Independent assessment for new nuclear reactor safety

Abstract

Abstract. A rigorous framework for safety assessment is established in all countries where nuclear technology is used for the production of electricity. On the one side, industry, i.e. reactor designers, vendors and utilities perform safety analysis and demonstrate consistency between results of safety analyses and requirements. On the other side, regulatory authorities perform independent assessment of safety and confirm the acceptability of safety of individual reactor units. The process of comparing results from analyses by reactor utilities and regulators is very complex. The process is also highly dependent upon mandatory approaches pursued for the analysis and from very many details which required the knowledge of sensitive proprietary data (e.g. spacer designs). Furthermore, all data available for the design, construction and operation of reactors produced by the nuclear industry are available to regulators. Two areas for improving the process of safety assessment for individual Nuclear Power Plant Units are identified: New details introduced by industry are not always and systematically requested by regulators for the independent assessment; New analytical techniques and capabilities are not necessarily used in the analyses by regulators (and by the industry). The established concept of independent assessment constitutes the way for improving the process of safety assessment. This is possible, or is largely facilitated, by the recent availability of the so-called Best Estimate Plus Uncertainty approach.

The Best Estimate Plus Uncertainty approach in nuclear reactor safety and licensing: Brief history and the elements after licensing

“…The stakes as so ci ated with the cost of the NPP, the com plex ity of the sys tem and the po ten tial im pact of ra di a tion upon the hu mans and the en vi ronment jus tify IA: safety must be dem on strated by experts in de pend ent from de sign ers and own ers of the con cerned sys tem who take a ben e fit from the op er ation of the same sys tem. The im ple men ta tion of the IA re quire ment may re veal un fea si ble out side BEPU, [11]; namely this is the only log i cal ap proach for the licen sor for get ting the IA of the li censee sub mis sion: the un cer tainty in in put pa ram e ters is de rived in depend ently and sub sti tutes, and even tu ally is con sis tent with, the con ser va tism of the li censee pos si bly based on pro pri etary (best es ti mate) in for ma tion.…”

The technological challenge for current generation nuclear reactors

“…Safety Margin (SM) is a well-known concept in NRS: suitable safety margins must be demonstrated and are part of design, construction and operation of existing reactors, D'Auria et al 2017c, andD'Auria et al 2017d.…”

Introduction of an Additional Safety Barrier for Nuclear Power Reactors

“…The additional barrier B5 is constituted by a combination of the following elements, which have a heterogeneous nature and role: the As Low As Reasonably Achievable (ALARA) principle, the Independent Assessment (IA) requirement, the Best Estimate Plus Uncertainty (BEPU) approach, the Extended Safety Margin (E-SM) concept and the Emergency Rescue Team (ERT), now a virtual reality. ALARA, IA, BEPU and E-SM are discussed in [11] with more details given in [2], [12] and [13] and ERT is introduced in [14]. The elements are shortly discussed in sections 3.1 and 3.2, distinguishing between 'software' and 'hardware' and their combined role is outlined in section 3.3.…”

“…The IA requirement, although established since the early developments of nuclear technology, later on became of difficult application owing to the increasing sophistication of NPP which implies (more) proprietary data needed for safety demonstration [13].…”

“…IA, left of the diagram, constitutes a requirement for the 'new' FSAR. Independent assessors should have access to the NPP Unit design and licensing information (first and second database above mentioned) and develop the 'new' FSAR, [13]. Because of the proprietary nature of information in the databases, although independent assessors are not in competition with industry (either designer or owner of the NPP), the IA is expected as the critical element for the overall process.…”