A dissertation submitted to the Department of Physics, University of Surrey, in partial fulfilment of the degree of Master of Science in Radiation and Environmental Protection
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- Current Site Authorisation
- DRDL Gaseous Discharge Annual Limits Table 1
- Option 1; Decay Store Unconditioned Spent Resins On-Site Until Activity Levels Qualify As LLW Then Dispose To LLWR Directly Or Via Winfrith.
- RSV Number Activity of RSV (GBq) Yrs to LLW
- RSV Number C-14 Solid Co-60
Figure 6 Figure 6 is an illustration of how Devonport systematically works through the waste hierarchy, striving to achieve the option at the top of the pyramid. The Environmental Management System, ISO 14001 states that Devonport has a commitment to promoting recycling and the use of recycled materials, if fit for purpose, meet technical specifications but must not be more expensive than brand new products. The consumption of resources should be minimised whilst obtaining value for money. [3] The waste hierarchy applies to all stages of work involving radioactive materials and waste. In 1999, it was found that boat resins and the shore-based resins arising from the submarines primary circuit decontamination contained significantly more 14C than previously thought. The quantities of 14C typically present in the waste streams represent a significant fraction of the existing disposal limit for the LLWR. The estimated inventory of 14C in spent resins from Devonport over the period 2000-2030, has been estimated to be ~450GBq which represents about one third of the total authorised disposals over the lifetime of the LLWR (1500GBq). Spent resins are transferred into Resin Storage Vessels (RSV’s). These are suitable for longer-term storage within a purpose-built facility at Devonport. Samples of resin are taken and analysed for radionuclide content (in accordance with Environment Agency regulations). There are resins which contain concentrations of ß/γ nuclides (mostly 60Co) in excess of 12GBq/t which cannot be disposed of at LLWR. Currently this material is stored at Devonport until it qualifies as LLW. Resins with ß/γ concentrations <12GBq are taken to Winfrith for treatment and encapsulation and disposal as LLW at LLWR. Most resin is currently encapsulated at Winfrith in 200 L drums. These are loaded into half-height International Standards (ISO) containers for disposal at LLWR. The current way in which DRDL deals with its radioactive waste is by sending LLW to an interim station, Winfrith, for initial treatment and processing before sending for final disposal at LLWR. Annual limits are set for the disposal of LLW to Drigg which are as follows;
Annual limits set for disposal to Winfrith LLWR are as follows; [31]
The Devonport site is surrounded by a heavily populated residential area, (250 000 people) and there are many concerns among members of the public about the amount of nuclear waste already existing on the site without the accumulation of additional resins. The Local Liaison Committee (LLC) have had many concerns raised by the public regarding the activities at Devonport and public opposition to further activity is strong. The public feel that the Nuclear Activities within Devonport are not communicated effectively and this encourages suspicion and misunderstanding. The Dockyard provides many jobs for the local community and is a large profit making business. There remains a fine balance of limiting nuclear activity to such a level so as not to cause massive unemployment. The local council conducted investigations into the matter to try and persuade the public and also other politicians who wish to send all of the work to Faslane, that Plymouth really does depend on the Dockyard for a solid economical standing. Accompanying this pressure are the Environmental Protection groups who have been actively trying to stop submarines from being decommissioned in the dockyard for fear of pollution occurring in the River Tamar. This is an ongoing matter. Current Site Authorisation The certificate of Authorisation is issued by the EA under section 13 of Radioactive Substances Act 1993 (RSA 93). It permits disposal of specified radioactive wastes from the specified site, subject to limitations and conditions. The Act is concerned with the control of radioactive material and the accumulation and disposal of radioactive waste. The Authorisation allows EA to place requirements on the operator to carry out various actions. DRDL waste for disposal arises in gaseous, liquid and solid form. Gaseous waste is discharged to the atmosphere and aqueous liquid waste is discharged to the estuary of the river Tamar, at the Hamoaze and also to the sewer. Solid, LLW is transferred for disposal at Drigg, Cumbria, either directly or via Sellafield or Winfrith. Combustible waste may be transferred to the holder of an authorisation to dispose of radioactive waste by incineration at Hythe, Hampshire. Intermediate Level Waste (ILW) items are transferred to a facility at Windscale, Cumbria, and metal components may be transferred to a recycling facility at Lillyhall in Cumbria. Solid, VLLW is disposed of to landfill.
In accordance with the authorisation, Devonport need to be continually looking for improvements that can be made to be environmentally sustainable and also to supply additional information to the EA when requested. Below is a list of requirements Devonport must comply with along with the completion date.
For each of the points above, completion date 2 years from the effective date of the authorisation and at such intervals thereafter as the EA specifies in writing.
Completion date no later than 31st March of each calendar year. [8] The policies of a BPEO are intended to ensure radioactive waste production is minimised as far as practicable and disposed of in a safe, environmentally sustainable fashion and at an acceptable cost. Spent resins arise through the clean up of a range of liquids and effluents produced during refitting and refuelling of nuclear powered submarines. The current option of waste treatment is identified as the BPEO, involving short-term storage at DRDL, followed by transfer to Winfrith for pre-treatment, encapsulation and final disposal to LLWR. Issues at DRDL have arisen which make the distinction between chelating-agent containing resins, and those without difficult.
The cost of treating uncontaminated resin, not requiring pre-treatment, cementation and disposal via Winfrith is £50k per RSV. About 5 RSV’s require treatment and disposal per year from Devonport. There are significant radiological protection measures in place to keep doses very low for operators. The resins can be very active, so adequate shielding and remote handling is employed. Between the period 1999-2004, operator doses in the Nuclear Utilities Building (NUB) were ~0.1mSv y-1 with a collective dose of 2 man mSv. If this option was employed, worker doses are predicted to be 0.1mSv y-1 with a collective dose of 1mSv y-1. Operators involved in the transport of waste are unlikely to receive doses higher than background, due to the very tight radiation protection controls in place. Within the NUB building the filled RSV’s are stored within purpose built storage pits and as a consequence of this has low dose rates in the storage room. Movement of filled RSV’s on-site is done using shielded on-site transport containers. This helps to keep the dose for resin handling and storage ALARP. A RSV is assumed to contain half the inventory of a Modified Magnox Flask (MMF). However, it is assumed to undergo catastrophic failure on impact and to lose 100% of the contents. It is assumed that the spillage forms a 0.6m3 pool of 4m radius and 1.2cm deep. The corresponding radiation dose rate to the containment building is calculated using microshield software package to be 21.1 mSv/h, which, for a 5 minute exposure gives a dose of 1.8mSv. The operator inhalation dose is assumed to be a factor of 50 greater than for an impact on a MMF ie 2mSv. The normal operating doses are 0.5mSv/hr. The RSV’s are designed to hold a total activity level of 740GBq, but they do not contain more than 90GBq generally. The public would be exposed in the following ways;
It is considered that the public doses would be negligible due to very high levels of containment during handling and treatment of spent resins. The only significant doses to the public would arise from the discharge of 14C from an additional process. Through 3H release during the drying process, some 7.8GBq are released to the environment along with 60Co, giving rise to a public dose of ~0.1µSv y-1. All of these doses are predicted over a 30 yr period, 2000-2030. Over a 50 yr period, the public collective dose is estimated at 5 man mSv, and is considered to be negligible. It is considered that there are sufficient radiological protection measures in place to keep the magnitude of discharges and environmental impacts from potentially hazardous material very low. However, a moderate amount of electricity would be required to operate the wet oxidation process, having a negative environmental impact.  Figure 7
The current authorisation of 14C transfer to Winfrith will need to be increased in order to deal with future resins, significantly exceeding the current 10GBq annual limit. The application process for increased transfers could take 12 months or more. The knock-on effect is that AEA Technology would also need to apply for an increase in their 14C authorisations for gaseous discharges to deal with the increase in demand for the treatment of radioactive waste. [10] There has been extensive BPEO investigation into the management and disposal of 14C which is oxidised and processed. The outcome is that the discharge of 14C to the atmosphere is the preferred method, involving demisting, gas cooling, scrubbing through a packed tower acid column and High Efficiency Particulate Air (HEPA) filters. Using the predicted 15GBq y-1 14C atmospheric discharge value, the dose to the most exposed member of the public was ~0.13µSv y-1. For a large discharge, this may increase to 0.19 µSv y-1. The dose to operators from this process would be ~0.5 µSv/GBq of 14C.
Figure 8
This option is not favoured by the regulators; EA and NII, especially for long-lived radionuclides, as the resins at Devonport are not passively stored. As far as the NII are concerned, the expectations of passive safety include radioactivity being immobilised with the waste form and container being both physically and chemically stable. This then means that the need for safety systems, maintenance, monitoring and human intervention is minimised. Treatment would involve a process of encapsulating using concrete and this causes additional complications when trying to transport the waste to the interim storage and treatment facility, Winfrith. There are currently storage facilities for 210 RSV’s with half of the storage pods already occupied. There currently are only a few RSV’s out of ~100 which meet LLW criteria (activity of α <4GBq and ß/γ <12GBq) and all others are ILW (activity of α >4GBand ß/γ >12GBq). See table 2. Table 2
The total dose to an operator due to a dropped load onto a RSV is therefore 3.8mSv. [23] At Devonport, the resins are replenished when the decontamination factor falls below 2. The cost of disposal is massive, with an initial fee per m3 and another fee paid per MBq, which is 25 p for 60Co and £60 for 14C (owing to its 5730y half-life).This means that currently, Devonport has £8.5M of waste waiting to be disposed of. Table 3 shows just 20 RSV’s contributing to this cost.
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