The ANSWERS Seminar, 25-27 May 2004


This year's ANSWERS Seminar was once again held at the Wessex Hotel in Bournemouth, a location near to the superb Dorset coast and in close proximity to the town centre. Over sixty 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 this year's Seminar was devoted to Radiation Shielding and Dosimetry. During the morning session there was a good mix of application talks and development talks. The first talk gave an overview on a sample limit problem encountered by some code users, now that computers are running so much faster than previously. This was followed by a talk on the validity of MCBEND results and testing new Build-up factors in RANKERN. Later in the morning a presentation was made on the new simplified Monte Carlo code MCFANG, which was very well received. Three applications talks were provided by guest presenters in the morning which include calculation of ex-core responses with adjoint MCBEND, modelling dose-contours using MCBEND and calculating dose-rates through a hoist penetration to support decommissioning operations. The final talk of the morning was on a study carried out at Winfrith entitled the inverse shielding problem.

The afternoon started with a demonstration of a prototype 'modelbuilder' which is a graphical user interface to help the user prepare, run and analyse results from a calculation using MCFANG, MCBEND, or MONK. New features of VISTA-TRACK, VISAGE, VISTA-RAY, LaunchPad and PUNDIT were also demonstrated throughout the afternoon, which were very impressive. Technical talks in the afternoon session included a talk on dose-rate calculations for a reconnaissance vehicle travelling through contaminated terrain and modelling Tori in MCBEND. The day ended with a presentation on the ANSWERS Hot-line charter and 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, which was the reactor physics day, started with a presentation on the void coefficient in RBMK reactors showing the factors that led to the void coefficient for this reactor type being positive. This was followed by a presentation on the use of WIMS8 to predict reactivity effects in the AGR stations in the UK. This presentation was from British Energy and looked at 300 years operational experience. The final presentation before a break was a dual presentation outlining some recent developments to WIMS which introduced an adjoint flux solution into the collision probability methods in the code and used that flux to evaluate prompt neutron lifetime and the delayed neutron fraction beta-effective. After the break a review of the collision probability methods in WIMS was followed by 2 guest presentations reviewing work with both WIMS8 and WIMS9. The first presentation covered work on VVER assemblies, which contain gadolinium poison, this was followed by work on burnup in MOX type assemblies related to the European project VALMOX. The morning finished with a paper on actinide transmutation in a series of moderated target designs. In this study gas cooled fast reactors were used for the transmutation. The afternoon started with a presentation on possible criticality in repositories due to long term migration of fissile material. This was followed by a talk on future deterministic transport methods which featured some visually stunning graphics. Then before the next break there was another talk on advanced methods this time relating to the use on a PBMR international benchmark. After the final break there were 2 further guest presentations. The first from Tractebel Engineering looked at some work on coupling PANTHER to either RELAP or COBRA to enhance PWR accident analysis. The second from British Energy outlined work carried out on the effect of actinide depletion on reactivity and spatial power distributions in Sizewell B. As is customary the day concluded with a look at the future outlining work on the reactor physics codes and then a demonstration session where the JANIS code was shown and all ANSWERS reactor physics products were available for trial use.

The final day focussed on criticality safety and in particular the MONK code. The day began with a presentation of work on hydrogen thermal scattering, demonstrating the effects of bound data. This was followed by a presentation from HSE on the history of UK experimental reactor systems and their contribution to our knowledge. The next talk was oriented towards the MONK modeller, describing how to model both fissile and fissile/water mixtures. The first session finished with an unscheduled demonstration of the new MODELBUILDER GUI, showing how it would read an input file, display it, then allow modifications to be made.

The second session began with a presentation describing the structure, work and responsibilities of the Department for Transport. BNFL then gave a presentation on their work in quantifying real safety margins, instead of relying on the results for worst-case models. This was followed by a further BNFL talk on the handling of obsolete uranium hexafluoride cylinders, and the efforts taken to ensure their safe remediation. The morning session closed with a review of the recent ICNC-2003 conference in Japan, with relevant papers being highlighted for discussion.

The first afternoon session began with a review of the new features of MONK version 9, and finished with a HMS Sultan presentation detailing their collaboration with France in training the future designers and modellers of marine nuclear propulsion systems.

The final session started with a demonstration of the HSE-funded 'Electronic Criticality Handbook Demonstrator' for displaying handbook data and allowing data comparison and interrogation. The next presentation was from Imperial College and described the use of their FETCH code for solving multiphase transient criticality events. The day was brought to a close by a talk on the status of MONK and some of the planned future developments. As on the previous days, attendees were invited to make use of the computers available in the seminar room for further demonstrations of any of the codes.


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