UK regulators have asked Hitachi-GE to address a series of "shortfalls" in the probabilistic safety analysis (PSA) of its Advanced Boiling Water Reactor (ABWR). The request takes the form of a Regulatory Issue, which is the second in as many months in the generic design assessment (GDA) of the reactor for its use in the UK.
In June, the Office for Nuclear Regulation (ONR) and the Environment Agency raised a Regulatory Issue for their concerns about reactor chemistry matters related to the UK ABWR. Hitachi-GE was required to provide a "suitable and sufficient definition and justification for the radioactive source terms in UK ABWR during normal operation".
The document outlining the latest Regulatory Issue, which was published on ONR's website yesterday, states that the regulators consider a "suitable and sufficient" PSA to be an integral aspect of the UK ABWR's safety analysis within GDA.
"Overall, the UK ABWR PSA information received so far does not provide ONR with confidence that Hitachi-GE, without further work and changes, will be able to deliver a modern standards full-scope PSA for the UK ABWR, which is suitable and sufficient for ONR to carry out a meaningful assessment within the project timescales," ONR said. "This is considered a serious regulatory shortfall which ONR, in line with our Guidance to Requesting Parties, is now escalating to a Regulatory Issue."
The term 'Requesting Party' is used to identify an organisation seeking a GDA and to distinguish it from a nuclear site licence applicant.
ONR informed Hitachi-GE that it had identified the need for further work on the PSA when it reported its review of Step 3 of GDA between February and May. The outcomes of the review are captured in a series of related Regulatory Observations, Regulatory Queries and other regulatory feedback.
The Regulatory Observations ONR highlighted include: identification and prioritisation of hazards for the PSA; identification of internal initiating events at power; containment performance analyses; and system analyses. The two Regulatory Queries are: accident sequences analyses and success criteria; and PSA quantification, identification of assumptions, uncertainty and sensitivity analyses, interpretation of results and use of the PSA. The feedback concerns Hitachi-GE's allocation of PSA resources.
ONR said that these Regulatory Observations, Regulatory Queries and feedback highlight that the arguments supporting the PSA safety claims do not meet the relevant expectations in ONR's PSA technical assessment guide.
In its response to ONR, which the regulator also published yesterday, Hitachi-GE said it acknowledged that the PSA submissions it made in December did not meet UK regulatory expectations. As a consequence, the company said it must "develop a revised approach in line with UK good practice, in order to build the UK regulator's confidence in our ability to deliver a suitable and sufficient full-scope, modern standards PSA by June 2016."
Hitachi-GE stressed that the design process used in the development of the Japanese ABWR reference plant is "rigorous" and that the company is confident it will demonstrate that the proposed UK ABWR generic design is safe and will meet UK environmental and safety standards.
The company added: "In view of the challenges we have faced in meeting the UK regulator's expectations, Hitachi-GE has enhanced its PSA team, including securing the support of internationally recognised PSA experts to ensure that our PSA submissions meet UK regulatory expectations."
Hitachi-GE told the regulator it will provide: a project plan; sufficient suitably qualified and experienced PSA resources; a quality assurance plan; and PSA model and technical documentation, in order to "provide confidence that we can prepare a suitable and sufficient design assessment stage PSA in GDA".
ONR is expected to be in a position to close out the Regulatory Issue in October 2016.
The ABWR design is already licensed in Japan and the USA. Four units have been built in Japan, and two are currently under construction in Taiwan. Horizon Nuclear Power hopes to build two ABWR units at Wylfa Newydd site on the island of Anglesey in north Wales and start them up in around 2025. The units would be the first commercial boiling water reactors in the UK.
Researched and written
by World Nuclear News