Corresponding author: Pavel A. Alekseev (palekseev@ippe.ru)

Academic editor: Yuri Korovin

The paper investigates the possibility for reducing the radial power peaking factor _{r}

A _{r}

It is proposed that the core should be split into sections with each section having its own uniform lattice pitch which increases in the direction from the center to the periphery leading so to the radial power density factor decreasing to 1.06. The number of the sections the core is split into depends on the lattice pitch, the

This approach does not require the reactor dimensions to be increased, different

The use of thermionic converter reactors (

Instead of zirconium hydride and sodium-potassium eutectics (

A water-cooled water-moderated converter reactor for a small NPP (AIST-MP), capable to serve as a cost effective independent heat and electricity source, is described in (_{(el)} of electric power.

A cooperation of J SC «SSC RF-IPPE named after A.I. Leypunsky», FSUE «SRI SIA «LUCH» and JSC «Afrikantov OKBM» has presented an innovative design of a small NPP based on a thermionic nuclear system for supply of power to remote facilities in the Arctic region (Fig. _{(el)} is ensured by 106 and 331 TFEs successfully verified in the

Conceptual design of an NPP based on a thermionic

Such a large number of TFEs in the core is arranged in a hexagonal lattice, in contrast to the arrangement in concentric circles as in a traditional

To compare with, the TCRs in the TOPAZ and Yenisey nuclear power systems had 79 and 37 TFEs respectively. Heat was removed by the forced coolant circulation in the annulus of each _{r}_{r}

Cross-section of the TOPAZ-type converter reactor (

With a large number of TFEs arranged in concentric circles, the power density flattening through a nonuniform spacing leads to a greater core diameter.

On the other hand, with TFEs arranged in a uniform-pitch lattice, all other conditions being equal, it is not possible to influence the power density distribution.

Fig. _{r}

Dependence of the

It follows from the figure that the steady-state and continued operation of a _{r}

Power density flattening in a core with a uniform lattice pitch can be achieved, e.g., through using different fuel enrichment in core or using additional structures inside the core. The former requires different

The paper investigates the possibility for reducing the radial power peaking factor in a core with a uniform lattice pitch. It is proposed that the core should be split into sections, each with its own uniform pitch which increases in the direction from the center to the periphery.

The core of a water-cooled water-moderated

The core of a water-moderated water-cooled

The MNCP code (

This model contains 301 TFEs, and the core diameter is such that the rotary-type _{r}

For the power density calculation, the _{r}_{r}

Fig.

Power density distribution by fuel elements with the core split into two (a) and three (b) sections

It can be seen from the power density distribution that even a minor increase in the lattice pitch leads to a major reduction of _{r}

The core splitting into three sections (Fig. _{r}

The

In a general case, the power density distribution will depend not only on the lattice pitch but also on the _{r}

Power density distribution by fuel elements with the core split into four sections

It is worth noting that the core diameter was 5.7% as small with the minimum uniform lattice pitch, but this required the reactivity margin decrease to be compensated by a larger reflector thickness. The _{r}_{r}_{r}

Therefore, one may talk only about _{r}

Such approach to power density flattening is useful when one needs to increase the _{r}_{r}

And with the TFEs arranged in a hexagonal lattice and the core split into three sections, the _{r}

Power density distribution by fuel elements with the core split into three sections

The pitches for each of the sections were found in this case using an optimization procedure based on a genetic algorithm technology (_{r}

As a result, the lattice pitches related as 1/1.018/1.055 have been achieved, leading to _{r}

The power density surge in the central TFEs takes place due to the excessive water formed as the result of the core splitting, that is, such surges can be suppressed through the optimization of the

This paper investigates the possibility for reducing the radial power peaking factor inside a core with a uniform lattice pitch. The core splitting into sections, each having its own uniform pitch with the lattice pitch increasing in the direction from the center to the periphery, leads to the radial power peaking factor reduction to 1.06. This approach does not require the reactor dimensions to be increased greatly, different

_{el}

* Russian text published: Izvestiya vuzov. Yadernaya Energetika (ISSN 0204-3327), 2017, n.4, 27–37