To construct and operate a nuclear research reactor, the licensee is required
to obtain the authorization from the regulatory body. One of the tasks of the
regulatory authority is to verify that the safety analysis fulfils safety
requirements. Historically, the compliance with safety requirements was
assessed using a deterministic approach and conservative assumptions. This
provides sufficient safety margins with respect to the licensing limits on
boundary and operational conditions. Conservative assumptions were introduced
into safety analysis to account for the uncertainty associated with lack of
knowledge. With the introduction of best estimate computational tools, safety
analyses are usually carried out using the best estimate approach. Results of
such analyses can be accepted by the regulatory authority only if appropriate
uncertainty evaluation is carried out. Best estimate computer codes are
capable of providing more realistic information on the status of the plant,
allowing the prediction of real safety margins. The best estimate plus
uncertainty approach has proven to be reliable and viable of supplying
realistic results if all conditions are carefully followed. This paper,
therefore, presents this concept and its possible application to research
reactor safety analysis. The aim of the paper is to investigate the
unprotected loss-of-flow transients "core blockage" of a miniature neutron
source research reactor by applying best estimate plus uncertainty
methodology. The results of our calculations show that the temperatures in
the core are within the safety limits and do not pose any significant threat
to the reactor, as far as the melting of the cladding is concerned. The work
also discusses the methodology of the best estimate plus uncertainty approach
when applied to the safety analysis of research reactors for licensing
purposes.
The Oak Ridge Research Reactor: safety analysis: Volume 2, supplement 2