NDA PhD BursarySpent Fuel Theme

Carwyn Jones, Nuclear Technologies (representing NDA)

25th August 2015

NDA Spent Fuel Inventories

Over 90% of the lifetime arisings of Magnox fuel have already been reprocessed.

2

Expect to need to interim store ca. 6,000tU of spent AGR fuel.

There are ca. 500tU of exotic fuels.

Includes intact, damaged and degraded material of various types (e.g. metal, oxide and carbide).

NDA Spent Fuel Strategies

“Our strategy is to reprocess all Magnox fuels”.

“Our present strategy is to complete the LWR and AGR reprocessing contracts as soon as reasonably practicable and cease reprocessing at THORP. We plan to place into long-term storage at Sellafield any fuel not reprocessed pending disposal, including future arisings of AGR fuel”.

“We will treat exotic fuels to achieve a final disposition form as soon as reasonably practicable. This may entail reprocessing, conditioning or immobilisation”. 3

NDA Strategy 2011

Spent fuel R&D needs

• Strategies for the management of spent fuels exist, together with plans for their implementation and appropriate contingency measures.

• There is a requirement for R&D that can help to underpin strategies, improve confidence in managing contingencies and enhance the understanding of alternative options for storage and pre-treatment for disposal.

PhD call spent fuel topics

• AGR cladding corrosion– Research to determine the fundamental mechanisms of the

corrosion and corrosion inhibition of irradiated AGR fuel cladding under pond storage conditions, including the impact of potential impurities in the water, for example chloride, and of corrosion inhibitors such as hydroxide or boron.

• AGR dry storage– Research into the behaviour of irradiated AGR fuel cladding under

moist and dry storage conditions, notably behaviours which could compromise future containment or mechanical strength. This might consider potential storage gas compositions and impurities; and the influence of variables such as temperature, humidity, radiation dose rate and free or ‘fixed’ moisture.

PhD call spent fuel topics

• Damaged and degraded fuel conditioning– Research into potential methods of treating damaged and degraded

spent fuel materials, e.g. from ceramic, oxide or metal fuels, following exposure to water or air,  to stabilise and immobilise them in a form suitable for long-term storage and/or final disposal.

• Damaged and degraded fuel packaging– Research into methods of improving potential package performance

for intact or damaged, degraded spent (oxide and/or metal fuels) to facilitate long-term interim storage and/or final disposal. Such improvements might, for example, include ‘gettering’ or recombination of radiolysis products from moisture or cover gas impurities; residual moisture capture; or provisions to limit container pressure while maintaining radionuclide containment.

AGR cladding corrosion

• Sustainability of wet storage of AGR fuel until GDF disposal (2075) is of great strategic importance.

• Operational experience underpins wet storage of AGR fuel at pH11.4.

• But, fundamental mechanisms of corrosion and inhibition of AGR cladding are not fully understood.

AGR cladding corrosion

• Examples of potential areas of interest:

– What are the fundamental mechanisms involved in the initiation and propagation of inter-granular corrosion of sensitised AGR cladding in water?

– Why does caustic inhibit or prevent inter-granular corrosion of sensitised AGR cladding?

– How might an early warning of fuel cladding failure and activity release be provided in a pond environment, and the release traced to its source?

AGR dry storage

• Dry storage is a potential alternative for AGR fuel, in the event that wet storage is not sustainable.

• There is considerable worldwide experience of dry storage of Zircaloy clad LWR fuels.

• But, there is no equivalent experience of dry storage of stainless steel clad AGR fuel.

AGR dry storage

• Examples of potential areas of interest:

– What are the fundamental mechanisms involved in the initiation and propagation of inter-granular corrosion of sensitised AGR cladding in gaseous atmospheres containing water vapour?

– Is there a threshold in water vapour concentration below which inter-granular corrosion of sensitised AGR cladding does not occur and, if there is, why?

– What radiolysis products might be generated in dry storage environments, and do they have any influence on the corrosion of sensitised AGR cladding?

Damaged and degraded fuel conditioning and packaging

• Exotic fuels inventory includes a variety of damaged and degraded material (e.g. PIE debris).

• Need to condition/stabilise and package materials for interim storage and/or final disposal.

• Potential challenges include residual water content and radiolytic gas generation.

Damaged and degraded fuel conditioning and packaging

• Examples of potential areas of interest:

– How might damaged and degraded fuel (ceramic and metallic) be stabilised/conditioned for long-term storage and/or disposal?

– How would damaged and degraded fuel evolve in a deep geological repository, how would its evolution be different to that of intact fuel, and what might be the impact on repository safety cases?