Monte Carlo Method

Introduction

The Nuclear Science Committee has during recent annual meetings discussed the role Monte Carlo methods play in design and prediction of behaviour of systems in nuclear applications and radiation physics.  It has fostered the organisation of sessions at international conferences to discuss the impact this method can have in industrial use. Progress in removing some unjustified reluctance existing in industry, for application in which the method has proven to be advantageous, should be achieved by demonstration of its potential and successful use.

Monte Carlo training courses are organised every year by the NEA Data Bank and the Radiation Safety Information Computational Center (RSICC) as this helps to attain a safer and more productive use of the codes they distribute. Participation in these courses (over 400 have attended the courses already) has proven to give attendees advantage over others as a more competent and effective use will be made of the simulation possibilities offered.

A list of Monte Carlo codes, sorted by application field and available in the public domain has been prepared.

The NEA Secretariat was asked by the Nuclear Science Committee to summarise results from recent conferences addressing the Monte Carlo (MC) methods. This text is enclosed in the following.
 

Results from Recent Conferences Addressing the Monte Carlo (MC) Methods (note by the NEA Secretariat)

During the last two years five conferences, cosponsored by the OECD/NEA, have taken place during which particle transport MC methods had an eminent place in the programme or were the subject of the conference itself. These are: M&C'99, Madrid, Spain; ICRS9, Tsukuba, Japan; PHYSOR'2000, Pittsburgh, USA, SNA'2000, Tokyo, Japan, and MC2000, Lisbon, Portugal.

Brief summaries are accesible through the respective hyperlinks above  describing the specific MC aspects presented in these. Each of these conferences has shown that the Monte Carlo method is used more widely than ever before. The reasons are:

• Computer architectures have evolved that are particularly well suited to increase the speed of MC codes in problem solving.
• It removes unnecessary model simplification
• Powerful biasing schemes and well established, widely known computer codes are used, statistical analysis has been further developed, the method has become user-friendlier; in short it has matured a lot.

These recent conferences have confirmed that use is made now in large areas of applications. Particularly intensive is the use made in radiation physics, diagnostics in material identification, material science, radiological and medical applications. Another area of wide use is deep penetration of radiation into matter and radiation shielding, including intermediate particle energies applications. Criticality safety is a field were MC methods are used as a standard analysis tool. It is particularly suitable for calculating the integral parameter k-eff describing the level of criticality, however the convergence of loosely coupled systems is still a challenging problem.

The use of MC in the area of nuclear power has undergone an important evolution. Notable are the extensions to compute burnup in reactor cores, and full core neutronic simulations. The aspects concerned with material or geometry perturbation are starting to be successful after a long development period. First results from sensitivity analysis with MC have been presented that are promising, but still timid. Adjoint MC is being used more widely now.

In many aspects of NPP simulation the MC method is still not applicable and its use would require much further development. Deterministic methods will continue to play an important complementary role. We can predict a symbiosis of stochastic and deterministic methods (including coupled and hybrid methods) for many more years.

Two examples of difficulty:

• Most MC codes provide variance of stochastic nature, not uncertainty due to modelling. Besides perturbation and sensitivity, general uncertainty analyses need to be further developed and integrated into MC if it is to be widely used for engineering and safety applications. Deterministic methods used today have developed more general uncertainty analysis modules than MC codes.
• Reactor core transient simulations require coupling of 3D neutronics with thermal hydraulics, fuel behaviour and eventually with structural mechanics. Success in this area has been achieved with deterministic methods. Monte Carlo codes have to go through a long development and validation phase before this can be achieved. Also computing times would at presently available computing power still be prohibitive.

In order to meet the increased interest and needs of the nuclear community, several training courses are organised every year, during which code users learn how to carry out efficiently modelling with MC. Several hundred, mostly young persons, were trained during the last few years.

For more Information, please contact Dr. Enrico Sartori (sartori@nea.fr)

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