Medical source of neutrons, nuclear reactor for a medical neutron source, and method of application of a medical neutron source

Abstract

A coolant having a set temperature is fed into the nuclear reactor core of a medical neutron source, which is in a subcritical state. The nuclear reactor core is transitioned from the subcritical state to a critical state until the nominal power of the nuclear reactor is achieved. A neutron output channel is opened in order to conduct a neutron therapy session, and the operation of the reactor is maintained at nominal power while the neutron therapy session is conducted. At the end of the session, the neutron output channel is closed at the same time as the reactor core is transitioned to a subcritical state. The temperature of the coolant entering the core is maintained unchanged and equal to a set temperature, both when the core is transitioned to a critical state and during the operation of the nuclear reactor at nominal power.

Claims

1. A medical neutron source comprising: a nuclear reactor comprising: a core formed by a flat housing shaped as a parallelepiped, the housing having a front wall, a rear wall, two side walls, a lid, and a bottom; a neutron reflector covering having a rear reflector, two side reflectors, a top reflector and a bottom reflector, and covering the rear wall, the two sides walls, the lid, and the bottom of the core, respectively, wherein the front of the core is free from the neutron reflector covering; an upper supporting grid and a lower distancing grid, both grids being disposed on the housing; fuel rods comprising upper ends and lower ends, the upper ends of the fuel rods being immovably fixed to the upper supporting grid, wherein the fuel rods are capable of experiencing thermal expansion, and wherein the lower ends of the fuel rods extend through the lower distancing grid and are capable of vertically moving when the fuel rods thermally expand; the housing lid having channels disposed on the lid with controls of a control and protection system (CPS controls); disposed on the housing a supply pipe and a discharge pipe of a coolant of a primary circuit of a hydraulic system; partitions separating an internal volume of the housing to ensure washing over of the fuel rods and the channels with CPS controls by the coolant; a collimator with a hole shaped as a truncated cone; a neutron filter placed in the hole of the collimator in such a way that a larger diameter of the truncated cone hole is adjacent to the front wall of the housing of the core of the reactor; a protection that covers the neutron reflector covering and the collimator, the protection being subdivided into a front protection, rear protection, two side protections, top protection and bottom protection; a neutron capture therapy channel formed by a hole in the front protection, the hole being coaxial with the hole of the collimator; a fast neutron therapy channel formed by a through hole in the side protection and the side reflector; a first movable gate that opens and closes the neutron capture therapy channel; and a second movable gate that opens and closes the fast neutron therapy channel.

2. The medical neutron source according to claim 1, wherein the primary circuit comprises a circulation pump, a heat exchanger and a pressurizer.

3. The medical neutron source according to claim 2, wherein the circulation pump, the heat exchanger, and the pressurizer connected to a hydraulic circuit are located outside of the protection.

4. The medical neutron source according to claim 1, wherein the rear protection and the rear reflector comprise openings for disposing the supply pipe and the discharge pipe.

5. The medical neutron source according to claim 1, wherein the housing lid is provided with at least four openings for placing CPS controls.

6. The medical neutron source according to claim 5, wherein the openings are provided with threaded connections with associated actuators.

7. The medical neutron source according to claim 6, wherein the top protection and the top reflector comprise openings for disposing the actuators for moving the CPS controls.

8. The medical neutron source according to claim 7, wherein at least four control rods are used as the CPS controls, the at least four control rods being movable by the actuators the channels for the CPS controls.

9. The medical neutron source according to claim 7, wherein one of the control rods is a regulator for providing a rated power of the nuclear reactor.

10. The medical neutron source according to claim 1, wherein uranium dioxide (UO.sub.2) with .sup.235U enrichment selected from an interval of 15% to 20% is used as fuel in the fuel rods.

11. The medical neutron source according to claim 1, wherein B.sub.4C is used as an absorbing material of the control rods.

12. The medical neutron source according to claim 1, wherein Pb is used as a collimator material.

13. A method of using a medical neutron source comprising: providing the medical neutron source of claim 1; supplying the coolant at a predetermined temperature to the core of the nuclear reactor, the core being in a subcritical state; transitioning the core of the nuclear reactor from the subcritical state to a critical state until a rated power of the nuclear reactor is reached; opening the neutron capture therapy channel or the fast neutron therapy channel for a neutron therapy session; supporting operation of the nuclear reactor at a rated power during the neutron therapy session; and simultaneously closing the neutron therapy channel used in the neutron therapy session and transferring the core to the subcritical state after completion of the neutron therapy session while maintaining the temperature of the coolant at an entrance to the core unchanged and equal to the predetermined temperature both during transitioning the core to the critical state and during operation of the nuclear reactor at the rated power.

14. The method of claim 13, wherein water is used as the coolant.

15. The method of claim 14, wherein the predetermined temperature of the water at the entrance to the core is selected from an interval of from 18° C. to 24° C.

16. The method of claim 15, wherein transitioning the core from the subcritical state to the critical state and from the critical state to the subcritical state, respectively, comprises removing one of the CPS control rods from the core or moving one of the CPS control rods into the core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the nature of the suggested invention, a description will now be given which is not a restrictive example of the practical implementation of the claimed group of inventions, with reference to the drawings, where:

(2) FIG. 1 shows a general view and application of a medical neutron source.

(3) FIG. 2 shows an axonometric section of the structure of a medical neutron source.

(4) FIG. 3 shows a general view of the reactor core of a medical neutron source.

(5) FIG. 4 is a view of the reactor core from the rear.

(6) FIG. 5 shows a flow chart of the coolant in the core of the reactor.

(7) FIG. 6 shows a section through the reactor core.

(8) FIG. 7 shows a generalized hydraulic circuit of the reactor of a medical neutron source.

(9) FIG. 8 shows view A of a generalized hydraulic circuit of the reactor of a medical neutron source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) The medical source of neutrons 1 (FIG. 1) includes the following elements (parts): nuclear reactor 2, protection 3, neutron capture therapy channel 4, fast neutron therapy channel 5, first movable gate 6 for opening and closing the neutron exit channel for the neutron capture therapy, and a second movable gate 7 for opening and closing the neutron exit channel for the fast neutron therapy.

(11) As shown in FIG. 2, the medical neutron source 1 also includes a lead collimator 8 with a conical hole and is designed to receive a bundle of the required spectrum of a neutron filter 9 located in the conical hole of the collimator 8.

(12) The nuclear reactor 2 of the medical neutron source comprises a hydraulic system 10, a core 11, a reflector 12 and a control and protection system 13.

(13) A schematic diagram of the hydraulic system 10 is shown in FIG. 3. In the described embodiment, the nuclear reactor is a three-circuit reactor.

(14) The first circuit 14 includes a core 11, a circulation pump 15, a heat exchanger 16 and a pressurizer 17. Water is used as the coolant of the primary circuit.

(15) The second circuit 18 includes a circulation pump 19, a pressurizer 20, and a refrigeration unit 21. Water is also used as the primary coolant. Cooling of the refrigeration unit 21 is carried out by tap water, which runs through a third circuit 22.

(16) The use of the refrigeration unit 21 in the second circuit allows to stabilize the temperature of the coolant at the entrance to the core 11 at 20° C. Stabilization of the inlet temperature of the coolant makes it possible to substantially reduce the changes in reactivity of the reactor at all stages of its operation.

(17) The core of the reactor of the medical neutron source is shown in FIG. 4-7. The core 11 consists of a parallelepiped-shaped housing 23 with internal dimensions 494×397×120 mm. The core housing 23 has a front 24, a rear 25 and two side walls 26. The housing 23 is closed at the top and bottom, respectively, by a lid 27 and a bottom 28, which are connected by flanges to the housing by the studs 29. The housing 23 is sealed by welding the whiskers around the housing perimeter with the lid 27 and the bottom 28.

(18) The upper supporting grid 30 and the lower distancing grid 31 are disposed on the housing 23. Upper ends 50 of fuel rods 32 are fixedly attached to the support grid 30. The fastening is carried out by means of a wire 33 threaded through the holes in the upper ends 50. Lower ends 51 of fuel rods 32 pass through the distancing grid 31. In this case, the lower ends 51 are able to move vertically with thermal expansion. Fuel rods 32 are located in a square grid with a pitch of 12×12 mm Since the length of fuel rods 32 is a small value of ˜395 mm and, taking into account the low velocity of the coolant, only the grids 30 and 31 are used to separate the fuel rods 32 with no means of distancing in between.

(19) In order to arrange the circulation of the coolant of the 1.sup.st circuit, the housing 23 is divided by transverse partitions 34, which allow to obtain acceptable washing rates of fuel rods. Seven such partitions are installed in a “checkerboard” order with the formation of a labyrinth channel. FIG. 6 shows the flow pattern of the coolant in the core of the reactor (the front wall 24 is not shown). This core design makes it possible to obtain a uniform washing of fuel rods at acceptable rates.

(20) In addition to the organization of the flow of the coolant, the baffles 34 play a force role, allowing a significant reduction in the thickness of the front wall 24 from the exit side of the neutron beam to 2 mm, which in turn allows increasing the neutron flux density at the exit from the core of the reactor. On the back wall 25 of the housing 23 there is a supply branch 35 and a branch pipe 36 for draining the coolant from the core 11.

(21) On the cover 27 of the core housing, channels 37 are arranged to placement the CPS controls. As shown in FIG. 7 and FIG. 8, the channels 37 are located in the housing 23 instead of four fuel rods. The channels 37 are formed by pipes ø 10 mm with a wall thickness of 0.5 mm and terminate with threaded terminals 38 to which the movement mechanisms of the CPS controls are attached.

(22) The reactor reflector 12 covers the core 11 from the rear, side, top and bottom sides and is divided into the rear, top, bottom and two side. The rear, upper, lower and side reflectors are made of stainless steel blocks (steel 12X18H10T) and have a total thickness of 300 mm each.

(23) The protection of 3 reactors is subdivided into the front 39, the side 40, the rear 41, the top 42 and the lower 43 of the protection. As the basic materials of protection, borated polyethylene and depleted uranium are used, used in the form of blocks set by the ledge with overlapping joints of the blocks c to prevent the radiation “bursting”.

(24) The front protection 39 provides the required dose situation in the medical box at the outlet of the NCT beam and in adjacent rooms. The frontal protection 39 in the direction of the NCT beam output includes:

(25) a) the filter itself, which performs both protective functions;

(26) b) lead collimator, also carrying protective functions (mainly from gamma radiation); the thickness of the conical part of the collimator is 150 mm, the thickness of the cylindrical part is 100 mm;

(27) c) a multilayer protective composition (away from the core) of depleted uranium (U) and borated polyethylene (PB):
PB (400 mm)+U (220 mm)+PB (130 mm)+U (20 mm)

(28) Side protection 40 provides the required dose situation in the medical box at the FNT beam outlet and in adjacent rooms. The side protection in the direction of the FNT beam output consists of:

(29) a) a steel reflector 300 mm thick;

(30) b) a multilayer structure of depleted uranium and borated polyethylene (in the direction away from the core):
U (100 mm)+PB (300 mm)+U (200 mm)+PB (150 mm)+U (30 mm)

(31) The side protection in other directions by composition and structure is similar to the upper 42 and lower 43 protections. This is a three-layer composition of the following composition:
U (100 mm)+PB (500 mm)+U (100 mm)

(32) Rear protection 41 is designed to protect other rooms adjacent to the reactor.

(33) The rear protection structure includes a steel reflector (300 mm) and a three-layer composition:
U (120 mm)+PB (900 mm)+U (100 mm)

(34) Channel 4 for the neutron-capture therapy is formed by aperture 44 in the front shield located coaxially with the conical hole of the lead collimator 8.

(35) The channel 5 for the fast neutron therapy is formed by a through hole 45 in the side shield and the side reflector.

(36) The first movable gate 6 allows blocking the neutron beam of NCT, when a neutron therapy session takes place on the FNT beam. In this case, to minimize the neutron background at the location of the fast neutron therapy patient, a plug 46 of borated polyethylene is introduced into the channel of the NCT beam.

(37) The second movable gate 7 allows the beam to be blocked by the FNT during irradiation on the NCT beam. In this case, a plug 47 of borated polyethylene is also added to the FNT channel. When the reactor is shut down, both beams are blocked by sliders and in the channels there are corks of borated polyethylene.

(38) The CPS 13 of the reactor system includes four control rods 32. The rods are moved through dry channels 37 using actuators 48. The neutron absorbing material of the control rods—boron carbide (B4C) is placed inside cylindrical rods 7 mm in diameter and with a shell thickness of 0.3 mm.

(39) In order to place the actuators 48 of the CPS movement mechanisms in the upper protection 42 and the upper reflector, channels are made. In the rear protection 41 and in the rear reflector, channels are arranged for placing conduits 49 of the first circuit connected to the supply branch pipe and the outlet for the coolant to the core.

(40) The operation of a medical neutron source to minimize the number of attendants and to minimize the accumulation of radioactive waste is carried out in a “start-stop” mode, implying the operation of the reactor at rated power only during a therapy session for about one hour.

(41) The operation of the reactor on power is needed for approximately 3 hours per day for irradiation of 1-2 patients. Taking into account the preparatory, starting and stopping operations, the time for the service shift will be 5-8 hours. For the rest of the time (at night or weekends), the reactor is put into temporary shutdown mode. The presence of supervisory personnel during the temporary stop is not required.

(42) To carry out the neutron therapy, a medical neutron source is used as follows. A coolant with a temperature of 20° C. is supplied to the core of the nuclear reactor in the subcritical state, where the water is used.

(43) The core of the nuclear reactor is withdrawn from subcritical to critical before the nominal power of the nuclear reactor is reached. Transfer of the core from the subcritical state to the critical one is carried out by removing one of the CPS control rods from the core.

(44) The patient is placed in front of the necessary neutron exit channel. The choice of a specific neutron output channel is determined by the indications of an oncological disease. After that, the neutron output channel is opened for the neutron therapy session. During the time of the neutron therapy session, the operation of the reactor at rated power is maintained.

(45) At the end of the neutron therapy session, the neutron exit channel is simultaneously closed and the reactor core is transferred to a subcritical state. The core is transferred from the critical state to the subcritical one by introducing one of the CPS control rods into the core.

(46) The temperature of the coolant at the entrance to the core is kept constant and equal to the set temperature, both during the core withdrawal to the critical state and during the operation of the nuclear reactor at rated power.

(47) The daily schedule for the operation of the reactor of a medical neutron source in the therapy of 2 patients may be as follows:

(48) TABLE-US-00001 checking systems and equipment, turning on circulation on the contours, the reactor output to a power of 0.1-0.5 kW at a stable temperature regime 2 hours, Preparation of the patient for irradiation 0.5 hours, irradiation session with a power output up to 10 kW 0.3-1 hour, patient replacement (power 0.1-0.5 kW) 1 hour, irradiation session with a power output up to 10 kW 0.3-1 hour, reactor shutdown, patient removal 0.3 hour, cooling down, setting the mode temporary stop 1 hour. Total 5.4-6.8 hours.

(49) After a double irradiation session, the reactor is silenced by all CPS controls, the set time is damped, then the chiller and technological systems are shut down. The reactor is left in this state until the next working day.

(50) While various aspects and embodiments of this invention have been described herein, specialists in this sphere of technique will understand that other approaches to the implementation of this invention are possible. Various aspects and embodiments of the present invention are set forth herein for illustrative purposes and are not intended to be limiting, and the scope of protection of the present invention is set forth in the following claims.