Radiant energy – Radiation controlling means – Shielded receptacles for radioactive sources
Reexamination Certificate
2002-07-10
2004-08-31
Wells, Nikita (Department: 2881)
Radiant energy
Radiation controlling means
Shielded receptacles for radioactive sources
C588S016000, C588S002000, C588S003000, C588S004000, C588S015000, C588S249000, C588S252000
Reexamination Certificate
active
06784444
ABSTRACT:
BACKGROUND
The invention is related to the containment of radioactive items, and in particular to methods and apparatus for the containment, transportation, and storage or disposal of decommissioned nuclear reactor pressure vessels.
Nuclear power is now a mature technology. In the United States more than a hundred nuclear power plants have been at work for decades, providing a substantial portion of the commercial electrical power sent to the nation's power grid.
Like most machines, however, nuclear power plants, and in particular the nuclear reactors which form the hearts of nuclear power plants, have limited useful lifetimes. And when their useful lives have expired nuclear reactors must, like other machines, be disposed of. But nuclear machines present more complex disposal problems than most non-nuclear machines. Nuclear machines, and in particular nuclear reactors, are, in significant part, radioactive, and therefore require special handling and containment. And when such machines must be moved for storage (or, in most cases equivalently, for disposal), the problems associated with their containment are compounded.
To date few nuclear reactors have been decommissioned or otherwise processed for disposal. This is particularly true of reactors of substantial size. In fact, only four nuclear reactor pressure vessels of relatively large size have been transported for disposal. These reactors are of the pressurized water (PWR) type and include reactors from the Shippingport, Trojan, Yankee Rowe and Saxton plants. And throughout the process of dismantling and removing these four reactors it was noted that improved methods and apparatus were needed.
In two of these instances, Trojan and Saxton, the reactor pressure vessel (RPV) was transported intact containing all of the highly radioactive internals components, in operating configuration. In the handling of these PWR pressure vessels it was determined that one preferred method for transporting a decommissioned RPV would be to place the RPV with its internals within another container, the container adapted to provide both shielding and structural integrity for the RPV and its contents during transportation. To date only with the Saxton RPV was this tried.
To meet the stringent requirements for safe containment during transportation and disposal of such a potentially dangerous item as the Saxton RPV, highly specialized and innovative apparatus and methods were employed. The reactor pressure vessel was disconnected from the piping which connected it to the remainder of the power plant, and placed otherwise intact, with its internal components in operating configuration, its pressure head in place, and with its inlet and outlet nozzles untrimmed, within another container, encased in grout to hold it in place within one section of the container, and transported. The containment configuration used in the Saxton decommissioning is illustrated in FIG.
1
. Containment package
200
comprises RPV
202
and canister
201
. Canister
201
comprises first and second sections
236
and
237
, respectively. RPV
202
, intact with all internals
217
(not shown in their entirety) and with reactor pressure head
215
in place, firmly attached to the RPV by means of head-to-body attachments
232
, is disposed within canister
201
. External fittings
203
have been severed, but substantial portions
204
of the fittings have been left in place. External insulation
206
has been left in place. Interior
209
of RPV
202
has been filled with grout, and gap
251
between RPV body
214
and the canister has been filled with grout. Surface contaminants have been sealed by grout on RPV interior surface
210
and on RPV exterior surface
205
. Exterior surface
213
of canister
201
comprises no fenders or other protection against shocks.
While the containment apparatus and the methods applied in decommissioning the Saxton RPV represented an innovative approach to the problem of transporting a large radioactive waste item, it became increasingly clear to those concerned as work progressed that there was substantial room for improvement. For example, the container, being designed for containment of the entire RPV, with its internal structures, the head, external insulation, and all external fittings in place and intact, was substantially larger and heavier than necessary. The complete package measured about 21½ feet in length, 9 feet in diameter, and weighed about 120 tons. And Saxton was a relatively small and light reactor vessel package. Therefore, when larger PWR and boiling water reactor (BWR) pressure vessels, often weighing in excess of 600 tons without container packaging, are considered, it becomes necessary to consider improved methods of handling and packaging.
Other approaches for the handling and transport of radioactive waste for disposal have been suggested, but none provides a truly satisfactory solution to the particular problems associated with the containment and transportation of large radioactive machinery such as RPVs of commercial size. For example, U.S. Pat. No. 5,894,134 to Kissinger, “SHIPPING CONTAINER FOR RADIOACTIVE MATERIAL”, and U.S. Pat. No. 5,061,858 to Mallory, “CASK ASSEMBLY FOR TRANSPORTING RADIOACTIVE MATERIAL OF DIFFERENT INTENSITIES”, describe tubular shipping containers for radioactive material comprising impact limiters disposed at either end of the containers; U.S. Pat. No. 5,297,182 to Cepkauskas, “METHOD OF DECOMMISSIONING A NUCLEAR REACTOR”, discloses a method for encapsulating portions of the reactor vessel and reactor internals into a solid reactor capsule and then converting this reactor capsule into a plurality of decommissioned segments; and U.S. Pat. No. 5,263,062, Guigon et al., “PROCESS AND APPARATUS FOR DISMANTLING THE INTERNAL EQUIPMENT OF A WATER-COOLED NUCLEAR REACTOR”, discloses a method of decommissioning a water-cooled nuclear reactor vessel where elements of the vessel are separated and compacted underwater for extraction and further transport. But the containment vessels and methods disclosed are not suitable to the safe, efficient, and economical containment, storage or disposal, and transport of decommissioned nuclear reactor pressure vessels. Their construction is more complex, and therefore more costly, than necessary; and the resultant containment package is either larger and heavier than need be or is cut at great expense and considerable risk to personnel into a number of smaller, yet still heavy, objects which must be transported and stored separately. None of these adequately addresses questions of weight, bulk, shock absorbency, or manageability for dismantlement, containment, and transport of nuclear RPVs or similar large radioactive machinery in the decommissioning process.
Thus there is a need for suitable and efficient methods and apparatus for containing, storing, and transporting nuclear reactor pressure vessels with essential intact internals components, and other radioactive machinery items, particularly during the decommissioning, dismantlement, or disposal process.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide methods and apparatus for containing, transporting, storing, and disposing of nuclear reactor pressure vessels and other radioactive machinery items, particularly during the decommissioning or dismantlement processes.
It is another object of the invention to provide such methods and apparatus which result in lighter and safer packages which provide adequate containment and also meet federal and state requirements for transport, storage, and disposal.
It is another object of the invention to provide such methods and apparatus which result in smaller and more easily, safely, and economically handled packages for containment, transport, storage, and disposal.
It is another object of the invention to provide such methods and apparatus which provide improved containment and shielding for radioactive portions of items stored within the items themselves.
It is another object of the invention to provide such methods and apparatus
Freitag Albert A.
Tuite Kevin T.
Tuite Peter T.
Brown Raysman Millstein Felder & Steiner
Kalivoda Christopher M.
Wells Nikita
WMG, Inc.
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