Flexblue^®core design: optimisation of fuel poisoning for a soluble boron free core with full or half core refuelling

Abstract

Abstract. Flexblue ® is a 160 MWe, transportable and subsea-based nuclear power unit, operating up to 100 m depth, several kilometers away from the shore. If being underwater has significant safety advantages, especially using passive safety systems, it leads to two main challenges for core design. The first one is to control reactivity in operation without soluble boron because of its prohibitive drawbacks for a submerged reactor (system size, maintenance, effluents, and safety considerations). The second one is to achieve a long cycle in order to maximise the availability of the reactor, because Flexblue ® refuelling and maintenance will be performed in a shared support facility away from the production site. In this paper, these two topics are dealt with, from a neutronic point of view. Firstly, an overview of the main challenges of operating without soluble boron is proposed (cold shutdown, reactivity swing during cycle, load following, xenon stability). Secondly, an economic optimisation of the Flexblue ® core size and cycle length is performed, using the QUABOX/CUBBOX code. Thirdly, the fuel enrichment and poisoning using gadolinium oxide are optimized for full core or half core refuelling, with the DRAGON code. For the specific case of the full core refuelling, an innovative heterogeneous configuration of gadolinium is used. This specific configuration is computed using a properly adapted state-of-the-art calculation scheme within the above-mentioned lattice code. The results in this specific configuration allow a reactivity curve very close to the core leakage one during the whole cycle.

An innovative core design for a soluble-boron-free small pressurized water reactor

“…Strictly speaking, this may be impractical because control rods are typically checker‐boarded in a conventional commercial PWR core, which results in insertion of control rods in about 50% of the total assemblies in the core. However, work has been ongoing to increase the number of rodded assemblies in a small integrated PWR core up to 100% by introducing a compact control rod driving mechanism . It is thus assumed that this innovative mechanism can possibly be implemented in our BigT‐loaded SMR core.…”

“…They all reached the same conclusions: (i) An alternative reactivity control system must be precisely defined and (ii) the SBF operation is technically feasible and less restrictive for a small PWR core. These conclusions were demonstrated in a catalog of SBF small modular reactor (SMR) paper designs . Nevertheless, as of today, there is still no successful commercial SBF PWR core design.…”

“…However, work has been ongoing to increase the number of rodded assemblies in a small integrated PWR core up to 100% by introducing a compact control rod driving mechanism. 16 It is thus assumed that this innovative mechanism can possibly be implemented in our BigT-loaded SMR core.…”

“…These conclusions were demonstrated in a catalog of SBF small modular reactor (SMR) paper designs. [11][12][13][14][15][16][17][18] Nevertheless, as of today, there is still no successful commercial SBF PWR core design.…”

Flexblue® Underwater Reactor: Introduction To The Concept And To The Passive Safety Strategy For A Steam Generator Tube Rupture Accident

“…The second one is the gravity-driven emergency boron injection system, which is actuated only in case of anticipated transient without scram. Both these devices can independently shutdown the reactor and keep it subcritical up to cold shutdown state [4].…”