Large and Associates

Large & Associates
Consulting Engineers

R3238 ASN Authorisation of 1300MWe NPP Steam Generator Tube Plugging Limit

In June 2016 the French nuclear power plant (NPP) operator, Électricité de France (EDF), applied to the nuclear safety regulator Autorité de Sûreté Nucléaire (ASN) for an upward revision in the total number of individual tubes of steam generators (SG) of the 1300MWe series NPPs that could removed from service by plugging. In February 2017, ASN reauthorized the upper limit of plugging be raised from the previously maximum limit of 10% to 18%, this being the second reauthorisation of the plugging limit raised from 5% to 10% in 2013. In addition to allowing a greater number of SG tubes to be plugged, ASN also agreed in May 2017 to permit EDF to repair certain defective tubes by a technique known as sleeving.

This Review analyses the reasoning underpinning this unusually high tube plugging limit and considers the consequences, particularly relating to any performance changes during and in the aftermath of small and large break LOCAs.

R3234 - Operational Nuclear Safety of the Ōma Nuclear Power Plant

The Ōma NPP, located in Aomori, Japan was first planned to commence commercial operation in or about 2008 but that this was subsequently delayed to enable design amendments in account of the national review of Japanese seismic standards. Then, following the catastrophic failure of the three operating BWR units at Fukushima Daiichi during the earthquake and associated tsunami of March 2011, further construction at Ōma was again suspended until around October 2012.

Further delays and uncertainties arose because of the upheaval to the Japanese nuclear safety regulatory framework following Fukushima Daiichi events of 2011 and, thereafter, the progressive introduction of the newly formed (September 2012) Nuclear Regulation Authority’s (NRA) Draft New Safety Standards for Nuclear Power Stations (1) and, separately, the Outline New Regulatory Requirements for the Design Basis (2), Severe Accident Measures (3), and Earthquakes and Tsunamis (4) respectively, all introduced in outline or draft form in April 2013. The latest position with the construction programme at Ōma is that ‘safety upgrades’ to suit the NRA’s New Safety and Regulatory Standards and Requirements (items 1, 2, 3 and 4 of paragraph 5) are not planned to commence until 2018 for completion in or about 2023.

This project, comprising a number of Expert Evidence Statements to the Court, argues that it is not practical to revise the pre-Fukushima Daiichi design of the Ōma NPP because of its advanced stage of construction and so could never satisfy the New Regulatory Requirements brought about by the Fukushima Daiichi disaster. It is in support of the legal action taken by the City of Hakodate to prevent resumption of construction and the eventual commercial operation of the Ōma NPP in or around 2023.

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R3233 - Hinkley Point C - Regulatory Oversight of High Integrity Components

Recent concerns about the non-compliance of the Flamanville 2 (FA2) reactor pressure vessel (RPV) installed in the reactor pit of the European Pressurised Reactor (EPR) has drawn attention away for the identical but yet to be assembled high integrity components (HIC) destined for the virtually identical Hinkley Point C EPR NPPs now under construction in the South-West of the United Kingdom.

In 2015 the French nuclear safety regulator (ASN) announced that the RPV head components of the FA2 RPV include areas of non-compliance heterogeneity along with the associated drop off in the carbon steel toughness characteristic, thereby rendering the components vulnerable to fast fracture failure. EdF-AREVA submitted to ASN their reasoning that the RPV even with the toughness lowered was fit-for-purpose - part of this demonstration approach included test results from identical RPV top and bottom heads for the now abandoned United States EPR and the UK HPC NPPs. ASN has yet to publish a decision of whether it considers the FA2 RPV fit for purpose but, whatever, both the US and HPC components failed the material tests for toughness.

The failed HPC heads were manufactured in advance of confirmation of the HPC order so the question arises whether these critical safety components were subject to UK regulatory oversight via the UK nuclear safety regulator the Office for Nuclear Regulation (ONR) - all the indications to date suggest that no UK regulatory oversight was in place during the manufacture and, not unexpectantly, the French regulatory ASN has stated that it has no role in any aspect of the quality and compliance of the design and manufacture of components destined for overseas NPPs.

The regulatory status of the remaining HPC heads is being sought from ONR via a request under the Environmental Information Regulations 2004 although, that said, ONR has been notoriously unreliable in responding to past requests.

R3238 - Dry-Out Erosion of Fuel Cladding at Leibstadt NPP - Extended Outage

At Leibstadt, the planned 2 August 2016 partial refuelling outage was originally scheduled to end on 27 August, was first extended by a further 8 weeks until 29 October, but is now projected to last through to February 2017.

The reason for this extended outage is damage to the nuclear fuel pin cladding, now acknowledged to be due to an in-core phenomenon referred to as ‘dryout’ dating back to the 2012-2013 fuel core cycle. It is now reported that similar levels of fuel pin surface scarring arose in subsequent fuel core cycles.

For the 2015-16 fuel cycle Axpo put in place specific measures to eliminate what it believed to be the root cause triggering dryout but examination of the 2015-16 fuel core fuel removed in mid-August revealed the problem persisting with similar area of fuel pin dryout surface scarring developing during the fuel cycle. In other words, the root cause solution implemented by Axpo did not address and rectify the dryout phenomenon. In order for Leibstadt NPP to be allowed to start up again, ENSI has stated (20 December 2016) that “. . .the fuel core loading and reactor operation must be such as to exclude dryout during normal operation, in the event of operational malfunctions and in accident categories 1 and 2 of the design basis accidents”. Preparations towards satisfying this ENSI requirement seems to have been the reason why a normally 3 to 4 week refuelling outage of 2016 has now been extended indefinitely until at least February 2017 (24 weeks+).

R3235 - Irregularities and Anomalies relating to Nuclear Reactor Primary Coolant Circuit Components installed in Japanese Nuclear Power Plants

One consequence of the ongoing French nuclear industry debacle reaches back to Japan.

The French are still wrestling with what to do about the 47 potentially flawed steam generator components supplied by the Japan Casting and Forging Company (JCFC), although an immediate measure in the interim has been to somewhat hurriedly shutdown all 12 of the nuclear power plants believed to contained the flawed JCFC SG components, with a decision on the future of these plants awaited from the French nuclear safety regulator Autorité de Sûreté Nucléaire - see LargeAssociates Review R3233.

The flawed JCFC SG bottom channel heads so far identified in France serve a Class 1 function in the reactor primary coolant circuit and, being break-precluded items, catastrophic failure by fast fracture cannot be permitted because the potential off-site radiological consequences could be intolerably severe. The regulatory loophole exposed is that these components have somehow been accepted into the French supply chain but to do this the flawed components somehow also had to slip the through the quality assurance controls and safeguards of the JCFC works.

In other words, this composite that has resulted in the French failure includes two elements that are entirely founded in Japan, these being i) that the defective components were wholly manufactured in Japan and ii) that the quality control safeguards that should have prevented the flawed components leaving the place of manufacture failed. The final barrier preventing entry into the nuclear equipment supply chain is iii) the Japanese regulatory system as administered by the NRA - in France this final barrier also failed.

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R3233 - Anomalies in the Forged Components of le Creusot Forge

In late 2014, AREVA notified Autorité de Sûreté Nucléaire (ASN) of the results of material tests carried out on a component manufactured at the Creusot Forge. These tests were undertaken by AREVA as part of the much-delayed Qualification Technique of components for the European Pressurised Reactor (EPR) presently under construction at the Flamanville 3 nuclear power plant. The part tested was a supernumerary equivalent of each of the two components, the upper and lower head shells, that had already been incorporated into the FA3 reactor pressure vessel now installed within the nuclear island at the NPP site.

To much consternation the test results revealed that the material characteristics, particularly the impact or fracture toughness, did not conform to the design-basis specification and, moreover, it arose from a small but nevertheless significant increase in the carbon content across a large zone of macrosegregation present throughout most of the thickness of the equivalent head shell – this is the so-called ‘carbon anomaly’.

This Review traces the origins of the carbon anomaly and identifies fundamental flaws in the quality controls applied across the AREVA manufacturing route of the Creusot Forge. Similar problems are identified in the steam generators manufactured by Creusot Forge and the Japanese Casting and Forging Company (JCFC}.

R3229 Tephra Fall-Out and Operational Safety of Sendai Nuclear Power Plants

The Review comprises three aspects of the present nuclear safety measures relating to the functioning of the Sendai nuclear power plant (NPP) when subject to high levels of tephra ash fallout from an erupting volcanic event.

First, the LargeAssociates Review seeks to describe the present regulatory constraints and requirements placed upon the Sendai NPP operator to adequately forecast the nature and risk of occurrence of the general volcanic hazard; second, the effectiveness of the screening process adopted to determine which volcanoes and to what extent these represent a hazard to the Sendai NPP; and, third, if the severity of the projected volcanic event complies with the 2013 revised design-basis requirements of the Nuclear Regulation Authority (NRA) and, in this regard, if the preparation and countermeasures at the Sendai NPP site are sufficient to protect the region from a significant radiological outcome in the event that nuclear plants are subject to a prolonged period of tephra fallout.

R3218 San Onofre Nuclear Generating Station - Replacement Steam Generator

After 25 years of operation, the San Onofre operator, Southern California Edison (SCE), replaced the original steam generators of Units 2 and 3 reactor power plants. Units 2 and 3 are virtually identical pressurized water reactors (PWR) built by Combustion Engineering (CE) and commissioned in 1983 and 1984; each original plant included two steam generators (SGs), both containing about 9,400 thin-walled tubes.

The four Mitibushi replacement steam generators (RSGs) were installed and commissioned into service in April 2010 and February 2011 in the Unit 2 and 3 plants respectively. However, on January 31 2012, while the Unit 2 fuelling outage was in progress, the virtually identical Unit 3 was forcibly shut down when an alarm alerted SCE operators that a breach had occurred with reactor primary circuit water leaking across the RSG tube interface to the secondary steam circuit.

Large & Associates provided technical evidence to the Atomic Energy Licensing Board in the Friends of Earth successful challenge to shut down the two San Onofre nuclear power plants. This Review includes this evidence, analysis and other technical representations compiled by Large & Associates.