L - KTH

40 C, J. WOOD
not removed, these residues seem to contribute to rapid recontamlnatlon on return to
service. Several alternatives to permanganate are under development, including ozone,
parmanganlc acid, as in the KWU CORD process, potassium ferrate, and chromous LOMI
reagents. None of these reagents have been plant tested in the USA as yet, but some appear
to offer significant potential advantages compared to permanganate.
3. LWR DECONTAMINATION APPLICATION TECHNIQUES
3.1 BWR reactor water recelculation system (RWR) applications
The majority of RWR systems In U.S. BWRs consist of two piping loops, each containing a
high flow centrifugal pump complete wlth suction and discharge isolation valves and
interconnecting piping. The piping on the suction side of the pump runs vertically from
the reactor vessel near the bottom of the annulus. On the discharge slde, the piping
connects to a header above the pump from which five discharge risers extend vertically
upward to where they penetrate the reactor vessel and rise approximately another ten
feet. Once inside the vessel their designation changes and they are called Jet pump risers
and are considered part of the Jet pump assembly rather than the RWR system. Despite the
designation change, each riser is a continuous pipe which is used to contain
decontamination fluid during the application.
Some RWR systems contain a cross-tie line which interconnects the two loops at the
discharge headers. This llne normally contains two isolation valves.
Two different techniques have been employed to decontaminate this system--one and two
phase applications. Due to the design of the RWR system it is not possible for the reagent
to wet all of its various parts in a single step and maintain circulation (as opposed to
fill, soak, drain techniques), unless some form of modification is performed. Thus, single
phase applications are normally performed at plants that are planning a piping replacement
and are prepared to modify the system in order to improve reagent access. Two phase
applications are normally performed on an unmodified RWR system. These techniques are
described in more detail in Sections 3.1.1 and 3.1.2.
The decontamination equipment is common to both types of applications. In each case,
the temporary equipment used has performed all of the process functions required to
complete the decontamination. This consists of circulating and heating up the fluid,
injecting chemicals, reversing flow directions, sampling, monitoring process parameters,
controlling fluid levels and removing the dissolved activity and chemicals on Ion exchange
resins. Only minor variations In the equipment have been required to accommodate the
differences from one chemical decontamination process to another.
Flexible, high pressure, reinforced rubber hoses are used to connect the equipment to
the system or component to be decontaminated. Occasionally the entire system has been
hard-plped, but experience with the rubber hoses has been excellent, and this is now the
preferred option. Hoses typically in the range of 2" to 4" diameter are typically used.
3.1.1 Two Phase RWR Decontaminations. This is the most common approach to RWR
decontamination. It is most effective when extensive inspection or maintenance work,
rather than modifications, are scheduled for the system. The decontamination is performed
In two phases, a discharge side phase and a suction side phase. It can be used whether or
not the RWR system contains a cross-tle llne connecting the discharge headers of each loop,
and whether or not the lower portion of the annulus is to be included in the flowpath.
As shown in Fig. 2, the temporary decontamination equipment is connected to the RWR
system at the suction of each RWR pump. Flanged connections are available for Just such
work on virtually all U.S. BWRs. The equipment is normally located Just outside the
drywell in the vicinity of the equipment access hatch. It is placed and shielded to
minimize radiation exposure to both contractor and plant staff during the application.
To commence the discharge side decontamination, the pump isolation valves on the suction
side are closed, those on the discharge side and on the cross-tie header are opened, and
the discharge piping is filled to a predetermined level of fluid (Just about half way up
each of the ten discharge risers). Flow is established through the discharge half of the
system from the temporary equipment into one loop via the decon flange, through the RWR
pump bowl, and up the discharge piping into the header. The fluid passes into the second
loop via the cross-tie llne and back down the discharge piping, through the pump and back
to the temporary equipment. By adjusting the valve lineup on the decon equipment the
direction of flow can be reversed through the discharge loops.