Concerns about reactor chemistry issues related to Hitachi-GE's Advanced Boiling Water Reactor (ABWR) have been raised by UK regulators in their assessment of the design. The company, however, is confident these concerns can be resolved.
As part of the generic design assessment (GDA) of the ABWR, the Office for Nuclear Regulation (ONR) and the Environment Agency (EA) raised a regulatory observation in April 2014 requesting Hitachi-GE to define and justify the reactor design's source terms, amongst other related matters.
According to the regulators, "The definition of the radioactive source term; the nature and amount of radioactivity, is a fundamental part in understanding and therefore being able to control the hazards associated with any nuclear facility. Once defined, it is important that the requesting party is able to demonstrate and justify that this source term is appropriate to be used as the basis for the safety and environmental cases. Failure to adequately define or justify the source term could ultimately mean that the design, operations or controls specified for the UK ABWR may not be soundly based."
Hitachi-GE responded with its definition and justification in January 2015. However, the regulators said the responses "do not meet our expectations". This, they said, "is considered to be a serious regulatory shortfall".
The ONR and EA have now raised a regulatory issue to state their "expectations with respect to Hitachi-GE providing a suitable and sufficient definition and justification for the radioactive source terms in UK ABWR during normal operation."
They noted, "It is clear that some uncertainty still remains, as insufficient progress has been made to build regulatory confidence in the approach proposed by Hitachi-GE to address the shortfalls."
In their latest GDA progress report, for the first quarter of 2015, the regulators said, "Reactor chemistry is proving to be a very challenging topic for Hitachi-GE, and project risks have been identified during the quarter which challenge whether a meaningful assessment of reactor chemistry during Step 3 can be achieved."
Hitachi-GE has proposed a "staged delivery plan and a series of meetings to allow the regulators the opportunity to sample the work and provide feedback and advice to ensure alignment with regulatory expectations at appropriate points."
In its response to the regulators, Hitachi-GE noted: "The Japanese ABWR reference plant upon which the UK ABWR is based has been designed, constructed and operated in accordance with some of the highest safety and environmental standards. Worker dose and environmental discharges are amongst the lowest of any operational plant in the world."
"We are therefore confident that whilst we may have interpreted differently what is required to define and justify the source term within the UK regulatory environment, our proposed ABWR generic design is safe and will meet appropriate UK environmental and safety standards," the company stressed.
The GDA forms part of the approval process for new reactor projects in the UK, allowing regulators to assess the safety, security and environmental implications of new reactor designs separately from applications to build them at specific sites.
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.
Researched and written
by World Nuclear News