Advanced concept design studies

Various advanced design concepts have been proposed and evaluated against the design requirements which were established to satisfy the Generation IV technology goals of sustainability, safety and reliability, economics, prolifer-ation resistance and physical protection. In order to improve the economics, the rated power was increased from the 600 MW(e) of the KALIMER-600 to 1200 MW(e) [2, 3]. Breakeven cores loaded with metallic fuels do not have blankets in order to strengthen the proliferation resistance and employ a safety grade residual heat removal system, the PDRC, which operates passively by natural circulation. Table 1 shows the key design parameters of the advanced SFR being developed at KAERI.

Two types of conceptual core design, and breakeven and TRU burner cores were developed. The breakeven core is a reference concept for the 1200 MW(e)

TABLE 1. KEY DESIGN PARAMETERS OF THE ADVANCED SFR Overall

Reactor core I/O temperature (^°C) 390/545 Total PHTS flow rate (kg/s) 15 455.4 Primary pump type Centrifugal

Number of primary pumps 4

IHTS

IHX I/O temperature (^°C) 325/528 IHTS total flow rate (kg/s) 11 777.7

IHTS pump type Centrifugal

Total number of IHXs 4

SGS

Steam flow rate (kg/s) 1326.6 Steam temperature (^°C) 503.0

Steam pressure (MPa) 16.5

Number of SGs 2

Note: PHTS: primary heat transport system; IHTS: intermediate heat transport system;

IHX: intermediate heat exchanger; SGS: steam generator system.

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advanced SFR. According to the current study [4], the TRU burning rate increases linearly with the rated core powers from 600 MW(e) to 1200 MW(e).

Considering (i) the realistic size of the SFR demonstration reactor planned to be constructed by 2028 in accordance with the long term R&D plan, and (ii) the availability of a KALIMER-600 reactor system design, a TRU burner of 600 MW(e) was selected. Figure 4 and Table 2 show the layout and key design parameters of the two cores, respectively.

The heat transport system comprises a PHTS, an IHTS, an SGS and a residual heat removal system. The heat transport system was established through trade studies in order to enhance the safety and to improve the economics and performance of the KALIMER-600 design. From the study, the heat transport system of the advanced SFR has design features such as two IHTS loops, a Rankine cycle energy conversion system, two double-wall straight tube type SGs and a passive decay heat removal system, as shown in Fig. 5.

TABLE 2. KEY DESIGN PARAMETERS OF THE CORES

Core design parameters Breakeven core TRU burner core

Power (MW(e)) 1200 600

Core height (cm) 80 89

No. of fuel regions 2 3

Cycle length (effective full power month) 18 11

Charged TRU enrichment (inner, middle, outer cores, wt%)

13.16/ - /16.79 30.0

Conversion ratio (fissile/TRU) 1.0/- 0.74/0.57

Sodium void reactivity (EOEC, $) 7.25 7.50

PLENARY SESSION 1

125 The passive decay heat removal circuit (PDRC) consists of four independent loops, and each loop is equipped with a single sodium-to-sodium decay heat exchanger (DHX), a single sodium-to-air heat exchanger (AHX), and the piping connecting the DHX with the AHX. During normal plant operation, the DHX is partially dipped into the cold pool sodium in order to prevent unexpected freezing of the PDRC loop sodium. Under accident conditions, such as a total loss of normal heat sink, the level of the cold pool is raised to that of the hot pool because of the loss of head difference between the hot and cold pools, similar to the PHTS pump trip following the reactor shutdown, as depicted in Fig. 6.

After reactor shutdown, the level of sodium increases from the expansion of primary sodium due to accumulation of reactor core decay heat. If the sodium level increases higher than the slots in the DHX, the hot pool sodium overflows into the shell-side of the DHX. As the sodium flow rate through the shell-side of the DHX increases, the heat transfer rate through the DHX increases due to the enhancement of convective heat transfer. The heat transferred to the PDRC is finally dissipated into the atmosphere through the AHX by natural circulation in the PDRC loop.

In order to secure the economic competitiveness of an SFR compared with a PWR, several concepts were implemented in the mechanical structural design without losing the reactor safety level. Figure 7 shows the reactor internals and component arrangement in the reactor vessel. The material of the reactor vessel and the internal structure is a type 316 stainless steel. The outer diameter of the

FIG. 5. Configuration of the heat transport system.

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reactor vessel is 14.5 m, which is a very compact size compared with other designs. The primary system consists of four sets of primary pumps, IHX and DHX in the reactor vessel. Each intermediate heat transport loop has a mechanical type pump and an SG connected by large diameter pipes. The piping material is a Mod.9Cr–1Mo alloy, which can allow shortening the piping length to about 60 m compared with stainless steel, because of its higher mechanical strength and lower thermal expansion. The piping diameters for the hot and cold legs are 80 cm and 110 cm, respectively.

FIG. 6. PDRC configuration and decay heat removal process.

FIG. 7. Preliminary NSSS arrangements of two loop system.

PLENARY SESSION 1

127 3.2. R&D activities for the advanced SFR

Various R&D activities have been performed in order to support the development of advanced design concepts and features which will better meet the Generation IV technology goals on sustainability, safety and reliability, economics, proliferation resistance and physical protection, as shown in Fig. 8.

These activities include the PDRC experiment, the conceptual design of the supercritical carbon dioxide (S–CO₂) Brayton cycle system, the Na–CO₂ interaction test, under sodium viewing technique, sodium technologies, development of codes and validation, and metal fuel.

4. PYROPROCESS TECHNOLOGY DEVELOPMENT

Pyroprocessing is one of the promising technologies used to treat spent fuel and to reduce its volume [5–7]. It mitigates a repository burden by the separation of uranium from spent fuel and shortens a repository management period by transmuting TRUs. The pyroprocessing technology listed in the long term development plan includes an electrolytic reduction system of PWR spent fuel, a high throughput electrorefining system, an electrowinning system for TRU recovery, waste salt regeneration and solidification, and system engineering technology development.

FIG. 8. R&D activities for the advanced SFR.

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