Innovative nuclear fuel cycle development

As indicated before, there have been a variety of actions taken to adjust nuclear energy sector to new realities that have been set in motion since the early nineties. One of those endeavours is to prepare for the future by development of innovative nuclear energy systems for long term sustainability of nuclear energy utilization, of which criteria could be measured in terms of such criteria as safety, economics, proliferation resistance, etc [55]. At present, there are several international initiatives that have been implemented in an effort to pave the way

toward the innovation of nuclear systems with enlarged utilization scopes including such non- power applications as sea water desalination and hydrogen production.

The technical concepts envisioned in the scope of innovative systems development include some new systems like accelerator driven system (ADS) for nuclear transmutation of actinides or long-lived fission products, but the majority of them are evolutionary technology based on the technology which have already been in more or less advanced stage of research and development in the past. Particular reference has to be made in this regard to the past efforts extended to the development of fast neuron reactor and associated fuel cycle systems at national labs in the US and in the former Soviet Union where progresses had been advanced to pilot demonstration phase, but came to a halt short of industrialization due to decline of FBR programmes in most countries during the eighties and nineties.

Some new requirements emerging for innovative systems are common to many applications (such as high temperature and extended burnup operations) while some other requirements are particular to some other applications (such as fast transmutation rate). Those technical factors of the innovative nuclear systems that might bring impacts on the applications of remote systems technology in the future development of nuclear fuel cycle may be identified as following:

4.2.1. High burnup fuel cycles

Many of the reactor concepts considered to be innovative anticipate taking advantage of high burnup fuel, which can be regarded in this sense as an extension of the current high burnup trends noticeable in the commercial operation of LWRs and HWRs. This aspect implies that those issues arising from use of high burnup fuel (and in that context MOX fuel) with corresponding impacts on the downstream fuel cycle are also relevant to be considered for the innovative systems.

Some of the design features for achieving high burnup include dispersion or particle type of fuel forms as well as new cladding materials that are corrosion resistant or that have improved creep strength.

4.2.2. Plutonium burning

The past objective of FBR which was meant to breed plutonium from fertile material (U-238) has been faded out, due mainly to the cheap price of uranium and proliferation concern of separated plutonium stock. The design of the fast neutron reactor can be converted to such mode that the fertile fuel is not used so that plutonium is consumed instead.

4.2.3. Partitioning and transmutation

While most of the major programmes in FBR technology development have subsided through the past decades, the renewed interest in innovative reactor and fuel cycle systems in the context of partitioning and transmutation (P&T) might call for increased applications of the remote concepts, especially for processing and fabrication of radioactive targets for spallation. In the long-term case of sustainable development of nuclear energy, remote technology applications would be required for fabrication of some types of fuels, which bear gamma radioactivity. That would be the case when minor actinides are included in the MOX fuel for example by adding of Np-232 which will increase the gamma source due to Pa-233 or build

up Pu-238 resulting in additional neutron source by (α, n) reactions. Significant increase by a factor of 4.5 in gamma dose can result from addition of americium to the U-Pu powder. In the worst case of curium, the neutron dose from MOX fuel could increase as high as a factor of hundred that substantial shielding and subsequent remote systems would be required for the powder blending process. Another case of extensive application of remote technology would arise for refabrication of thorium fuel elements that contain Th-228, which decays through a series of daughter product emitting gammas. In a similar way, fuel using recovered uranium from reprocessing requires remote systems technology because of the associated U-232, which is a gamma emitter [56].

The technological experience of remote operation and maintenance in head-end processes for spent fuel reprocessing could become an important base for future industrial implementation of advanced fuel cycle concepts for innovative nuclear systems now in research and development as an international initiative.

4.2.4. Remote fabrication of radioactive fuels

The Republic of Korea (ROK) reported some R&D activities associated with laboratory scale test of remote fuel fabrication for direct use of spent PWR fuel in CANDU reactors (DUPIC) which has been recently conducted in hot cell facilities at Korea Atomic Energy Research Institute (KAERI). In collaborative work with Atomic Energy of Canada Ltd (AECL), the DUPIC fuel fabrication demonstrated extensive application of remote systems technology both for the sequence of fuel fabrication process operation and maintenance. Several pins of DUPIC fuel were refabricated at an AECL hot cell facility for irradiation in a test reactor. This exercise was followed by another campaign with full processes of powder-pellet route equipment in a larger hot cell facility at KAERI [57]

While this technology would be simplified in comparison with the conventional PUREX type of aqueous process, the radioactivity that is encountered throughout the processing will require fully remotized operation and maintenance of the hot cell facility. Another example of remote systems applications that has recently been development is the direct refabrication of spent fuel into a new fuel for reuse, a case in point being the DUPIC (Direct use of spent PWR

fuel in CANDU reactors). This concept requires fully remote operation and maintenance over

the entire process of radioactive fuel refabrication that must be contained in shielded hot cell facilities. Another challenge in the DUPIC concept is inspection and quality control in a remotely operated facility.

India reported another example of remote disassembly and refabrication of some radioactive fuel for fast reactor programme. Sophisticated automation and robotics systems have been developed for application to the refabrication of advanced fuel and dismantling of irradiated fuel from the fast breeder test reactor at Kalpakkam, near Madras. It is to be noted in this context that the fast reactor fuel recycle programmes in some countries have historically been home to extensive applications of remote technology.