Health and Safety
Executive / Commission
Nuclear
LLC reports
This report is issued as part of the Health and Safety Executive's commitment to make information about inspection and regulatory activities relating to the above sites available to the public. It is for distribution to members of the West Cumbria Sites Stakeholder Group (WCSSG) and covers activities associated with the regulation of safety at BNGSL Sellafield and Drigg, and UKAEA Windscale.
These reports are distributed quarterly and will be available on the Internet. Site Inspectors of HM Nuclear Installations Inspectorate (NII) attend WCSSG meetings and will be happy to respond to any questions raised there. Any other person wishing to inquire about matters covered by this report should contact HSE, Nuclear Safety Directorate Information Centre on 0151 951 4103.
This report will be put onto the HSE Website at http://www.hse.gov/nuclear/llc/index.htm.
NII Inspectors made a total of 62 visits to the Sellafield, Calder Hall, Windscale and Drigg sites during the quarter. This involved a total of 248 days on site (see Table 1 for details). The more significant issues identified during these inspections are summarised below.
Level 1 Emergency Exercise “Fieldfare” was carried out on the 22 nd March 2007 to demonstrate BNGSL’s response, under the Emergency Plan, to an incident associated with B30. The scenario was both realistic and challenging and is considered by NII to be a well prepared test of the BNGSL Emergency Response.
A number of NII inspectors observed the exercise from a variety of locations and judged the exercise to be an acceptable demonstration of BNGSL’s emergency preparedness on the day, with particularly strong performances in the ICC and SECC. A good performance was provided by the ACP team who were under some pressure because of the space constraints, and a fairly challenging scenario. The Fire & Rescue Services and response teams also performed well.
The transfer of a simulated contaminated casualty to and through the reception process at the West Cumberland Hospital, Whitehaven. The inclusion of the hospital into this exercise did give us the opportunity to observe this interface and the contamination control at the hospital which was both considered to be of good standard.
Work commenced with BNGSL on a part of the Sellafield Corporate Intervention Strategy relating to Competency Framework. An initial meeting was held with the Head of Assurance and his team, to gain a joint understanding of the scope of the intervention and to identify particular topics within it. The outcome is being assessed and topic work strands are being developed. The aim of this project is to work with BNFL, BNG and BNGSL to achieve sustained improvements in managing for safety and safety culture.
Useful discussions were held with several Safety Representatives and Trades Union Convenors on the way Safety Representatives and NII work together to make safety improvements. Some good practice, developed on other nuclear installations, was shared and there is common support to build upon this practice at Sellafield.
Operations in the Magnox Reprocessing Plant ceased during the quarter due to difficulties being experienced with downstream plants. NII continues to meet with BNG along with other key stakeholders to discuss the key issues surrounding the reprocessing of fuel in accordance with the Magnox Operating Programme.
BNGSL has carried out a detailed investigation into the cause of the elevated Cs-137 aerial discharges experienced in FHP in last year. The cause has been attributed to aerosols resulting from the operation of the wind water line sprays around the ponds. BNGSL has changed the spray operating regime and the airborne activity levels have reduced to those last seen several years ago. NII is satisfied that there are no significant safety issues of concern. Environment Agency is the lead regulator on offsite discharges.
Fuel decanning operations have ceased in the Fuel Handling Plant due to difficulties being experienced with downstream plants.
BNGSL’s project for delivering a permanent installed neutron monitoring system to replace the current interim neutron monitoring implemented within the plant is nearing completion of the installation phase and will commence commissioning during the next quarter. It is anticipated that there will be a period of operation where both systems will be operated in parallel until the permanent system has been adequately proven. The site inspector for PF&S continues to monitor both the implementation of the interim monitoring and the delivery of the permanent installed system closely.
On 9 January NII issued a Consent to allow the restart of THORP as it was satisfied that BNGSL had done all the work necessary to ensure that THORP could be restarted safely. NII also published two reports on its website, one concerning the investigation undertaken by NII, because of the leak in the Feed Clarification Cell, and the other concerning the decision to issue a Consent for restart.
Although a Consent was issued, evaporator problems in the Highly Active Liquid Evaporation and Storage (HALES) plant, which accepts high-level liquid waste from THORP, delayed the resumption of routine reprocessing of irradiated fuel. However the issue of the Consent allowed some active work to be undertaken on the plant and, at the end of the quarter, one of two tanks of plutonium nitrate left from earlier reprocessing operations had been successfully processed.
MEB decontamination problems continued to delay the start of active commissioning of the MEBXF. BNGSL is hoping to resolve these problems during the next quarter.
Useful and open discussions were held with BNGSL following indications that AGR fuel cladding failures had occurred within the ponds. BNGSL is keeping NII and EA appraised of the situation, and the implications of the findings and any necessary remedial measures will be followed up with BNGSL during the next quarter.
In the WCSSG report for October to December 2006, NII recorded that strategically significant concerns associated with HALES had been raised in relation to the integrity of evaporators and HASTs, and to staffing levels in HALES. NII has continued to press for improvements, and the current status is as follows:
Evaporators
There remain significant uncertainties as to the remnant life of the evaporators. NII has continued to engage BNGSL on its evaporator recovery programme and on the development of new evaporative capacity.
HASTs
HAST cooling coil failure rates and, perhaps more significantly, the distribution of failed coils within the newer HASTs leads to considerable uncertainty as to the capability of the new-side HAST fleet to continue to deliver within the current stocks strategy. BNGSL is in the process of evaluating the need for replacement HASTs.
Staffing
Events earlier in the financial year indicated that the staffing capability was not fully adequate for an ageing high hazard facility such as HALES. Shift teams responsible for the day-to-day running of the plant are fully resourced, and BNGSL has considerably increased the number of people working on the evaporator recovery programme by transferring experienced engineers from other Sellafield plants. But there are still significant shortfalls in engineering and manufacturing support required to progress plant improvements. NII is aware that BNGSL is actively recruiting new staff and we recognise the difficulties of recruiting suitably qualified and experienced personnel, but we continue to press BNGSL to improve staffing levels and to focus on staff retention.
Matters related to evaporators and HASTs are expanded upon elsewhere in this report.
There are currently three evaporators within HALES (referred to as Evaporators A, B and C). They are used to evaporate High Active (HA) raffinate produced during reprocessing and to process effluent from WVP. Once concentrated through evaporation, the raffinate is called Highly Active Liquor (HAL). HAL is stored in the HALES facility prior to feeding to WVP for vitrification, which immobilises the waste for long term storage and eventual disposal. The status of the evaporators (as of April 2007) is:
The increase in the numbers of experienced engineers working on the evaporator recovery programme has led to significant improvements, for example in the rate and quality of safety case production, and with the developments of new techniques for the non-destructive testing of evaporator heating/cooling components.
NII continues to engage BNGSL on the provision of new evaporative capacity. Groundworks for Evaporator D have already started, and NII anticipates receiving the pre-construction safety case for Evaporator D shortly. NII is working closely with BNGSL, the Environment Agency and the Nuclear Decommissioning Authority on opportunities to accelerate Evaporator D whilst ensuring that the safety of design and construction is not compromised. BNGSL is also considering the need for further evaporative capacity (Evaporator E).
The position on evaporative capacity is evolving quickly and it is not possible at present to be certain as to the implications. The restart of Thorp reprocessing has already been delayed and the reprocessing of Magnox.
BNGSL continues to provide NII with monthly reports summarising the quantities of highly active liquor (HAL) contained in the highly active storage tanks (HASTs). These figures, supported by our inspection activities, are used by NII to judge whether BNGSL continues to meet the HAL Specification (Licence Instrument No 343) issued in 2000, which provides a limit on the amount of HAL that can be stored at any time and which requires HAL stocks reduction. Satisfactory performance of WVP coupled with the extended outage at THORP has meant that HAL stocks are currently well below the levels required by the Specification. Consequently NII is content that BNGSL has kept within the requirements of the Specification.
NII’s 2006 Biennial Review of the HAL Stocks Specification is now complete and a statement is attached to this report. Among other things, the Review recommends tightening the Specification to lock-in gains arising from the THORP outage. Work is now ongoing to implement the Review Recommendations, which will lead to the Specification being re-issued. In the meantime NII will continue to regulate the HAL stocks according to the existing Specification.
Previous WCSSG reports have indicated that HAST cooling components have suffered over the years from corrosion. A number of cooling coils have been declared failed. A failure causes a breakthrough of activity into the cooling water circuits which can lead to a radioactive release if not properly managed. HAST cooling coil failure rates and the location of recent failed coils has led to uncertainties over the ability of the newer HASTs to service the needs of the HAL stocks strategy. If the plant starts to deteriorate more quickly, then the ability of HALES to receive raffinates will be prejudiced (with knock-on consequences).
BNGSL’s present contingency plan is a project to dose the cooling water circuits with nitrates as a way of stopping, or at least reducing the rate of, corrosion failures. At present NII has a number of outstanding concerns connected with nitrate dosing. One of the options to insure against these problems would be to build smaller, inherently safer replacement HASTs. In order for these to be effective on sensible timescales, work needs to start as soon as possible. NII wishes to see new HAST designs developed to a stage where their viability could be judged alongside other options under consideration. BNGSL is in the process of evaluating the need for replacement HASTs as part of its response to the Recommendations of NII’s 2006 Biennial Review of the HAL Stocks Specification.
The performance of all three vitrification lines was variable during the reporting period as a result of planned and unplanned outages. Line 3 exceeded its production target in 2006/07, although overall WVP performance was less than anticipated because of the outages. There have been no significant effects on HAL stocks reduction.
Line 1 is undergoing extensive refurbishment associated with BNGSL’s link with COGEMA: this work should lead to lasting improvements to the throughput and reliability of Line 1, and similar work will be undertaken on Line 2 in due course. Both Lines 1 & 2 are nearing completion of their respective outages and are expected to return to HAL feed early in May. Line 3 is currently in planned rebuild following a successful eight month campaign and is expected to return to HAL feed in mid May.
WVP continues to experience difficulties with the processing of radioactive waste from the breakdown cells, after a period of an improved performance over the last two years. These cells hold a significant amount of waste that originates largely from failed vitrification components removed during vitrification line rebuilds. If waste volumes accumulate to an extent that further rebuilds are not possible then it may become difficult to maintain progress with vitrification, which in turn could have consequences for HAL stocks reduction. NII plans to carry out an inspection of WVP waste management in May 2007 to better understand the issues and to consider improvement options: the outcome of this inspection will be reported to the WCSSG.
REF is progressing reasonably well though it is running slightly behind programme. Inactive commissioning is proceeding in stages. NII continues to maintain regular contact on this strategically important project in advance of the start of active commissioning in 2007. Regulatory issues include the necessary interfaces with other facilities at Sellafield to ensure the safe and timely export overseas of containers of high level waste (in accordance with government policy on waste substitution). Standards of housekeeping and health and safety on REF remain generally good, although efforts continue to be made by BNGSL to learn from a number of minor conventional safety incidents and to improve safety awareness. The safety case for active commissioning is expected to be submitted to NII in April 2007.
NII and EA inspectors carried out a joint team inspection to evaluate the effectiveness of the HLWP asset care regime in managing ageing and degradation of plant with nuclear safety and environmental functions. The outcome of this inspection has been conveyed to BNGSL by letter. The regulators are to meet BNGSL in April to discuss the findings and the proposed action plan.
NII carried out an inspection of HLWP for compliance with Licence Condition 28 (Examination, inspection, maintenance and testing). We found that examination, inspection and maintenance required for nuclear safety were not addressed to the level that NII believe is necessary, and that the safety case process tends to focus on proof testing at the expense of examination, inspection and maintenance. These issues could be site-wide and are being followed up accordingly. We also found a shortfall in the awareness of nuclear safety risks from poor housekeeping, plus examples of failure to follow procedures and of poor control and supervision. The site inspector will convey the outcome of the inspection to BNGSL.
The first European fuel campaign was completed and delivered to the reactor site. SMP MOX commissioning operations continued with the manufacture of pellets for another European customer. In the meantime, the rod manufacture and fuel assembly areas of the plant have been engaged in a large campaign change project, to switch over to a different variant of PWR fuel for this customer. NII are expecting to permission several Category B modification proposals for this work, which link with the Licence Instrument (633) for the campaign change Overarching Strategy Paper, described last quarter. A routine SMP - Regulator (NII & EA) Liaison meeting was attended, which provided a useful update on SMP progress in general and an exchange of information. A range of Safety performance indicators were reviewed which continue to be adequate. Following completion of the THORP Feed Clarification Cell event work, the Site Inspector undertook some compliance inspection in SMP, for example relating to Alarm Logging and Glovebox inventory arrangements. Some shortcomings were brought to the attention of SMP management, which are being resolved.
In January 2007, a contamination event occurred within the SMP rod manufacture area, which involved five workers. Biological sampling initiated by BNGSL has confirmed that the doses received by the workers were all less than the annual limit for intake. BNGSL initiated a Board of Inquiry that will report its finding during the next quarter. NII has undertaken its own investigation into the event and this will be completed during the next quarter.
On 10/1/07 a contamination event occurred within SMP involving five workers. Biological sampling initiated by BNGSL has confirmed that the doses received by the workers were all less than the annual limit for intake. BNGSL initiated a Board of Inquiry that will report its finding during the next quarter. NII has undertaken its own investigation into the event and this will be completed during the next quarter.
Progress on the programme to meet the Magnox Storage Pond specification on removal of sludge is mixed. The Sludge Packaging Plant (SPP1 - the plant that will receive sludge from the Magnox Storage Pond) delay has been evident for a while but worse than hoped for condition on some of the skip handler steel work could further delay that particular element of the work. Risk reduction activities are, however, keeping broadly to programme and success here will aid other enablers for the retrievals .
The Piles Storage pond programme to meet the specification for sludge removal is generally on track and there is encouraging progress being made on the means for retrieval of metal fuel.
BNGSL’s evidence pack, containing details of committed programmes of future work, together with our recent inspection has enabled NII to judge that they have satisfactorily discharged the improvement notice on the maintenance arrangements for Legacy Ponds and Silos. BNGSL’s discovery of further corroded, redundant pipe work associated with the Magnox Storage Pond serves to underline the importance of the improved asset care process.
During high winds on the afternoon of 18th January, several BNGSL individuals observed one of the Separation Area stacks to be moving. The movement was observed in only the top half of the stack. The stack is adjacent to the Analytical Services Building, and is the contaminated extract ventilation stack for several of the buildings in Separation Area. Observation of the stack using binoculars did not indicate any signs of damage, cracking, or spalling of the concrete.
The Sellafield Emergency Control Centre (SECC) was not formally set up, but the Emergency Control Team assembled and provided support to the Site Shift Manager. The team formulated contingency plans for the site. Plant Services management team established the engineering situation, and produced a specific response for Analytical Services. There appeared to be no immediate risk as the wind speeds fell considerably from a peak of 77 mph, although winds of ~50 mph were forecast for the following weekend.
Likely scenarios were being considered in the event of the stack falling, including assessments of the radiological consequences. A drop zone of 43m radius was estimated, which would include most of the Analytical Services building, and a pipebridge carrying no process liquor, but most utilities (steam, compressed air, 11 kV electrical supply etc). The Plant Services team assessed the potential effects to buildings supplied via the pipebridge. Other buildings in Separation Area were not in the estimated drop zone. There were limited process activities being carried out in the area around the stack, with restricted movement of hazardous materials.
The BNGSL Site Team issued advice that if the wind speed rises to >40 mph, then the potentially affected buildings will be put on alert. If the wind speed rises to >50 mph, then the buildings will be evacuated. The BNGSL Site Emergency Team are to be alerted if the wind speed rises to >60 mph.
A survey company, who use optical and laser measurement equipment, have surveyed and taken video of the stack movement. Inspections and sampling from 30m and 70m mobile platforms were carried out. Core samples of the concrete have been taken for analysis to determine any effects of chloride attack, close-up videos were taken of the structure to identify any cracking, and a camera inspection of the interior of the stack has taken place.
The latest information from BNGSL on the stack movement is that it was estimated as being within that calculated for the maximum wind speed measured (~77 mph). More sophisticated analyses are being undertaken by the Risley Engineers, and these will be further refined when the information from the laser targeting, sampling and video exercise is available. The BNGSL Civil Engineers have started to consider options for strengthening the stack, and also alternative discharge routes for the Separation Area ventilation systems if the stack becomes unavailable.
A meeting was held with Infrastructure and Plant Services management to discuss the future strategies for Analytical Services. The short term strategy will be based on the recommendations from the delayed Periodic Safety Review and their impact on the use of the Analytical Services building. A facilities plan incorporating medium- and long-term strategies is close to being completed by BNGSL that includes consideration of the following:
An assessment has been made of the numbers of future samples requiring analysis by Analytical Services. There are a series of peaks in sample numbers between 2020 and 2040 which indicate that extensive analytical facilities will be required in the medium to long term. Plant Services have determined that a decision on the long term future of the Analytical Services building will need to be made in 2014, in order to ensure that the required facilities are available by the predicted rise in sample numbers in 2020. NII are considering the best way to regulate the strategy.
The operational challenges that were being experienced in the floc retrieval plant have now been resolved and reduction of inventory is continuing in conjunction with outstanding commissioning tasks. It is expected that BNGSL will submit their request for Consent to Operate at the end of April 2007.
Encapsulated Product Store
The first phase of the project to deliver the new Encapsulated Product Store (EPS3), site preparation and foundations, is progressing. There has been some slippage and this phase of the project has overrun. The second phase of the project, construction of the store, has been sanctioned by NDA and DTI approval has also been given. DTI’s approval was received later than expected and has resulted in a revaluation of the project and a delay to the start of this phase of the project. Work on the second phase is due to commence in June 2007 and the anticipated date of a commissioned store is early 2011.
MBGWS Waste Management Inspections
A programme of inspections is being planned to enable NII to form a view on the adequacy of the current arrangements for storage of ILW in MBGWS. It is recognised that MBGWS is currently accumulating legacy waste that will require reworking before disposal. NII is keen to work with BNGSL in ensuring that this continued accumulation is minimised and progress towards a waste form that will be disposable. To this end, inspection of a selection of consignors to MBGWS has been proposed. The inspection will seek to establish the adequacy of compliance with current arrangements and identify any potential improvements.
The safety case for B13 expired at the end of December 2006. UKAEA approached NII in September to discuss how the safety case could be kept extant given the late start in making safety improvements to the building. UKAEA prepared a modification to the new safety case and, having received advice from its Nuclear Safety Committee, sent this to NII in mid December. The Nuclear Safety Committee also advised UKAEA that it could accept a one-month extension of the old safety case to allow time seeking NII agreement to the proposal. The proposal allows use of the new safety case, but restricts operations that are permitted until safety improvements are completed.
NII’s has been concerned at the lack of progress with safety improvements over the two-year period since the new safety case was originally submitted to NII. NII has issued three Licence Instruments to allow work to proceed but to keep a tight regulatory oversight.
These areas are:
An event was reported by UKAEA in early January. During maintenance of the Cave 12 transfer tunnel and shield doors the outer shield door opened unexpectedly before the inner door had fully closed. Further use of the transfer tunnel was embargoed by UKAEA, and, after advice from NII the following working day, the embargo was extended to the other shield doors in B13. The embargo has since been lifted for Caves 1 and 13 after UKAEA presented NII with an adequate justification to allow continued use of the shield doors. The Cave 12 embargo will remain until a modification is completed and a return to service can be justified.
NII is assessing a proposal received from UKAEA to permit removal of the remaining Isotope cartridges from Pile 2. NII is concentrating its assessment on the use of the 31Te crane for lifting the repackaged isotopes to ground level.
NII completed its assessment of the new B2 Operational Safety Case a Licence Instrument allowing it to be Adopted as the Extant safety case.
No Exercise has been observed this quarter.
NII has had a team of inspectors working since January on the Windscale site transition project that will lead to re-licensing of the site in 2008. Windscale will remain as a separate licensed site at that time.
NII is following two guiding principles as the site restructures and separates from the rest of UKAEA
NII has recently written to BNGSL confirming that we are content that the “shadow working period”, to demonstrate that they could be relicenced as a stand alone licencee, has been satisfactorily completed. The timing of relicensing is now dependent on removal of PCM from the site, as – by prior agreement - the shadow working arrangements did not include this element of the current site activity. Our understanding is that the PCM is likely to be off the in a few months time.
| BNGSL SELLAFIELD 1 | BNGSL CALDER HALL 2 | BNGSL DRIGG | UKAEA WINDSCALE | |
|---|---|---|---|---|
| NUMBER OF VISITS | 55 | 2 | 2 | 3 |
| INSPECTION DAYS ON SITE | 218.5 | 14.5 | 3 | 12 |
| ENFORCEMENT ACTIONS 3 | 1 | 0 | 0 | 0 |
| Incidents in the quarter likely to be published in HSE’s quarterly “Statement of Nuclear Incidents at Nuclear Installations” | 0 | 0 | 0 | 0 |
| CONSENTS, APPROVALS | 0 | 0 | 0 | 0 |
| LICENCE INSTRUMENTS | 3 | 0 | 0 | 0 |
1 The figures shown for BNGSL Sellafield are those for BNGSL’s chemical plants. They do not include figures for the plants within the Electricity Generation Group (see note 2 below)
2 The figures shown for BNGSL Calder Hall are those for the plants on the Sellafield site operated by (or for) the Electricity Generation group, primarily Calder Hall nuclear power plant.
3 An enforcement action may be a Direction issued by HSE under the nuclear site licence, an Improvement Notice, or a Prohibition Notice, or the laying of information in pursuit of a prosecution.
| Date | Type | Ref. No. | Description | |
|---|---|---|---|---|
| BNGSL DRIGG Nuclear Site Licence no. 29A | ||||
| BNGSL Sellafield (and Calder Works) – Nuclear Site Licence no. 31G | ||||
| BNGSL Windscale – Nuclear Site Licence no. 46B | ||||
| Date | Type | Ref. No. | Description | ||||
|---|---|---|---|---|---|---|---|
| BNGSL DRIGG Nuclear Site Licence no. 29A | |||||||
| BNGSL Sellafield (and Calder Works) – Nuclear Site Licence no. 31G | |||||||
| 13/02/07 | Agreement | 640 | Agreement to commence installation of plant and equipment in areas 100 & 600 of the Sellafield Product and Residue Store | ||||
| 13/02/07 | Agreement | 639 | Agreement to commence modification to an existing plant – operation of Evaporator ‘A’ under the revised safety case | ||||
| 08/01/07 | Acknowledgement | 634 | Acknowledgement of receipt of safety documentation for active commissioning of the local effluent treatment plant | ||||
| UKAEA WINDSCALE – Nuclear Site Licence no. 46B | |||||||
The storage of liquid high level waste at Sellafield: HSE's 2006 biennial review.
Highly active liquor (HAL) is produced at Sellafield from the evaporation of raffinates. The raffinates are a waste stream from the nuclear reprocessing plants and contain the fission products and waste actinides extracted from spent fuel. The safety of the storage of these heat-generating wastes has been a matter of public interest for many years. Recognising this, the Health and Safety Executive (HSE) has published a series of reports Ref. 1, 2, 3, 4 on the key safety issues associated with HAL storage and our regulatory approach to these.
The HAL is stored in a number of Highly Active Storage Tanks (HASTs) located in the HAL Evaporation and Storage plant (HALES) at Sellafield. In 1990, the Waste Vitrification Plant (WVP) began converting the HAL into glass to retain the hazardous radioactivity in a non-mobile form. Vitrification enables long-term passive storage of the waste.
In January 2001, HSE’s Nuclear Installations Inspectorate (NII) used its legal powers under the nuclear site licence to place limits on the volume of HAL stored at Sellafield. Specification 343 requires the backlog of HAL stocks accumulated since reprocessing began in the 1950s to be reduced to a minimal working level, known as the buffer volume, by 2015. The Specification sets a limit on the total volume of HAL stored and a secondary limit on the amount of oxide HAL (liquors arising from the reprocessing of oxide fuel). This secondary limit is known as the Oxide Control Curve (OCC) and was imposed because of the higher hazard associated with the oxide HAL (see para. 29 ). NII confirms compliance with Specification 343 by reviewing the Licensee’s monthly HAL stocks reports and through our inspection activities at HALES.
HSE’s 2001 public report Ref. 4 stated that the Licensee at Sellafield (now British Nuclear Group Sellafield Limited, BNGSL) should provide an annual report to NII on its progress in reducing the HAL stocks compared to the specified limits and against its programme of committed improvements to plant and procedures. In addition, to take account of technological advances and any changes in circumstance, we carry out a critical review of the Licensee’s strategy and overall programme every two years in order to identify any further, reasonably practicable HAL stocks reductions.
In line with these commitments, HSE’s quarterly reports to the West Cumbria Sites Stakeholder Group (WCSSG) have included information on the Licensee’s performance against Specification 343, details of safety and operational issues at HALES and the outcomes of our previous biennial reviews in 2002 and 2004. Ref. 5, 6
NII has recently completed its third (2006) biennial review of BNGSL’s HAL stocks strategy. This included a re-analysis of the reduction in HAL stocks achieved since January 2001 and consideration of the adequacy of the Specification in the light of changes in circumstance (e.g. ongoing plant issues at HALES and across the Sellafield site), technological advances and the Health and Safety Commission (HSC) Enforcement Policy Statement. Ref. 7
As a consequence of this review NII will make changes to Specification 343 and have asked BNGSL to resolve and consider a number of actions. These are highlighted in Bold in this report.
NII is satisfied that BNGSL has complied with Specification 343 and welcomes the incorporation of the Specification limits within a more integrated approach to overall site planning at Sellafield.
BNGSL has made considerable progress in reducing its total HAL stocks over the last two years, resulting in HAL volumes that are now well below the limits set by the Specification. In particular, the volume of HAL stored at the site has fallen approximately five times faster than the rate required by the Specification over this period. These gains are due mainly to the prolonged shutdown of the Thermal Oxide Reprocessing Plant (THORP) following the discovery in April 2005 of a leak Ref. 8 (see also para. 19) .
The OCC sets a limit on the volume of oxide HAL stored separately or blended with Magnox liquors. When Magnox or other liquors are added to an oxide or oxide-Magnox blend HAST, the entire liquor volume is counted as oxide HAL for the purposes of comparison with the OCC. Specification 343 allows the OCC to be exceeded on up to six occasions before April 2007, but for a maximum total period of no more than six months. This allowance was made since, when choosing where to set the Specification, NII considered that setting a tight limit which could be exceeded for short periods was preferable to setting a looser, but rigid, limit, as this would then encourage better operational planning. The modelling carried out at that time predicted that the chosen OCC would be exceeded on around four occasions, so the Specification was set to permit a maximum of six excursions. Ref. 4
The OCC was exceeded twice since the last biennial review, for a total of 11 weeks; these are the first such instances since the Specification was put in place. In detail the OCC was exceeded:
In addition, there have been two further occasions when oxide HAL volumes came close to the OCC limits; both when a shortage of oxide HAL, necessitated Magnox HAL being added to blend tanks in order to keep WVP operating.
None of these occurrences is considered to be of any safety significance, and in each case we agree that the operational decisions made by BNGSL were appropriate from a safety perspective. However, each serves to highlight how compliance with the OCC can, in certain circumstances, encourage the Licensee into actions that are not necessarily in the best interests of safety. (see para. 21)
WVP has had two record-breaking years during the period covered by the present review. The production figures for 2004-5 and 2005-6 were within 0.5% of the target, and are an improvement of over 40% on the previous record set in 2003-4. However, the annual production rate is still 13% less than the production target envisaged when Specification 343 was originally set.
The limits identified in Specification 343 are based on consideration of the Licensee’s formal response to the 22 recommendations set out in HSE’s 2000 report, Ref. 2 which addressed a number of aspects of the future HAL strategy. In our 2006 biennial review, we considered whether the Specification needs any amendment to include further reasonably practicable stock reductions owing to changes in circumstances, technological advances or based on a review against the HSC’s Enforcement Policy Statement. Ref. 7
Our review considered the recent improved performance of WVP, improvements in the overall performance of HALES arising from investment by BNGSL to develop its HAL stocks modelling capability and the potential to move to ‘near real-time vitrification’ as undertaken by the French and Japanese.
We do not consider that advances in any of these areas warrants a change to the Specification at present, although we will continue to encourage BNGSL to move towards ‘near real-time vitrification’. During the review, BNGSL argued that the buffer volume limit set by the Specification from July 2015 onwards will make operations unworkable because the limit is set too low for efficient and safe working. Therefore, NII has asked BNGSL to resolve the technical issues associated with buffer volume working before the next biennial review in 2008, including consideration of building inherently safer replacement HASTs to minimise buffer volumes.
Our review considered the effects of the unplanned, long term shutdown of THORP, the ongoing difficulties with the HALES evaporators and HAST cooling component failure trends.
THORP
THORP was shut down in April 2005 following the discovery of liquor discharged from a failed pipe onto the floor of its Feed Clarification Cell (FCC) Ref. 8 . THORP remained shut down following the incident and HSE issued a Notification under Nuclear Site Licence Condition 21(8) notifying BNGSL that it must submit a safety case for the modified plant and not commence movement of fuel from THORP’s feed pond to its shear cave without a Consent from HSE. This Consent was granted on 9 January 2007 following NII assessment and inspection of the modifications to the plant and BNGSL’s response to the 55 recommendations made following our investigation. Ref. 9
At present, THORP remains shut down because of ongoing problems with the HALES evaporators (see para. 22 ). The unplanned, long term shutdown of THORP has contributed significantly to the reduction in HAL stocks, and in particular to the volume of oxide HAL now stored in HALES. Our review concluded that since total HAL volumes have not yet reduced to buffer levels, and in the light of expected further stock reductions based on BNGSL’s past performance, it would not be reasonable to permit the gains made as a result of the THORP shutdown to be lost. Therefore, NII will tighten Specification 343 to lock-in reductions in HAL stocks arising from the unplanned, long-term shutdown of THORP. However, to ensure that the Specification is set at a reasonably practicable level, the reduction in Specification limits will be determined by our assessment of further BNGSL HAL stocks modelling work.
The shortage of oxide HAL stocks has caused BNGSL operational problems in keeping WVP running and has created difficulties in keeping below the OCC (See para. 11 & 12 ). This has caused conflicts between the legal requirement of the Specification and operations that might have been considered in the best interests of safety. Therefore , NII will remove the current OCC from the Specification and replace it with another more suitable limit. When setting this limit, we will consider the extent to which it is reasonable to tighten the oxide HAL component of the Specification in the light of stock reductions arising from the long term shutdown of THORP.
Evaporators
There are currently three evaporators in HALES; these are used to reduce the volume of raffinates received from the reprocessing plants for storage in the HASTs prior to subsequent vitrification. These evaporators are ageing and are prone to internal corrosion. Owing to revised remaining lifetime assessments, which predict shortages in long-term evaporative capacity, a new evaporator (Evaporator D) is now being designed and constructed. In addition to their main duties, the HALES evaporators are also needed to process effluents produced by WVP. In view of its problems with evaporative capacity, BNGSL has had to optimise the use of its evaporators so that priority is first given to WVP effluents, followed by Magnox raffinates, followed by THORP raffinates. This policy, which is supported by NII, ensures that continuing to reduce the HAL stocks will always take precedence over BNGSL’s fuel reprocessing activities.
In the short-term, the current and ongoing shortage of evaporative capacity has allowed an accelerated reduction of HAL stocks as WVP continues to remove HAL from the HASTs whilst no new HAL can be received. However this situation cannot continue since there is a need to reprocess spent Magnox fuels and spent oxide fuels. Unfortunately, present uncertainties in the residual lifetime of the existing evaporators and the timing of when Evaporator D comes on stream make predicting the longer term evolution of stock levels, particularly near the back end of the fuel strategy (i.e. around 2015), difficult. Therefore, our review concluded that these issues, coupled with the absence of any pressing need to change longer term aspects of the Specification now, warranted a postponement of any decision here until these uncertainties reduced significantly. Nevertheless, NII considers that a change to Specification limits will likely prove necessary, due to evaporative capacity issues, at the 2008 Biennial Review.
HASTs
In the period covered by the current review, several HAST cooling coils have failed. Statistical analysis of these failures indicates that cooling coils in the newer HASTs appear to be failing at a faster rate than previously expected. Nevertheless, BNGSL predicts that, based on statistical projections, an excess of cooling capacity will continue to be available until the currently planned end of reprocessing.
Although the current excess cooling capacity remains substantial, NII considers that the distribution of HAST cooling component failures could significantly affect BNGSL’s ability to deliver its HAL strategy. Therefore, NII has asked BNGSL to consider and substantiate operational contingencies and integrate these into its HAL strategy. This includes consideration of building replacement HASTs. (see para. 17)
HSC’s Enforcement Policy Statement Ref. 7 requires that our health and safety regulation, and in particular that relating to the Specification, is proportionate, consistent, targeted, transparent and accountable.
Our review against the Policy Statement raised no new issues beyond those already identified in advance of this biennial review. Completion of the work activities arising from this review (as identified within this statement) will therefore ensure that our regulatory activities associated with Specification 343 will continue to comply with overarching policy principles.
The present review has confirmed the findings of our 2004 review Ref. 6in relation to hazard, risk and safety indices. In addition this review considered the merits and dis-benefits of using other measures of hazard and risk, such as the Radiological Hazard Potential (RHP) Ref. 10 , heat content, Normalised Volume and BNGSL’s own Safety Index, as alternative means of setting Specification limits.
Our review confirmed that oxide HAL is significantly more hazardous than Magnox HAL, to an extent that imposing a secondary limit to restrict the quantity stored is both proportionate and targeted. However, because oxide blends also count against the current OCC, continued use of this measure in the Specification may not promote optimal behaviours (see para. 21) as the volume used for the OCC is a relatively poor measure of hazard potential. Hence, as stated above, NII will remove the current OCC from Specification 343 and replace it with another more suitable measure of hazard potential. NII’s preferred secondary measure is the Normalised Volume of oxide HAL stored in the HASTs.
The review also concluded that the potential hazards posed by ‘old side’ Magnox HAL (historic arisings) and oxide HAL produced from high burn-up fuels are not sufficiently different from typical Magnox and oxide HAL to warrant any additional limits within, or exemptions from, Specification 343. Our analysis showed that there may be a case for exempting wash out liquors from Specification 343 when redundant tanks are decommissioned, but BNGSL’s plans for cleaning out these tanks are not sufficiently advanced for NII to make an informed decision at present. In consequence, NII has asked BNGSL to develop its plans for the clean out of redundant HASTs leading to improved predictions of the anticipated volumes and timings of wash liquors.
Our review concluded that total liquor volume should remain the primary measure used by the Specification, as this has worked well to date, it has advantages in terms of transparency, consistency and accountability and the benefits of using other measures are insufficient to warrant any change at present. In contrast, continuing to use the measured liquor volume for the secondary, oxide-HAL limit does not always promote optimal behaviours, and so we concluded that a different measure is now needed. Weighing the merits of the candidate options, we concluded that limiting the Normalised Volume of oxide HAL represents the optimal solution, since it is proportional to the hazard posed, whilst being relatively easy to verify.
NII will tighten Specification 343 to lock-in reductions in HAL stocks arising from the unplanned, long-term shutdown of THORP.
NII will remove the current OCC from the Specification and replace it with another more suitable limit, as under certain conditions strict compliance with the OCC does not promote optimal behaviours. NII’s preferred secondary measure is the Normalised Volume of oxide HAL stored in the HASTs.
NII has asked BNGSL to resolve the technical issues associated with buffer volume working before the next biennial review in 2008, including consideration of building inherently safer replacement HASTs to minimise buffer volumes.
NII has asked BNGSL to consider and substantiate operational contingencies and integrate these into its HAL strategy.
NII has asked BNGSL to develop its plans for the clean out of redundant HASTs leading to improved predictions of the anticipated volumes and timings of wash liquors.
Formally known as the Sellafield & Drigg & UKAEA Windscale sites Local Liaison Committee (LLC)
Spent Magnox fuel corrodes creating additional legacy hazards if not reprocessed.
There is currently no facility or safety case for the long-term storage of spent oxide fuels.
The Normalised Volume is the volume (m 3) that a quantity of HAL would occupy at conditions optimal for its vitrification, i.e. with water or acid added or removed so that an ideal dilution is achieved compliant with WVP technical constraints and other operational and safety criteria.