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Reducing Critical Path IVVI Time Through the Use of Submersibles Reducing Critical Path IVVI Time
Through the Use of Submersibles




ABSTRACT


Nuclear plant operators and service companies use submarines or Remotely Operated Vehicles (ROVs) to
cut costs and increase efficiency in four (4) ways. ROVs reduce outage time by taking most IVVI time off
the critical path, reducing the inspection manpower requirements, reducing total exposure and accelerating
delivery of specialized tooling into tight or remote areas. ROV performed tasks provide clear advantages in
terms of reducing cost while increasing safety and viewing in confined spaces. ROVs are also well suited
for emergency work. They require little setup or manpower scheduling to provide emergency support, such
as removing debris from the reactor vessel. However, as with any mission, ROV tasks must be well thought
out as many different aspects can impact their overall success. Issues to consider include the specific
application, ROV design, operations and the operating area, and vehicle storage and maintenance.


1. Introduction

Planned or unplanned reactor outages can cost the owners of the more than 250 active nuclear plants
upwards of $1,000,000 per day. Specific country regulations require nuclear power plants to be completely
inspected over an 8 to 10 year cycle. Outages are scheduled well in advance with tasks aimed at achieving
total inspection over that cycle. Outage efficiency and quality drop directly to the bottom line, so utilities
should be willing to invest in time saving and quality improving technologies. Simply guiding a fuel
assembly into proper alignment can save many times the capital cost of an ROV.

A well-designed ROV should be thought of as versatile, cost effective tool or end effector. The sub should
be able to accomplish the task in question, and be able to complete other tasks as well. Preferably several
different types of subs (with different capabilities) should be operable from the same control console. Sub
operation and control should be intuitive, and the system should be flexible, for addition of tools or sensors
such as manipulators, lights and radiation hardened cameras. The sub should be easy to trouble shoot and
repair with gloved hands, so it will remain an active tool in the inventory. Finally, these tethered swimming
vehicles should be manufactured of radiation tolerant materials with all parts captive.

2. Applications


Nuclear ROV applications generally focus on reactor IVVI tasks. These tasks are traditionally on the
critical path. ROVs can remove IVVI work from the critical path by allowing operators to conduct these
tasks in parallel with other in-vessel work. The sub can help prevent mishaps by supplying a different or
otherwise unobtainable camera view of another critical path task. For example the crane operator is greatly
assisted by ROV video showing PWR upper internals as they are lowered onto the stand. Other in-vessel
applications include lost part location and retrieval, general underwater observation, verification of tooling
tasks, delivery of tooling fixtures and quality checks on other in-vessel maintenance operations. ROVs also
have applications in non-vessel related areas. Subs can be used in other contaminated areas such as spent
fuel pools, equipment pools, suppression pools and various other tank and piping systems. ROVs can be
used on the clean side of a nuclear plant too. Vehicle inspections can include cooling water intake Reducing Critical Path IVVI Time Through the Use of Submersibles
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structures, outfalls, tunnels, towers and service water systems. It is important that the ROV is flexible
enough to meet changing inspection requirements that might be mandated by any new regulations. Refer
to Appendix A and B for actual task times.

In both Boiling Water Reactors (BWRs) and Pressurized Water Reactors (PWRs) ROVs have been proven
to reduce outage costs. For example many Boiling Water Reactor (BWR) tasks require use of the bridge
over the reactor. Consequently it partially defines the critical path of the outage. Since ROVs do not
require use of the bridge, they can accomplish tasks in parallel with bridge usage, reducing outage time and
cost by:
1. Removing inspection jobs from the critical path, shortening the outage duration.
2. Reducing inspection manpower requirements, as fewer personnel are needed.
3. Reducing radiation exposure to personnel, as most required personnel are further away from source.

3. ROV Design

ROVs basically come in two types: vertically designed and horizontally designed. Many BWR and confined
space service applications are best conducted using ROVs designed to perform in vertical thermal currents
and confined spaces. The stability of vertically designed vehicles is in these currents is generally greater
than horizontally-designed subs of the same class due to their taller profile, higher center of buoyancy and
lower center of mass.


The Firefly was designed to handle thermal currents and
tightly confined spaces. Its reduced surface area in the
vertical axis, reduces vertical current buffeting effects, and
allows it to pass through confined spaces to inspect such
areas as beneath a BWR core plate
.




The Dragonfly was designed to carry heavier payloads
beneath the top guide of a BWR and to operate in the
annulus above the jet pump restrainer bracket. It can
support multiple cameras simultaneously, a three (3) degree
of freedom camera manipulator, lasers and be maneuvered
under computer control.
Where thermal currents or access are not an issue, a horizontally designed ROV generally provides a better
solution. Horizontally designed ROVs are intended for use in areas where currents primarily flow in a
horizontal direction. These vehicles offer superior handling characteristics and performance, especially in
small tunnels and pipes. Larger vehicles can maneuver large equipment into place. Reducing Critical Path IVVI Time Through the Use of Submersibles
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The Phantom 150 was designed specifically for PWR
coolant piping and in-vessel inspections. It is equally able to
perform inspection, NDT work, pick debris from the fuel
bundle and retrieve small objects in confined areas.




The Micro-Pipeliner was the first ROV to enter and inspect
a PWR coolant pump head. It was designed to inspect pipes
down to 7.8 inches (200mm) in diameter. This inspection
saved the utility time, money and exposure compared to a
complete head disassembly.


3.1 Imaging


One of the main features of an ROV is the imaging capability. Whether it is inspection, locating a lost
object or simply navigation, the pilot is dependent upon the imaging system. The main inspection camera
ought to have a fairly wide angle of view (70 degrees minimum in water), zoom capability and at least +/-90
degree camera and light tilt. Lighting is always critical. The ROV must carry its own light, and preferably
lots of it. As long as it is variable intensity one can never have too much light. The sub should be able to
accept a broad range of cameras, from color, to low light, to rad hardened. Cameras are continually
evolving with improved image quality, smaller size, higher rad ratings etc. It is critical that the sub be able
to take advantage of these improvements over its lifetime. The sub should also be able to support multiple
cameras simultaneously, for example a rear facing camera to track the umbilical or back out of a tunnel.

3.2 Control


The control system and pilot proficiency play the dominant role in a successful operation. It is preferable to
have all control electronics topside, not in the vehicle where they are prone to radiation effects. The control
system should allow for easy integration of a deck cable to extend the control system off of the refuel floor
to a clean area if necessary. Controls should be ergonomic and comfortable for long duration operations-
up to 6-hour shifts. Auto pilot controls such as auto depth, or computer control which further reduce pilot
workload should be features available for the sub. For precise maneuvering, thruster controls should be
proportional, the more one displaces the joysticks the more thrust is applied. Finally, the sub should be
stable and well balanced when maneuvering in all axes to minimize induced pitch, yaw and roll.

3.3 User
Interfaces


The ROV should be flexible and versatile to accommodate additional tools and sensors. This in turn Reducing Critical Path IVVI Time Through the Use of Submersibles
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requires available power, telemetry and payload. These features should be included in the basic package, as
upgrades later could require complete and expensive changeouts of existing subassemblies. A versatile
system should include at least spare power wires, spare video telemetry path and 8 lbs. (3.6 kg) of payload.
Maneuvering large equipment into place requires larger payloads and proportionally larger amounts of
thrust.


Phantom S2 with 30 lbs (14 kg) payload and 90 lbs (41 kg) of thrust was used to