The AP1000 Nuclear Reactor Design is not fit for purpose: several safety flaws

The AP1000 advanced passive nuclear reactor design has a weaker containment, and fewer back-up safety systems than current reactor designs..

The AP1000 appears to be vulnerable to a very large release of radioactivity following an accident if there were just a small failure in the steel containment vessel, because the gasses would be sucked out the hole in the top of the AP1000 Shield Building due to the chimney effect.

 Recent experience with existing reactors suggests that containment corrosion, cracking, and leakage is more common than previously thought, and AP1000s are more vulnerable to containment corrosion than conventional reactors.

In addition the AP1000 shield building lacks flexibility and so could crack in the event of an earthquake or aircraft impact.

The AP1000 reactor design is not fit for purpose and so should be refused a Design Acceptance Confirmation (DAC) and Statement of Design Acceptability (SDA). 


NuClear News No 90 26 Nov 16
 The AP1000 Reactor Design

NuGen, a consortium of Toshiba and Engie (formerly GDF Suez), is proposing to build three AP1000 reactors at Moorside in Cumbria – a site adjacent to Sellafield. These three reactors together would have a capacity of up to 3.8GW.

The AP1000 reactor is a pressurised water reactor (PWR) designed and sold by Westinghouse Electric Company, now majority owned by Toshiba. But unlike other PWR designs it is what is called an advanced passive design. The idea behind advanced passive design is that it shouldn’t require operator actions or electronic feedback in order to shut it down safely in the event of a loss of coolant accident (LOCA). Such reactors rely more on natural processes such as natural convection for cooling and gravity rather than motor-driven pumps to provide a backup water supply. Westinghouse claims that AP1000 plant safety systems are able to automatically establish and maintain cooling of the reactor core and maintain the integrity of the containment which holds in the radioactive contents indefinitely following design-basis accidents.

The nuclear regulators – the Office for Nuclear Regulation (ONR) and Environment Agency – have been carrying out a new process called ‘Generic Design Assessment’ (GDA), which looks at the safety, security and environmental implications of new reactor designs before an application is made to build that design at a particular site. Initially the GDA for the AP1000 was expected to be completed around spring 2011, when the regulators would have issued a statement about the acceptability of the design. By the end of 2010 it was clear that the ONR would only be able to issue “interim” approvals for the Areva EPR and Westinghouse AP1000 reactor designs at the end of the generic design assessment (GDA) in June 2011. Construction could only occur after any outstanding “GDA issues” had been resolved.

Eventually on 14th December 2011 the Regulators granted interim Design Acceptance Confirmations (iDACs) and interim Statements of Design Acceptability (iSoDAs) for the UK EPR and the AP1000 reactor designs. The Regulators also confirmed that they are satisfied with how EDF and Westinghouse plan to resolve the GDA issues identified during the process.

ONR’s interim approval for the AP1000 contained 51 GDA Issues. At this point Westinghouse decided to request a pause in the GDA process for the AP1000 pending customer input to finalizing it. Westinghouse has since become part of the NuGen consortium with its parent company Toshiba taking a 60% stake, the process for AP1000 has resumed, and is scheduled to be completed by March 2017 with issuance of DAC and SODA. By March 2016, the cost of the GDA for the AP1000 had reached £30 million. (5)

The GDA process is being carried out in, what is described as, an open and transparent manner, designed to facilitate the involvement of the public, who are able to view and comment on design information published on the web. Questions and comments can be submitted electronically via the Westinghouse website, or direct to the UK regulators. The deadline for making a comment on the AP1000 plant, as part of the GDA process is 30th November 2016. (6)

Edinburgh Energy and Environment Consultancy was commissioned by Radiation Free Lakeland to write a report on the AP1000 reactor design to submit to this consultation.

(Available here http://www.no2nuclearpower.org.uk/wp/wpcontent/uploads/2016/11/AP1000_reactors.pdf )

The report came to the following conclusions:

The AP1000 advanced passive nuclear reactor design has a weaker containment, and fewer back-up safety systems than current reactor designs. Conventional reactors rely on defence-indepth made up of layers of redundancy and diversity – this is where, say, two valves are fitted instead of one (redundancy) or where the function may be achieved by one of two entirely different means (diversity). In contrast advanced passive designs rely much more on natural processes such as natural convection for cooling and gravity rather than motor-driven pumps to provide a backup water supply.

The AP1000 appears to be vulnerable to a very large release of radioactivity following an accident if there were just a small failure in the steel containment vessel, because the gasses would be sucked out the hole in the top of the AP1000 Shield Building due to the chimney effect.

Recent experience with existing reactors suggests that containment corrosion, cracking, and leakage is more common than previously thought, and AP1000s are more vulnerable to containment corrosion than conventional reactors.

In addition the AP1000 shield building lacks flexibility and so could crack in the event of an earthquake or aircraft impact.

A thorough review of the AP1000 design in the light of the Japanese accident at Fukushima has shown that:

  • Ongoing nuclear fission after a reactor has supposedly been shutdown continues to be the source of significant pressure inside the containment. The AP1000 containment is extraordinarily close to exceeding its peak post accident design pressure which means post accident pressure increases could easily lead to a breach of the containment.
  • At least seven ways in which an AP1000 reactor design might lose the ability to cool the reactors in an emergency have been identified. These include damage to the water tank which sits on top of the shield building and some sort of disruption to the air flow around the steel containment.
  • The accidents at Fukushima, especially the overheating and the hydrogen explosions in the Unit 4 Spent Fuel Pool showed that the calculations and assumptions about the AP1000 Spent Fuel Pond design were wholly inadequate.
  • Fukushima showed that when several reactors share a site an accident at one reactor could damage other reactors. In the AP1000 the water tank on top of the reactor, and the shield building could be vulnerable to damage.
  • Westinghouse assumes that there is zero probability of an AP1000 containment breach. But the accidents at Fukushima have shown that there is a high, probability of Containment System failure resulting in significant releases of radioactivity directly into the environment.

The AP1000 reactor design is not fit for purpose and so should be refused a Design Acceptance Confirmation (DAC) and Statement of Design Acceptability (SDA).  http://www.no2nuclearpower.org.uk/nuclearnews/NuClearNewsNo90.pdf

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