Nuclear Design-Resilience

Vulnerability of French NPPs to Accidental Aircraft Crash

Analysis and evaluation of French NPP vulnerability to direct crash of a civil airliner on the nuclear island and other safety crucial parts of the plant.

San Onofre Replacement Steam Generator Root Cause Analysis - Summary



This Summary combines two recent assessments undertaken by Large & Associates on the replacement steam generator  problems and proposals to restart at least one of the two nuclear power plants at the San Onofre Nuclear Generating Station. The first assessment considers the proposals of the plant operator and licensee, Southern California Edison  to restart Unit 2, operating the plant at 70% of its thermal rated power.  The second assessment considers whether the NRC's Confirmatory Action Letter was anther form of de facto license amendment.



Degradation of AGR Graphite Moderator Cores

The graphite core of an AGR nuclear power plant is a central nuclear safety component. The core is a loose stack of several thousand graphite bricks assembled to form a facet-sided cylinder of about 12m diameter by 10m height. The core serves to moderate (slow) the neutrons initiating fission in the nuclear fuel but in doing so its materials properties change and there is a pronounced loss of weight of graphite. This Review examines the importance of graphite radiolytic ageing to the nuclear safety case.

THORP Feed Clarification Cell Leak - Corroded Dissolver Pipework


Following discrepancies in the inventory and nuclear material balance controls at the front end of the irradiated fuel thermal oxide reprocessing plant (THORP) at Sellafield, on 20 April 2005 a remotely operated camera revealed a significant quantity of highly radioactive liquor in the sump of Cell 220. In total and over several months previously, approximately 84m3 of liquor, in the form of a nitric acid solution of fuel and fission products, had built-up in the sump, leaking from a feed pipe connection to one of two accountancy vessels located in the cell.



Mae’r Adolygiad hwn yn ystyried sut y gellid disgwyl i’r broses heneiddio effeithio ar berfformiad a diogelwch yr orsaf ynni niwclear yn Wylfa.

Yn achos Wylfa, mae’r broses heneiddio yn cyfeirio at nifer fawr o ddeunyddiau a rhannau o’r adweithyddion. Mae rhai o’r prosesau heneiddio hyn yn rhai cymharol syml ac yn rhai yr ydym yn eu deall yn weddol dda; mae eraill yn fwy cymhleth sydd heb eu deall yn llwyr eto. Gyda threigl amser, daw yn fwy a mwy anodd, os nad yn fwy annibynadwy i geisio rhagweld pa broblemau sy’n deillio o heneiddio sy’n debygol o godi yn awr ac yn y dyfodol. Yn wir, wrth i oes yr adweithyddion ymestyn dros yr 20 neu 25 mlynedd a fwriadwyd ar eu cyfer yn wreiddiol, mae’n rhaid dibynnu fwyfwy ar archwilio deunyddiau a rhannau’r adweithyddion a dim ond trwy wneud hyn y gellir canfod beth yn union yw effeithiau’r broses heneiddio. Y broblem yma yw nad yw’r adweithyddion yn Wylfa yn cynnwys nodweddion sy’n ein galluogi i archwilio’r holl rannau hynny sy’n debygol o gael eu heffeithio wrth iddynt heneiddio.

Regulatory Control

Leibstadt NPP in-core Dry-Out extends enforced 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+).

Carbon Anomaly Spreads to the World's Oldest Operating Nuclear Power Plant at Beznau

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EPR GDA incomplete but design given go-ahead LargeAssociates Final Review identifies shortfalls

LargeAssociates 1st , 2nd Interim and Final Reviews not challenged by Office for Nuclear Regulation's Response Letter - see also later LargeAssociates reporting on Carbon Anomaly at Flamanville 3 RPV.


Olkiluoto 3 Finland - STUK Regulatory Assessment


The substantive findings of this review relate inadequacies and incompleteness of the regulatory assessment at the Construction Licensing stage; if the speed at which STUK completed its assessment facilitated proper examination and testing of the nuclear safety case of this world-first installation of the Generation III EPR nuclear power plant; the failure to publish a full assessment of the plant’s resistance to commercial aircraft crash (previously promised to be an essential nuclear safety prerequisite) and, similarly, the lack of demonstration in any aspect whatsoever that the plant will be sufficiently robust against all reasonably foreseeable terrorist action; and failure to give meaningful account to the radioactive waste management and eventual decommissioning of the plant and its nuclear island at some future time.

Sizewell A Irradiated Fuel Pond Drain Down



This is a review of the Nuclear Installations Inspectorate’s decision not to prosecute Magnox Electric Ltd over its involvement in the Sizewell A radioactive discharge incident of 7 January 2007. The radioactive release arose as a direct consequence of a breach in the pipework of the spent fuel pond water recirculation system resulting in uncontrolled spillage of 40,000 gallons (180m3) of (radio)active water over a period of about 45 minutes. About one-quarter of this spillage discharged completely untreated to the marine environment via the Sizewell A site storm drainage system.

United States NRC News

US nuclear safety regulator NRC casts doubts on adequacy of AREVA EPR Control and Instrumentation systems - Nucleonics Week 11 July 2013 - confirming findings of LargeAssociates

Lost WANO 2000 Assessment for Laguna Verdi NPP Mexico

Confidential World Association of Nuclear Operators inspection report hides significant shortfalls at Laguna Verdi in 2000.

ONR's TiP on Aircraft Crash NOT to study Aircraft Crash

Terms of Reference for ONR's aircraft crash TAP will not include for NPP containment damage severity, release inventory and radiological consequences of potential release scenarios 


Operational Nuclear Safety of the Ōma Nuclear Power Plant - Legal Action Underway by the City of Hakodate

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.

Hinkley Point

An Taisce challenges DECC Secretary of State over Hinkley Point C decision

LargeAssociates Witness Statement features in An Taisce (National Trust of Ireland) challenge to DECC Secretary of State's decision not to consult with the Republic of Ireland over Hinkley Point C consultation.

Ms X's Clash with a Nuclear Weapons Carrier in the Dead of the Night

Ms X


Submissions to the Foreign Affairs, Defence and Trade Committee on the New Zealand Nuclear Free Zone Extension

Review of the physical stability and dispersion characteristics, etc., of unirradiated Mixed Oxide (MOX) nuclear fuel involved in Maritime Incidents and Accidents.

San Onofre Mitsubishiaircraft
This analysis links the Mitsubishi action items determined at design meetings for the replacement steam generators meetings to progress of the design and knowledge of Edison and Mitsubishi of the problems as these developed.
| Summary | Report | Reposte|

Adequacy of the Proposed Amendment to the Third Party Liability Finance Arrangements Covering Nuclear Damages  from Swiss Nuclear Plants

At present, all nuclear operators must take out private insurance cover with a Swiss insurer of at least CHF 500 million for each NPP with an additional CHF 50 million for procedural and interest costs as these might arise. Separately, the operators also have to pay into a Nuclear Damage Fund that is administered by the Federal Office of Energy with the objective that this fund will be sufficient to make up any liability shortfall of the private insurance cover up to a total of CHF 1,000 million  to meet all third party claims for any single radiation incident. The Swiss federal government  considers these liability cover arrangements to be sufficiently robust that it has not been necessary for Switzerland to ratify the international nuclear liability treaties (notably the Paris-Brussels Convention and Revision Protocols) to which it is signatory.


Information Commissioner's Office finds against ONR on EIR Claims

Information Commissioner's Office finds against ONR on EIR Claims for journalist Rob Edwards Relating to aircraft crash on a NPP, the ICO Decision Notice FER0377581 concluded that although the ONR was correct in withholding the requested information, the time taken do so, over 13 months compared to the statutory period of 20 working days, was excessive.

IAEA Mission to Fukushima Daiichi fails to identify cause of 2011 catastrophe

During the last week of May 2011 the International Atomic Energy Authority (IAEA) sent a team of about 20 nuclear experts to Japan to investigate the ongoing nuclear situation a Fukushima, publishing

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Accidents and Incidents

Chernobyl 20 Years On

Chernbyl - A nucleaor catastrophe 20 years on - Review of the Radiological Situation in 2006.

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Accidental Atmospheric Release Analysis for Flamanville and Other French NPPs

Using European Community Standard modelling software (COSYMA), this assessment compares the proposed Flamanville EPR to the radiological consequences of a severe radioactive release arising from a containment-bypass or containment failure at each of a number of existing NPPs in France, including Tricastin, Nogent-sur-Seine and Fessenheim. Because France has in place a programme to utilise reactor grade plutonium fuel (MOX) in certain of its existing NPPs and specifically in the EPR development at Flamanville, the impact of a radioactive release of MOX is examined in comparison with a low enriched uranium (LEU) fuelled NPP. The assessment includes account of the type of nuclear fuel, both LEU and MOX that is currently in use in French NPPs, and it projects the higher radiological consequences should the Generation III European Pressurised Reactor (EPR) proposed at Flamanville be subject to a severely damaging incident

La Vulnérabilite des Centrales Nucléaires Françaises aux Chutes d'Avion

TEPCO Plan to Flood Primary Containment at Fukushima Daiichi


EPCO plans to flood Unit 1 containment considered unwise.

THULE-2003 - Investigation of the Plutonium Contamination

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MOX Fuel Transportation Risks

Hazards and risks accompanying the transportation of new MOX fuel from Sellafield to Beznau NPP - dispersion analysis considers the greater release fraction of MOX when subject to intense heat possible in a rail tunnel and/or ship fire.

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HEU Irradiated Fuel Transport from Australia to COGEMA France

Hazards and risks accompanying the transportation of new MOX fuel from Sellafield to Beznau NPP - dispersion analysis considers the greater release fraction of MOX when subject to intense heat possible in a rail tunnel and/or ship fire.

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HEU Irradiated Fuel Transport by Rail in the United Kingdom - Risks and Hazards

This Review identifies potential accidents and malevolent acts that could severely damage a spent fuel transportation flask, thereby enabling the release of radioactivity, in the form of particles and aerosols, and the corresponding health risk imposed on unprotected members of public. Because the rail routes take the spent fuel trains through major urban conurbations (London, Bristol, etc) many thousands of population could be subject to radiation exposure in the aftermath of such an event.

Swedish Irradiated Fuel CLAB Strategy

Sweden’s irradiated fuel management strategy involves moving spent fuel from each of the nuclear power stations to a central fuel storage facility (CLAB). Spent fuel will remain at CLAB until it can be transferred to a deep disposal repository (SFL) some time after year 2008. All fuel movements from the NPPs to CLAB, except for the Oskarshamn reactors nearby, are by the specially adapted ship M/S Sigyn using internationally approved transportation flasks.

Export of Uranium Hexafluoride Tailings and Spent Containers

This analysis considers the hidden international exchange of empty but highly contaminated UF6 containers from  the Portsmouth uranium enrichment plant in the United States, where the export is little more than a ruse to ship radioactive waste abroad, to the Russian Federation Siberian radioa-chemical plant at which, or so it is claimed, the residue

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Risk and Hazards of the Road Transport of Plutonium Dioxide Powder Across France

MOX carrying trucks being involved in accidental and terrorist incidents are assessed in terms of the radiological and potential health consequences arising from a release of plutonium dioxide.


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Ageing NPP