ML103210349
| ML103210349 | |
| Person / Time | |
|---|---|
| Issue date: | 12/31/2010 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Orr M RES/ RGDB 301-251-7495 | |
| Shared Package | |
| ML103200450 | List: |
| References | |
| DG-3030 RG-3.071, Rev 2 | |
| Download: ML103210349 (6) | |
Text
Comments on DG-3030 (Rev. 2 to RG 3.71), Page 1 Response to Public Comments for Draft Regulatory Guide DG-3030, Nuclear Criticality Safety Standards for Fuels and Material Facilities Proposed Revision 2 of Regulatory Guide 3.71, dated October 2005 A notice that DG-3030 (proposed Revision 2 of Regulatory Guide 3.71) was available for public comment was published in the Federal Register (75 FR 45166) on Monday, August 2, 2010. The following comments were received and the final version of revision 2 of Regulatory Guide 3.71 incorporates the NRC resolutions described below.
Comments were received from:
Mr. James Baker Los Alamos National Laboratory, Nuclear Criticality Safety Group TA-3, Building 332, MS F691 P.O. Box 1663 Los Alamos, NM 87545 Phone: 505-665-2814 E-Mail: JBaker@lanl.gov Ms. Janet R. Schlueter, Director Fuels & Materials Safety Nuclear Energy Institute 1776 I Street, NW, Suite 400 Washington DC 20006-3708 Phone: 202-739-8098 E-Mail: JRS@nei.org S. Philips & S. Kane Canberra Industries, Inc.
Comment No.,
Comment From Comment NRC Response
- 1.
J. Baker (LANL) 2nd paragraph under Section B, 2nd sentence of 2nd paragraph -
the word Nonetheless should be deleted.
Agree. Change to Additionally for clarity.
- 2.
J. Baker (LANL) 1st sentence in Section C - replace procedures and methodologies with criteria. The current wording indicates a lack of understanding of the nature of the ANS-8 Series standards.
Agree that the standards may not necessarily provide procedures but provide guidance and criteria for acceptable methods. Recommend to change to criteria and practices.
Comments on DG-3030 (Rev. 2 to RG 3.71), Page 2 Comment No.,
Comment From Comment NRC Response
- 3.
J. Baker (LANL) 1st sentence of the paragraph under Section C.2.a: - the word procedure should be replaced with criteria. Again, a misunderstanding that this is not intended to be a procedure.
Agree that the standards may not necessarily provide procedures but rather provide guidance and criteria for acceptable methods. Recommend to change to practices.
- 4.
J. Schlueter (NEI)
Introduction, 2nd paragraph, last sentence - This sentence states, Similarlycertificate holders are required by 10 CFR 76.87 (c) to include in their technical safety requirements, procedures and/or equipment that address criticality prevention. The statement implies that the procedures or equipment are to be specifically listed in the technical specification requirements (TSRs). 10 CFR 76.87(c) states appropriate references to established procedures and/or equipment to address criticality prevention that must be included in the TSRs. The current NRC-approved TSRs for the gaseous diffusion plants address criticality safety; however, not all procedures or equipment are specifically listed. Please clarify the NRCs intent on this matter.
Agree. This wording was changed from the original FCSS revision to the RG and how its stated now is not the intent. 10 CFR 76.87 (c) states that, Appropriate references to established procedures and/or equipment to address each of the following safety topics must be included in technical safety requirements The regulation only requires references to procedures.
Originally, this sentence stated, Section 76.87, Technical Safety Requirements, states that the technical safety requirements should reference procedures and equipment that are applicable to criticality prevention.
For clarity, recommend changing this statement as follows:
Similarlycertificate holders are required by 10 CFR 76.87 (c) to include in their technical safety requirements, appropriate references to procedures and/or equipment that address criticality prevention.
Comments on DG-3030 (Rev. 2 to RG 3.71), Page 3 Comment No.,
Comment From Comment NRC Response
- 5.
J. Schlueter (NEI)
Section C, Regulatory Position, Section 2, Standards Endorsed with Exception -- The exception to 8.1 is not an exception to any aspect of the standard, but rather a stated expectation on how the standard is implemented. It appears more appropriate that the implementation guidance be included elsewhere, e.g., in NUREG-1520 or in an Interim Staff Guide until NUREG-1520 can be updated.
Also, the bases for the exceptions to 8.24 do not appear technically valid. For example, a licensee would not typically reject an entire set of critical mass experiments due to a single outlier. If the experiment is statistically an outlier, then it should be excluded and its reasons for being an outlier well understood through a detailed investigation. However, the purpose of validating the computer code and verifying that any bias is accounted for is to ensure the code accurately predicts k effective. Identifying a potential discrepancy in the experiment itself by noticing a statistical outlier does not necessarily impact the ability of the code to accurately predict k effective.
Disagree. This RG discusses the NRC endorsement of certain ANSI/ANS criticality related standards, so the RG is the appropriate place to state any NRC exception to a particular standard.
Disagree. An outlier should not be rejected based purely on statistical reasons. The NRC agrees that if a case appears to be an outlier, then the analyst should try to determine (for example, through a detailed investigation) if there is some physical reason for the case being an outlier. Discovering an error in the experiment set would be one such physical reason that would cast doubt on the entire experimental series.
Note that the use of the word should in the exception denotes a recommendation and not a requirement.
The NRC is open to review and consider valid technical arguments from a licensee.
Comments on DG-3030 (Rev. 2 to RG 3.71), Page 4 Comment No.,
Comment From Comment NRC Response
- 6.
J. Schlueter (NEI)
The requirement to discount a positive bias does not appear to be technically unfounded. If careful bench marking demonstrates that the code over predicts k effective, then including the bias should be acceptable. One should not assume that a conservative bias (over predicting k effective) is the result of some error in calculating benchmark cases when a non-conservative bias (under predicting k effective) is not. We either have confidence in the benchmarking process and the statistical treatment of bias and uncertainty or we do not.
Disagree. This merely restates existing NRC policy, as noted in this RG and also pg. 8 of NUREG/CR-6698, Guide for Validation of Nuclear Criticality Safety Calculational Methodology. Note that the exception states that a positive bias should not be used to determine calculational margin. The use of the word should denotes a recommendation and not a requirement. The NRC is open to review and consider valid technical arguments from a licensee.
- 7.
J. Schlueter (NEI)
For the staffs information, ANS/ANSI 8.6 is directly related to the subject of the Draft Guide. It is currently being balloted for re-affirmation and will likely be reaffirmed prior to DG-3030 being issued in final. Therefore, to the degree possible, NRC should ensure that the final guide reflects or, at a minimum, is not inconsistent with the final ANS/ANSI 8.6 standard.
Reaffirmation does not change the content of the standard. If this standard will be reaffirmed this year, the reaffirmation date in the RG can be changed. In Section 1.b, change to ANSI/ANS-8.6-1983 (Reaffirmed in 2010, "Safety in Conducting Subcritical Neutron-Multiplication Measurements In Situ"
- 8.
S. Phillips (Canberra)
Comment on Section C, Item 2b:
We recognize the importance of the detection of both neutron (n) and gamma (() radiation in criticality accident alarm systems, since the detection of criticality events is dependent on both the characteristics of the event and the presence of moderating and shielding materials in the facility. It is also important for a criticality accident detection system to account for the relative contribution of neutrons and gamma rays as pointed out in Section B.2.2 of the ANSI/ANS-8.3-1997.
We recommend that the standards reinforce the importance of criticality accident alarm systems being equipped with both neutron and gamma detectors.
General comment on the standard. Comment noted.
No NRC response necessary.
Comments on DG-3030 (Rev. 2 to RG 3.71), Page 5 Comment No.,
Comment From Comment NRC Response
- 9.
S. Phillips (Canberra)
Comment on Section C, Item 2b:
With regard to the third exception, we recognize difficulties in the setting of the detection system alarm threshold based on absorbed-dose-in-tissue versus absorbed-dose-in-free air. The absorbed-dose-in-tissue value can differ significantly from the absorbed-dose-in-free-air depending on the dose conversion factor that is used and the geometry between the dose point and the detector. Typical computational methods (MCNP) can be closely matched to the absorbed-dose-in-free-air.
In addition (and related), as described in Section B.2.2 of the ANSI/ANS-8.3-1997, an accurate estimation of the n/( ratio is strongly influenced by the type of accident and on whether the absorbed-dose is determined in tissue or free-air. As mentioned previously, the n/(, ratio is an important factor in criticality accident detection systems.
For these reasons, it appears that the absorbed-dose-in-free-air would be preferred as used in the ANSI/ANS-8.3-1997 standard.
The commenter makes the case that the absorbed dose in free air should be preferred as opposed to the absorbed dose in soft tissue as we state in the exception. However, this exception to the standard is consistent with the regulations (70.24 (a)(1) and 76.89(b)) and the regulatory guide should be consistent with the rule. The only way we would alter this exception would be if there were a rule change. The commenter has the option to submit a petition for rulemaking on this issue.
- 10.
S. Phillips (Canberra)
With regard to the first exception, the conservative approach is certainly prudent whereby a criticality alarm system is required in each area (compared with only an evaluation per area).
General comment. No NRC response necessary.
- 11.
S. Phillips (Canberra)
With regard to the second exception, again a conservative approach is favored by using two or more detectors per system to ensure redundancy in the alarming system. There is the added benefit in the reduction of false alarms when requiring a 2-of-3 voting logic when using a 3 detector system.
General comment. No NRC response necessary.
Comments on DG-3030 (Rev. 2 to RG 3.71), Page 6 Comment No.,
Comment From Comment NRC Response
- 12.
S. Phillips (Canberra)
As a general comment, it would appear that some uncertainty exists in the full understanding of historical criticality events (ANSI/ANS-8.3-1997 standard). Uncertainty of the relative n/( contributions and saturation of the detectors likely limits the evaluation of this data, and hinders the post-accident response. Going forward it may be advantageous to ensure that the criticality accident alarm systems are capable of providing more data for post-accident analysis.
General comment on the standard. Comment noted.
No NRC response necessary