Method for guaranteeing fast reactor core subcriticality under conditions of uncertainty regarding the neutron-physical characteristics thereof

Abstract

A method for guaranteeing fast reactor core subcriticality under conditions of uncertainty involves, after assembling the reactor core, conducting physical measurements of reactor core subcriticality and comparing the obtained characteristics with design values; then, if there is a discrepancy between the values of the obtained characteristics and the design values, installing adjustable reactivity rods in the reactor at the level of a fuel portion of the reactor core, wherein the level of boron-B10 isotope enrichment of the adjustable reactivity rods is selected to be higher than the level of boron-B10 isotope enrichment of compensating rods of the reactor core. The technical result consists in improving the operating conditions of absorbing elements of a compensating group of rods, eliminating the need for increasing the movement thereof, simplifying monitoring technologies used during production, and simplifying the algorithm for safe reactor control.

Claims

1. A method for controlling reactivity of a fast reactor under conditions of uncertainty, wherein the fast reactor includes a reactor core, comprising the steps of: conducting physical measurements of reactor core subcriticality; after assembly of the reactor core, comparing obtained values with design values of neutron-physical characteristics of the reactor core; wherein, if there is a discrepancy between the obtained values with the design values of the neutron-physical characteristics of the reactor core, installing adjustable reactivity rods in the fast reactor at a level of a fuel portion of the reactor core; wherein a level of boron-B10 isotope enrichment of the adjustable reactivity rods is selected to be higher than the level of boron-B10 isotope enrichment of compensating rods of the reactor core; wherein the adjustable reactivity rods are located in one or more replaceable core reflector modules; wherein the adjustable reactivity rods are inserted in core reflector slots formed in the replaceable core reflector modules; and wherein after installation of the adjustable reactivity rods at the core fuel portion level, additional physical measurements of the core subcriticality are performed, and in the event of a discrepancy between the obtained and design values, the adjustable reactivity rods with an insufficient enrichment are replaced with adjustable reactivity rods with an enrichment ensuring subcriticality of the reactor core, wherein the adjustable reactivity rods are replaced by removal of one or more of the replaceable core reflector modules and replacing the replaceable core reflector modules with the adjustable reactivity rods of a required enrichment.

2. A method for controlling reactivity of a fast reactor under conditions of uncertainty, wherein the fast reactor includes a reactor core, comprising the steps of: conducting physical measurements of reactor core subcriticality; after assembly of the reactor core, comparing obtained values with design values of neutron-physical characteristics of the reactor core; wherein, if there is a discrepancy between the obtained values with the design values of the neutron-physical characteristics of the reactor core, installing adjustable reactivity rods in the fast reactor at a level of a fuel portion of the reactor core; wherein a level of boron-B10 isotope enrichment of the adjustable reactivity rods is selected to be higher than the level of boron-B10 isotope enrichment of compensating rods of the reactor core; wherein the adjustable reactivity rods are located in one or more replaceable core reflector modules; and wherein the adjustable reactivity rods are inserted in core reflector slots formed in the replaceable core reflector modules; and wherein after installation of the adjustable reactivity rods at the core fuel portion level, additional physical measurements of the core subcriticality are performed, and in the event of a discrepancy between the obtained and design values, the adjustable reactivity rods with an insufficient enrichment are replaced with adjustable reactivity rods with an enrichment ensuring subcriticality of the reactor core, wherein the adjustable reactivity rods are replaced by removal of adjustable reactivity rods from the core reflector slots and their replacement with other adjustable reactivity rods of a required enrichment.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The drawing shows a scheme of the nuclear reactor core.

IMPLEMENTATION OF THE INVENTION

(2) The nuclear reactor comprises a vessel (omitted in the drawing), where the core 1 is located, surrounded by the core reflector 2. The core 1 comprises fuel assemblies made up of rod-type fuel elements (FE), wherein one or several fuel assemblies comprise shim rods with absorber elements (AE) (e.g., compensating rods 10) forming a shim rod bank. The rods of the shim rod bank allow vertical shifting.

(3) The core reflector 2 may be constructed of separate replaceable modules (e.g., replacement core reflector modules 20). Slots 30 are made at the core fuel portion level in the core reflector 2 (FIG. 1) or core reflector replacement modules for adjustable reactivity rods. The core reflector 2 or its separate modules may be designed so as to allow insertion and removal of adjustable reactivity rods in/from the slots.

(4) Enrichment of the core shim rod bank by B10 boron isotope is selected lower than that of the adjustable reactivity rods 3 installed in the core reflector modules.

(5) In accordance with the claimed method, process uncertainties, errors (constant, methodical, systematic) of calculated values of the main functionalities (effective multiplication factor, control and protection system rod weights, power density fields) are compensated at the core 1 assembly stage as follows.

(6) After assembly of the core 1, physical measurements of core subcriticality are performed according to the known methods and the obtained characteristics are compared with the design values.

(7) In case of discrepancy between the obtained and design values, adjustable reactivity rods with enrichment ensuring the design subcriticality are installed in the reactor at the fuel portion 4 level.

(8) After installation of the adjustable reactivity rods at the core fuel portion level, additional physical measurements of core subcriticality are performed and, if discrepancies between the obtained and design values are found again, some of the core reflector 2 modules with adjustable rods reactivity are replaced with reflector replacement modules with adjustable reactivity rods with a different enrichment, namely, the one necessary and sufficient to obtain the desired design subcriticality value.

(9) Furthermore, process uncertainties, errors may be compensated without partial replacement of core reflector modules. In this case, adjustable reactivity rods are inserted in the slots of the reflector 2 or reflector module (s) of the or are removed from the slots of the reflector 2 or reflector module (s) and replaced with adjustable reactivity rods with the required enrichment that allows to obtain the set subcriticality value.

(10) Core characteristics are fine-tuned by means of AE of the core shim rods installed in the fuel assemblies in the core.

(11) The number of adjustable reactivity rods and side reflector modules with adjustable reactivity rods installed in the same is determined after neutron-physical measurements are performed in order to check the acceptance characteristics of the core during its assembly.

(12) Use of adjustable reactivity rods provides a greater margin during operation of the nuclear reactor due to the fact that the shim rod bank AE control the characteristics of the core operating under conditions close to the design conditions both during commissioning and in the course of operation, which is possible due to a shorter travel of the shim rods.

(13) For instance, for a specific core design, enrichment of the adjustable reactivity rods by B10 boron isotope may be higher (up to 80-90%) than that of the core shim rods that may amount to 40-50%. In other cases, the enrichment of the core shim rods by B10 boron isotope may reach 90%, then the enrichment of adjustable rods may reach 96%. However, their efficiency will depend on the number of 93% rods in the core. If they are few and the average enrichment is below 93%, then the higher the enrichment of the adjustable rods is, the higher their efficiency.