Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
  • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
  • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
  • G01F23/284—Electromagnetic waves
  • G01F23/288—X-rays; Gamma rays or other forms of ionising radiation
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C17/00—Monitoring; Testing ; Maintaining
  • G21C17/02—Devices or arrangements for monitoring coolant or moderator
  • G21C17/035—Moderator- or coolant-level detecting devices
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• the present invention refers to a device for securing the presence of cooling medium at certain levels in a reactor tank.
• the device also permits detecting the density of the cooling medium in the reactor tank.
• the device according to the invention is preferably intended to be used in con ⁇ nection with near-accidents and in the case of reactor ac ⁇ cidents to enable a rapid establishment of the presence of cooling medium at certain levels in the reactor tank.
• the density of the cooling medium at these levels is also es- tablished. With a knowledge of the measured values obtained suitable measures may thereupon be taken for correcting the fault, for example refilling cooling medium.
• Devices for detecting the level of the cooling medium in a reactor tank are known and usually include a level tube which is in communicating connection with the upper and lower portions of the reactor tank. Floats arranged in the level tube operate micro switches, whereby an indication of the cooling medium level in the reactor tank is obtained.
• Another prior device for detecting the level of the cool ⁇ ing medium includes a variant of the level tube described above but utilizes differential pressure measurement for indicating the level.
• the prior devices show several disadvantages, inter alia that the level tube is arranged on the outside of the re ⁇ actor tank but within the reactor enclosure. If a near-ac ⁇ cident or break-down occurs so that hot water s-ceam spurts into the reactor enclosure the level meter may become mis ⁇ leading or be destroyed. Another disadvantage is that in the case of a near-accident or in the case of reactor break ⁇ downs the level tube may be filled with steam whereby an er ⁇ roneous indication of the level of the cooling maxim is ob- tained.
• the present invention aims at producing a device of the kind described by way of introduction, the reliability of measurement of the device not being allowed to be influenced mechanically, electrically etc., if steam flows into the re ⁇ actor enclosure.
• the main parts of the device consist of a radioactive source which emits high energy ra ⁇ diation right through the reactor tank and a detector device which detects the radiation from the radioactive source transmitted through the reactor tank.
• the radioactive source has to emit radiation which has a pulse structure, by which is meant that the number of particles or photons per unit of time varies.
• both the radioactive source and the detector device are located outside the reac ⁇ tor enclosure so that the radiation will penetrate also the latter, whereby the correct function of the radioactive source and the detector device is not influenced at all by steam which flows into the reactor enclosure.
• the radiation detected is compared with the radiation issuing from the radioactive source and may form a reference value which when the reactor is in normal operation is put equal to uni ⁇ ty and may represent the density of the cooling medium at normal operation conditions. If a near-accident or a break ⁇ down occurs so that the cooling medium sinks under the le ⁇ vel of the beam or so that the proportion of steam in the
• the cooling medium is altered the detected radiation is in ⁇ creased and this alteration can be shown in a simple way.
• the magnitude of.the alteration in relation to the refer ⁇ ence value is a measure of the reduced density or altered level of the cooling medium.
• the emergency cooling system is caused to pump cooling medium into the reactor tank un ⁇ til the measurement results show that the level or density, respectively, are within the desired values.
• the high energy radia- tion is caused to pass through the reactor tank at diffe ⁇ rent levels. It is thereby possible to obtain additional information regarding the level of the cooling medium by combining the measurement results obtained at the different levels with each other.
• the radiation at the different le- vels of the reactor tank may be produced either by using a separate accelerator at each level and a separate detector device at the corresponding level or by using only one ac ⁇ celerator at one level and deflection magnets for deflecting the beam to the remaining levels, it being understood that at each level there is a separate detector device.
• Figure 1 shows a cross-sectional view of a reactor building equipped with the device accord ⁇ ing to the present invention.
• Figure 2 shows a detailed cross-sectional view of the device according to the present invention installed in the reactor building in Figure 1
• Figure 3 shows a block diagram of the electric circuits in ⁇ cluded in the device according to the invention
• Figure 4 shows a block diagram of an alternative embodiment of the electric circuit shown in Figure 3.
• the heart of the reactor building shown in Figure 1 is a reactor tank 1 with fuel rods 2 and circulation conduits 3 for cooling medium.
• the reactor tank is surrounded by a concrete jacket 4, serving as a biological radiation pro ⁇ tection.
• the lower portion of the reactor tank is situated over a conventional concrete container 5 for receiving a possible melt-down- By 6 is designated a reactor enclosure which has a condensation basin 7 for the cooling medium in its lower portion.
• An emergency cooling system 8 ' can pump cooling medium into the reactor tank 1 as well as into the reactor enclosure 6 in the case of near-accidents and reac ⁇ tor breakdowns.
• the reactor tank is fil ⁇ led with cooling medium to the level shown in Figure 1.
• a radioactive source 9 is arr- anged outside the reactor enclosure 2.
• the radioactive sourc sends a narrow, high energy beam right through the reactor enclosure 6, the biological protection 4 and the reactor tank 1.
• a detector device 10 placed outside the reactor en ⁇ closure 6 measures the radiation transmitted through the reactor tank.
• the detector device 10 is situated diametric ⁇ ally opposite the radioactive source 9 and the beam from the radioactive source passes through the reactor tank 1 - 5 "
• the level of the cooling medium should sink below the path of the beam or, alternatively, the content of steam in the cooling medium should increase a drastic increase of the intensity of the radiation which reaches the detector device 10 takes place.
• the alteration of the signal from the detector device is utilized for indicating the level of the cooling medium as well as for indicating the density of the latter.
• FIG. 2 shows the device according to the invention in detail.
• the radioactive so ⁇ urce includes a so called race-track microtron 11 of a kind known per se which accelerates an electron beam up to a high energy.
• the electron beam taken out from the microtron strikes a target 12 of suitable material for forming so called brems radiation.
• the brems radiation passes a pho ⁇ ton detector 13 which measures the photon flow.
• An additio ⁇ nal detector not shown may possibly measure the electron flow to the target 12.
• the beam from the target 12 is very well confined and in turn penetrates the reactor enclosure • ⁇ « 6, which moreover in a conventional way may have an embedded steel sheet 14, an air gap 15, a channel 16 in the biologi ⁇ cal protection 4, another air gap 17, one wall of the reac- tor tank 1, the cooling medium in the reactor tank, the op ⁇ posite wall of the reactor tank 1, the air gap 17, a chan ⁇ nel 18 which besides serves as a collimator, in the biolo ⁇ gical protection 4, the air gap 15 and finally the reactor enclosure 6 with its steel sheet 14 so as finally to strike the detector device 10 which includes a number of scintilla ⁇ tion detectors 19 which are aligned with each other and with the target 12 in the radioactive source 9.
• Each discriminator is arranged so that it passes the electrical signal only if the voltage of the signal exceeds a threshold value which corresponds to a radiation energy which is higher than the energy of the radiation which is dispersed from the core or from other reactor components and which is desired not to influence the measurement result.
• the microtron 11 emits radiation in the form of short pulses. The pulse lengths are of the magnitude a few micro seconds. In order to re ⁇ consider the influence of the background radiation on the mea- surement result to the greatest possible extent the photon detector 13 or the current signal from the said additional detector, not shown, in front of the target 12 is connected to an additional input of the coincidence circuit 21.
• the coincidence circuit 21 is open only during the duration of the pulse from the photon detector 13.
• the signals are counted during said period and pass to one input of a quo ⁇ tient circuit 22, while the other input of the ratio circuit receives the output signal from the photon detect-or 13.
• the quotient circuit forms the ratio of the signals at its two inputs and its output signal passes to the input of a loga ⁇ rithm-forming circuit 23 the output of which is connected to a display 24.
• the radioactive source is surrounded by a radiation protec- tion 25 which both forms a biological protection and damps the radiation of the radioactive source in all directions except the direction of radiation shown.
• tion 26 is arranged around the detector 10 and is primarily intended to prevent dispersed undesirable radiation from striking the detector device 10.
• an energy screening 29 in the form of a plate of suitable material may be used.
• the function of the plate 29 is to pass only radiation the energy of which exceeds the energy of the dispersed radiation from the core or from other reactor components.
• the detector device includes a number of de ⁇ tectors aligned with each other and with the radioactive source furthermore involves a possibility of controlling that only radiation which comes in the direction of the line which connects the radioactive source with the detec ⁇ tor is detected, since a predeterminable relation bet ⁇ ween the signals in the detectors is to be present.
• the detector device may consist of a single detector device.
• a pair production detector device shown in Figure 4 may be used. This device includes two pair production detectors each consisting of a mass 30 and 31, respectively, of a material with a high atomic number, for example lead, lying in the path of the beam.
• the masses 30 and 31 are aligned with each other and with the radioactive source.
• the masses pair production takes place which is detected by means of crystals 32, 33 and 34, 35, respectively, known per se.
• the signals from the crystals pass to a co- incidence circuit 36.
• the output signal from the photon de ⁇ tector 13 is supplied to an additional input of the coinci ⁇ dence circuit 36, whereby the influence of the background radiation on the measurement result is reduced.
• the output signal from the coincidence circuit 36 passes to the ratio circuit 22 which is activated by the output signal from the photon detector 13.
• the output of the ratio circuit 22 is connected to the input of the logarithm-forming circuit 23 after which the detector is built in the same way as accord ⁇ ing to Figure 3.
• an ordinary microtron instead of producing the brems radiation by means of a race- -track microtron 11, an ordinary microtron, a linear acce ⁇ lerator, a betatron, or some other electron accelerator may be used. Practical considerations may determine what energy the radiation is to have. In the case of too low en ⁇ ergy the absorption will be too great and it will be diffi ⁇ cult to discriminate the radiation from the background radi ⁇ ation from the reactor etc. , and in the case of too high ra ⁇ diation energies the absorption will be too high owing to pair production. Thus, there exists an energy range which is the most favourable one.
• the radioactive source 9 instead of using brems radiation it is possible to demon ⁇ strate the level and density of the cooling medium by using neutron radiation, the radioactive source 9 then preferab- . ly including a cyclotron.
• the detector device in such a case consists of neutron detectors of a suitable type.
• the reactor tank may, according to the invention, be passed by beams at various levels, either deflection magnets 37, 38 or additional acce ⁇ lerators being used for deflecting the beam or locating it at one or more other levels than that shown, respecti ⁇ vely.
• the deflection magnets deflect the primary radiation of the accelerator which at the said additional levels stri ⁇ kes the target 39 for producing the desired kind of beam.
• the device according to the invention is to be in a initial setting at normal reactor operation. If a near-accident or a reactor breakdown occurs the device according to the pre ⁇ sent invention is started automatically or manually and with- in about 1/2 minute reliable detection may be obtained.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Electromagnetism (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Thermal Sciences (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Radiation (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (4)

Citations (6)

Family Cites Families (1)

• 1980
  • 1980-11-27 SE SE8008340A patent/SE8008340L/ not_active Application Discontinuation
• 1981
  • 1981-11-27 DE DE8181850230T patent/DE3171847D1/de not_active Expired
  • 1981-11-27 WO PCT/SE1981/000345 patent/WO1982002090A1/en unknown
  • 1981-11-27 EP EP81850230A patent/EP0053597B1/en not_active Expired

Patent Citations (6)

Non-Patent Citations (2)

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