NEI Steam Generators

8/17/2019 NEI Steam Generators

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JANUARY 2008www.neimagazine.com

I N T E R N A T I O N A LENGINEERINGNUCLEAR

P h o t o c o u r t e s y o f B r u c e P o w e r

GENERATOR BLASTINGGENERATOR BLASTINGCLEANING CANDU SG TUBESCLEANING CANDU SG TUBES


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Reprinted from Nuclear Engineering International, January 2008

STEAM GENERATORS

usually being cleaned at one time.

Preheaters can also be cleaned.Once the heavy water has been

emptied from the steam generator andit has been dried, remotely-controlledrobotic manipulators are used to con-nect equipment to the tubesheet todeliver the blasting material into thesteam generator tubes. The blastmaterial is recycled; only the debris, orwaste material, is disposed of.

The cleaning equipment is a mod-ular system that can be adapted toany plant layout. Its major compo-nents include: shot delivery system;waste collection/vacuum system;robotic manipulator system; operatorcontrol system; and egress system.

The shot delivery system includes a

In November 2005, work began

at Bruce B in Ontario, Canadaon the first steam generators tobe cleaned using AECL’s

CANDUclean technology. Theprocess exceeded expectations in per-centage of ‘available’ (those that canbe reached with steam generator-specific tooling) tubes cleaned.

The CANDUclean system uses aspecial blasting material to loosen andremove fouling deposits from steamgenerators, while ensuring that theadjoining areas are not contaminated.The equipment is designed to operateautomatically and to be controlledremotely. Primary side cleaning canbe performed on multiple steam gen-erators in parallel, with four tubes

shot generator that meters shot into

the blast hose. The blast system fea-tures automatic shot loading, shotlevel indication, pressure control, leak detection, and has the ability to auto-matically accept the recycled shot.

The shot, transport air, and wastemagnetite are collected, vacuumedup and carried to the shot reclaimerwhere the recycled shot is aerody-namically separated from the wastemagnetite. The shot is fed back intothe shot generator for re-use, min-imising the amount of contaminatedshot within the waste volume.

The waste magnetite is moved by vacuum hoses into the downstream‘dust collector’ during blasting opera-tions. The dust collector houses a

A CANDU ® steam generator tube cleaning process results in

improved plant performance, significant reductions in radiation

fields and improved eddy current inspection signal-to noise ratios.

By Eric Wilson

Mechanical cleaning

for steam generators

During blasting operations, operators monitor robot

and blasting equipment position, alarm annunciations,

blast zone, and each tube’s blast status


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STEAM GENERATORS

dual, redundant filtration system thatseparates out the magnetite beforethe vacuum air is directed into theplant active ventilation system. At theend of the blasting process, the samedust collector serves as a waste con-

tainer. Once the cleaning campaignis completed, these waste containersare transported to long-term storageusing shielded flasks. The solid wasteconsists of removed oxide scales anddeposits, and spent blasting material,which is dry and chemically-inert.

Remotely-controlled roboticmanipulators are installed in thesteam generator primary head andprovide a reliable means of repeated-ly positioning the blasting equipmentin the specified tube location. Therobotic system is programmed offline

with the aid of 3D graphics simula-tion software, before the cleaning campaign begins. The simulationsoftware ensures that the manipula-tor fits inside the bowl and that itmoves in the most efficient pattern,avoiding collisions with the bowl,tubesheet, and any other obstructionsthat may be present. AECL carriesout system and software testing andprocess simulation before a cleaning campaign. A major advantage hasbeen the development of an effectivepath planning code and development

process, which is used to program therobot for the optimum cleaning pathfor each steam generator.

The robot’s four degrees of freedomand the small-sized blasting equip-ment typically enables 100% of thetubes and tubesheet to be reached.

Four tubes can be cleaned at onetime, in either one or two steamgenerators. In preheater cleaning campaigns, the equipment cleans twopreheaters at the same time.

CANDUclean is controlled by aseries of programmable logic con-

trollers (PLCs) and PCs networkedtogether and encompassing all aspectsof the cleaning process. Two humanmachine interfaces (HMIs) areimplemented: one that controls andmonitors the robotic manipulator anda second for the process system.

The process HMI displays what ishappening at every step of the blast-ing process and alerts operators toany alarms or trips that occur. Aswell, the blast cycle, including suchsteps as blasting, leak checking,purging and filter cleaning, are pre-programmed into the HMI. TheHMI also displays a tubesheet map,which presents a graphical displaywith each tube’s blast status marked.

At the completion of the project, adatabase containing information on

each tube of the steam generator isprovided to the client as a part of theproject completion report.

AECL’s CANDUclean team con-sists of a project manager along withengineers, planners, shift supervisors,operators and tradespeople, typicallyworking in two shifts, 24 hours a day. At its laboratories in Mississauga,Ontario, AECL uses full-scale mock-up models of the plant steam genera-tors – in conjunction with simulationsoftware – to prepare for major cam-paigns. The software used is a real-time, 3-D graphics-modelling packageused to design, simulate, and optimiseautomated systems and to programthem offline.

Building on the success of therecent campaigns at Bruce, AECL

is now conducting a feasibility studyto evaluate the use of CANDUcleanin decontaminating steam generatorsremoved from PWRs. The processcould lead to decontamination of thetubing so that the material could besalvaged. The modified process understudy involves reviewing and assessing more abrasive techniques that can yield increased decontamination fac-tors and reduced blasting times. Another possible application yet to beinvestigated is the cleaning of steamgenerators in operating PWRs.

Eric Wilson, Manager, Steam Generator Services,

AECL, 2251 Speakman Drive, Mississauga, Ontario,

L5K 1B2, Canada

AECL uses mock-ups of the CANDUclean blasting and robotic equipment to train personnel and to

develop and refine procedures


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Reliability. Safety. Performance. Responsiveness.

And a services team that’s always “on”.

At AECL, we understand your high expectations, andcan anticipate your needs. Find out how our nuclear

technology expertise, advanced engineering tools and

dedicated team can help you optimize your nuclear plant

performance, increase safety and reduce costs.

You expect nothing less

www.aecl.caAtomic Energy of Canada Limited

NEI Steam Generators

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