Method for checking core of shipboard water-cooled nuclear power plant for condition

FIELD: nuclear power engineering; shipboard nuclear power plants.

SUBSTANCE: proposed method for checking core of shipboard water-cooled nuclear power plant for condition includes measurement of reference-radionuclide specific beta-activity in primary coolant samples taken from running reactor followed by evaluation of core condition. Sample for evaluating core condition is taken downstream of ion-exchange filter under any operating conditions of reactor. Used as reference radionuclide is tritium. Such method makes it possible to check reactor core for condition under any of its operating conditions, including shutdown condition.

EFFECT: reduced dose rate suffered by attending personnel under poor tightness condition of cans.

2 cl

 

The invention relates to the field of nuclear technology and can be used to control the state of an active zone of marine nuclear power plants with water cooled.

A known method of monitoring the integrity of the membranes of the fuel elements (cartridges), based on registration of delayed neutrons emitted mainly short-lived isotopes of bromine and iodine. A significant drawback of this method is that the measurement of delayed neutrons is difficult because of the presence of a large background that is generated by the induced activity17N [1].

Closest to the claimed method of monitoring the status of the reactor core is radiochemical monitoring of water of the primary circuit. The basis of radiochemical control is the determination in water samples of the first circuit unit total beta-activity of radionuclides of iodine [2]. Radiochemical control is carried out by sampling through the sampling system to filter ion exchange purification and subsequent analysis. The purpose of comparability of results of specific analyses of total beta-activity of radionuclides of iodine is measured two hours after sampling and linearly converted at par (100%) power reactor. When values of the total beta-activity of radionuclides of iodine excess, if l is the battle Energoservice active zone limit value (3,7× 108Bq/kg), operation of the reactor plant is not permitted, except under the circumstances, due to the special situation. Sampling is performed under the following conditions:

- the power level of the reactor should be constant in the range from 40 to 60% of nominal power;

the time of operation of the reactor at the selected DC power level, within the limits listed above, prior to sampling should be not less than 24 hours.

The objective of the invention is to provide a method that allows monitoring the status of the active zone of the reactor at all power levels and operating conditions of the reactor depending on the energy production of the active zone.

The technical result achieved by the invention is the ability to control the state of the active zone under all modes of operation of the reactor, including the mode of Parking, and reduced radiation burden on the staff in terms of leakage of fuel claddings.

To achieve the technical result it is proposed to use the method based on the radiometric measurement of the activity of tritium in samples of the primary coolant. The main source of formation of tritium in the reactor vessel NPU is the division of nuclear fuel. The fuel light water react the ditch on one fission 235U238U239Pu is formed (0,85; 2; 2)×10-4atoms of tritium, respectively [3]. As a result of diffusion through the membrane of the fuel rods, as well as cracks and microcracks in the membranes of tritium from the fuel can flow into the coolant. The release of tritium from the fuel rods with cladding made of corrosion-resistant steel is 1%, and zirconium alloy is 0.1% of the total number of under cover [4]. Thus, the release of tritium from the fuel elements can be represented in the form of two processes: diffusion constant output and random associated with depressurization. The contribution of other sources in the formation activity of tritium in the coolant disproportionately small, so in terms of accidental depressurization of the fuel cladding can be neglected.

A distinctive feature of the proposed method is that the sample for conducting radiometric analysis for the determination of tritium can be extracted through the sampling system of how to filter the ion-exchange treatment, and after, because tritium is not sorbed on the ion and the surface. This distinctive characteristic is significant from the perspective of dose loads on the staff in terms of leakage of the fuel cladding, especially in emergency situations, when the sampling fluid to filter impossible due to the extremely high radioactivity γ-emitting radionuclide is C. Therefore, in emergency situations known methods of operational control of tightness cladding unacceptable. Unlike the method using the share of total beta-activity of radionuclides of iodine, the proposed method for determining the activity of tritium in the sample fluid does not require prior long-term operation of the reactor at a fixed power level, exposure of the sample for two hours and conversion of measurements at rated power. In addition, when using this method of assessment of the active zone does not require compliance with strict conditions when sampling fluid as a sample of fluid taken after the standard filter of the first loop, i.e. after sorption γ-emitting radionuclides in ion exchangers, which provides for creating and maintaining a favorable radiation environment for all technological operations for monitoring the status of active zones.

According to the proposed method, the state of the active zone during the campaign evaluated as follows:

- active area sealed when the condition is met:

- active area perfectly sealed when the condition is met:

where

AndAZ- activity tritium, obrazovash the jaś in the active area at the time of measurement, Bq;

AndIk- measured activity of tritium in the water of the primary circuit, Bq;

G is the rate of formation of tritium in the reactor, Bq/MW·h;

Q - Energoservice, MW·h;

Toothe yield coefficient of tritium through the shell fuel rods for fuel rods from corrosion-resistant steel is 0.01, and for fuel with zirconium alloy cladding is 0.001 of the total number under the shell.

The method is as follows. After sampling of the coolant in all modes of reactor operation, including Parking, taken aliquot of the sample to conduct radiometric analysis for the measurement of tritium activity. The measured value of the activity of tritium taking into account the dilution that occurs due to drainage of coolant and subsequent fertilization, is mapped to the value of the activity of tritium formed in the active area at the time of measurement yield factor. If the condition (1) active zone is recognized sealed, and if the condition (2), when the obtained value is greater than the activity of tritium formed in the active area at the time of measurement yield factor, the active area is recognized leaking.

For measuring the activity of tritium in the primary coolant can be used, for example, RA is biometrically method using the liquid scintillator.

Sources of information

1. Ovchinnikov V., Golubev LI, Dobrynin E, and other Operating conditions for water-cooled nuclear power reactors. M, Atomizdat, 1977, 280 S.

2. OST 95 10002-95 Standards of water quality the first and third circuits of the reactor vessels of the Maritime transport Department of the Russian Federation with water-cooled reactors of the type KLT-40. Moscow, 1995, 17 S.

3. Ionizing radiation: sources and biological effects. Dokl. UNSCEAR for 1982, new York: United Nations, Vol. 1, 1982.

4. Production and emission of tritium from nuclear facilities, and the resulting problem. in: Processing of the Behavior of Tritium in the Environment: San Francisco, 16-20 October, 1978. Vienna: IAEA, 1979, p.105-123.

1. Method of monitoring the status of the active zone of the ship's nuclear power plants with water cooled, including the measurement of specific beta-activity reference radionuclide in the sample of the coolant at operating reactor with subsequent assessment of the active zone, wherein the sample to assess the status of the active zone selected after ion exchange filter in any mode of operation of the reactor, and as a reference radionuclide use tritium.

2. The method according to claim 1, characterized in that the active zone during the campaign at any given point in time estimate for the following conditions:

active area sealed with the implementation of the attachment conditions

the active area of the leaks when the condition

where

AndAZthe activity of tritium formed in the active area at the time of measurement, Bq;

AIk- measured activity of tritium in the water of the primary circuit, Bq;

G is the rate of formation of tritium in the reactor, Bq/MW·h;

Q - Energoservice, MW·h;

Toothe yield coefficient of tritium through the shell of the fuel cladding for fuel rods of stainless steel is 0.01, and for fuel with zirconium alloy cladding is 0.001 of the total number under the shell.



 

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FIELD: nuclear power engineering; shipboard nuclear power plants.

SUBSTANCE: proposed method for checking core of shipboard water-cooled nuclear power plant for condition includes measurement of reference-radionuclide specific beta-activity in primary coolant samples taken from running reactor followed by evaluation of core condition. Sample for evaluating core condition is taken downstream of ion-exchange filter under any operating conditions of reactor. Used as reference radionuclide is tritium. Such method makes it possible to check reactor core for condition under any of its operating conditions, including shutdown condition.

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