ML20195G591
| ML20195G591 | |
| Person / Time | |
|---|---|
| Issue date: | 06/02/1999 |
| From: | Thadani A NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Collins S, Cyr K, Paperiello C NRC (Affiliation Not Assigned), NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS), NRC OFFICE OF THE GENERAL COUNSEL (OGC) |
| Shared Package | |
| ML20195G576 | List: |
| References | |
| NUDOCS 9906160110 | |
| Download: ML20195G591 (7) | |
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i UNITED STATES eg
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NUCLEAR REGULATORY COMMISSION f 15
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MEMORANDUM TO: Carl J. Paperiello, Director e
Office of Nuclear Material Safety and Safeguards Samuel J. Collins, Director Office of Nuclear Reactor Regulation Karen D. Cyr, General Counsel Office of the General Counse!
FROM:
Ashok. C. Thadani, Director D
Office of Nuclear Regulatory Res rch -
SUBJECT:
CONCURRENCE ON COMMISSION INFORMATION PAPER ON THE VIABILITY OF THE ENTOMBMENT OPTION AS A DECOMMISSIONING ALTERNATIVE FOR TERMINATING POWER REACTOR LICENSES The Commission requested the staff to consider the viability of the entombment option as an alternative for dt: commissioning power reactors in an April 3,1997 SRM. The staff contracted with PNNL to provide an information report containing preliminary recommendations on the technical feasibility of this decommissioning alternative and how the entombment option could be incorporated into the NRC regulatory requirements. The staff provided the Commission with preliminary views on the entombment option in SECY-98-099, May 4,1998.
J This Information Paper provides the staff's analysis on the viability of the entombment option, along with the PNNL paper. Both of these documents have been attached for your review. The SRM and earlier Commission Information Paper have also been enclosed for background j
information. Please provide your concurrence and/or comments within two weeks of the date of i
this memo.
Attachments: As stated i
Contact:
Carl Feldman 415-6194, cxf j
9906160110 990610 PDR ORG NRRA L
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iThe Commissioners t
FROM:
I William D. Travers -
Executive Director for Operations
SUBJECT:
INFORMATION PAPER ON THE VIABILITY OF ENTOMBMENT AS A DECOMMISSIONING OPTION FOR POWER REACTORS PURPOSE: i u
$ o provide the staff's assessment of the viability of entombment as an option for T
decommissioning power reactors.
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.q" BACKGROJ.lND:
p This is in response to an SRM dated April 3,1997, that requested an analysis on whether the l
staff views entor6bment as a viable decommissioning option and how licensee entombment i
option requests have been dealt with in the past by the Commissioni The SRM further stated
- that if the staff concludes that entombment is not a viable option, the staff should describe the
' technical requirements and regulatory actions that would be necessary for entombment to become a viable option for decommissioning. Furthermore the staff analysis should consider the resources involved, potential savings on decommissioning costs, and vulnerabilities. A status -
report of the staff's efforts in response to this SRM was provided to the Commission on May 4, l
1998, in SECY-98-099. That report summarized the present NRC regulatory position and.
requirements pertaining to the use of the entombment option and, based on a preliminary-assessment of the Pacific Northwest National Laboratory's (PNNL's) efforts, the NRC staff
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indicated that entombment appeared to have merit, but that rulemaking would be needed before
- this option could be treated as a generic attemative.
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PNNL ASSESSMENT:
In response to the Commission's request of April 3,1997, the staff contracted with PNNL to evaluate the relevant technical issues associated with using the entombment option to decommission power reactors. PNNL was not asked to address other issues that might be of J
concern when a draft rulemaking plan is developed. Examples of such issues would be the impacts of permitting the entombment option on the LLW Compacts and the Agreement States.
These issues would be considered if the Commission directs the staff to undertake rulemaking.
i The PNNL assessment (enclosed) addressed several realistic entombment scenarios that could serve to bound licensee contemplated entombment activities, and considered the ability of these entombment scenarios to isolate the contained radioactive materials - similar to the considerations for the in-situ disposals at some of the Site Decommissioning Management Plan (SDMP) sites. This assessment considered f actors such as the physical and chemical
_ properties of the radioactive materials expected to be entombed, the integrity of the entombing structure, the site-specific sorptive and hydro-geological properties of the surrounding media, and relevant hypothetical radioactive contaminant transport behavior resulting in possible public exposure.
PNNL used an approach that is similar to their previous analysis of the reasonableness of decommissioning power reactors by dismantlement (" Technology, Safety and Costs of Decommissioning a reference Pressurized Water Reactor Power Station," NUREG/CRs-0130, 1978, and NUREG/CR-0672,1981 for the equivalent report for the BWR). Their approach was to (1) examine information from actual reactor entombments for comparison with NRC's power reactor entombment considerations, (2) consider available information from operating systems and activities that have similarities to entombment, and (3) perform a comparative analysis of significant component system behaviors that are similar to the entombment option systems.
Using these approaches, PNNL examined information from three small DOE-licensed reactors that were entombed about 30 years ago. These were the only reactors ever entombed and PNNL described lessons learned from these entombments that would be applicable for NRC-licensed power reactors, such as use of adequate structural design criteria and proper construction practices for the entombment and the performance of periodic surveillance and monitoring to verify containment of the radioactivity. PNNL also considered relevant information 2
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from successful DOE waste burial activities, such as the contaminant isolation assessments that were made,'and the associated health and safety requirements imposed. DOE evaluated the potential doses to individuals from the entombed contaminants for various entombment configuration scenarios. The dose pathways considered when DOE performed their analysis c were from either direct intrusion into the entombing structure or from transport of ' radioactively -
contaminated materials to the surrounding environment. PNNL's conclusion from their study is that " entombment appears to be a viable decommissioning alternative for nuclear power reactors in that it protects public health and safety as defined by existing NRC requirements."
a STAFF ANALYSIS OFTHE PNNL ASSESSMENT:
l The PNNL evaluation provides convincing evidence that entombment of radioactive wastes within the reactor structure can isolate the contained radioactivity to the degree necessary to l
ensure that health and safety is not compromised nor is the environment degraded.
Assuming that the site conditions are not limiting (such as might be the caso for shallow water table dose-pathway concerns), the license can be terminated safely by effectively isolating the
' entombed radioactive contamination such that any exposure of contaminants to the individual (either directly or from transport through the surroundings - e.g., soil) results in a dose (i.e.,
average member of the critical group - as denoted in Subpart E of Part 20) that is within acceptable limits (e.g.,25/ mrem /yr). Additionalissues to be considered include tha design of j
the entombment system, and the monitoring and maintenance that are necessary to provide
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assurance that the intended ' estrictions will continue to remain effective. Of course, if the r
entombment'falled and could not be remediated effectively, the radioactive contaminants could be removed prior to any environmental releases that would result in the public doses being
' exceeded. However, removal of the entombed material may be costly because of the disposal of large amounts of previously uncontaminated materials (e.g., soil, grout, concrete) being used to shield and contain the radioactive contaminants within the entombed structure if these materials become contaminated. Consequently, it is essential that the waste isolation assessment bh carefully evaluated and properly implemented.
To permit the entombment option,'some changes in the current rules would be needed in 10
. CFR 50.82(a)(3), there is an expectation that decommissioning (i.e., license termination) will be 1 completed within 60 years of permanent cessation of operation, except for very special 3
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circumstances (e.g., a lack of waste disposal space). In order for entombment to be treated on an equal basis with the prompt (DECON) and deferred (SAFSTOR) dismantlement options cited in the original 1988 rule, the 60 year time limit would need to be increased or removed. Revision of Subpart E of Part 20 for license termination under restricted release conditions is also required. The possibility of the restrictions failing is considered and limits are placed on the maximum doses permitted should failure occur. Under an entombment scenario, the most likely source of exposure, should entombment fail, would be due to slow leakage of contaminants from the structure.
Failure of institutional controls and intrusion into the entombed reactor vessel, although highly improbable, would result in the intruder gaining access to the radioactive materials inside the structure. While this was analyzed in the PNNL assessment, it is highly unlikely that such an intrusion would ever occur because of the grouting and reinforced concrete structures used in the entombment. As noted in SECY-98-099, it would be necessary to demonstrate that failure of the entombment system would be extraordinarily unlikely during the time when failure could
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more likely result in doses above those currently permitted. Therefore, additional requirements would be needed to provide assurance that the institutional controls would be sufficient to ensure s
that the limits in 10 CFR 20, Subpart E would not be exceeded.
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in addition, any rule amendments would require a supplemental environmentalimpact statement j
on use of the entombment options because this was not evaluated in the either the 1988 or 1997 rule. Entombment scenarios where this would be most significant are situations where most of the radioactive inventory remains onsite and when license termination occurs promptly.
The issue of whether Greater Than Class C (GTCC) wastes can be entombed also needs to be considered. As stated in the PNNL report, the GTCC waste is composed of very long-lived activation products that can result in doses up to a few rem /hr (e.g., for Nb-94, a gamma emitter with a half-life of 20,000 years). This waste is confined to small areas in the reactor vessel that were subject to high neutron flux irradiation (e.g., the lower plenum of a PWR) and typically consist of about 11 cubic meters of material that can be readily removed and shipped offsite.
However, when packaged for offsite shipment, this waste material takes up a greater disposal volume (about 100 cubic meters). The GTCC waste is of moderately low activity but is confined to areas containing very high activity, and its removal results in potentially large radiation doses 4
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to workers. However, this limited amount of moderately low radioactivity material (i.e., steels)
. confined within the reactor vessel most likely will degrade very slowly. Consequently, the resultant dose from this contaminant, when entombed, is expected to be inconsequential because of the small release amounts and large dilution occurring should the contaminant reach the biosphere.
As noted in the Enclosure, the major monetary cost for prompt or delayed decommissioning through dismantlement is the cost of waste disposal. Depending on the amount of waste entombed, this cost can be significantly reduced. However, the cost of maintaining and monitoring the entombed facility could offset these savings, depending on the contaminants entombed and the entombment system chosen (see Table 1 of the enclosed PNNL report).
The waste volumes requiring disposalin the entombment scenarios are reduced from the waste volume arising from DECON by about 1 order of magnitude. Most of the waste volume from the entombment scenarios arises from tLa post-shutdown deactivation activities, which is common to all scenarios. Even these reduced volumes could be essentially eliminated by proper treatment and packaging of the deactivation wastes for inclusion within the entombment enclosure. As a result, the entombment scenario costs are not very sensitive to the rates charged by the LLW disposal facilities. The LLW disposal costs of the DECON scenario are the largest single cost element for that scenario and may comprise from 40% to 80% of the total cost, depending upon charge rates at the LLW disposal facilities. Using the most current disposal cost document, NUREG-1307, Revision 8, for disposal at Barnwell in 1998 dollars,
.. direct disposal by the licensee of decommissioning wastes results in the waste cost comprising 75% of the total cost. More efficient disposal of this waste by the licensee through the now permitted method of shipping it to a waste processing vendor, with a much smaller portion of the waste disposed of at Barnwell, still results in a substantial waste disposal cost and gives 55% for this ratio.
Much larger differences between the dismantlement and entombment option comparison of costs and occupational doses would occur if the GTCC waste were also entombed rather than removed because of significant waste disposal costs and occupational radiation exposures.
Finally, it is likely that using the entombment option could result in some cost savings over those 5
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STAFF CONCLUSIONS:
Based on the PNNL assessment, the staff believes that decommissioning a power reactor using the entombment option can be safe and viable if done properly, and would provide additional flexibility to licensees. Also, the staff believes that this option would require minimal changes to regulatory requirements and guidance and thus there are no fundamentally different rulemaking options. If the entombment options are properly implemented, the impacts on health, safety, and the environment should be small, as concluded in the enclosed PNNL report. The entombment option could result in greater positive impacts than the other decommissioning options because the decommissioning waste could be disposed of onsite, eliminating monetary costs and dose risks to workers and the public that would be incurred in the removal, packaging, transport, and offsite disposal of decommissioning waste. Moreover, other industrial, nonradioactive risks involved with the removal and disposal of these wastes offsite would be eliminated, such as those activities used in the removal, packaging and transport of waste.
As mentioned earlier, non-technical issues, such as impacts on the LLW Compacts and the Agreement States, if use of the entombment option was to be permitted, were not addressed.
Accordingly, these other issues would need to be addressed as part of any rulemaking activity.
The staff intends to forward to the Commission its proposal plans for rulemaking in this area in the next update to the rulemaking activity plan.
William D. Travers Executive Director for Operations ENCLOSURE: " Viability of the Entombment Option as an Alternative for Decommissioning Commercial Nuclear Power Reactors," PNNL, May 13,1999.
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