Category Archives: Nuclear

Neutron measurement system for TRIGA® reactors

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Introduction

Neutron flux mapping is key for research reactors operators. Over years this mapping can change from the theoretical configuration and a requalification of the in pile neutron flux can be required to maintain a safe operation and the expertise in reactor physics.

The challenge : develop an efficient and cost effective solution for neutron flux measurement for research reactor.

GENERAL ATOMICS designed the TRIGA reactor in the 50s and it became the most important research reactor fleet in the world.

THERMOCOAX has been awarded a contract to develop a neutron flux monitoring system for a TRIGA reactor in Malaysia.

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Reactor pool

Based on this successful experience, THERMOCOAX is now offering to market the NEUTROCOAX system, developed with the assistance of SCK.CEN in BELGIUM.

The benefits of NEUTROCOAX® system : a modular and real time solution for neutron flux measurement.

Activation dosimetry is a well-established and accurate method but it is not offering an online data acquisition but only “a posteriori” information on neutron flux.

Based on NEUTROCOAX SPND (Self Powered Neutron Detector) our solution iuses a robust, simple, self-powered and cost-effective sensor compared to other technologies associated with the state-of-the-art data acquisition system.

NEUTROCOAX SPND generates a current proportional to the reactor power.

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Recorded Currents of Vanadium SPNDs (nano Amperes) versus reactor power (MW). Test performed in BR2 reactor (SCK.CEN)

SPND is directly immersed in the reactor pool to do an in situ measurement. 4 x SPND are supplied as standard, but more SPND can be connected.

The NEUTROCOAX® system comprises SPND associated with a data acquisition system and a measurement Display Unit.

It offers a measurement on a wide spectrum ranging from 0.05% to 100% of the reactor power (i.e. 6.109 to 2x 1013 nv in the specific TRIGA in Malaysia) and a real time visualisation of the measurement. There is no upper limit in terms of neutron flux, and the SPND signal remains linear with the reactor power (see curve above).

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Fluxes versus time as seen on the display unit

This versatile system can also be used to monitor irradiation samples during material test irradiation or radio medical isotope irradiation.

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SPND cabling from the sensitive head to the junction box

 

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SPND sensitive head. Vanadium emitter. Small Outer diameter of 3.7 mm

THERMOCOAX and nuclear sensors

THERMOCOAX Nuclear specialised in In-core and Ex-core sensors such as :

  • Radiation sensors (neutron flux & gamma flux)
  • Temperature measurement
  • Level and flow measurement

We also offer SERVICES such as DESIGN, EXPERTISE, INSTALLATION, and COMMISIONING.

 

TRIGA® is a trade mark of GENERAL ATOMIC

SCK.CEN is the Belgian Nuclear Research center. See www.sckcen.be

 

Corrosion Cracking of Pressurizer Heaters in Nuclear Power Plants

Nuclear, , , , ,

Introduction

Pressurizer heaters in Nuclear Power Plant are subjected to the most severe working conditions in the primary loop. They cumulate mechanical, thermal and electrical stresses.

Since the nineties, incidents of pressurizer heaters using 316L grade sheath tube in nominal primary water environment cracking have been encountered in many Nuclear Power Plants (Pressurized Water Reactor type).

This kind of incident is very detrimental in heaters due to possible leakage and dissolution of the MgO in the primary coolant. Costly unplanned downtime cannot be avoided.

Destructive testing has been conducted on damaged heaters to determine the origin of cracking.

In parallel, an R&D program has been implemented in order to understand the micro-mechanics and to determine the key factors for the occurrence of Primary Water Stress Corrosion Cracking (PWSCC) at 680 °F (360°C).

Based on this understanding of failure mechanisms, a program of experiments jointly run by EDF R&D and CEIDRE in collaboration with Thermocoax was conducted in order to develop a thermal treatment by induction heating.

The aim was to reduce the susceptibility to Stress Corrosion Cracking of the sheath material of pressurizer heaters while maintaining the electrical properties of mineral insulating material.

 The challenge : develop an efficient solution for pressurizer heater while maintaining superior reliability.

The challenge was to develop an efficient solution while maintaining the outstanding electrical performance over time of Thermocoax pressurizer heaters.

Due to its  53 nuclear power plants- EDF has compiled an impressive and unique database on the performance of standardized components over decades (year x experience). Thermocoax pressurizer heaters have demonstrated a superior electrical performance over time compared to other technologies over tens of thousands years of operational experience in nuclear power plants.

Nuclear safety had to be taken into consideration and the impact of modifications minimized to avoid “new” causes of failure. Thereby our approach was to define a thermal treatment having no possible effect on the insulating material of the heater.

From R&D to industrialization

Heat treatment modeling and laboratory tests conducted by EDF’s R&D enabled the feasibility and the efficiency of this kind of heat treatment by induction to be demonstrated.

Qualification tests helped in determining the key parameters for good results, in terms of hardness and residual stresses.

Thermocoax has implemented a fully automated superficial heat treatment by induction that meets EDF requirements in terms of distribution of hardness.

The new process was qualified on December 2010 and several hundreds of pressurizer heaters have been delivered to date.

 

The benefits of  pressurizer heaters Thermocoax technology combined with the EDF patented solution.

The surface annealing process based on induction heating developed to reduce the surface cold working and the residual stresses avoid any initiation of PWSCCwhile maintaining the electrical properties of the mineral insulating material.

A fully automated surface heat treatment by induction that meets EDF requirements in terms of distribution of hardness is now in operation.

EDF promotes safer power plants through risk mitigation and continuous improvement policies.  Despite a patent protecting this innovative thermal treatment, EDF encourages THERMOCOAX from proposing this solution to others utilities.

Four major international players have been persuaded so far and have replaced their equipment with our pressurizer heaters treated against Stress Corrosion Cracking.

THERMOCOAX PRZ heater design :

  • “Solid” construction with enhanced thermal conductivity
  • Thermal treatment and ultimately designed not to expand.

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THERMOCOAX and pressurizer heaters

Thermocoax has been continuously producing pressurizer heaters over the last 40 years and has the largest installed base in the world. Heaters can be designed and manufactured as replacements for installed heaters supplied by the same electrical and mechanical interface.

Our pressurizer heaters are eligible for all PWR designs with benefits such as:

  • rugged construction
  • compliant with construction codes
  • qualified thermal treatment
  • reduced MgO content
  • ultimately no expansion

Thermocoax has implemented two different quality assurance systems: ASME and ISO. Both systems have been audited and approved by major nuclear power plant builders.

If you need any further information, please contact :

sales@thermocoax-nuclear.com

 

 

Twisted MI cable against magnetic interferences

Nuclear, , , , ,

Thermocouple & Transmission cables for sensors in harsh environment and high magnetic interferences

Sensors manufacturer are looking for extension cables offering:
The lowest perturbation on sensor’s signal
A life time superior to the life time of the sensor itself.
If cable/sensor are exposed to adverse conditions like heat, fire, pressure, radiation or electro magnetic interferences, cabling solutions using organic compound do not offer sufficient life time nor maintain screening performance of measurement chain.

Turbines, large scientific instrument, fusion reactor, induction motors

Our nuclear experience initiated in the 50’s was the opportunity for a continuous improvement of the manufacturing technics of the Mineral Insulated cable.

As an answer to growing demand for cables insensitive to magnetic interferences, THERMOCOAX has developed a unique process to guarantee a steady twist of the cable conductors enhancing the EMC noise rejection characteristics.

A constant pitch of the twist of conductor pair cancel the induced currents and balance capacitances to ground..

The stainless steel sheath and –if required- additional layer of soft iron- provides a superior EMC screening than other cable systems.

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TWISTCOAX®

  • Cable design tailored to meet customer’s demand
  • Built on specification
  • Single pair or multiple pairs
  • No impact on outer sheath metallurgy
  • No organic compound: no thermal or radiation ageing
  • Cost effective process compared to others technologies

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Advantage of the twisted pair in high magnetic environment:

  • successive half-twists (pitch 2,5 cm / 1 inch) reduce magnetic noise by a factor higher than 100 compared to straight type
  • Balanced capacitances to ground

THERMOCOAX to build Long-Lived In-Core Instrumentation Assemblies for a R&D Project of KHNP.

Nuclear, , , ,

THERMOCOAX the expert in nuclear instrumentation has been awarded a contract with KHNP Central Research Institute, the Korean Electrical Utility, to manufacture and deliver in 2015 several Long-Lived In-Core Instrumentation Assemblies.

This innovative instrumentation based on neutron detectors and thermocouple will be demonstrated in the OPR 1000 in Korea.
This instrumentation will offer an enhanced life time compared to existing technologies without compromise on safety and reliability.
This project represents an important milestone in THERMOCOAX nuclear business unit expansion and pave the way for others applications with utilities or Tiers 1 instrumentation system supplier.
THERMOCOAX offers support to its customers through the design, delivery and support phases of a program. miller88 | Infographics | Graphs.net