUS benchmark gives direct experimental validation for the prediction of core reactivity and control rod worths in the PBMR. The final main presentation of the day gave a description and explanation of the treatment of P1 scattering in WIMS including the row sum and column sum corrections to the transport cross-section. The day was completed by a short presentation on future plans for the enhancement and development of the WIMS code. Informal discussions including a problem clinic followed the days presentations.


The final day of the 2006 ANSWERS Seminar comprised the Criticality related technical presentations. These presentations covered a wide range of topics covering different areas of the criticality community.


The morning session began with a review of the imminent release of MONK version 9A, its testing, release package and new features. This was followed by a British Nuclear Group presentation on the work undertaken to re-furbish a ‘new’ fissile material store to replace two existing stores that raised issues concerning concrete composition and its behaviour, the limited validation data available and how to handle regions with varying reactivity. The final presentation of this session covered the new bound carbon data in BINGO that should be used for graphite systems, and the problem identified with the Pu239 resonance data in JEF2.2, concluding with statement that updated libraries are available through ANSWERS on request.


The second session began with a description of a proposed scheme to enable a MONK calculation to be spread over several machines on a typical computer network, commenting that several of the required capabilities have already been demonstrated in existing software. This was followed by an update of the continuous-energy burnup MONK code that was reported as a prototype last year, and the gamma heating calculations that require a MONK-MCBEND-MONK link to enable MCBEND to track from the gamma source supplied by MONK and to feed the calculated heating response back into MONK. The morning session concluded with a British Nuclear Group presentation on the requirements, processes and regulatory demands required for new transport flask designs, and how these compared with the more risk-informed plant assessments.


The afternoon session began with a review of the effects of fire-damage in transport flask assessments, and how the variation in hydrogen content due to fire damage was the major contributor to changes in reactivity for arrays of particular types of flasks. This was followed by a review of the new PIPES hole designed to allow various pipes to be positioned and linked within a room, and updates to the QUADRIC hole to simplify the input for tori and ellipses – and a revised process for pipe cross-sections normal to the pipe axis. The final talk of the third session described and demonstrated Launchpad and its new CaseViewer, VISAGE and VISTA-RAY enhancements, and a test harness showing how the new 3D viewer in Visual Workshop will look – including the bacon-slicer views through several models.


The final session of the 2006 ANSWERS Seminar began with a review of the present Advanced Review of MONK course, and how it is planned to revise it in the future to give it more of an applications focus and both more and targeted practicals. The session concluded with a review of the status of MONK, and both the short- and long-term development plans for the code, and a request from us to all our customers to please let us know what you need our codes to do so we can prioritise and direct our efforts accordingly.


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