Office for Nuclear Regulation

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1 Office for Nuclear Regulation ASSESSMENT REPORT Document Title Title: Assessment of Sizewell A REPPIR HIRE RoA Project: Sizewell A REPPIR HIRE Report of Assessment Document Identifier Identifier Revision TRIM Reference(s) ONR-CNRP-AR / Step-based Document Review Step Description Role Name Date TRIM Revision * 1 Initial draft, including identification and mark-up of SNI/CCI Author 2 Main editorial review Author 3 Peer Review in accordance with AST/005 Issue 1 Peer Reviewer 4 Assessor update / sentencing of comments and return to Peer Reviewer Author 5 Final editorial / clean draft review Author 30/09/ Acceptance review in accordance with AST/003 Issue 4 AUH 17/10/ Report Sign-off Author / Peer Reviewer / AUH 19/10/12 3 Document Acceptance Role Name Position Signature Date Author HM Inspector 19/10/12 Peer Review HM Inspector Acceptance HM Superintending Inspector 19/10/12 * TRIM revision to be identified upon completion of activity and incorporation of any changes to document. Where required in accordance with ONR How2 BMS Document AST/005 Issue 1. Hard-copy of document signed-off, TRIM version updated with authors / approver / acceptor names and dates and record finalised.

2 Office for Nuclear Regulation ASSESSMENT REPORT Revision History Revision Date Author(s) Reviewed By Accepted By Description Of Change 0 First formal issue. Circulation (latest issue) Organisation Name Formatting notes Headings Use CTRL ALT 1 thru CTRL ALT 3 for heading levels 1, 2 and 3 (etc). (All 9 levels are formatted but only Levels 1 3 appear in Table of Contents by intention, it is not recommended to use more than 4 levels of headings in the text). Use CTRL ALT N for non numbered paragraphs (ONR Normal Style) Use CTRL ALT P for numbered paragraphs Put a blank line before sub heading EXCEPT where there are more than one headings following each other (blank lines defeat window/orphan protection). Foreward (if present) and Executive summary are formatted with no paragraph numbers. Bullets Use CTRL ALT B for square bullets top level Use CTRL ALT R for sub bullets under square bullets Numbered lists Do not use the numbering or bullet buttons on the toolbars these are notoriously flaky in Word. Either use the pre defined shortcut keys, or else apply directly using Format Bullets and Numbering, or else use the indent button on a numbered paragraph. Other Do not use force page breaks again these are notoriously flaky in word. Do not edit any of the pre existing styles without reference they will be restored during final production anyway.

3 Office for Nuclear Regulation ASSESSMENT REPORT Live with the 6pt trailing space after paragraphs Word just prefers it this way. Do not attempt to auto number references, or add in hyperlinks in text to references if this is needed then consult first on the best way to do this. Tables and Figures Table titles above table, 10pt text TableX: bbbbbbbbb, justified in line with text. Figure titles below figure, 10pt text Figure Y: bbbbbbbbbbbbbb, justified in line with text. Table format as per ONR standard ONR Toolkit provides shortcuts to do this for you (colours, heading rows etc.) i.e. not ie or ie. e.g. not eg or eg. Ref. 7X but Refs XX and YY. Not Reference XX or using superscripts. No requirement for references to be sequentially numbered as they occur in report. No references in Executive summary or Assessment Findings or GDA issue s spell out items fully. Safety related, safety critical, on site, off site, load following etc. make sure hyphenation Is correct. ONR, HSE, IAEA etc. (no the UNLESS you are talking about something belong to an organisation e.g. the ONR Assessment Report. Headers and Footers Do not delete blank rows in the tables in headers and footers these are design to state the protective marking of a document, if applicable, and to provide spacing above the text in the body of the document. Leave blank if there are none this will also preserve page formatting when adding removing markings. Abbreviations and Acronyms Defined as singular (e.g. SAP) and but can then be used in text as plural (e.g. SAPs). Always introduce with capitalised text and in () brackets on first use. Define in Executive summary but re define as they occur in main body of text. No bar on re introducing later in text where this helps clarity. Copying in from other documents Use Paste Special and select unformatted text from the options this will avoid dragging in potentially different formatting and styles from another document. Figures should be converted to WMF (windows metafile) format before inserting reduces size of file and makes positioning easier JPO can do the conversion for you. Redaction of SNI / Commercially Sensitive Information All text to be redacted must be highlighted in grey background text (enclosing between symbols is not know required). HSE redaction tool should be used, but needs to be requested via DIRECTA since it has to be installed on a PC (see intranet/information/foi/redaction.htm). NOTE! If the document contains SNI / commercially sensitive information you must also add appropriate protective markings in all headers and footers before entering the sensitive information. If in doubt, or the content is under discussion mark anyway and remove later if resolved.

4 Office for Nuclear Regulation ASSESSMENT REPORT Production Notes To do: All blue highlighted text needs to be tailored for the Requesting Party / Reactor Design (Inspector). Do not alter any other parts of standard text without reference. All text above, and including the line below, will be redacted as a matter of course from any published version of this document. Other SNI / commercially sensitive information contained elsewhere in the document, and protective marking in headers and footers, will also be redacted as appropriate.

5 Office for Nuclear Regulation Civil Nuclear Reactors Programme Assessment of Sizewell A REPPIR HIRE RoA Assessment Report: ONR-CNRP-AR October 2012

6 Crown copyright 2012 COPYRIGHT You may reuse this information (excluding logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view the licence visit write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or Some images and illustrations may not be owned by the Crown so cannot be reproduced without permission of the copyright owner. Enquiries should be sent to Unless otherwise stated, all corporate names, logos, and Registered and Trademark products mentioned in this Web site belong to one or more of the respective Companies or their respective licensors. They may not be used or reproduced in any manner without the prior written agreement of the owner(s). For published documents, the electronic copy on the ONR website remains the most current publically available version and copying or printing renders this document uncontrolled. Page (i)

7 EXECUTIVE SUMMARY This report presents the findings of the assessment of Magnox Limited s Radiation Emergency Preparedness and Public Information Regulations (REPPIR) hazard identification and risk evaluation report of assessment for Sizewell A, as required by REPPIR regulation 6(4). Assessment was undertaken in accordance with the requirements of the Office for Nuclear Regulation (ONR) How2 business management system. The Health and Safety Executive s (HSE) guidance on REPPIR, together with the draft supporting technical assessment guide have been used as the basis for this assessment. This assessment has been focussed primarily on the determination of adequacy of the dutyholder s submission with respect to the requirements of Schedule 5 of REPPIR, and the determination of a suitable technical basis for discussions on the setting of the detailed emergency planning zone for the site. The report concludes that Magnox Limited s submission satisfies the requirements of REPPIR Schedule 5. The report further concludes that the discussion into the setting of the detailed emergency planning should proceed on the basis that the 5 milli Sv dose contour is less than 1 km, the minimum radius permitted for a detailed emergency planning zone according to existing HSE guidance. Page (ii)

8 LIST OF ABBREVIATIONS BMS HIRE HSE ONR REPPIR RoA TAG (ONR) How2 Business Management System Hazard Identification and Risk Evaluation Health and Safety Executive Office for Nuclear Regulation (an agency of HSE) Radiation Emergency Preparedness and Public Information Regulations Report of Assessment Technical Assessment Guide(s) (ONR) Page (iii)

9 Office for Nuclear Regulation TABLE OF CONTENTS 1 INTRODUCTION Background Scope Methodology ASSESSMENT STRATEGY Standards and Criteria Safety Assessment Principles Technical Assessment Guides National and International Standards and Guidance Use of Technical Support Contractors Integration with other Assessment Topics Out-of-scope Items ASSESSMENT OF DUTYHOLDER S SUBMISSION Format and Content of Report of Assessment Radioactive Substances on Site Potential for a Radiation Emergency on Site Reference accident CONCLUSIONS Key Findings from the Assessment Recommendations REFERENCES Page (iv)

10 1 INTRODUCTION 1.1 Background 1 The Radiation Emergency Preparedness and Public Information Regulations (REPPIR) regulation 6(4) requires the dutyholder, in this case Magnox Limited, to undertaken and submit to the HSE an adequate report of assessment. 2 Magnox Limited has submitted to the Health and Safety Executive (HSE), in Ref. 4, its hazard identification and risk evaluation (HIRE) report of assessment (RoA) for Sizewell A. 3 HSE is empowered to specify the minimum area of the detailed emergency planning zone (DEPZ) under regulation 9(1) of REPPIR. It does this based in part on a technical assessment of the information provided in the HIRE. 4 This report therefore considers whether the HIRE submitted by Magnox Limited is adequate, and assess the information contained therein to support discussions relating to the setting of the DEPZ. 1.2 Scope 5 This report presents the findings of the assessment of Magnox Limited s REPPIR HIRE RoA as presented in Ref. 4 and supporting documentation provided by Magnox Limited. Assessment was undertaken in accordance with the requirements of the Office for Nuclear Regulation (ONR) How2 Business Management System (BMS) procedure AST/001 (Ref. 1). HSE s guidance on REPPIR (Ref. 2), together with the draft supporting Technical Assessment Guide (TAG), Ref. 3) have been used as the basis for this assessment. 1.3 Methodology 6 The methodology for the assessment follows ONR business management system document AST/001, assessment process (Ref. 1), in relation to mechanics of assessment within ONR. 7 This assessment has been focussed primarily on the determination of adequacy of the dutyholder s submission with respect to the requirements of Schedule 5 of REPPIR, and the determination of a suitable technical basis for discussions on the setting of the DEPZ for the site. Page (5)

11 2 ASSESSMENT STRATEGY 8 The intended assessment strategy for the dutyholder s REPPIR HIRE RoA is set out in this section. This identifies the scope of the assessment and the standards and criteria that have been applied. 9 HSE is required to judge the adequacy of the dutyholder s submission and is empowered, under regulation 9(1) of REPPIR, to specify the minimum area of the DEPZ. It does this based in part on a technical assessment of the information provided in the HIRE. Specifically, the minimum area of the DEPZ is based upon an around the site, within which a member of the public could receive a dose of up to and including 5 milli Sv in the year following a reasonably foreseeable radiation accident. 10 This report therefore considers: Whether the contents of the report of assessment meet the requirements set out in REPPIR; Whether there is sufficient radioactive material on site for REPPIR to apply; Whether a radiation emergency, as defined by REPPIR, is reasonably foreseeable; Whether a suitable reference accident has been chosen; What the 5 milli Sv dose contour is, to feed into discussions on the setting of the DEPZ. 2.1 Standards and Criteria 11 The relevant standards and criteria adopted within this assessment are hose contained within the guidance on the Radiation (Emergency Preparedness and Public Information) Regulations 2001 (REPPIR), Ref. 2 and the draft internal ONR Technical Assessment Guide (TAG), Ref Safety Assessment Principles 12 The Safety Assessment Principles are not relevant to the assessment of REPPIR submissions Technical Assessment Guides 13 The following draft Technical Assessment Guide has been used as part of this assessment (Ref. 3): T/AST/082 The Technical Assessment of REPPIR Submissions National and International Standards and Guidance 14 The following national guidance has been used as part of this assessment (Ref. 2): A guide to the Radiation (Emergency Preparedness and Public Information) Regulations International guidance is not applicable to the assessment of REPPIR submissions. Page (6)

12 2.3 Use of Technical Support Contractors 16 N/A 2.4 Integration with other Assessment Topics 17 N/A 2.5 Out-of-scope Items 18 The following items are outside the scope of the assessment. The setting of the DEPZ, although informed by the technical assessment of the dutyholder s submission, is not limited by it. The setting of the DEPZ is therefore outside the scope of this assessment. Page (7)

13 3 ASSESSMENT OF DUTYHOLDER S SUBMISSION 3.1 Format and Content of Report of Assessment 19 Schedule 5 of REPPIR places specific requirements on the content of reports of assessment. The Sizewell A RoA, Ref. 4, takes each of these requirements and addresses it in turn, making reference to Appendices as appropriate. It is therefore easy to see that the requirements have been met. I note however that there is a requirement under Schedule 5 (j) to address those factors which could precipitate smaller but continuing releases of radioactive substances. Ref. 4 does this by considering routine gaseous and liquid discharges, but there is no discussion of unplanned discharges which, if undetected, could continue for 24 hours or more. Although not explicitly covered in Ref. 4 it is my opinion that such a circumstance is adequately dealt with in Sizewell A s arrangements for demonstrating compliance with Licence Condition Radioactive Substances on Site 20 To decide if REPPIR applies, operators need to identify the quantities of radionuclides or fissile material present and compare them with threshold quantities given in Schedules 2 (for the quantity of radionuclides, measured in Becquerels) and 3 (for the quantity of fissile material, measured in grams) for premises. These threshold values are set such that, if they are exceeded, there may be the potential for a radiation emergency. In this case REPPIR applies and the operator is required to undertake a technical assessment in the form of a HIRE, and to provide the HIRE report to the HSE. 21 Ref. 4 explains that the greater part of the radioactive substances present at Sizewell A is contained in the irradiated nuclear fuel. The fuel is natural uranium encased in a cladding of magnesium alloy. In its un-irradiated state (i.e. as brought on to site) the fuel contains very little radioactivity. However, exposure to the nuclear chain reaction, and the radioactive decay of the products of that chain reaction, cause the fuel to become highly radioactive. The radioactivity of fuel increases with irradiation in the reactor but decays when removed from the reactor or if the reactor is shut down. 22 There is other radioactive material on site in the form of waste, although the amount of radioactivity it contains is very much less that is present in the reactor fuel. Inventories which exceed the levels specified in Schedule 2 of REPPIR include: Approximately 27,000 m 3 of solid and wet radioactive waste; Approximately 15 m 3 of liquid (oil) waste. 23 In addition to these sources, radioactivity will also be present by activation of structural materials. Structures that contain sufficient radioactivity to exceed the levels specified in Schedule 2 of REPPIR include: Approximately 3,600 m 3 of graphite moderator; The reactor vessel and internals, the equivalent ingot volume of which is approximately 650 m However, the activity is fixed in the structures and would be unlikely to contribute significantly to any release from the environment, even in the case of a severe accident. 25 It is clear from the above that REPPIR applies and that the provision of a HIRE is appropriate. Page (8)

14 3.3 Potential for a Radiation Emergency on Site 26 REPPIR defines a radiation emergency as an event that is likely to result in a member of the public receiving an effective dose of 5 milli Sv during the year immediately following the emergency. In calculating the effective dose received, health protection measures (for example, sheltering) during the 24 hours immediately following the event are to be disregarded. The dose must include the sum of direct external radiation, internal radiation and/or ingesting contaminated food or drink. 27 If site and facility specific technical assessment shows that a radiation emergency can occur, then there is a need for the operator to prepare further technical assessments to address whether the likelihood of a radiation emergency is reasonably foreseeable. Guidance in the REPPIR ACoP states that in the context of a radiation emergency, a reasonably foreseeable event would be one which was less than likely but realistically possible. 28 Sizewell A have undertaken, in Ref. 5, a review of their consolidated fault schedule, which itself is a comprehensive list of the faults contained within the fault schedules associated with the main site safety cases. For the purposes of identifying whether a radiation emergency is reasonably foreseeable they have first considered faults meeting one or more of the following criteria: Faults with a likelihood of occurrence of 1 in 100,000 years or greater; Faults with a public dose consequence of 5 milli Sv. 29 Furthermore, faults that are within an order of magnitude of either criteria are also considered. It is my judgement that this is an adequate approach for determination of a reasonably foreseeable accident. 30 A total of fifteen faults with the potential to result in a radiation emergency were identified based on the criteria above. Noting that HSE s expectation is that technical assessment supporting REPPIR should be undertaken using a suitable best estimate approach where possible, whereas the technical assessment underpinning a deterministic safety case tends to be conservative, those faults were subjected to further analysis to remove significant pessimisms. As a result of this analysis, six faults were removed from further consideration in the HIRE RoA, as follows: Over-pressurisation faults were removed on the basis that steam generation is no longer credible, and the purge air system is shown to be capable of limiting overpressurisation to levels that are within its design strength; Primary coolant faults were removed on the basis that, even in the absence of cooling, fuel temperatures cannot now reach levels that would cause fuel damage; Fuel handling faults at the fuelling machine were removed on the basis that they assumed the ignition of a dropped fuel element, which would require it to be at a temperature that is no longer achievable; Aircraft crash on the splitter vane store was removed as the frequency is pessimistically assumed to be the same as the whole site frequency in the safety case; scoping calculations performed by the dutyholder demonstrate that the frequency of a crash on the store itself are much lower, and that a crash would be unlikely to lead to a release as the splitter vane store is a substantial, shielded structure; Page (9)

15 Seismic events leading to a uranium hydride fire in the splitter vane store were removed as the resulting exposure of uranium hydride to air would not in itself be enough to cause a fire, and a seismic event would not introduce a source of ignition; Partial loss of cooling water faults were removed as they result in a aqueous release, which is not suitable for re-calculation using the NEAF methodology. 31 In addition, the consequences of one of the faults (fire in the combustible active waste void) have been recalculated for the purposes of the HIRE, and are now significantly reduced. 32 Dismissal of the faults here does not mean that those faults can be removed from the site s safety case, or that the engineered and procedural controls in place are no longer required. The dismissal of the faults described above is purely for the purposes of the analysis contained within the rest of the HIRE RoA, which aims to determine: Whether a radiation emergency is reasonably foreseeable; The nature of the reference accident. 33 Sizewell A have not attempted to argue that a radiation emergency is not reasonably foreseeable, so I have considered the dismissed faults in the context of their suitability for further analysis of their potential to be the reference accident, using the NEAF methodology. 34 It is my judgement, based on the information provided and my own knowledge of the Sizewell A site, that the removal of the faults listed in paragraph 30 is reasonable, for the following reasons: The removal of the over-pressurisation and primary coolant faults is a recognition that the reactor is now depressurised and cooled by natural circulation of air. It is my expectation that these faults will be removed from the safety case as well, at its next issue; The fuel handling fault at the fuelling machine requires the fuel to be at a temperature above 250ºC. Ref. 6 demonstrates that the fuel temperature would not now be above 100 ºC. On the basis that the margin between for the predicted temperature and limit is significant (and therefore allows for substantial errors in either or both calculations) and that the calculated frequency was in any case much lower than other, higher consequences faults (particularly the total loss of pond water), I am prepared to accept the removal of this fault from further consideration in the HIRE RoA; Based on examination of the site plan, and the size of the splitter vane store (actually the whole ponds complex, including the effluent treatment plant, of which the splitter vane store is part) relative to the main part of the site, I can confirm that the frequency of aircraft crash would be of the order of 10-8 per year if it is assumed that the frequency scales with area. In reality, I note that the splitter vane store is shielded on two sides (on one side from the reactor building) so the frequency is likely to be further reduced. On that basis, and considering that the frequency and consequence of the fault were already significantly less than those of the total loss of pond water fault, I consider removal of the aircraft crash fault from further analysis within the HIRE RoA to be reasonable; The likelihood of a seismic event leading to a uranium hydride fire in the splitter store is already of the order of 10-9 per year, which is in any case arguably less than reasonably foreseeable. Furthermore, the consequence of 5.2 milli Sv only just exceeds the limit for definition of radiation emergency, and is not bounding. For Page (10)

16 these reasons, I am content for this fault to be removed from further analysis within the HIRE RoA; The partial loss of cooling water fault can be discounted because it is clearly bounded by the total loss of pond water, which would unarguably result in a radiation emergency; The original calculation for the consequences of a fire in the combustible active waste void assumed combustion of 100% of the inventory; the revised calculation assumes combustion of the worst 20% of the inventory, including all of the most heavily contaminated items. However, this is not in itself a significant factor as it is clear from the examination of the source term presented in Ref. 7 that these most heavily contaminated items account for over 90% of the activity. What is more significant is that the calculation uses a much more accurate waste inventory, based on remote survey and examination of historical records, and a more sophisticated fire model. It is my understanding that this revised calculation will form the basis of the next issue of the safety case. 35 I note also that the sum of the public consequences of all the excluded faults is approximately 75% of the consequence of the total loss of pond water fault. 36 The consequences of the remaining eight faults, plus the recalculated fire in the combustible active waste void fault, were recalculated using the NEAF methodology to find the dose to a member of the general public at 75m from the source of the release (75 km is taken as being the closest a member of the public could come to the source of release for the duration of the accident). The recalculation took into account the requirements placed on two specific parameters in the REPPIR guidance, Ref. 2, namely: The age group chosen (which should be the age group giving rise to the highest dose; The weather (the use of Pasquill Category D weather should be used for REPPIR applications). 37 The final list of faults was as follows: Fuel handling faults causing a fuel drop and/or fuel damage at the reactor; Fuel handling faults causing a fuel drop and/or fuel damage in the dry fuel route; Fire in the combustible active waste void; Incineration of a miscellaneous contaminated item; Radioactive waste facility faults due to internal hazards (hydrogen explosion in the splitter vane store, low level waste fires and dropping a drum of incinerator ash); Seismic events leading to a breach of sludge tank containment; Seismic events leading to a gaseous release from the splitter vane store; Pond faults leading to a total loss of pond water; Pond faults resulting in fuel elements being damaged in the pond or damaged or stranded in the flask handling passage. 38 Both before and after the recalculation, only one fault was identified that could give rise to a radiation emergency; a total loss of water from the spent fuel pond. This fault is the only one identified that could give rise to an off-site dose of 5 milli Sv (regardless of frequency); it is also worthy of note that all of the more frequent faults identified give rise to doses that are an order of magnitude (or more) below the 5 milli Sv limit. Page (11)

17 39 Sizewell A make the claim in Ref. 4 that even if one assumes an extreme beyond design basis event that somehow results in all faults occurring simultaneously, the total dose to the critical individual at the site boundary would essentially be no different to the dose from the loss of pond water event on its own. It is my judgement that the evidence supplied by Sizewell A supports this claim; calculated using the NEAF methodology, the sum of the consequence of all other faults is 0.13 milli Sv, compared with a consequence of 70 milli Sv for the total loss of pond water fault. 40 Note that the review of the safety case described above does not include a review of security events that could lead to an off-site release. The Licensee s submission does include a discussion of security events, and concludes that they are no reasonably foreseeable events that could give rise to a significant off-site dose Reference accident 41 Taking the above into account, I conclude that the use of a single fault, a total loss of water from the spent fuel pond, for the calculation of the 5 milli Sv contour is reasonable. I note also that the total loss of pond water fault is unusual in that its consequences include both external radiation exposure and the release of contamination. This combination may make the fault a more robust basis for extendibility planning. 42 Ref. 5 takes data from Ref. 8, which models dose rates in pond failure scenarios at distances representing the site boundary (61m, modelled in five regions from 50 m to 75 m) and point of nearest habitation (510m modelled in ten concentric regions from 500 m to 600 m). From these two sets of data Sizewell A derive two trend lines, which for convenience I shall refer to as D 61 and D 510, for the dose accrued in 24 hrs at a point x metres from the centre of the ponds as follows: D 61 = e x milli Sv D 510 = e x milli Sv 43 Sizewell A note that the two trend lines D 61 and D 510 meet at approximately 170 m and therefore assume that D 510 applies from that point to 600 m. 44 The proposed 5 milli Sv contour is made up as follows: The dose received by spending 24 hours at a distance of 225 m; Nine days exposure at the nearest residence. 45 The contribution from sky shine at 225m is 2.9 milli Sv, with another 0.9 milli Sv from the other nine-day exposure at the nearest residence and approximately 1 milli Sv from other pathways. 46 The ONR specialist inspector has disagreed that D 510 can be assumed to be applicable beyond 170 m without further demonstration. In particular, given that the results are based on computer modelling, it should be possible to re-run the calculation to produce results at and near to 225 m. However, in the absence of further justification the ONR specialist inspector would be prepared to accept that a bounding curve D bound could be described by taking he worst-case constants from D 61 and D 510 to provide a value for the dose at x metres. Such a curve would conservatively assume the highest dose rate at source and the slowest decrease of dose with distance, and would be described by the following equation: D bound = e x milli Sv Page (12)

18 47 If it is further assumed at the dose due to sky shine and other pathways remains constant over the area between 170 m and 600 m, then using the equation for D bound suggests that the 5 milli Sv dose contour should be set at 425 m. 48 I discussed with Sizewell A the possibility of providing a more definitive curve by modelling explicitly out to the required distance (i.e. 225 m, with some margin on either side). However, I also recognise that this would not actually materially affect the DEPZ. This is because it is ONR policy, set out in Ref. 9, that for large, modern plant the DEPZ will be not less than 1 km if a radiation emergency can be shown to be reasonably foreseeable, regardless of the results of the subsequent assessment of the reference accident. Although there is disagreement between Sizewell A and ONR on the exact radius of the 5 milli Sv dose contour, there is agreement that it is considerably less than this 1 km minimum. For this reason, I consider that there is little value in requiring further work from both Sizewell A and ONR to further substantiate the 225 m dose contour proposed by Sizewell A, and instead recommend that the minimum DEPZ of 1 km be used as the technical basis for discussion of the actual DEPZ (which will take into account factors other than just this technical assessment) at Sizewell A. Page (13)

19 4 CONCLUSIONS 49 This report presents the findings of the ONR assessment of Magnox Limited s Sizewell A REPPIR Regulation 6(4) HIRE RoA, Ref To conclude, I am satisfied that Ref. 4 satisfies the requirements of REPPIR Schedule Key Findings from the Assessment 51 The key findings from my assessment are: A radiation emergency is reasonably foreseeable at Sizewell A; It is reasonable to use the total loss of pond water fault as the reference accident; The consequences of the reference accident would fall to below 5 milli Sv beyond somewhere between 225 m and 425 m; This range (225 m to 425 m) sites well within the minimum DEPZ of 1 km allowed for by HSE policy. 4.2 Recommendations 52 My recommendation is as follows. Discussion into the setting of the DEPZ should proceed on the basis that the 5 milli Sv dose contour is less than 1 km. Page (14)

20 5 REFERENCES 1 ONR How2 Business Management System. Assessment Process. AST/001 Issue 4. HSE. April A guide to the Radiation (Emergency Preparedness and Public Information) Regulations L126. HSE The Technical Assessment of REPPIR Submissions. T/AST/082 working draft. HSE. July TR/SE/221 Issue 2 Sizewell A : REPPIR Regulation 6(4) Hazard Identification and Risk Evaluation Report of Assessment. September TR/SC/013 Issue 1 REVIEW OF SAFET YCASE FAULT SCHEDULES IN SUPPORT OF THE REPPIR HIRE REPORT OF ASSESSMENT. September MEN/EWST/SXA/EAN/0001/11 Temperatures of Long Cooled Fuel in the Sizewell A Fuelling Machine. July TR/SH/359 EVALUATION OF RADIOACTIVITY & RADIONUCLIDE INVENTORY IN SIZEWELL A COMBUSTIBLE ACTIVE WASTE VOID Issue 2. October MES/EST/SXA/REP/0010/07 An Assessment of Dose Rates in the Vicinity of Sizewell A Cooling Ponds with Reduced Water Levels. December 2007/January Arrangements for responding to nuclear emergencies. HSE Books Page (15)