Page 39 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

14 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

1.5.4.2 Description of the primary cooling system

During nominal operation (8MW(th)), heat is transferred from the core to eight steam
generators by forced circulation using eight primary coolant pumps, each operating at
a capacity of 164kg/s. The resulting increase in temperature over the core is 42K, and
the peak surface cladding temperature is estimated at 444°C. The total pressure drop in
the primary system is estimated at 120kPa, out of which 108kPa is over the core.
For the purpose of removing decay heat by natural convection, the thermal center
of the steam generators is located 2.2m above the thermal center of the core, providing
a buoyancy head in excess of 2kPa.

1.5.4.3 Description of the safety concept
SEALER is designed to rely on passive and natural safety, based on the following
principles:

l Gravity-assisted shutdown of the reactor
l Decay heat removal from the core by natural convection of the lead coolant
l Decay heat removal from the primary system by radiation from the vessel to the concrete pit
The aim of the design is that the only safety classified systems will be the shutdown
system and the postaccident monitoring system. Severe accidents are managed by
relying on the lead coolant to retain volatile fission products through formation of
compounds with low vapor pressure, such as lead iodide. Following a full release
of fission product inventory into the coolant at end of life, the calculated retention
factors of iodine, cesium, and polonium are in excess of 99.99%. This is sufficient
to keep radiological exposures at the site boundary below 20mSv and thereby remains
below the regulatory threshold for sheltering and evacuation to be required.

1.5.4.4 Deployment status and planned schedule
The conceptual design of SEALER was completed in 2017. In the same year,
SEALER was submitted to phase 1 of the vendor’s prelicensing review of the
Canadian Nuclear Safety Commission. The basic design of SEALER is to be com-
pleted in 2018 and the final design in 2019. Pending a conclusive investment decision,
a license application to build a demonstration plant on an existing nuclear site in
Canada would be submitted in 2019. A permission to construct the demonstration unit
may be granted in 2021, and the unit could be in operation by 2025.

1.6 Guidance

The next chapter will introduce and briefly explain the thermal hydraulic challenges in
liquid-metal-cooled nuclear reactors. After that, Chapter 3 will describe experimental
work in support of liquid-metal-cooled reactors, ranging from experiments with water
as simulant for liquid metals to real liquid-metal experiments. Not only attention shall
be paid to the design, the construction, and the operation of experimental liquid-metal