ML20053E038
| ML20053E038 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 06/01/1982 |
| From: | Blanchard D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML20053E035 | List: |
| References | |
| NUDOCS 8206070550 | |
| Download: ML20053E038 (12) | |
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a UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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Docket No. 50-155-OLA CONSUMERS POWER COMPANY
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(Spent FAl Pool 1
Modification) l (Big Rock Point Nuclear Power Plant)
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TESTIMONY OF DAVID P.
BLANCHARD IN RESPONSE TO BOARD QUESTIONS RELATING TO NATURAL WATER CONVECTION CURREh'fS My name is David P.
Blanchard.
I am employed as a technical engineer by Consumers Power Company at the Big Rock Point Plant.
My qualifications and experience were presented as a part of my testimony presented in response to Christa-Maria Contention 8 and O'Neill Contention III.E.2.
In a memorandum dated May 13, 1982, the Board requested comments relating to natural water circulation in the Big Rock Point spent fuel pool.
The Board presented three questions in this regard:
(1)
Is there anything in the geometry of the fuel pool, fuel elements or spent fuel storage racks that could substantially alter natural water convection currents?
i 8206070550 820601 PDR ADOCK 05000155 T
ppg (2)
Is there a credible scenario, during a TMI-type accident or during more normal operating conditions, in which insulation or other debris could fall into the fuel pool and substantially alter natural water convection currents?
(3)
If questions (1) or (2) are answered affirmatively, what l
are the implications of the affirmative answers for "k effective"?
In response to the Board's questions, I will show that there is nothing in the design of the pool, spent fuel racks or fuel assemblies the.t could substantially alter natural water convection currents as discussed by Drs.
Prelewicz and Gay in their testimony concerning O'Neill Contention II.E.3.
Further, I will show that there are no I
sources of debris in the vicinity of the Big Rock Point spent fuel pool which could obstruct natural circulation either during normal or accident flow conditions.
I have reviewed Dr. Prelewicz' testimony and Dr.
Gay's analysis to ensure that the pertinent design features of the spent fuel pool and fuel elements which affect the convec-tive flow rate have been included.
The analysis divides the pool up into several distinct regions, a fuel region, a down-comer region and a region above the elevation of the racks.
The flow areas of each of these regions appears to be accurate.
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Downcomer regions are those areas between the fuel racks and the pool walls through which colder water flows from the top to the bottom of the pool.
Downward flow of water along the pool walls is unobstructed.
The pool walls are smooth and vertical.
The space between the pool walls and the racks are wide (3-1/2 inches minimum) and spaces between the racks i
l themselves are on the order of 2 inches providing large down-comer areas distributed over the p' col.
On the bottom of the pool, the water flows under-l neath the racks before flowing upward through the fuel assemblies.
The pool floor is also smooth and free of obstruction.
The racks rest on legs allowing free circulation of water beneath them.
A 6-inch space exists between the bottom of the rack and the pool floor to accommodate this flow.
The rack is designed to allow this water to circulate through the fuel assemblies.
A 5-1/2 inch diameter hole is provided in each channel of the fuel rack allowing water to flow upward through the fuel.
Grid spacere maintain space between the fuel rods to allow water to flow between the rods.
The grid spacers them-selves hinder the convection of the water, but this effect has been accounted for by the local loss coefficients used in the Prelewicz and Gay testimony.
Water circulation in the spent fuel pool is slightly altered by the storage of various small hardware items and 1
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tools in the pool.
These items are generally suspended by cable or nylon ropes on the order of 6 to 10 feet below the l
pool surface.
This equipment includes irradiated reactor j
hardware and tools used during previous refuelings which are being stored in the pool to take advantage of the water as biological shielding.
The volume of this hardware is l
l small compared to the volume of the downcomer regions, leading to the conclusion that there is little if any effect of these items on the natural circulation within the pool.
The analysis of water circulation prepared by Drs.
Prelewicz and Gay adequately accounts for the minimal effects these items would have on water circulation by assigning. local loss coefficients for small flow obstruc-tions and ignoring downcomer regions on the west end.of the pool and the spaces between the racks.
It is my conclusion.that there are no features in the design of the fuel pocl, the storage racks or the fuel elements that would substantially alter natural water con-i vection currents which were not considered and adequately accounted for in the testimony and analysis of Drs.
Prelewic: and Gay.
i I will now examine potential external sources of debris which if introduced to the pool could result in a
reduction of the natural circulation flow rate.
In examining these sources it is important to note that the reactivity analysis performed by Dr. Kim is in fact " infinite" in nature.
That is, "k infinity" or "k effective" is determined assuming the fuel elements, storage racks and moderator extend infinitely in all directions (horizontally and vertically).
To affect significantly the reactivity of the fuel stored in the racks in this analysis, moderator density changes due to temperature and void fraction must also occur infinitely in all directions.
Localized increases in the temperature and void fractions of individual assemblies will not significantly alter the multiplication factor of the storage racks.
In other words, large portions of the racks in the fuel pool must be affected by flow restrictions before a significant increase in reactivity occurs.
It is therefore necessary to have a large amount of debris enter the pool before assuming that natural convection currents are detrimentally reduced.
1 It is noted that the Board makes specific reference to insulation falling into the pool in order to l
l substantially alter natural convection in the pool.
There is in fact no insulation on the walls or ceiling within the con-tainment.
All insulation on the containment is a polyurethane or cork mastic and is located on the external surfaces of the containment sphere.- There is no insulation located inside the
containment above or around the fuel pool.
Thus, insulation is not a source of debris which could enter the fuel pool.
I have examined the area around the Big Rock Point spent fuel pool, its location within the containment, as well as its functional interfaces with other plant systems to deter-mine sources for this debris during normal operation and accident conditions.
The following potential sources of debris have been noticed as a result of this review:
(1)
Particulates (or crud) introduced to the pool during normal refueling operation.
(2)
Particulates (or crud) introduced to the pool l
through the remotely operated makeup line following a reactor loss-of-coolant accident.
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(3)
Paint and coatings introduced to the pool after falling from the walls, ceiling and equipment above the pool following an accident.
(4)
Aggregate from the steam drum blowout panel introduced to the pool following a loss-of-coolant' accident.
For the reasons discussed below, none of these items result in significant alteration of convective circulation currents in the fuel pool.
l The first item is particulate matter as it normally exists in the spent fuel pool co61 ant.
The majority of this substance is iron oxide and is commonly referred to as crud.
The primary source of iron oxide is the surfaces of steel piping
and hardware of the primary coolant system.
The crud is suspended in the reactor coolant and plates out in a film-like layer on the surface of fuel and reactor internals hardware within the reactor.
During the course of normal refueling operations, the fuel, reactor internals and reactor coolant are moved into the pool from the reactor resulting in the transportation of this crud into the pool water.
Refueling operations are the primary source of crud.
Crud particulate size is very small (on the order of tens of microns.)
It does not contribute tu ~ reduction in flow rate l
through the pool, racks, or fuel elements due to the compara-tively large flow area associated with these components.
Therefore, crud can affect flow patterns in the fuel pool only if it collects in sufficiently large quantities within these components.
Such a collection of crud does not occur in the Big Rock Point spent fuel pool due to the filtration of the pool water in the fuel pool. coolant loop during normal opera-tion.
Throughout the course of refueling operations, as well as normal power operation, the pool coolant is cycled through a set of filter socks.
These are cotton socks pre-coated with diatomaceous earth which filter out crud particulates suspended in the pool coolant.
Operation of this l
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system and periodic change-out of the socks removes these crud particulates from the pool cooling system, preventing significant crud buildup resulting from successive refuelings.
The introduction of crud to the fuel pool as a result of normal refueling activities does not, therefore, detrimentally affect natural convective currents within the pool storage racks or fuel elements.
The second source of material which could be introduced to the pool is also a particulate or crud-like material.
Following a loss of the fuel pool cooling equipment during a loss-of-coolant accident, makeup to the pool may be necessary through the fuel pool makeup line.
The most likely source of water for this makeup is that which collects in the bottom of containment following the LOCA.
Any crud, dirt or debris which may be in this area of containment at the initia-tion of the LOCA could be introduced to the reactor or fuel pool through the post-incident recirculation system.
To preclude introduction of this material-to the reactor or spent fuel pool, fine mesh screens are provided on the strainers in containment through which the post-incident recirculation pumps l
l draw their suction.
These strainers provide a filtering function for water makeup to the pool and reactor, precluding buildup of this material in these areas.
Introduction of l
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significant amounts of crud or debris to the pool through the fuel pool makeup line is therefore limited by the design of the post-incident recirculation system.
The third source of material identified includes paint and coatings on walls, ceilings, and equipment above and around the fuel pool.
Unless these coatings are resistant to the high temperature, moisture and radiation associated with the environment resulting f om an event such as a loss-of-coolant accident, it is possible that these coatings could flake or peel from the containment surfaces and fall in the fuel pool.
The containment sphere surfaces e.bove the pool are coated with a zine dust metal primer and an alkyd semi gloss enamel top coat.
These surfaces have been evaluated for the loss-of-coolant accident. environment by Consumers Power Company and it has been concluded significant loss of these coatings from the containment walls will not occur.
l Zinc coatings generically have been subjected to a LOCA environment in tests performed by Oak Ridge National l
Laboratories showing their acceptable resistance to a LOCA environment.
The alkyd enamel coatings have not been tested in this environment, but this material is not expected to come off of the walls following a LOCA.
This conclusion is based on the fact that the original coating of paint still exists on the l
walls over the pool and no subsequent coating has been applied.
This original coating is tenacious in its adherence to the surface of the walls.
These walls are not subject to steam impingement resulting from a LOCA as they are not located in the vicinity of primary coolant piping.
They are also at an elevation well above any conceivable water level I
which would exist following a LOCA so that the walls would not be submerged and the enamel coating soaked from the surface.
It is expected, therefore, that these coatings would success-fully withstand the environment associated with a LOCA and 1
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would not result in an addition of debris to the pool during these conditions.
A fourth source of debris which could result in the addition of material to the pool following an accident is l
the steam drum blowout panel.
This panel is mounted to the north side steam drum wall over the reactor deck.
The panel is filled with high density aggregate, which very simply are rocks on the order of 1 to 2 inches in diameter.' The purpose of these rocks is to provide biological shielding for the reactor deck area adjacent to the steam drum.
The original purpose of the panel was to equalize pressure between the steam drum enclosure and the remainder of containment following a LOCA within the steam drum area.
The panel would perform this function by failing (called " blowout") at a given differential pressure between the drum and containment and falling on to the reactor deck.
The large vacant area left by the panel would allow pressure to equalize in the con-1/
tainment structure;-
In falling on the reactor deck, some of the aggregate could end up in the fuel pool.
The amount of this rock which could be added to the pool is small.
t This is because the blowout panel is not directly above the fuel pool and it would not fall toward the pool but laterally along the west end of the pool.
As a result, only a small portion of the aggregate, if any, could fall into the pool and this portion of the aggregate is limited to that within the easternmost section of the panel.
It is concluded that only an insignificant amount of aggregate can fall into the pool.
Any effects this aggregate may have are limited to a few assemblies in the westernmost end of the pool.
In reviewing the location of the fuel pool and the design of systems which interface with the pool, no source of debris has been identified which would result in a significant 1/
A recent analysis done by Consumers Power concluded that the differential pressure between the steam drum cavity and the rest of containment during a LOCA is in fact l
not great enough to cause the panel to blow out.
Pressure equalization between these areas is effected through other passages without causing the panel to fail.
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introduction of debris into the fuel pool.
Material which can be potentially introduced to the pool is small compared to the flow area which water must circulate in cooling the fuel or limited in the amount of material which can be added.
There is no credible scenario in which debris could fall in the water and substantially alter natural water convection currents.
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