Heater Pin Research Articles

Experimental investigation of partially ballooned fuel bundle under low injection flow rates

A postulated loss of coolant accident in a PWR with failure of emergency core cooling systems causes loss of heat sink for the fuel pins. Overheating of the fuel pins and difference in the internal and external pressures leads to clad ballooning over large portion of the fuel pin length. The re-flood behaviour of ballooned fuel pins has been studied extensively in the past for ballooned heater pin configurations, with up to 20 cm ballooned length of the total length, and with water injection rates typically equal to Emergency Core Cooling System (ECCS) injection rates. An experimental setup is thus developed to study the effect of large extent of ballooned region (up to 60 cm of the total length) on the re-flood behavior. The experimental setup employs 5 × 5 matrix of indirectly heated, pre-fabricated ballooned fuel pin simulator (FPS) surrounded with 20 heated non-ballooned and 12 dummy FPS. The objective of this experiment is to study the effect of water injection rate and initial temperature on the quenching behaviour of ballooned heated pins under bottom re-flood condition. The water injection rates are kept lower (0.11–0.45 g/s per unit length per FPS) than the typical SAMG injection flow rates for typical PWR (1.12 g/s per unit length per fuel pin) and the initial temperatures range from 260 °C to 650 °C. In all experiments FPS are observed to be quenched, and enhanced quenching is observed in the ballooned region towards the exit of the region owing to lesser carryover. Increase in water injection flow rate is found to result in a transition in the rewetting pattern from conduction controlled rewetting to fluid controlled rewetting.

Investigation of Effect of Ballooned Fuel Pins on Quenching Behavior: Design of Experiment and Preliminary Analysis

Heat transfer characteristics of intact fuel pins under reflood conditions have been extensively studied to understand the quench behavior of a typical pressurized water reactor (PWR). Overheating of fuel pins due to loss of nucleate boiling under exposed conditions causes the clad to balloon over large portions of the fuel pin length (up to 60%). The reflood behavior of ballooned fuel pins has been studied experimentally for ballooned heater pin configurations with an up to 15% ballooned length of the total length. Substantial changes in the reflood behavior are observed for a higher extent of the ballooned region. An experimental setup is thus being developed to study the effect of the large extent of the ballooned region (up to 60% of the total length) on the reflood behavior. The experimental setup employs a 5×5 matrix of indirectly heated fuel pins surrounded by 32 dummy fuel pins. The scaling analysis carried out for the design of the experimental setup is presented here. The nondimensional π terms pertaining to the quench phenomena have been conserved as compared to the typical PWR values. The evolution of some of the nondimensional π terms under reflood conditions has been discussed for simulations done with RELAP5 for ballooned as well as nonballooned test cases. Delayed quenching is observed in the extended ballooned fuel pins due to poor heat transfer in the ballooned region.

High temperature dissolution of oxide deposits formed over structural materials under PHWR and BWR chemistry conditions

A formulation consisting of nitrilo triacetic acid (NTA) and hydrazine at high temperature (160 °C) was optimized for its application in cleaning an SS-316 “High Temperature High Pressure (HTHP) re-circulation system”, which was operated under Pressurized Heavy Water Reactor (PHWR) chemistry conditions. This system was contaminated with magnesium ions released from a failed heater pin. The attempt was successful with the removal of 110 g of iron, 35 g of magnesium along with chromium and nickel with acceptable corrosion of structural materials.The same formulation was tested for its efficiency in dissolving oxides formed under Boiling Water Reactor (BWR) conditions on SS-304 surfaces. Characterization of the oxide was carried out by wet chemical methods and by various surface techniques viz., SEM-EDAX, XRD, XPS and Laser Raman spectroscopy. SEM showed the presence of two distinct layers of oxide and XRD showed the oxide to be spinels as the major phase along with haematite (α-Fe2O3). The average thickness of the oxide coating was found to be 0.7 μm. NTA-hydrazine formulation at 160 °C was able to dissolve the oxide in a single step without requiring any oxidation step.

Numerical simulation of MHD effects on convective heat transfer characteristics of flow of liquid metal in annular tube

A numerical study is conducted in an annular duct formed by a SS316 circular tube with electrically conducting walls and a coaxial heater pin, with liquid Lithium as the working fluid for magnetic field ranging from 0 to 1 T. The Hartmann and Stuart number of the study ranges from 0 to 700 and 0 to 50 respectively. The Reynolds number of the study is 10 4. It was shown that the convective heat transfer and hence the Nusselt number decreases near the walls perpendicular to the magnetic field due to reduction in turbulent fluctuations with increase of magnetic field. It was observed that the Nusselt number value increases near the walls parallel to the magnetic field as the mean velocity increase near the walls. A singular rise was observed near both the walls near Stuart number ∼10 which is due to the increase of turbulence levels in the process of changing from turbulent to electromagnetically laminarized flow. When a very low Reynolds number ∼300 is used, the reduction in Nusselt number near the perpendicular walls is less. This shows that the reduction in Nusselt number near the perpendicular walls for the high Reynolds number study is due to the reduction in turbulent fluctuations. The Nusselt number was found to increase near the parallel walls as the mean velocity increases near the walls. When an insulating duct is used the Nusselt number near the parallel walls did not increase for the case with insulating walls as in the case with conducting walls showing the contribution of the ‘M’ shaped velocity profile in the Nusselt number increase near the parallel walls. The Nusselt number near the perpendicular walls was found to decrease at a higher rate in case of insulating walls than that of the study with conducting walls.

Assessment of Applicability of Two-Fluid Model Code ACE-3D to Heat Transfer Test of Supercritical Water Flowing in an Annular Channel

A supercritical-water-cooled reactor (SCWR) is a high-temperature, high-pressure water cooled reactor that operates above the critical pressure of water. In order to perform efficiently the thermal design of the SCWR, it is important to assess the thermal hydraulics in rod bundles of the core. Experimental conditions of mockup tests, however, may be limited because of technical and financial reasons. Therefore, it is required to establish an analytical design technique that can extrapolate experimental data to various design conditions of the reactor. Japan Atomic Energy Agency (JAEA) has improved the three-dimensional two-fluid model analysis code ACE-3D, which was originally developed for the two-phase flow thermal hydraulics of light water reactors, to handle the thermal hydraulic properties of water in the supercritical region. In the present study, heat transfer experiments of supercritical water flowing in a vertical annular channel around a heater pin, which were performed at JAEA, were analyzed with the improved ACE-3D to assess the prediction performance of the code. As a result, it was implied that the ACE-3D code is applicable to the prediction of wall temperatures of a single rod that simulates the fuel bundle geometry of the SCWR core.

Assessment of Applicability of Two-Fluid Model Code ACE-3D to Heat Transfer Test of Supercritical Water Flowing in an Annular Channel

A supercritical-water-cooled reactor (SCWR) is a high-temperature, high-pressure water cooled reactor that operates above the critical pressure of water. In order to perform efficiently the thermal design of the SCWR, it is important to assess the thermal hydraulics in rod bundles of the core. Experimental conditions of mockup tests, however, may be limited because of technical and financial reasons. Therefore, it is required to establish an analytical design technique that can extrapolate experimental data to various design conditions of the reactor. Japan Atomic Energy Agency (JAEA) has improved the three-dimensional two-fluid model analysis code ACE-3D, which was originally developed for the two-phase flow thermal hydraulics of light water reactors, to handle the thermal hydraulic properties of water in the supercritical region. In the present study, heat transfer experiments of supercritical water flowing in a vertical annular channel around a heater pin, which were performed at JAEA, were analyzed with the improved ACE-3D to assess the prediction performance of the code. As a result, it was implied that the ACE-3D code is applicable to the prediction of wall temperatures of a single rod that simulates the fuel bundle geometry of the SCWR core.

Salvation of S. S. Surge Tank for HTHP Loop

As constituents of nuclear industry, we all know the significance of the stringent specification to the practical level on the manufacture of nuclear components. More so for the primary system of High Temperature High Pressure Loop (HTHP) situated at Water & Steam Chemistry Division (WSCD). The pressurizing of the system is done by heating through immersion heaters provided in the surge tank. The surge tank, at its rated condition, has steam on the top, above the water level. The surge tank has got a l5 0 NB size nozzle at the bottom dished end. A 1500 # flange is welded to this nozzle. The heater unit of the surge tank is connected to this flange. The heater unit consists of a 150 NB, 1500 # blind flange (tube sheet) with eight number of SS U-type immersion heater pins welded to it. Welding of stainless steel heater pin is a demanding task. The task becomes even greater when the job involves welding of 16 pins with a triangular pitch of 25 mm, such as those for the high temperature & pressure loop. Actually, the tank was manufactured by a private firm. During final leak testing, it was found that there were leaks through the heater pins to sleeve welding in three of the heater pins. They could not rectify the leak. Subsequently, the rectification of the weld was referred to CWD. A novel technique was developed and due care was taken to weld the heater pins. The tank was successfully salvaged and tested hydrostatically at 170 bars and pneumatically at 7 bars. The method of fabrication of heater assembly, problems anticipated, problems encountered and measures taken to solve them are dealt with.

Study on Pb-Bi-water direct contact boiling two-phase flow and heat transfer

For the development of 45w%Pb-55w%Bi cooled direct contact boiling water small fast reactor (PBWFR), Pb-Bi-water direct contact boiling two-phase flow loop has been fabricated and operated. The loop consists of a Pb-Bi flow loop (four heater pin bundle, a chimney, an upper plenum, a level meter tank, an air-water cooler, and an electromagnetic flow meter) and a water-steam flow loop (a pump, a preheated, an injection nozzle, the chimney, the upper plenum with mist separators and dryers, a condenser, a buffer tank, and an air-water cooler). At the rated operating condition system pressure is 7 MPa. The sub-cooled water was injected into a Pb-Bi flow in the chimney. A power of the heater pin bundle was controlled to obtain the inlet and outlet temperatures of the heater bundle. The Pb-Bi and steam flows were simulated analytically using one-dimensional models of frictional and form losses and a drag force. The Pb-Bi-steam two-phase frictional pressure loss was calculated by means of the two-phase flow multiplication factor of Lockhart-Martinelli model. It was found that Pb-Bi temperature decreased quickly in the chimney due to high heat transfer rate of Pb-Bi-water direct contact boiling. The volumetric overall heat transfer coefficient was 60–310 kW/m 3K, and decreased with the superheat.

Heat transfer enhancement in lithium annular flow under transverse magnetic field

Magnetohydrodynamic (MHD) effect on heat transfer in liquid lithium annular flow was investigated with an emphasis on heat transfer enhancement and local turbulence. A test section was made of 10 mm heater pin and 2 in. B pipe of 304SS. The experiment covers ranges of U=0.1–3 m/s ( Re=4×10 3–1.4×10 5), B=0–0.8 T ( Ha=0–3×10 3). The heat transfer was observed to increase over a region of St from unity to 100, and the peak value was 5–10% higher than that for B=0 T. This was explained as a result of local turbulence enhancement in the vicinity of the heating wall. A new concept of heat transfer diagram was proposed with considering a current load factor of the test channel.

Forced Convection Heat Transfer and Temperature Fluctuations of Lithium under Transverse Magnetic Fields

The MHD effects on a heat transfer of liquid lithium flowing in an annular channel were studied, using a newly constructed comparatively large-scale lithium loop. The data on the heat transfer characteristics were arranged in Nu-St diagrams where St=Ha2/Re. The diagrams indicate that Nu decreases as St increases as a whole trend. However, singular peaks of Nu were observed at about St=13, corresponding to the singular increments of temperature fluctuations, whereas the peaks occurred at St=1.5 in the previous experiment with a smaller channel. In considering a predominant MHD effect due to conductive wall duct, the current load factor KP for external circuit was taken into account. And Miyazaki number Mi=KPSt, which means the effective electromagnetic interaction, was adopted in substitution for St and the heater pin diameter was taken as the characteristic length in place of the conventional hydraulic equivalent diameter. Thus, an appreciably good agreement was obtained concerning the peaks at Mi=0.13 in the previous and at Mi=0.14 in the present experiments. Generation of vortex series in the singular phenomena was suggested from both the periodicity of temperature fluctuations in their PSD analysis and the proportionality between peak frequency and mean flow velocity, resulting in a 32 mm interval length of series.

Natural convective heat transfer of lithium under magnetic field

The magnetohydrodynamic (MHD) effect on a natural convection heat transfer of liquid metal lithium was experimentally studied. The test section consisted of a lithium pool and, a heater pin, which was settled in the center of the pool. The results are summarized as follows, (1) with increasing B ( Ly≥50), the Nusselt number decreased to 70 of the highest value at 0.05 T of the magnetic field; (2) large scale circulation flow profile and temperature profile were found to change drastically with the application of the weak field of 0.01 T.

Natural circulation in parallel vertical channels with different heat inputs

When forced circulation of the coolant is lost in a gas cooled reactor, natural circulation takes place in the reactor core. Natural circulation in the many parallel vertical channels with different heat inputs is quite complicated because the flow rate and direction depend on the time history of the heat input of each channel. Since only a few previous studies were concerned with this problem, an experimental and analytical study was performed to investigate the natural circulation in an array of parallel channels with different heat inputs. The experimental apparatus consisted of four vertical channels filled with water. Each channel was furnished with a heater pin and heated by various combinations of time-varying heat inputs. Flow velocity of the water was measured, and an abrupt change of the flow direction was observed. An analytical code predicted well the experimental results.

Natural Convection Heat Transfer of Liquid Lithium under Transverse and Parallel Magnetic Fields

Stagnant liquid lithium contained in a vertically 1.3 m long and 46 mm I.D. 316-SS cylindrical vessel up to a 0.3 m level was heated by a concentrically inserted heater pin of 12.5 mm O.D. and 54 mm active length. The parallel magnetic field to the vessel was imposed by a superconducting magnet. The experiment covered the ranges of the lithium temperature: 320∼510°C, the heat flux: 10∼40 W/cm2, the transverse B: 0∼1.2 T (Ha = 0∼2,730) and the parallel B= 0∼3T (Ha = O∼6,860). The temperature fluctuation is enhanced by imposing a weak magnetic field of B = 0.1 ∼ 0.3 T for both parallel and transverse fields and almost completely suppressed with increasing to B = 1 T in the case of the transverse field but its low frequency component still remains large, becoming oscillatory, up to B = 3 T in the case of parallel field. The heat transfer shows a similar trend to the temperature fluctuation. It increases singularly by a weak B especially in the perpendicular sector to the transverse magnetic field and decreases with increasing B. In the case of parallel magnetic field, the heat transfer increases in a weak field of B = 0.1 ∼ 0.5 T, the same as in the transverse magnetic field, but it does not decrease so much in a strong field of B = 1∼3 T, presenting a rather higher value than in B = 0 T.

Natural convection heat transfer of liquid lithium under transverse and parallel magnetic fields.

Stagnant liquid lithium contained in a vertically 1.3 m long and 46 mm I.D. 316-SS cylindrical vessel up to a 0.3 m level was heated by a concentrically inserted heater pin of 12.5 mm O.D. and 54 mm active length. The parallel magnetic field to the vessel was imposed by a superconducting magnet. The experiment covered the ranges of the lithium temperature: 320510°C, the heat flux: 1040 W/cm2, the transverse B: 01.2 T (Ha = 02, 730) and the parallel B = 03T (Ha = 06, 860).The temperature fluctuation is enhanced by imposing a weak magnetic field of B = 0.10.3 T for both parallel and transverse fields and almost completely suppressed with increasing to B = 1 T in the case of the transverse field but its low frequency component still remains large, becoming oscillatory, up to B = 3 T in the case of parallel field. The heat transfer shows a similar trend to the temperature fluctuation. It increases singularly by a weak B especially in the perpendicular sector to the transverse magnetic field and decreases with increasing B. In the case of parallel magnetic field, the heat transfer increases in a weak field of B = 0.10.5 T, the same as in the transverse magnetic field, but it does not decrease so much in a strong field of B = 13 T, presenting a rather higher value than in B = 0 T.

Heat transfer and temperature fluctuation of lithium flowing under transverse magnetic field.

For providing background information on the liquid metal cooling of fusion reactors, the MHD effects on heat transfer of flowing lithium was experimentally studied with an emphasis on temperature fluctuations. The test section was constituted of a 15.8 mm I.D., 1.65 mm thick, 316-SS tubing and a 7.6 mm O.D. heater pin with nine 0.5 mm thermocouples. The experiment covered the range of B=0–1.0 T, U=0.2–4.0m/s, T=320–390°C and q=0–68 W/cm2. The results are summarized as follows: (1) With increasing magnetic flux density B, Nusselt number Nu decreases to a value of flat flow velocity model: 6.38 but rises in B=0.1–0.4T. (2) The RMS of temperature fluctuation has strong dependence on B and presents a peak near B=0.25T. (3) The singular rise of Nu is inferred to result from enhanced turbulence due to steepening of radial gradient of velocity near the wall as a result of MHD effect. (4) The transit velocity estimated from temperature cross-correlation in the parallel sector coincides with the mean velocity when...

Natural circulation in parallel vertical channels with different heat inputs.

When forced circulation of the coolant is lost t in Gas Cooled Reactor, natural circulation takes place in the rector core. The natural circulation among the many parallel vertical channels with different temperatures is quite complicated because the flow rate and direction depend on the time history of the channel temperatures. Since only a few previous studies were concerned with this problem, an experimental and analytical study was made on the natural circulation in many parallel channels with different heat inputs. The experimental apparatus consisted of four vertical channels filled with water. Each channel was furnished with a heater pin and heated by various combinations of time-varying heat inputs. Flow velocity of the water was measured, and an abrupt change of the flow direction was observed. An analytical code predicted well the experimental results.

Heat Transfer in Nucleate Boiling of Oil-freon Rll3 Mixtures : 1st Report, Effect of Oil Concentration on Boiling Heat Transfer

This paper describes heat transfer studies in nucleate boiling of polyolester oil and freon R113 binary mixtures done to obtain design data on heat transfer performance characteristics of an evaporator. Pool boiling experiments were performed around horizontal straight heater pin at atmospheric pressure, heat flux was changed from 0 to 70 kW/m2, and mixture oil concentrations from 0 to 100 weight %. These data were compared with published studies on oil-freon binary mixtures. The oil concentration influenced the heat transfer coefficient of oil-freon R113 mixtures ; with lage oil concentrations, a remarkable reduction in heat transfer occurred. Then based on the data, an empirical correlation for the heat transfer coefficient of oil-freon R113 mixtures was obtained. The correlation included terms for wall superheating of freon R113, oil temperature difference, and oil mole fraction. Comparisons were made between experimental and calculated results. The proposed correlation was found valid for the prediction of heat transfer coefficients of oil-freon R113 mixtures.

Flow and Heat Transfer Characteristics in Lithium Loop under Transverse Magnetic Field

A medium-scale lithium-loop with 40 l/min and 3bar ratings was constructed to gain basic information on MHD effects on the flow and heat transfer characteristics. The loop has two parallel test sections for pressure drop and heat transfer experiments, which were made of 15.75 mm I.D. and 19.05 mm O.D. 316-SS tubes and placed between magnet poles of 500 mm vertical length. The pressure drop test section was provided with two strain gage type pressure transducers and the heat transfer test section with a 300 mm long 7.6 mm O.D. high flux electric heater pin. The experiment covered the ranges of the magnetic flux density: 0-1.0 T, The Li flow velocity: 0.2 -5.0 m/sec, the heat flux: 0-120 W/cm/sup 2/ and the Li temperature: 350-400/sup 0/C. The experimental results of potential and pressure drop agreed well with the theoretical prediction based on the uniform-velocity thick wall model. The heat transfer coefficient, or Nusselt number, was decreased with increasing magnetic flux density, but not monotonically in a weak magnetic field region of 0.2-0.4 T, where a singular phenomenon, i.e. an elevation of Nusselt number was observed.

Boiling of Potassium in Vertical Tube under Transverse Magnetic Field

The experimental study was conducted to examine the applicability of boiling potassium two-phase flow to the blanket cooling of fusion power reactors. A high flux heater pin of 44mm heating length and 6.5mm O. D. with eight thermocouples of 0.5mm O. D. was inserted from the bottom of a vertical channel which was made of a 4m long, 14.9mm I.D. and 17.5mm O. D. stainless steel tube and placed in a D.C. magnet of 50cm long poles. The experimental conditions were the heat flux: 0~67W/cm2, the magnetic field strength: 0~1.8T, the Ar cover gas pressure: 1.0bar, the potassium level above heater: 1.8m, and the temperature of upper unheated section: 400°C. In the absence of magnetic field, boiling occurred intermittently, repeating the cycles between superheating with moderate temperature fluctuation and desuperheating with condensing shock pulses. When a weak magnetic field was applied, the temperature fluctuation was enhanced by natural convection, the incipient boiling superheat was reduced, and the boiling pattern became continuous. With increasing the magnetic field strength, the fluctuation was suppressed and the incipient boiling superheat increased but tended to level off around 1.5 T. Violent incipient boiling caused by a large superheat inherent in liquid metals was mitigated by magnetohydrodynamic interaction under a transverse magnetic field of 1.0T or larger, and subsequently followed by continuous saturation boiling with small fluctuation. No burn-out of the heater pin occurred in spite of symptom of dryout within the experimental range: q=67W/cm2 and B=1.5T.

Boiling of potassium in vertical tube under transverse magnetic field.

The experimental study was conducted to examine the applicability of boiling potassium two-phase flow to the blanket cooling of fusion power reactors. A high flux heater pin of 44mm heating length and 6.5mm O. D. with eight thermocouples of 0.5mm O. D. was inserted from the bottom of a vertical channel which was made of a 4m long, 14.9mm I.D. and 17.5mm O. D. stainless steel tube and placed in a D.C. magnet of 50cm long poles. The experimental conditions were the heat flux: 0~67W/cm2, the magnetic field strength: 0~1.8T, the Ar cover gas pressure: 1.0bar, the potassium level above heater: 1.8m, and the temperature of upper unheated section: 400°C. In the absence of magnetic field, boiling occurred intermittently, repeating the cycles between superheating with moderate temperature fluctuation and desuperheating with condensing shock pulses. When a weak magnetic field was applied, the temperature fluctuation was enhanced by natural convection, the incipient boiling superheat was reduced, and the boiling pat...