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    Proceedings of ICAPP 2007 Nice, France, May 13-18, 2007



    P.N. Alekseev, E.I. Grishanin, A.A. Polismakov, B.I. Fonarev.

    RRC ?Kurchtov Institute? Moscow, Russia

    Tel:(495)1967621 , Fax:(495)19676 , Email:,

    Abstract The constructive of a boiling water reactor with a core on a basis pebble bed coated particles (BWR-PB)

    is developed, directly cooled by the boiling water. Reactor is supplied under lit of vessel store for "fresh" coated particles ,

    and on the bottom of vessel - store for burn-up coated particles. Every fuel assembly is supplied with ball stop armature and the electromagnetic drives placed on the bottom of the vessel. This design allows use in the maximal degree opportunities

    coated particles pebble bed for realization of continuous refueling of core at work on capacity.

    I. INTRODUCTION a lifetime-core operation without refueling, they are

    The proposed concept of an innovative passive especially important for NPP with reactors of small-to-safety 300 MW(e) boiling water reactor with coated medium power. The simplicity in operation of such particle (CP) in the consideration of an option to use CP as reactors accompanied by high efficiency and close-to-directly cooled by boiling light water. Initially, in Russia deterministic safety can make such NPP competitive, and other countries the coated particle fuel was developed, while elimination of the access to fissile materials in the fabricated and tested in application to high-temperature course of a whole core lifetime (an additional proliferation gas-cooled reactors of HTGR type. In this paper resistance barrier) may broaden the geography and market considered at a conceptual level is an option to use CP in for their implementation. Namely for the above reasons BWR. the coated particle fuel use was considered in application

    The main reason for CP use in boiling water to BWR of small-to-medium power. BWR-PB design base reactor is an option to improve nuclear safety of the is follows:

    reactor up to deterministic level, i.e., to provide a 1) NPP has to provide wide operational time practically perfect elimination of fission products release (about 25 years) without opening of the reactor in design basis and beyond-design accidents. The vessel lid;

    prerequisites for such options are provided by the unique 2) after operation during 25 years the design has properties of CP. Another reason is that the option to use to provide a loading of “fresh” CP and particle-bedded fuel has already been preliminarily discharge of burn-up CP without opening of the investigated in application to PWR [1,2]. In particular, vessel lid with using of special transport corrosion resistance of CP in the conditions simulating equipment;

    normal and accident regimes of PWR was experimentally 3) fuel cycle characteristics of BWR-PB have not justified [3]. to lose similar ones of state-of-the-art reactors.

    The additional reason for particle-bedded fuel use 4) radiational safety has to provide on the in namely boiling water reactor is a potential option to deterministic base, i.e. considerable fission provide higher degree of reactor self-control in reactivity product release is impossible under any accidents at the expense of the combination of the self-accidents, including any acts of terrorists or control properties inherent to BWR (effective negative inimical personal, also fall from a height of feedback by coolant density) and the extremely low time of heavy lifter.

    heat transfer from fuel to coolant characteristic of the

    particle-bedded fuel directly cooled by boiling coolant-II. REACTOR DESIGN DESCRIPTION


    The reason to consider coated particle fuel Fig.1 presents BWR-PB reactor design scheme, which namely in particle-bedded (not matrix) variant is to realizes the above-listed design base, witch includes the provide a long-life operation option for a small to medium vessel 1, core 2, steel reflector 3, jet pumps 4, guiding power BWR at the expense of higher volume fraction of tubes 5 of control rods, protective tubes 6 of the pivot of a fuel in the core provided by namely particle-bedded fuel. control rods drive, internal metallic shaft 7, block of

    The potential benefits of a boiling water reactor with protective tubes 8, anti-holdup device 9, first and second-

    particle-bedded coated fuel are high degree of nuclear stage separator 10 and 11, re-hydrator 12, vessel lid 13, safety, a possibility to increase fuel burn-up and to provide electromagnetic drives 14 of control rods, internal store 15

    Proceedings of ICAPP 2007 Nice, France, May 13-18, 2007

    for fresh CP, weld plug 16, branch pipes 17 for loading of Transition rate of fuel CP in a fuel assembly are fresh CP, upper block 18, pipeline for ball transport 19, inversely proportional to its relative power. Radial ball-stop armature 20, internal store 21 for burn-up CP, distribution of power density is constantly at time, and drive ivot 22 of ball-stop armature, drive of pivot 23, burn-up all of discharge CP is equal. At the second biological shielding 24, device for spent CP discharge 25, operational regime, minimal volume burn-up peaking

    factor and high quality of fuel cycle characteristics are 26- weld plugs 26, transport equipment 27. reached. 145 electromagnetic drives of ball-stop armature for Under steady state refueling mode the average value every fuel assembly are located upon the reactor vessel of fuel burn up in CP is equal to 6% at fresh fuel bottom. The vent aligned with the discharge ball transport enrichment of 5%. And peak value of fuel burn up less pipeline of 20 mm diameter is located in the reactor vessel than 7%. At such fuel burn up in CP with outer diameter bottom. It is intended for burn-up CP from the internal of 1.8 mm the multiplayer covering thickness of 0.2 mm is store of the reactor vessel discharge. 3sufficient (100 μ-layer of carbon with density of 1.0 g/cm, Internal store for fresh CP is divided into 30 sections. 35 μ-layer of carbon with density of 1.8 g/cm, 95 μ-layer of Each section is attached to branch pipe of 20 mm outer 3SiC with density of 3.2 g/cm). diameter for loading of fresh CP. From below each section The life-time of the reactor for 2-regime changes with is attached to the pipe collector, which distributes CP volume of in-vessel store of “fresh” CP and storage of among groups of 4-5 fuel assemblies. To provide that, discharge CP. For the proposed reactor design can operate pipelines lay within the block of protective tubes and about 13 years without vessel reloading until depletion separators. The upper ends of these pipelines are aligned upper “fresh” fuel store and fill-up of bottom store with with the pipe collectors, while the bottom ends are fixed to burn-up CP. the inlet ball transport pipeline in the fuel assemblies. After depletion store of “fresh” CP and fill up of All of joints are detachable. When it is necessary, bottom store the reactor shout downs. The reactor vessel the unloading all of internal devices and fuel assemblies refueling starts at atmospheric pressure without opening of for a maintenance and re-equipment could be carried out. the vessel lid. The reloading of reactor vessel is realized by Ball-stop armature in the discharge pipeline inside the the use of transport equipment of “fresh” and bun-up CP, reactor vessel is produced in the knee form, where the which is supplied with devices of hydro-transport of CP. movement of CP is possible only by using of hydraulic

    transport. The ball transport pipeline of internal store of

    spent CP and all of sections of internal store of fresh CP AAare welded at the reactor operation. They are re-welded at

    the core refueling after reactor operation during 25years,

    shutdown, cooling and depressurization. The return valve

    Ais located in the ball transport pipeline of every section of Athe internal store, which eliminates the possibility of a

    suck of fresh CP from the reactor vessel. BBDesign of fuel assembly with cross flow of coolant BB

    includes three axial stage (Fig.2). Outlet collectors of 20000500200lower stage are connected with inlet collectors of upper

    stage. Structural material of fuel assemblies is ZrNb1%

    alloy. Boiling of coolant in the lower stage of fuel

    assembly is absent. Upper stage have 12,5% steam

    quantitative. CCPermanent reloading of CP in three-stage fuel 4200assembly normally provides spectral regulation of fuel

    burn-up process. In upper part of fuel assembly “fresh” CP Cwith maximum content of uranium-235 isotope are C

    irradiated at minimum of coolant-moderator density, i.e.

    under spectral condition of fast reactor. As burning process the fuel CP go down from upper to middle axial Fig.1 Reactor design scheme stage, which is characterized more thermal neutron spectra. In the lower axial stage of fuel assembly the CP Table 2. Axial displacement of GdO ball 23 are irradiated at peak density of water that provides Height, H/U GdOGdOGdO23 23 23 maximal fuel burn-up.

    Proceedings of ICAPP 2007 Nice, France, May 13-18, 2007

cm ratiballs, density, Initial enrichment (and for fresh store), % 9 (6) diameter3o fraction g/cm , Lifetime without refueling core (permanent 13 (12) mm refueling core) , years

    380-400 2,4 0 - - Store volume of fresh CP, % core volume 50

    260-380 2,4 1/30 3,75 0,65

    140-260 3,6 1/30 7,5 0,65 III.NEUTRON-PHYSICAL CHARACTERISTIC 10-140 4,2 1/30 7,5 0,7 0-10 4,2 0 - - During first operational regime (first 13 years of CCreactor operation) axial transition of coated particles

    within reactor core is absent. This operational regime is

    characterized by a high non-uniformity of fuel burn-up

    along radial and axial directions of the core.

    Reactor core of BWR-PB can be divided on three

    axial zones with essentially different neutron-physical

    properties. At the lower zone, coolant density has a

    maximum value, hydrogen-to-heavy metal ratio is equal to

    4.2 and neutron energy spectrum is the most thermal. At

    the middle zone, hydrogen-to-heavy metal ratio is equal to

    3.6 due to decreasing of coolant density, which hardens

    the neutron spectrum. At the upper zone of reactor,

    hydrogen-to-heavy metal ratio is equal to 2.4 and neutron 23 spectrum is nearly epithermal. Multiplication factor of the infinite lattice of fresh

    fuel (without control rods) is equal to 1.4250.

    Main results of neutron-physical analysis of last

    year can be presented as follows:

    - radial power peaking factor of fuel assemblies in

    reactor core is equal to 1.83, the most heated fuel

    assembly is central fuel assembly at the beginning

    of the work; axial power peaking factor is equal

    to 2.2 and radial power peaking factor inside the

    fuel assembly does not exceed 12%;

    - total reactivity effect including temperature effect

    and xenon’s poisoning effect is equal to 9%;k/k;

    - reactivity effect of neutron leakage in radial

    direction is equal to 2,5%;

    - core lifetime is equal to 3900 effective full power

    days (average fuel burn-up is about 5,2 heavy atoms) at burn-up reactivity margin of 40%; Guide tube Inlet collector Outlet collector Accepted accommodation and geometrical sizes of guiding tubes allows to compensate total reactivity effect only at Fig.2. Longitudinal and cross sections of fuel assembly: the maximum possible outer diameter of control rod (1.22 1- guiding tubes for control rods, 2-inlet collector, 3-cm), but worth of the reactivity control systems outlet collector (10.4%;k/k) is not sufficient for compensation of burnup reactivity margin. Table 1. Major characteristic of BWR-PB At application of poisons elements with gadolinium Name Value ball the main task consists of choice of kernel diameter Thermal power, Mw 890 and density of gadolinium oxide for every axial stage of Pressure, bar 7.5 reactor core (see Tab.2 and Fig.3). Steam quantitative, % 12,5

    Diameter of CP (UOkernel), mm 1,8(1,3) 2

    Core high, mm 4000

    Load of uranium dioxide, tons 70

    Proceedings of ICAPP 2007 Nice, France, May 13-18, 2007

    operational conditions”. Atomic energy (Rus), v.10, issue

    4, 2006, pp.270-278.

    4.Polismakov A.A., Tchibiniaev A.V. Structure computer

    code. Computational method./ Benchmark on

    Deterministic Transport Calculations Without Spatial

     Homogenization: A 2D/3D MOX Fuel Assembly Fig. 1. ICAPP ’07 logo. Benchmark. NEA/OECD 2003, pp. 132-134. 1.45

    1.40Absorber contentWithout absorber1.35Optimized variant



    K eff1.20





    050010001500200025003000350040004500Time operation (eff. days)

     Fig.3.Keff versus operation time for optimized variant of axial distribution of GdO balls and the variant without 23



    The advantages in fuel burn-up (i.e., fuel cycle economy) and nuclear safety as provided by coated particle fuel may be of special importance for NPP with reactors of small power, because they broaden the options for site selection, enlarge the geography and market for implementation of such power (heat and power) plants.


    1. N. Ponomarev-Stepnoi, N. Kukharkin, E. Grishanin, etc. “Aspects for application of coated particles in VVER”. Atomic energy (Rus), vol.86, Issue 6, june 1999.

    2. G. Philipov, N. Kukharkin, E. Grishanin, etc. “Aspects for development of vessel boiling reactor with a steam overheating”. Atomic energy (Rus), Issue 3, march 2006, pp. 197-204.

     3.G. Filippov, L. Phalkovsky, E. Grishanin, V. Trubachev, etc. “Research of corrosion stability of SiC and PyC cover layers of coated particles under light-water reactor

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