SI24756A - A method and a device for indirect characterization of the damage to the pool for spent nuclear fuel - Google Patents

Abstract

The method and apparatus for the indirect characterization of damage to the nuclear fuel pool envelope allows, on the basis of the monitoring of the measurements of the leakage of the coolant from the system, the implementation of the indirect characterization of the damage of the envelope and the forecast of the development of an extraordinary event; that is, the forecast of the development of the height of the coolant level in the spent fuel pool and the forecast of the development of the dose rate near the pool. Additional parameters, such as the inflow and temperature of the coolant, the temperature of the coolant in the pool, the dose rate near the pool and some others, are also taken into account in calculating the damage characterization and the forecast of the development of an emergency, including the announcement of the extreme time for evacuation.

Description

METHOD AND DEVICE FOR INDIRECTLY CHARACTERIZATION OF DAMAGE TO A POOL FOR SPREADED NUCLEAR FUEL

FIELD OF THE INVENTION

The present invention relates to a process and a device for the computational assessment of a spent fuel pool and the prediction of an extreme event.

Background and prior art

The spent fuel pools of the pressurized nuclear power plants were basically designed as a transient storage of highly radioactive used nuclear fuel, where reliable heat sinks and protection against ionizing radiation are ensured. These pools often remained the only used fuel storage facilities. In the wake of the lack of space, nuclear power plant operators have restructured the grid and the way the fuel bundles are stored. Some of them for the second time. There is a lack of re-consolidation options. Increasing the density of nuclear fuel in pools, however, raises new safety concerns regarding criticality and structural overload of the pool. The Fukushima nuclear catastrophe has raised precisely these issues, which have attracted a great deal of attention from both the professional and the general public; safety issues related to used fuel storage in facilities that were never designed for long-term storage.

Interruption of cooling during an extreme event such as an earthquake could lead to unacceptably high and possibly fatal levels of radiation near the spent fuel facility. The identified damage to the used fuel pool would require an immediate response from operators who, in the circumstances, would have to act in the absence of reliable data needed to determine the optimal intervention strategy. This could lead to radiation doses received, far exceeding the statutory limits, delaying repairs, incompletely completed tasks and delays in evacuation, which could lead to fatal and irreparable consequences for humans and the environment.

Given the magnitude of the aforementioned risk, increasing attention is being paid to the development of spent fuel pool monitoring systems that, based on a history of measurable indicators, allow the early detection of hazardous events and possible damage to the fuel tank. Such systems could predict the development of an emergency, allowing measures such as remediation and evacuation to be implemented in a timely manner before radiation levels become critical.

In a research paper Characterization of spent-fuel-pit rupture based on water-level monitoring, Annals of Nuclear Energy 63 (2014), p. 674-679, M. Matkovič et al., The authors described a method that allows characterization of the damage to the used fuel pool and the prediction of the development of the coolant level in the used fuel pool. The method is based on monitoring the history of the refrigerant level in the pool, and the results of the method are characterized by a relatively large uncertainty of the predicted values.

In September 2013, R. Bizjak and S. Slavic presented an approach and a computer program that computes the time it takes for water to reach the desired level of coolant in the pool, in a paper by Time to Boil at the Neclear Energy for New Europe International Conference. The authors attributed the decline in the level of cooling water in the pool to the evaporation and leakage of the pool for used fuel. The authors assume the known size and location of idealized pool damage. In the event of an emergency, finding the location and measuring the fracture size would very likely be impeded by the inaccessibility of the affected sites and other difficult circumstances, including high radiation dose rates to accompany the event.

Depending on the prior art, there is a need for a method and apparatus that would allow a reliable assessment of the condition of the spent fuel pool and to predict the development of the coolant level in the pool.

Overview of the present invention

This objective is achieved by the method and the apparatus for calculating the condition of the spent fuel facility according to independent claims 1 and 14. The relevant claims relate to preferred embodiments of the method and apparatus.

The method for computationally assessing the condition of a spent fuel tank according to the present invention comprises the steps of measuring a coolant leak from said pool and predicting the development of a coolant level in said pool.

The inventors have shown that the prediction of the development of a level of coolant level based on the measurement of refrigerant leakage from said pool is reliable and accurate. The invention provides better accuracy over existing techniques that rely on monitoring the height of the cooling water surface. As a result, it is possible to more reliably predict a critical drop in the refrigerant level in said pool and predict evacuation in a timely manner, which improves overall safety during an extreme event.

Used fuel pools are typically equipped with a collecting area under the pool. Existing stairwells already have the ability to measure leaks, so that with minimal infrastructure intervention the system could be routinely equipped with accurate flow meters. This data would then be used in the present invention to evaluate the condition of a used fuel pool.

The spent fuel system typically comprises a spent fuel pool connected to a transmission channel and a space for maneuvering the fuel. The transfer channel serves to transport fuel between said pool and the flooded reactor cavity. In the event of an emergency, damage to the envelope of said system can occur either in the pool or in the transmission channel or in the fuel maneuvering room. Most or all of the spent fuel is typically stored in said pool, so the height of the coolant level in the pool is critical to determine and predict the condition of the system. In the context of the present invention we understand the prediction of the development of a coolant level in a spent fuel system as the prediction of a coolant level in a spent fuel tank.

A method for indirectly characterizing a spent fuel pool damage and predicting the development of a coolant level in said system may take into account the geometry of said system including fuel bundles and / or the characteristics of said coolant and / or nuclear fuel characteristics. The method according to the invention in a preferred embodiment involves repeatedly / continuously measuring said coolant leakage from the system and updating said coolant level prediction in the pool on an ongoing basis based on said continuous measurements.

Repeated measurements over time improve the reliability and accuracy of the prediction of the development of the refrigerant level in the pool.

Said method may, in a preferred embodiment, comprise a step of predicting the development of a radiation level, in particular a prediction of the development of a dose rate near said spent fuel pool, based on said prediction of the coolant level in the pool.

Based on the known level of the coolant in the pool, the characteristics of the fuel used and the shielding properties of the coolant, it is possible to determine the expected radiation level or dose rate near said spent fuel pool. Based on the projected dose values, measures can be taken to protect and evacuate personnel before being exposed to hazardous radiation levels.

The method can predict the maximum evacuation time based on the prediction of the development of the coolant level in the spent fuel pool and the predicted dose rate near said pool.

The method makes it possible to characterize the pool cover for used fuel; determines the sizes and locations of damage to the envelope of said system based on the monitoring of the history of pool coolant leaks.

The inventors have shown that the size and location of damage to the pool envelope can be determined by monitoring the history of refrigerant leakage. Such an approach represents a significant advantage over existing techniques based on the known / assumed size and location of the sheath damage.

Here, predicting the location of a sheath damage represents determining its vertical position above the ground or above the bottom of the spent fuel tank.

In a preferred embodiment, the spent fuel system typically comprises a spent fuel pool connected to the transmission channel and the fuel maneuvering space, said method taking into account the various leak points in the system; leakage from the used fuel pool, leakage from the transmission channel and leakage from the fuel maneuvering room.

Taking into account the different leakage sites allows for a more targeted and reliable prediction of the flow rate of the coolant level of the pool with said fuel and the dose rate near the pool.

In a preferred embodiment, the method includes monitoring radiation levels near said facility and predicting the development of a refrigerant level in a spent fuel pool and predicting dose rates near said pool based on said monitoring of radiation levels.

Monitoring radiation levels may include monitoring the dose rate in said vicinity of a used fuel pool.

The inventors have found that monitoring the radiation level, along with tracking the history of coolant leakage from the pool, significantly improves the reliability of the prediction. In addition, the measurement of the radiation level can serve as a "back-up" in the event of an uncertainty in the value of the leakage signal; for example, damage to the measurement infrastructure resulting from an emergency.

In a preferred embodiment, the method includes the continuous measurement of fresh coolant flow into a used fuel system, the monitoring of the fresh coolant and coolant temperature in the pool, the monitoring of the coolant level, and the prediction of the development of a coolant level in a used fuel pool based on the continuous measurement of the fresh coolant flow in the used fuel system, monitoring the temperature of the fresh coolant and coolant in the pool and monitoring the history of the height of the coolant level in said used fuel pool.

The inventors have found that the simultaneous monitoring of a large number of said quantities, in addition to monitoring the leakage intensity, significantly improves the reliability and accuracy of predicting damage to the spent fuel tank pool and developing coolant levels in said pool. Continuous monitoring of the aforementioned quantities provides an insight into the occurrence of an emergency when monitoring the values of leakage intensity and radiation level are not reliable or not available.

The method of the preferred embodiment also includes measuring the seismic activities to which the object is subjected, measuring the slope of said system and predicting the development of a coolant level in said basin based on the measurement of said seismic activities and said slope.

The inventors have found that monitoring the seismic activity of the object and the slope of the structure, in combination with monitoring the leakage of the cooler, enables a more reliable assessment of the damage to the used fuel pool, and can further be combined with the other measurements mentioned above, which further improves the accuracy of the prediction of the development of the coolant level in to the said pool.

The slope of the structure can be determined by measuring the height of the coolant level in at least three non-collinear locations of said basin.

The computational assessment of the damage to the spent fuel pool and the prediction of the development of the level of the coolant level in said pool can preferably be performed by a three-step procedure. In the first step, an emergency is characterized.

An emergency in the context of the present invention is understood as any event that may compromise the safe operation or structural integrity of a spent fuel system, such as an earthquake, uncontrolled input of material into a spent fuel pool, and uncontrolled refrigerant leakage from the system.

In the second step, a calculated estimate of the damage to the spent fuel tank pool is given. The size and location of the damage in the envelope is calculated on the basis of monitoring the aforementioned sizes.

In the third step, based on the characterization of the emergency and the computational assessment of the damage of the spent fuel system envelope, we predict the development of the level of the coolant level in the said pool.

In this configuration, the invention may include measuring the seismic activity of an object and / or the slope of a spent fuel system, characterizing an emergency based on said measurement of coolant leakage from a pool, and / or measuring the seismic activity of an object and / or measuring the slope of said system and known geometry of the said spent fuel system.

The method further comprises, in the preferred embodiment, a step of computationally estimating the size and location of damage to the spent fuel system jacket based on monitoring the coolant leakage from the system and characterizing the emergency.

In addition, the method may include measuring the fresh coolant flow and / or measuring the fresh coolant and coolant temperature in the pool and / or measuring the coolant level in said pool, the size and location of the damage being determined on the basis of said monitoring of coolant leakage from the system and / or measuring the flow of fresh coolant and / or measuring the temperature of fresh coolant and coolant in the pool and / or measuring the height of the coolant level in said pool.

Further development of the level of the coolant level in the said pool can be predicted on the basis of the aforementioned emergency characterization and / or on the basis of a calculated estimate of the size and location of damage to the spent fuel system envelope.

The step of predicting the development of the height of the cooling water level in said pool in the preferred embodiment takes into account the "loss" of the coolant mass flow due to evaporation from the pool.

Considering the loss of mass flow due to the evaporation of the coolant from the spent fuel pool allows a more reliable prediction of the development of the level of the coolant level in the said pool.

Given the known heat output of the residual heat and the heat losses, said evaporation of the coolant can be estimated by measuring the flow of fresh coolant, the temperature of the fresh coolant and the coolant in the pool and monitoring the height of the coolant level in said pool.

The invention further relates to a device for the computational evaluation of the condition of a spent fuel system, comprising a flowmeter for measuring coolant leakage from said system and a computational assembly for predicting the occurrence of an emergency.

The measuring assembly in a preferred embodiment includes a flowmeter. Said flowmeter may be located at the outlet of the sump located under said spent fuel system.

In a preferred embodiment, the measuring assembly is intended to monitor the intensity of coolant leakage from said system.

In the preferred embodiment, the computational assembly is intended to provide a computational prediction of an emergency occurrence based on the known geometry of said system including fuel bundles and / or the characteristics of said coolant and / or the characteristics of nuclear fuel.

Said device in a preferred embodiment includes repeatedly / continuously measuring said coolant leakage from the system and updating said coolant level prediction in the pool on an ongoing basis based on said continuous measurements.

The computational assembly in a preferred embodiment comprises the step of predicting the development of a dose rate near said spent fuel pool based on said prediction of the pool coolant level.

The computational set may predict an evacuation end time based on a prediction of the development of a refrigerant level in a spent fuel pool and / or a predicted dose rate near said pool.

The computational assembly in the preferred embodiment enables the characterization of the pool cover for used fuel; determines the sizes and locations of damage based on monitoring the history of pool coolant leaks.

The spent fuel system generally comprises a spent fuel pool connected to the transmission channel and the fuel maneuvering space, said computational assembly allowing for different leakage points within the system; leakage from the used fuel pool, leakage from the transmission channel and leakage from the fuel maneuvering room.

The measuring assembly in a preferred embodiment includes a radiation level meter located near said object. The meter allows monitoring the radiation level in the vicinity of the spent fuel system. The computational set allows predicting the development of the level of coolant in the spent fuel pool and predicting the dose rate near said pool based on said monitoring of coolant leakage and / or monitoring of radiation levels.

• ·

The measurement assembly in the preferred embodiment includes continuous measurement of the fresh coolant flow into the used fuel system, monitoring the temperature of the fresh coolant and coolant in the pool, and monitoring the level of the coolant level in the used fuel pool. The computational set enables the prediction of the level of the coolant level in the spent fuel system, based on the continuous measurement of the fresh coolant flow into the system with used fuel and leakage, the monitoring of the temperature of the fresh coolant and coolant in the pool, and the monitoring of the level of the coolant level in said used fuel pool.

The measuring assembly in a preferred embodiment also includes measuring the seismic activities to which the object is subjected and / or measuring the slope of said system. The computational set enables the prediction of the development of the level of the coolant level in the said basin, based on the monitoring of the said seismic activities and the measurement of the slope of the system together with the monitoring of the coolant leakage from the system.

The measuring assembly in the preferred embodiment includes measuring the seismic activities to which the object is subjected and / or measuring the slope of said system, since the computational assembly allows the prediction of the occurrence of an emergency, based on the known geometry of the spent fuel system, based on monitoring the coolant leakage intensity from said system and / or measuring seismic activity and / or measuring the slope of the system.

The aforementioned computational assembly allows characterization of the damage to the pool envelope for used fuel; determines the magnitudes and locations of damage based on the monitoring of the coolant leakage from said pool and the characterization of an emergency.

The measuring set preferably includes continuous measurement of the fresh coolant flow into the used fuel system, monitoring the temperature of the fresh coolant and coolant in the pool, and monitoring the level of the coolant level in the used fuel pool. The said computational assembly enables the computational assessment of the size and location of damage to the envelope of said system based on monitoring of the history of pool coolant leaks, measured or calculated residual heat power of spent fuel and thermal losses of the system, based on continuous measurement of fresh coolant flow into said system, based on temperature monitoring fresh coolant and coolant in the pool and monitoring of the level of coolant level in said pool with used fuel

The computational assembly in the preferred embodiment allows the prediction of the development of the coolant height in the spent fuel pool, based on the characterization of the emergency and / or the characterization of the damage to the wrapper of said system.

• · · ·

The computing set prioritizes the evaporation of the coolant from the spent fuel system.

Said computational assembly may provide a computational estimate of said refrigerant evaporation based on the measured / calculated value of residual heat output and heat losses, measured fresh coolant inflow, fresh coolant and pool coolant temperatures, and monitoring of the coolant level in said pool.

The invention further relates to a computer program for characterizing the damage of a spent fuel storage system envelope, said computer program receiving computer-readable instructions so that the program running on the computer implements a method that includes and performs all the operations described above.

Description of preferred embodiments

The features and numerous advantages of the present invention are illustrated in the detailed description of preferred embodiments with reference to the accompanying drawings in which:

Figure 1: shows a cross-sectional view of a spent fuel system according to one embodiment of the present invention;

Figure 2: shows a flow chart illustrating a method according to one embodiment of the present invention; and

Figure 3: shows an example of characterization of a spent fuel system wrap injury and an emergency development forecast for two different residual heat outputs and two different sites of damage to the wrap; one damage, located in the spent fuel pool, while the other illustrates the leak, either in the fuel maneuver area or in the transmission channel.

Figure 1 shows a cross-sectional view of a spent fuel system 10 in which the present invention can be used. The spent fuel system 10 comprises a spent fuel pool 12 in which a large number of fuel bundles 14 are stored in the cooler 16, such as water.

As can be seen from Figure 1, the spent fuel pool 12 is connected to the fuel maneuvering space 18 and to the transmission channel 20 via shallow passageways or doors. The fuel maneuvering compartment 18 is used to load or unload fuel elements 14, and the transmission channel 20 serves to transfer fuel 14 between the reactor cavity (not shown) and the spent fuel pool 12. Coolant 16 • Fills the free volume of the used fuel pool 12 , transmission duct volume 20 and coolant maneuver space 18. The size and depth, as well as the composition of the spent fuel pool 12, the fuel maneuvering volume, and the transmission duct 20 may vary. The narrow aisles connecting said pool 12 to the transmission channel 20 and the fuel maneuver space 18 are much shallower than said pool 12, the transmission channel 20 and the fuel maneuvering space 18, which is shown schematically in Figure 1.

In Figure 1, h ₀ indicates the maximum coolant height in the spent fuel tank 12, while h (t) indicates the coolant level in the pool 12 at some specified time t. The h _O o parameter indicates the location of damage to the pool envelope; the amount of damage (above ground) 22 that may occur in the outer wall of the pool 12 as a result of an emergency such as an earthquake. Damage to the sheath 22 has cross-sectional dimensions A as shown in Figure 1 and may lead to the loss of coolant 16 from the spent fuel pool 12, the coolant maneuvering space 18 and the transmission duct 20. The coolant escaping from the spent fuel system collects in reservoir 24 located below the spent fuel system 10.

As further illustrated in Figure 1, the spent fuel system 10 is routinely provided with a plurality of measured parameters that can be used in the context of the present invention and together form and determine the measurement assembly. The flow meter 26, which is the intended part of the reservoir 24, is arranged to measure the outflow of coolant from the reservoir24.

Meter 28 is provided for measuring the level of coolant level in said spent fuel system 10. Figure 1 shows a level meter 28 of the coolant level installed in the spent fuel pool 12. Said meter 28 is alternatively or additionally provided on other locations within the spent fuel system 10.

The spent fuel system 10 is further equipped with a thermometer 30 adapted to measure the coolant temperature 16 in the spent fuel pool 12.

The decrease in the coolant level can be corrected by the flow of fresh coolant via the inlet valve 32. The flowmeter 34 is mounted on the inlet pipe and is designed to measure the fresh coolant flow into the spent fuel tank 12, while the fresh coolant temperature is measured by a thermometer 36 .

The spent fuel facility 10 is further equipped with a dose rate gauge 38 and is located at the edge or near the spent fuel pool 12. The meter is adapted to monitor the dose rate of radioactive radiation from the fuel bundles 14.

The seismic activity meter 40, which may be mounted on the structure of the spent fuel system 10, is intended to identify the nature of the oscillation of the system, such as seismic activity.

As can be further seen from Figure 1, the coolant flow meter 26, the level meter 28 and the pool cooler temperature meter 30, the temperature meter 36 and the fresh cooler flow meter 34, the dose rate meter 38 and the seismic activity meter 40 of the structure of said system all connected via data lines (dashed in Figure 1) to the computational assembly 42, which collects data on measured values and performs characterization of the envelope damage. Part or all of the data obtained can be used to predict the development of coolant level in a spent fuel system 10, either alone or in combination.

A computational assembly 42 may be a general-purpose computer that performs computational operations on measured data. The computational unit 42 is connected to the display unit 44. The latter provides the measured and interpreted values of the measurement and computational unit. Provides early warning to responsible staff of potential contingency events. As shown schematically in Figure 1, within the display assembly, the measured and interpreted values can be represented through different media.

The results of the analysis are constantly updated and transmitted at two levels; Level 1 is used during normal operation and displays the current values as well as warnings when the limits for normal operation are exceeded. Level 2 applies after the initial event. Emergency characterization and damage characterization of the spent fuel system wrap shall be performed. At this level, an emergency development forecast shall be performed, including a projection of received doses of emergency personnel for the intended tasks. This is the time for evacuation.

In order to avoid overloading the operators of the nuclear installation, the level 1 information is minimized. Without a specific request, only a set of basic information is presented, together with warnings when the limit values are exceeded. Without the initial event, Level 1 shows only the measured data; no characterization of the incident, damage to the envelope and no prognosis for the development of the event.

• ·

The presentation of the results of the analysis of the calculation set is included at level 2 in the event of an emergency when the device detects an uncontrolled fall in the coolant level, a leak, an uncontrolled rise in the coolant temperature or an increase in the dose rate at the edge of the spent fuel pool 12. The results of the analysis of the calculation set allow for: characterization emergency, characterization of damage to the spent fuel system envelope, prediction of the development of the emergency, including the prediction of the evacuation time of the facility.

In the first step, we will explain in detail how we arrive at a computational prediction of the development of the coolant level in the spent fuel system 10, based on monitoring the coolant leakage from said system.

In the second step, we will explain how monitoring the coolant leakage from said system can be complemented in combination with other measured parameters in the spent fuel system 10, which increases the accuracy and robustness of the coolant level forecast and the expected dose rate in the system.

Forecast for the development of coolant level based on monitoring the coolant leakage from said system

The basis and background for characterizing the damage of the pool envelope 22 and predicting the occurrence of an incident are broadly similar to the inventors' approach of M. Matkovich et al., As described in the research article Characterization of spent fuel-based water rupture based on Annals of Nuclear Energy 63 (2014) 674 to 679.

For the purposes of analysis, we assume that the free surface of the coolant surface in the spent fuel system is much larger than the crack cross-section in the system sheath. This results in negligible coolant velocity, which is reflected in the insignificant increase in the kinetic energy of the system during leakage and negligible loss due to mixing and friction on the walls of the spent fuel tank 12. Under these assumptions, the energy balance for leaking coolant from the spent fuel pool 12 can be written , as the potential energy converted to the kinetic energy of the effluent minus the corresponding energy loss due to friction.

. _2 ίή 1 _2 mg & h = - · m - v + - - - p · k _5oc - rp 2 (l) dm m - - _; -

In Equation (1), at represents the mass of the leakage current, g the gravitational acceleration, Ah the height difference between the water level and the damage site, the average water discharge rate, p the water density and k, _{oc the} overall pressure drop coefficient. Assuming only one leak location and rigid structure of the system, it is possible to relate the rate of change of the cooling water surface height to the rate of coolant drainage from the crack.

dk dt • S =

Α _β · ι (2)

Here, dh / dt refers to the rate of change in the height of the cooling water surface, A _o to the cross-section of the crack in the system sheath and S to the free surface of the coolant surface in the spent fuel system. Considering Equations (1) and (2), we arrive at a physical model in the form of a differential leakage equation from the spent fuel tank 12,

CO (3) where h (t) refers to the height of the cooling water level at time t and hoo refers to the height of damage to the pool envelope.

in this case, the overall pressure drop coefficient does not depend on the discharge velocity through the crack. This is a fairly good approximation for turbulent flows with relatively large sheath damage. At high Reynolds numbers, the overall friction coefficient remains almost independent of the flow rate. On the other hand, if the hydraulic crack diameter is small enough that the laminar flow of the refrigerant leakage is expected, then the assumption of a fixed coefficient is poor. However, in the latter case, the overall coefficient of friction is inversely proportional to the Reynolds number, so the assumption of a constant value of the mentioned coefficient obtained at the initial stage when the height of the water and the velocity of leakage would give a conservative solution to the prognosis.

In the simplified velocity change equation of the coolant level (3), we assume that:

• · • there is one damage to the sheath of the system whose topology does not change during the observation; • no intake of fresh coolant; • the free surface of coolant S in the spent fuel system 12 is much larger than the crack cross-section in the sheath of system A _o (S »A _o ), • the crack cross-section in the system envelope A _o , the overall pressure drop coefficient, the free surface of the coolant S and the height of the sheath damage h ₀₀ do not change with time, • the overall pressure drop coefficient does not change with speed flow rate.

The mathematical formulation of the simplified physical model described by equation (3) gives the same results for a given location of the sheath damage for small damage and hypothetical frictionless coolant leakage as for larger damage with a correspondingly higher friction estimate during leakage. In this context, further simplifications have been introduced:

• the cross section of the crack in the system envelope is a hypothetical value that takes into account the actual cross section A _o and the overall pressure drop coefficient k | _0C , • the potential energy of the fluid is converted to the kinetic energy of leakage and friction energy loss.

With the above assumptions, the conservation of the leakage volume flow can be written in the form of a differential equation as follows:

Vit) = · j2-5 '(MV (t)) - fc ₀ . _o ) (4) where dt denotes the measured coolant flow 16 to the flow meter 26, which measures the coolant leakage through the damage of the sheath 22. Contrary to the existing approach [1], based on monitoring the rate of change of the cooling water level, that the accuracy of the subject approach does not depend on the size of the free surface of the coolant surface in said system. In Equation (4), the cross-sectional area of the crack in system A sheath and the height of damage to the pool sheath are hoo unknown variables, requiring the definition of two new boundary conditions.

Boundary conditions 1 and 2 (BC1, BC2): t = t ₀ , t = ti να ₀ ) = 4 · 72-5- (Mt _e ) -w (5) exercises = 4 - f2g- (h (ie-k ^ (6)

In equation (5), h (t ₀ ) represents the initial height of the cooling water level. Once the required boundary conditions are determined, we can determine h ₀₀ and A. Considering Equations (4), (5) and (6), the following notations can be used to express the height of damage to the pool envelope and the crack cross-section.

M) * · w ^s - Vfri) ⁵ (7) · g- (h (f _a ) - fast) (8)

It can be seen from Equations (7) and (8) that only two different measurements of the flow of coolant leakage over time are required to characterize the damage of the spent fuel tank envelope. Characterization of damage to the spent fuel system sheath defines the damage height of said sheath h ₀₀ and the crack intersection in said sheath A, while V (t) and h (t) are dependent variables bound across the free surface of the coolant surface S of the spent fuel system. fuel 12. It follows from the foregoing that the general solution of differential equation (4) can be written as follows:

(9)

As can be seen from equation (9), while solving equation (4), we encounter a new unknown C _o . The solution of the unknown (C _o ) is obtained via the definition of the third boundary condition t = 0.

Boundary Condition 3 (BC3): t = 0 -> h {t = O) = h ₀ • ·

C _o | 2 (h ₀ - hfi) ^Α Ί ^s (10)

Parameter C _o represents the time interval required to reduce the height of the cooling water surface from the initial height h ₀ to the height of said damage of the pool envelope h _O oKer, because of the damping capacity of ionizing radiation and neutron flux in the used fuel pool 12 associated with the height of the cooling water level in said basin, the characteristic times for the selected system can be calculated according to equation (9). These are times that are predicted in the event of an emergency when the level of cooling water in the spent fuel tank drops to a certain height. Similarly, characteristic times can also be calculated for certain dose rates at the edge of the basin or for certain limit values of projected cumulative doses received by emergency personnel. This information can help you prioritize emergencies and plan evacuation time.

By rearranging equation (9) and taking into account equation (10), we can write a definitive solution to differential equation (9) in terms of the time course of the height of the coolant in the used fuel pool. In the event of an emergency, the forecast for the development of the level of the coolant level in the said pool can be written:

A (O =

('7 ₀ ^- t) ^a + Aqo (11) |

Monitoring the cooling water leakage from the spent fuel system in a relatively short time after the initial event enables the computational characterization of the sheath damage determined by the crack section in sheath A and the height of damage of said sheath hoo- This characterization provides the basis for predicting the cooling water surface height in the spent fuel system 12 long after the initial event. The magnitude of the crack A can be calculated from equation (8), the height of damage to the pool h ₀₀ from equation (7), and the prediction of the development of the height of the cooling water level in the system can be calculated from equation (11).

.:. .:. * · · · · · · ·

An important advantage of this approach is the direct and indirect calculation of the damage characteristic of the pool envelope. In the event of an emergency, timely characterization of the emergency would be very difficult or even impossible if it were not obtained indirectly.

Comparison of the present invention with the present state of the art [1], based on monitoring the level of the coolant in the pool, shows that in determining the characterization of the damage to the wrapper, the present invention does not rely on the knowledge of the free surface of the coolant in the pool 12. This allows significantly greater accuracy of characterization damage to said jacket and correspondingly greater accuracy in predicting both the evolution of the coolant level in the spent fuel pool and the development of dose rate at the edge of said pool.

Based on information obtained preferentially in the initial phase of an emergency, the computational assembly of the device 42 may provide a computational estimate of damage to the spent fuel system 10 sheath; determine the size of the injury and its elevation in said system. Predicts the intensity of refrigerant leakage and evaporation from the system. This information can be used to determine the heat balance of the system and any change in criticality in the pool as a result of uncontrolled fuel accumulation. Based on this information, the computational set can predict the development of the coolant level, the dose rate at the edge of the basin, and the projection of expected integral absorbed doses by emergency personnel as well as the evacuation time. The invention can help optimize and prioritize emergency response by exposing emergency personnel to minimal radiation doses and in accordance with the law. If the consequences cannot be restored within acceptable doses of received radiation, the computational unit 42 provides for a maximum evacuation time for the facility.

Consideration and integration of various measured system parameters

Other measured parameters in the spent fuel system 10 significantly complement the monitoring of leakage 26 from said pool. The variety of measured quantities improves accuracy, and above all improves the reliability of the prediction of the height of the cooling water surface in the spent fuel pool and the prediction of the development of dose rate near the said pool.

Figure 2 shows an example of the data flow and measured values that are required for the computational characterization of damage to a spent fuel system 22 sheath 22. Characterization and the prediction of an emergency occurrence are based on the detected coolant leak measured by the flowmeter 26, the coolant level monitored by the meter. coolant level 28 and radiation level monitored with a dose rate meter 38 near the spent fuel pool. The block diagram in Figure 2 also takes into account the flow of fresh coolant.

• «

It is precisely the measurement of the inflow 34 and the temperature 36 of the fresh coolant, the temperature 30 of the coolant 16 in the spent fuel tank that can be used to estimate the residual thermal power of the used fuel in the pool and the heat losses to the surroundings. Evaporation can be estimated on the basis of the heat balance, which, in the variety of measured quantities, with emphasis on measuring the leakage of refrigerant 26 and with the known geometry of the spent fuel system, provides greater reliability and better accuracy in predicting an emergency.

Figure 2 shows in more detail the three-step emergency forecast.

(i) Characterization of an emergency and possible consequences:

The characterization of an emergency is based on monitoring the coolant leakage from the spent fuel system 10, which is measured with a flowmeter 26, monitoring the height of the coolant using a dedicated gauge 28, monitoring vibrations and fluctuations in the structure of said system, which is monitored with a seismometer 40. is important in determining the nature of the initial event. It is the basis for the assessment; whether due to the seismic activity the geometry of the spent fuel pool 12 has changed, whether there has been an introduction of foreign matter into the pool, whether a coolant has been leaked over the edge of the pool, or a slope of the structure has occurred, etc. It is important to properly define the loss of coolant from the pool. This may be due to loss of coolant due to the ripple over the edge due to the movement of the soil, to the slope of the structure, to overcharging, or to the displacement of the coolant resulting from the introduction of foreign matter into the pool. Although the loss of coolant in the event of a spill over the edge of the basin can be significant, damage to the system envelope is, from the point of view of minimal environmental impact, generally more problematic for humans. The lowering of the coolant height may be due to evaporation of coolant 16 due to insufficient cooling of used fuel 14. Individual contributions to changing the cooling water height in the spent coolant pool can be calculated using the known coolant temperature 30 in the pool, measured flow 34 and fresh coolant temperature 36.

(ii) Characterization of damage 22 of the spent fuel system sheath:

As shown above, the invention enables the damage of the system envelope to be calculated by the location and size of the damage. The basis for the above assessment is the characterization of an emergency, which, given the known geometry of the system infrastructure, gives the cause and nature of the altitude of the coolant level in the pool.

(iii) Emergency forecast:

In this last step, the prediction of the development of the coolant level 16 in the spent fuel pool 12 is made. The height of the coolant level in the pool 12 can be taken as the basis for calculating the dose rate at the edge of the pool 12 and for projecting anticipated absorbed doses of emergency personnel. On the basis of this information, the nuclear facility operator may: (a) draw up such a priority list of necessary emergency response work in a manner that would lead to minimal adverse effects on humans and the environment, (b) anticipate and distribute emergency operations among emergency personnel thus, absorbed doses of all participants within legally cumulative cumulative doses will be received, and (c) order the evacuation time of the facility when the emergency operations can no longer be performed within legally restricted doses of emergency personnel.

Figure 2 shows in more detail the estimation of the severity of an emergency under three different scenarios (left / center / right), which are defined by taking into account different measured parameters.

In each case, the characterization of an emergency begins with the recognition of patterns of measured parameters, as described in more detail above. In the next step, we consider the history of the coolant height h (t), which is monitored by the corresponding gauges 28 in the system. At the same time, the level of ionizing radiation is He (t), which is measured with a dose rate meter 38 near (preferably at the edge) of the spent fuel pool. The time derivation of each parameter in Figure 2 is indicated by a dot above the associated symbol.

In the first scenario (left side of Figure 2), the cooling water level decreases, which is reflected in an increase in the dose rate at the edge of the pool due to the reduced thickness of the water layer above the used fuel. A smaller amount of water in a non-cooling system causes a faster rise in temperature T3 as measured by the temperature sensor 30. If cooling water boils (T3 = 100 ° C or more), the leakage, evaporation and flow of fresh coolant are taken into account in the equation for the level of cooling water level. In the mentioned equation in Figure 2, dV4 / dt denotes the inflow of fresh coolant measured with the flowmeter 34, dV2 / dt indicates the coolant leakage from the system, which is monitored by the flowmeter 26 mounted on the reservoir 24. T5 indicates the temperature fresh coolant 36 and dQ _RE s / dt indicates the residual thermal power of the used fuel, which is less for the measured / calculated heat losses of the system.

If the water is not boiling in the pool and there is a leakage of coolant, use only the first part of the right-hand side of this equation, where the heat balance is not taken into account.

In the second scenario (center in Figure 2), the water level in the pool and consequently the radiation level in the spent fuel system do not change. If boiling (T3 = 100 ° C or more) is present, the supply of fresh coolant compensates for the leakage and loss of coolant due to evaporation. If the temperature of the coolant in the pool is below boiling point, the supply of fresh coolant just compensates for the loss due to leakage.

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· · · · ·

In both of the above scenarios, where a leak is present, characterization of the spent fuel system wrap damage as described above and emergency response is performed.

In the third scenario (right-hand side of Figure 2), we see an increase in the coolant level. Increasing the thickness of the coolant above the fuel also reduces the radiation level near the pool. This is when the supply of fresh coolant 34 exceeds losses due to leakage 26 and losses due to possible evaporation of the coolant (T3 = 100 ° C or more), or we are dealing with the introduction of foreign matter into the spent fuel pool. In this scenario, the situation is generally less critical. Further monitoring of the measured quantities is carried out, but no immediate measures are foreseen.

On the basis of mutual comparison of the measured parameters, the computational assembly of the device can identify invalid measurements which, in the event of an emergency, may occur due to damage to the infrastructure of the measuring assembly. The method described by the invention enables the selection of the available input parameters, which provide the best accuracy of predicting damage to the envelope and predicting the development of an emergency.

The device shall characterize the emergency and, based on at least 3 consecutive measurements, either the leakage intensity, the trend of declining refrigerant levels in the pool, or the trend of the dose rate near the spent fuel pool, allows characterization of the damage to the spent fuel system envelope and the prediction of the occurrence of an emergency.

The ability to characterize the damage of a spent fuel pool and the prediction of an emergency can best be compared to the performance of a rapid body temperature meter. A simple calculation of the time constant of this type of meter indicates that, within the few seconds required for successful measurement, the meter sensor does not reach the displayed temperature. Since it is assumed that the sensor and the measurement conditions do not change during the measurement of body temperature (mass, surface, specific heat and heat transfer / transfer), the measured temperature profile is uniquely determined by the temperature of the meter. The displayed temperature is thus the result of a computational algorithm that, on the basis of measured values, predicts an asymptote value - the measured temperature - in the initial phase of measurement. Since the time constant of the temperature gauge is unknown (heat transfer / transfer varies with the patient's condition), more than otherwise a minimum of two periodic temperature measurements over a known time interval are required to determine the asymptote.

Analogous to the indirect characterization of spent fuel pool damage, where the required temperature can be compared to determining the asymptote of the cooling water surface height - that is, the height of the damage caused, while the calculation of the crack size is directly related to determining the time constant of changing the cooling water level. Here, too, in the theoretical case of knowing the physical model of damage, the characterization of the injury could only be performed by three periodic measurements of the level of coolant in the pool.

In spite of the simple comparison of the device with the rapid body temperature meter, in the first case it is much more complex computational algorithms and taking into account a larger number of variables. Namely, the device enables the characterization of an injury and the prediction of an emergency, which takes into account:

a) variable geometry of the pool in height and possible change of slope of the pool,

b) change in thermal power of evaporation by detecting fuel elements,

c) any change in the criticality during the warming of the structure,

d) change in heat losses due to increase in coolant temperature,

e) reconciling measured values of different quantities and eliminating defective measurements,

f) coolant splash over the edge of the pool,

g) uncertainty in measurements, uncertainty in the characterization of damage to the pool envelope and uncertainty in predicting events;

h) different scenario development in case of leaks inside SFP or outside (CLA / TC).

The measuring unit 42 of the device enables the calculation of the heat balance in the spent fuel pool based on the measured input parameters.

The residual thermal power of the fuel elements, reduced by the heat losses to the surroundings, causes the cooling water temperature and the contacting infrastructure to rise. The higher their heat capacity, the slower the rise in cooling water temperature is expected. It can be calculated in two ways:

a) analytically - by means of the known geometry / mass and physical properties of said infrastructure,

b) empirically - in the absence of external cooling, it is determined by the known residual thermal power and the measured rate of change of the average temperature of the system.

Increasing the temperature in the basin is non-linear due to the change in the leakage heat capacity and the change in the heat losses to the surroundings, just as the height of the cooling water surface is nonlinear due to the changing static pressure of the coolant at the leakage point (Figure 3). Dynamic changes in the heat capacity of the system are also affected by the pool geometry, inventory and cooling water accumulation along the depth of the pool. These data are unique for each pool geometry, structure inventory and for each fill, so they are specific to each SFS.

When the coolant reaches saturation temperature, all the residual heat is "redirected" to the evaporation of the water from the pool. In the event of failure of the external cooling system or the failure of the supply of fresh coolant, evaporation is, in addition to any leakage, a major cause of the intense lowering of the cooling water surface in the pool (Figure 3).

Figure 3 shows the result of the calculation set prediction, which shows the time course of the development of the coolant level in the spent fuel tank. The time interval A in Figure 3 indicates the "dead" time of data capture, which is required in the first phase of an emergency to successfully characterize the damage to the system envelope and to first calculate the prognosis. Time interval B indicates the area of prognosis for the development of the coolant level during the time after the initial event.

Figure 3 compares the forecast of an emergency development for two different pool fillings. The solid line corresponds to 1.5 MW of residual thermal power of the fuel elements 14 in the pool, and the dashed line illustrates the course of filling the pool with a total thermal output of 8.5 MW. These are relatively short periodic periods during the normal operation of the power plant; during fuel change when the entire core of the reactor is transferred to the spent fuel pool. The decrease in coolant level in Figure 3 in the first phase is due to leakage and soon evaporation.

Figure 3 also compares two leakage scenarios in the spent fuel pool (bold line) and out (thin line), respectively, in the transmission channel 20 or the fuel maneuvering space 18. The rate of reduction of the cooling water surface is assumed to be the same under the given assumptions. the coolant level does not reach the bottom of the passage between the structures. When there is no longer a connection between the structures, the available refrigerant volume in the spent coolant pool is significantly smaller, causing a significant increase in the rate of decline in the coolant surface level in the pool when the pool cover is damaged. In the case of damage outside the pool, the rate of decrease in the level is slowed down by the disconnection with the source of leakage, but increases due to the smaller free surface of the coolant in the pool and the constant evaporation.

On the other hand, if the damage of the sheath 22 is located on the wall of the spent fuel tank sheath, the rate of decrease of the coolant surface increases because of the combined effect of the leakage and evaporation of the coolant from the pool.

The cumulative effect of leakage, evaporation, refilling of fresh coolant, material input into the pool and any changes in the geometry and slope of the pool are monitored by measuring the level 28 of the cooling water surface 16. A sudden change in the height without measured leakage is recognized by the computational assembly or as a change in the geometry (slope). or the introduction of material into the pool, the characterization of an extreme event can be complemented by the recognition of specific patterns of cooling water surface waves, where the computational assembly 42 detects the seismic activity of the terrain. Parallel control performs an independent measurement of the acceleration 40 of the pool structure. Smaller amplitudes of surface fluctuations with negligible acceleration readings are identified by the system as refreshing or showering.

In the case of a monotonous lowering of the cooling water surface 12 with a coolant temperature of 30 below the boiling point, the cooling water surface lowering speed is directly matched by measuring the leakage of 26 coolant from the pool. Based on the latter measurements, the system computing unit 42 characterizes the damage to the pool envelope and predicts the occurrence of an emergency with significantly greater accuracy and precision than is possible by measuring the trend in the cooling water level 12 or even by measuring the dose rate 38 at the edge of the pool. When the coolant 16 reaches the boiling point, the computational assembly 42 also considers the contribution due to evaporation.

The spillage over the edge of the pool is identified by the system by a discontinuous change in the water level 12 of the cooling water 16 and a specific flow of the leakage signal 26. While a possible change in the geometry of the pool adversely affects the accuracy of characterizing the damage of the envelope 22 and the prediction of the event, a possible change in the slope of the pool is reflected by a deviation measuring the level of water at different locations of the pool and deviation of the measured values from the expected dose rate near the pool. As a result, the calculated site of damage to the pool envelope is not characterized by height, but is defined by a plane parallel to the surface of the cooling water and which defines the further calculation of the emergency development forecast.

Due to the reliability and accuracy of characterization and computational forecasts, and due to the unpredictable consequences of an emergency, the system uses multiplicity and diversity of measured parameters. Based on the measurement uncertainty analysis, the computational assembly 42 of the device determines a hierarchy of selected input parameters that allow for the most accurate characterization of the envelope damage and the prediction of an emergency. Computational unit 42 updates the current characterization of the envelope damage and the forecast of an emergency with new computational results.

The description of the preferred embodiments and the accompanying drawings are intended only to illustrate the invention and the positive effects associated therewith and do not bring any limitations. The purpose of the invention is summarized in the appended claims.

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Legend

Spent Fuel System / Unit Meter

Spent Fuel Pool / Used Fuel Pool

Nuclear Fuel Package / Fuel Element

Thermal power of residual heat

Cooling water

Cooling room for maneuvering

Portable channel

Damage to spent fuel tank wrap 12

Coolant collector

Flowmeter for levee collection 24

Coolant water level meter

Refrigerant temperature sensor in spent fuel tank 12

Controlled inflow of fresh coolant

Fresh coolant flowmeter

Fresh air coolant temperature sensor

A dose rate meter at the edge of the pool

Seismometer

Computational circuit

Display assembly

Claims (21)

PATENT APPLICATIONS 1) A method for characterizing the damage of a spent fuel system liner 10, characterized in that it comprises: measuring the leakage of a coolant (16) from said system (10), preferably obtained by a flowmeter (26) on the coolant reservoir (24); the step of determining the size and location of damage to the sheath (22) in said spent fuel system (10), based on said monitoring of the coolant leakage (26); and a prediction of the development of the level of the coolant level in said spent fuel system (10) based on the known characterization of the damage to the wrapper. 2) The method of claim 1, further comprising the step of periodically repeating the measurements of the coolant leakage (16) and periodically updating the results of the computational characterization of damage to the system envelope and periodically updating the results of the computational prediction of the level of the coolant level in the system monitoring of repeated measurements of the mentioned parameters. 3) The method according to claim 1 or 2, further comprising the step of predicting the development of radiation levels, in particular predicting the dose rate near the spent fuel pool (10), and based on the prediction of the level of cooling water level. The method of any of the preceding claims, further comprising the step of monitoring the radiation level near the spent fuel pool (10) and predicting the development of the coolant level in said pool (10) and / or predicting the development of the expected dose rate near said pool (10) and based on monitoring the measured values of coolant leakage from the system and the dose rate near said pool. The method according to any one of the preceding claims, characterized in that it further comprises the step of continuously monitoring the measured quantities of fresh refrigerant (34) flow into the system (10) and / or the temperature of said coolant (36) and / or the height (28). coolants in the spent fuel pool (12) and / or temperatures (30) of said coolant (16) in said system (10) and forecasts of the level of cooling water level in the spent fuel pool (12) based on the measured / calculated residual heat output and heat losses, the fresh coolant (34) inflow into the system (10) and / or the temperature of said fresh coolant (36) and / or the coolant level (28) in the spent fuel pool (12) and / or to the temperatures (30) of said coolant (16) in said system (10). »· Method according to any one of the preceding claims, characterized in that it further comprises the step of measuring the seismic activity (40) of the spent fuel system structure (10) and / or measuring the slope of said system structure (10) and predicting the level of the cooling surface level water in said system (10) based on the measured seismic activity and / or slope of said system structure (10). Method according to any one of the preceding claims, characterized in that it further comprises the step of measuring the seismic activity (40) of the structure of said system (10) and / or measuring the slope of said structure of the system (10) and the step of characterizing an emergency event based on monitoring the measured values of coolant leakage from the system and / or monitoring said seismic activity and / or measuring the slope of said system structure (10) and the known geometry of said system. The method of claim 7, further comprising the step of characterizing the system envelope damage or determining the size and location of the envelope damage (22) in the spent fuel system (10) and based on monitoring the measured values of coolant leakage from said system and emergency characterization. The method of claim 8, further comprising the step of continuously monitoring the measured quantities of fresh refrigerant flow (34) into the system (10) and / or the temperature of said coolant (36) and / or the height of the pool coolant (28) (12) for spent fuel and / or temperature (30) of said coolant (16) in said system (10), the size and location of said damage of the sheath (22) being determined on the basis of said monitoring of the measured values of coolant leakage from said system, monitoring the measured quantities of fresh coolant (34) flow into the system (10) and / or the temperature of said coolant (36) and / or the height of the coolant level (28) in the spent fuel pool (12) and / or the temperature (30) of said coolant ( 16) in said system (10). A method according to claim 8 or 9, characterized in that the prediction of the development of the level of the coolant level in said system is made on the basis of the characterization of an emergency and the said characterization of damage to the system envelope. • · Method according to any one of the preceding claims, characterized in that the step of predicting the development of the level of the coolant level in said system (10) includes the step of estimating the evaporation of the coolant from said system, the estimation of the intensity of evaporation based on said monitoring of the measured leakage values and supplying fresh coolant (34) to the spent fuel system (10) and / or at the temperature of said coolant (36) and / or at the level of the coolant level (28) in the spent fuel pool (12) and / or at temperature (30 ) of said coolant (16) in said system (10) and on measured / calculated residual thermal power of fuel elements (14) and on heat losses of system (10). 12. An apparatus for characterizing the damage of a spent fuel system liner (10), characterized in that it comprises: a liquid flowmeter (26) adapted to measure the overall coolant leakage (16), which is preferably collected from said spent fuel system (10) in a dedicated reservoir (24); and a computational assembly (42) connected to said flowmeter (26) and adapted to receive the measured data from said meter (26), said measurement unit (42) of the device adapted to calculate the size and location of the envelope damage (22) in said spent fuel system (10) and for predicting the development of the level of coolant level in said system (10) based on said damage characterization. Apparatus according to claim 12, characterized in that the measuring assembly of the device further comprises a radiation dose rate meter (38) located near said spent fuel pool (12) and said meter (38) adapted to measure ionizing radiation in the vicinity of said spent fuel pool (10), wherein the computational assembly of the device (42) is adapted to predict the development of the level of coolant level in said spent fuel system (10) and / or to predict the development of dose rate near said pool, based on monitoring the measurements of refrigerant leakage from the spent fuel system and monitoring the dose rate measurements near said pool. Apparatus according to claim 12 or 13, characterized in that the measuring assembly of the device is further adapted to monitor the measured quantities of fresh coolant (34) flow into the system (10) and / or the temperature of said coolant (36) and / or the height ( 28) the coolant in the spent fuel pool (12) and / or temperature (30) of said coolant (16) in said system (10) and said computational assembly of the device (42) adapted to predict the development of the level of coolant level in the spent fuel pool fuel (12) based on the measured / calculated values of the heat losses of the system and the heat flow of the residual heat of the pool fuel and / or the fresh coolant flow into the system (10) and / or the coolant temperature and / or coolant level in said system (10) and / or at said temperature of said refrigerant (16) in said system (10). • · Apparatus according to any one of claims 12 to 14, characterized in that the measuring assembly of the device is adapted for measuring seismic activities near the structure of the spent fuel system (10) and / or for measuring the slope of said spent fuel system structure (10) ), and said computational assembly (42) of the apparatus being adapted to predict the development of the cooling water surface level in said system (10) based on the measured seismic activity and / or on said slope of said system structure (10). Device according to any one of claims 12 to 15, characterized in that the measuring assembly of the device is adapted for measuring the seismic activity (40) of the structure of the spent fuel system (10) and / or measuring the slope of said structure of the system (10) and a computational assembly (42) of an apparatus adapted to perform an emergency characterization based on monitoring the measured values of coolant leakage from the system and / or monitoring said seismic activity and / or measuring the slope of said system structure (10) and the known geometry of said system. Device according to claim 16, characterized in that the computational assembly of the device (42) enables the characterization of the system envelope damage or the calculation of the size and location of the envelope damage (22) in the spent fuel system (10) and based on monitoring of measured leakage values refrigerants from said system and emergency characterization. Device according to claim 17, characterized in that the measuring assembly of the device is adapted for continuous monitoring of the measured quantities of fresh coolant flow (34) into the system (10) and / or temperature of said coolant (36) and / or surface height (28). refrigerants in the spent fuel pool (12) and / or temperatures (30) of said coolant (16) in said system (10), and wherein the computational assembly (42) of the apparatus enables the calculation of the size and location of said damage to the wrapper (22) is based on said monitoring of measured values of coolant leakage from said system, monitoring of residual heat output and heat losses, monitoring measured values of fresh coolant flow (34) to the system (10) and / or temperature of said coolant (36) and / or surface height ( 28) refrigerants in the spent fuel pool (12) and / or temperatures (30) of said coolant (16) in said system (10). Apparatus according to claim 17 or 18, characterized in that the computational assembly (42) of the device is adapted for predicting the development of the level of coolant level in said system (10) and based on the characterization of an emergency and / or monitoring of residual heat output and heat losses and / or on the basis of said characterization of the sheath damage, i.e. based on the calculated sizes and location of said sheath damage (22). • · · · 29 ..... * Apparatus according to any one of claims 12 to 19, characterized in that the computational assembly of the appliance (42) is adapted to calculate an estimate of the evaporation of the coolant from said system, the estimation of the intensification of the evaporation based on said monitoring of the measured leakage values and the fresh inflow. coolant (34) to the spent fuel system (10) and / or at the temperature of said coolant (36) and / or at the level of surface (28) of the coolant in the spent fuel pool (12) and / or at temperature (30) of said coolant (16) in said system (10) and on the measured / calculated residual thermal power of the fuel elements (14) and the heat losses of the system (10). 21. The apparatus of claim 12 to 20, characterized in that the computer program includes computer-readable instructions and performs computational operations in a manner that involves and executes the method.