ML23209A716
| ML23209A716 | |
| Person / Time | |
|---|---|
| Site: | North Carolina State University |
| Issue date: | 07/28/2023 |
| From: | Hudson J NRC/NRR/DANU |
| To: | Hawari A North Carolina State University |
| References | |
| EPID L-2022-NFA-0004 | |
| Download: ML23209A716 (1) | |
Text
From: Justin Hudson To: Ayman I. Hawari Cc: Gerald Wicks; Colby Fleming; Edward Helvenston; Josh Borromeo; Duane Hardesty
Subject:
Audit Report Related to the NRC Staff Review of the North Carolina State University License Request Regarding Vented Fueled Experiments for the PULSTAR Research Reactor (EPID No. L-2022-NFA-0004)
Date: Friday, July 28, 2023 1:54:00 PM Attachments: Audit Report for NCSU.pdf
Dear Dr. Hawari:
By letter dated April 18, 2022 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML22108A16), as supplemented by letters dated July 11, 2022, March 13, 2023, May 12, 2023, and June 20, 2023 (ML22193A167, ML23075A056, ML23132A126, ML23171B001, respectively), North Carolina State University applied for an amendment to Facility Operating License No. R-120 for the North Carolina State University PULSTAR Research Reactor. The amendment revises the Technical Specifications and License Conditions to provide a single fission rate limit that applies to all fueled experiments; to allow NCSU to perform fueled experiments with plutonium, in addition to uranium-235; and to allow NCSU to perform vented fueled experiments.
Attached is a report on the regulatory audit conducted by staff of the U.S. Nuclear Regulatory Commission (NRC) from November 7, 2022, to July 28, 2023, in connection with its review of the application. The audit report does not make any licensing conclusions or findings, but it is part of the administrative record of the NRC staffs review of the application and may provide information supporting the NRC staffs safety evaluation. The audit followed the plan provided by letter dated October 31, 2022 (ML22304A184), unless otherwise noted in the enclosed report.
If you have any questions, please contact me at (301)287-0538 or by email at Justin.Hudson@nrc.gov.
Justin Hudson
Project Manager, Non-Power Production and Utilization Facility Licensing Branch (UNPL)
NRR/DANU U.S. Nuclear Regulatory Commission (301)287-0538
OFFICE OF NUCLEAR REACTOR REGULATION
REGULATORY AUDIT REPORT
REGARDING THE LICENSE AMENDMENT REQUEST FOR VENTED FUELED EXPERIMENTS
FACILITY OPERATING LICENSE NO. R-120
NORTH CAROLINA STATE UNIVERSITY
NORTH CAROLINA STATE UNIVERSITY PULSTAR RESEARCH REACTOR
DOCKET NO. 50-297
Location: North Carolina State University PULSTAR Research Reactor, Raleigh, North Carolina, and U.S. Nuclear Regulatory Commission Headquarters, Rockville, MD
Dates: 11/ 08/ 2022 - 07/ 28/ 2023
Audit Team Members: Justin Hudson, Audit Team Leader Edward Helvenston, Audit Team Member
Licensee Representatives: Dr. Ayman Hawari, Director Dr. Colby Fleming, Reactor Manager Gerald Wicks, Reactor Health Physicist
=
Background===
By letter dated April 18, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22108A16), as supplemented by letters dated July 11, 2022, March 13, 2023, May 12, 2023, and June 20, 2023 (ML22193A167, ML23075A056, ML23132A126, ML23171B001, respectively), North Carolina State University applied for an amendment to Facility Operating License No. R-120 for the North Carolina State University PULSTAR Research Reactor. The amendment revises the T echnical Specifications and License Conditions to provide a single fission rate limit that applies to all fueled experiments; to allow NCSU to perform fueled experiments with plutonium, in addition to uranium -235; and to allow NCSU to perform vented fueled experiments.
This audit allowed the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) to gain a better understanding of North Carolina State Universitys (NCSU) license amendment request related to fueled experiments and perform a more effective and efficient review with the objective of improving communication and avoiding unnecessary requests for additional information (RAIs). Reviewing underlying documentation and engaging in audit discussions about site characteristics facilitated the staffs understanding of the license amendment request application.
This report summarizes the regulatory audit conducted by the stafffrom November 7, 2022, to July 28, 2023, in connection with its review of the license amendment request. The audit report does not make any licensing conclusions or findings, but it is part of the administrative record of
the staffs review of the application and may provide information supporting the staffs safety evaluation. The audit followed the plan dated October 31, 2022 (ML22304A184), unless otherwise noted in this report.
Audit Activities
The primary objective of the audit was to enable an effective and efficient review of the license amendment request related to fueled experiments by allowing the staff to review and discuss supporting material with NCSU. Gaining access to underlying documentation and engaging in audit discussions about site characteristics facilitated the staffs understanding of the license amendment request. The audit improved communication and provided detailed information for the staff such that no RAIs were needed.
The audit was conducted from the months of November 2022, through July 2023, via G oogle Drive and involving one site visit in December 2022. The staff conducted the audit in accordance with the Office of Nuclear Reactor Regulation (NRR) Office Instruction NRR LIC-111, Revision 1, Regulatory Audits.
Prior to the audit, the audit team reviewed the license amendment request and provided preliminary questions by email on November 7, 2022 (ML22312A355). The NRC staff then discussed these questions with NCSU during the onsite visit on December 20, 2022. The resolutions of these questions are provided in the table below. This onsite visit also allowed the NRC staff to gain a better understanding of the experimental area and how the licensee intends to use vented fueled experiments.
In the course of the audit, virtual meetings were held between the staff and NCSU on February 22, 2023, May 4, 2023, and June 12, 2023.
The staff reviewed the following documents via Google Drive:
- Proposed technical specifications
- Proposed license conditions
- Dose calculations background information
- Justifications for proposed changes
Summary of Audit Outcome
The staffs audit focused on the preliminary questions sent to the licensee (ML22312A355) and reviewing additional documents to resolve these questions. The staff reviewed information through Google Drive and held discussions with NCSU staff to understand and resolve the questions. In many cases, modifications to the license amendment request were made and updated on the docket to resolve items discussed in the audit. The tables below summarize the resolution of these specific questions.
Exit Briefing
On July 28, 2023, the audit team held an exit briefing with the licensee representatives, including Dr. Ayman Hawari, Dr. Colby Fleming, and Gerald Wicks. The NRC staff received no questions, comments, or concerns regarding the audit or the audit process.
Deviations from the Audit Plan
There were no deviations from the Audit Plan.
OFFICE NRR/DANU/UNPL/PM NRR/DANU/UNPL/BC NRR/DANU/UNPL/PM NAME JHudson JBorromeo JHudson DATE 7/28/2023 7/28/2023 7/28/2023 Proposed License Conditions Question Question Resolution Number 1.a The LAR requests the authority to possess up to 20 grams of contained NCSU stated it would revi se its Plutonium-239 of any enrichment in the form of fission chambers. However, request to up to 20 grams of the NRC staff notes that all plutonium is considered special nuclear plutonium in the form of fission material, and therefore such a possession allowance should clearly include chambers or similar.
all plutonium including isotopes other than plutonium-239.
1.b The LAR also states this this requested plutonium is for fission chambers for NCSU stated that it had planned to upcoming planned experiments. However, it is not clear what types of use these fission chambers for experiments these fission chambers are for, whether these are characterization of their response commercially manufactured fission chambers, and whether they could to reactor conditions and potentially be reactor experiments (e.g., would be evaluated as part of a comparison with performance of reactor experiment), or would be used to monitor reac tor experiments. other fission chambers (e.g.,
uranium fission chambers). NCSU stated that they would not be safety channels. They could either be commercially manufactured or obtained from a collaborator but would not be made at NCSU.
NCSU stated that it would consider these to be detectors, and therefore not considered to be experiments per the existing TS definition. NCSU initially stated that the plutonium fission chambers could include both sealed fission chambers, and open-flow fission chambers; however, NCSU subsequently stated that it would limit its use of fission chambers in conjunction with this LC to sealed fission chambers to avoid potential concerns with open-flow fission chambers.
Enclosure
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2.a The LAR requests the authority to possess up to 35 grams of Uranium-235 NCSU changing wording to in any enrichment excluding uranium containing U -233 and up to 5 grams of something like up to 35 grams of plutonium for fueled experiments. This authority would replace the current contained U-235 of any allowance to possess up to 2 grams of contained uranium -235 of any enrichment in any form and enrichment in the form of foils. The NRC staff notes that the proposed changing wording to up to 5 revised LC would not clearly describe the uranium consistent with standard grams of plutonium in any form.
LC language. Also, the allowed form(s) of the uranium and plutonium are not clear.
2.b In addition, the NRC staff notes that the wording for fueled experiments in NCSU clarified that the total the proposed LC could limit the allowed uses of material possessed under material it is requesting to this portion of LC 2.B.(2), and it is not clear to the NRC staff i f this is NCSUs possess could include things like intent. flux foils (listed in its current LC and being merged into the proposed LC) as well as material for fueled experiments. NSCU will be removing for fueled experiments from the proposed language.
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Proposed Technical Specifications - Technical Specification Definition of Fueled Experiment Question Question Resolution Number 3.a The intended meaning of definition item e. with the proposed addition of and excludes NCSU is making the following may not be fully clear. fueled experiments exclude the following: a separate sentence Generally on item 3, NCSU stated that in addition to changes related to 3a through 3e it will also make the items currently listed in proposed TS definition item e.ii. separate items (e.g., e.ii through e.v) for clarity.
3.b Regarding detectors containing fissile material in the item e.ii. list: Could there be a Detectors will not be case where a detector itself is an experiment. experiments.
3.c Regarding sealed sources in the item e.ii. list: Is this intended to be limited to neutron NCSU clarified that it sources used in reactor operations? considers sealed sources to mean neutron sources used in reactor operations, e.g.,
the PuBe source.
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3.d Regarding naturally occurring elements in the item e.ii. list: What does this mean? The NCSU clarified that it staff notes that irradiation of, for example, uranium -containing minerals, could still intended naturally potentially be a fueled experiment. occurring elements to include things like geological samples and soil which could include incidental trace amounts of uranium, which it would not consider fueled experiments.
However, for clarity, NCSU stated that it would remove naturally occurring elements from the proposed TSs because it is generally understood that these types of experiments are not considered fueled experiments and the explicit exclusion is not needed.
3.e Regarding fuel used in operation of the reactor in the item e.ii. list: Is this intended to be NCSU stated that it will limited to, for example, research reactor fuel elements described in Section 5 of the revise fuel used in PULSAR reactor TSs? operation of the reactor to PULSTAR research reactor fuel described in TS 5.1.a or similar wording.
Proposed Technical Specifications - Technical Specification 3.5 Radiation Monitoring Question Question Resolution Number 4.a Does NCSU need an allowance to have proposed TS 3.5 not apply NCSU adding an exception statement
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when irradiated fuel or fueled experiments are not in e.g., a properly about shipping containers.
sealed and approved shipping container?
4.b Is it accurate that NCSU would never move fuel or experiments in the NCSU answered as Yes.
waste tank vault described in current TS 5.2.d being under the reactor license? (Question also applies to proposed TS 3.6.)
4.c The NRC staff notes an apparent error in proposed TS 3.5 in that are NCSU will revise back to the original should be is. is.
4.d NCSUs explanation for the changes to TS 3.5.b states The names of NCSU clarified that yes, its intent was the gas and particulate monitors are updated to better describe the to distinguish the monitors from monitors in light of potential experimental monitors which might be experimental monitors. NCSU also installed. Can NCSU elaborate on what is meant by this? Is the intent stated that it did not intend for to distinguish these monitors from gas or particulate monitors that will proposed TS 3.5.b to require a be part of experiments? specific Stack Gas or Stack Particulate monitor because multiple monitors in the exhaust system are fully capable of performing the functions of the required monitors; NCSU will revise the proposed TS from Stack Gas and Stack Particulate to Stack gas and stack particulate (i.e., lower case) to help clarify this.
4.e.i Does the required monitor include both gas and particulate monitoring? NCSU clarified that the required monitor only includes gas monitoring, as indicated by the TS wording exhaust gas radiation monitor.
4.e.ii Will the required monitors isolate the experiment if setpoints NCSU clarified that its intent is that the exceeded? If so, is this function part of the TS? required monitor would include an isolation function as indicated in the original LAR submittal dated April 18, 2022; however this function would not be part of the TS requirement.
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4.e.iii Will the required monitors detect if particulate activity is inadvertently NCSU stated the TS-required stack released from a vented fueled experiment? particulate monitor would detect if particulate activity were inadvertently released from a vented fueled experiment. Although NCSU plans to install filters in the experiment exhaust that could remove any particulate activity released from an experiment capsule before it could reach the main facility HVAC system and the stack particulate monitor, NCSU noted that other monitors in the vicinity of vented fueled experiments (including area monitors in the vicinity of the beam port where NCSU plans to install vented fueled experiments) would also help detect and provide early indication of any unusual radioactivity releases from vented fueled experiments including unanticipated particulate accumulation on experiment filters. NCSU also noted that it periodically (and with increased frequency if elevated readings occur) performs counts on stack particulate monitor filters to analyze isotopes deposited on the filters. NCSU noted that trends in this data could also give indication if vented fueled experiments are not retaining particulates as expected.
4.e.iv Will the vented experiment exhaust (after passing through experiment NCSU confirmed that all vented fueled radiation monitors) enter the main facility HVAC system upstream of experiment exhausts would enter the the stack monitors? main facility HVAC system upstream of the stack monitors.
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4.f Following the proposed removal of Ar-41 and Co -60 from TS 3.5-1, NCSU stated that it will keep Ar-41 how (i.e., to the airborne effluent concentration for what and Co -60 as included in its current radionuclide(s)) would NCSU calibrate its stack monitors for alert and TS Table 3.5-1. NCSU also stated that alarm purposes? it would provide an explanation of how the setpoints included the current TS would continue to be appropriate and conservative for operation with the proposed fueled experiments.
4.g It is not clear to the NRC staff why the proposed revision of TS 3.5, NCSU stated that it will keep TS 3.5, footnote (6), is necessary given that 10 CFR Part 20 dose limits only footnote (6), as written in the current include doses from licensed operation. TSs.
Regarding proposed TS 3.5, footnote (7), are vented fueled experiment NCSU confirmed that it intends radiation monitors also necessary during some period of time following experiment is in operation in experiment operation, for example, if some fission products may proposed TS 3.5, footnote (7), to 4.h continue to be released from the experiment, or if the monitors are include anytime the vented fueled located following some holdup volume? What is meant by experiment experiment exhaust is operating, is in operation or operable? even if the reactor is shutdown.
4.i Should TS 3.5, footnote (7), and the main text of TS 3.5, require that NCSU stated this it will revise vented fueled experiment radiation and flow monitors be operating operable to operating in the main versus operable consistent with the PULSTAR TS definitions?. text of TS 3.5 and in TS 3.5, footnote (7).
4.j The NRC staff notes that the proposed TSs do not appear to contain a Footnote 8 will be deleted.
TS 3.8.d.iv as referenced in TS 3.5, footnote (8). In addition, proposed TS 3.8 does not appear to contain any required radiation or flow monitor setpoints.
4.k Regarding the proposed revisions to the TS 3.5 bases, is Co-60 NCSU clarified that Co-60 is unlikely considered a potentially released radionuclide, or is it just used, e.g., to be a released radionuclide, but is as a convenient reference? used as a convenient reference due to its characteristics (e.g., high-energy gamma emitter).
4.l Regarding the proposed revisions to the TS 3.5 bases, the NRC staff NCSU will update the basis to reflect notes that proposed TS 3.8 does not appear to include monitoring of the changes discussed for LCO 3.5.
flow rates as referenced in the TS 3.5 bases.
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4.m Regarding the proposed addition of Radiation monitor setpoints are NCSU is deleting this from the basis.
analyzed as described in the documentation presented in the Fueled Experiment Analysis Report for TS Amendment 19 to the TS 3.5 bases, is this referring to the vented fueled experiment radiation monitors, and is this statement accurate following the revisions to NCSUs license amendment requirement discussed in NCSUs supplement dated July 11, 2022 (ML22193A167)?
Proposed Technical Specifications - Technical Specification 3.6 Confinement and Main HVAC Systems Question Question Resolution Number 5.a Does NCSU need an allowance to have proposed TS 3.6 not apply when irradiated fuel NCSU will be adding or fueled experiments are not in e.g., a properly sealed and approved shipping wording from the ANSI container? (See also ANSI/ANS-15.1-2007, Section 3.4.1, item (2).) standard to clarify this TS.
Proposed Technical Specifications - Technical Specification 3.8, Operations with Fueled Experiments Question Question Resolution Number 6.a Proposed TS 3.8.a states that mass and fission rate for fueled experiments are limited, NCSU stated that it will but the NRC staff notes that proposed TS 3.8.a only appears to include a fission rate revise to fission rate is limit. limited.
6.b The NRC staff notes that proposed TS 3.8.b appears to be redundant to TSs 3.5 and NCSU will be removing 3.6. Proposed TS 3.8.b also appears to use different wording than proposed TSs 3.5 3.8 b due to redundancy.
and 3.6 such that the requirements may not be clear.
6.c The NRC staff notes that proposed TS 3.8.c appears to be redundant to TS 3.2. NCSU will propose to delete current TS 3.8.c and provide justification (i.e., it is redundant).
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6.d.i Will vented fueled experiments still be non-corrosive for consistency with the intent of TS NCSU stated that it will 3.7.a? add language to proposed TS 3.8.d requiring that vented fueled experiments shall be designed to prevent interaction with reactor components or pool water, to ensure that the intent of existing TS 3.7.a continues to be captured.
6.d.ii How will NCSU ensure that having liquids in vented (unencapsulated) fueled NCSU stated that this experiments will not cause any undesirable interactions with reactor components or pool concern would be covered water and that the liquids are appropriately contained? by the language added for i). In addition, NCSU confirmed that its TS-required reviews of experiments would ensure that adequacy of the experimental design for any vented fueled experiments, including those containing liquids.
6.d.iii Proposed TS 3.8.d specifies that vented experiments do not need encapsulation, but NCSU stated that it will should this state vented fueled experiments? revise both instances of vented experiments in proposed TS 3.8.d to vented fueled experiments.
6.d.iv NCSUs discussion of TS 3.8.d changes stated that vented experiments are restricted to NCSU stated that will not allow particulate releases, but the NRC staff notes that it is not clear whether revise airborne activity in airborne activity clearly excludes particulates. proposed TS 3.8.d to gaseous airborne activity.
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6.e The NRC staff notes that proposed TS 3.8.e appears to be redundant to TSs 6.2.3 and NCSU will propose to 6.5. delete current TS 3.8.e and provide justification (i.e., it is redundant).
6.f The NRC staff notes that it is not clear if the list in proposed TS 3.8 beginning with Each NCSU will correct the TS type of fueled experiment shall meet the following items is part of TS 3.8.e, or should 3.8 formatting and be a separately numbered TS e.g. 3.8.[X]. numbering.
6.g Regarding proposed item ii. in the list in proposed TS 3.8 beginning with Each type of NCSU stated that it will fueled experiment shall meet the following items, how will NCSU ensure that remove the word powder experiment materials in powder form are appropriately contained? from this proposed TS item because powder is included in solid. NCSU confirmed that it will ensure powders are appropriately contained by, for example, use of a mesh that has a smaller size than the powder particle size, as discussed in the LAR.
6.h Regarding proposed item iii. (as numbered on page 27 of the proposed TS change NCSU confirmed that yes, pages submitted in NCSUs supplement dated July 11, 2022) in the list in proposed TS it will still perform such 3.8 beginning with Each type of fueled experiment shall meet the following items, will analyses for experiments NCSU still perform appropriate analyses for experiments located outside the pool water located outside the pool to ensure that thermal power is limited to prevent experiment failure? water, as appropriate.
NCSU also noted that for vented fueled experiments (which may be externally heated),
temperatures would be controlled to be low enough to avoid potentially driving any particulate fission products out of the experiments.
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6.i Regarding proposed item iv. in the list in proposed TS 3.8 beginning with Each type of NCSU clarified that this fueled experiment shall meet the following items, what locations for monitors would could include any location be considered at the exhaust of vented fueled experiments? between where the flow exits the vented fueled experiment capsule, and where the experiment flow enters the main ventilation system.
6.j Although NCSU did not propose to revise item v. in the list in proposed TS 3.8 beginning NCSU stated that it will with Each type of fueled experiment shall meet the following items, the NRC staff propose to delete current notes that the wording of item v. does not appear to be clear in the context of the revised item v. and provide list in proposed TS 3.8. In addition, the NRC staff notes that item v. appears to be justification (i.e., it is redundant to proposed TSs 3.8.c and 3.8.d. redundant).
6.k Regarding proposed TS 3.8.f, the basis for the addition of total site is not clear to the NCSU stated that it will NRC staff, and it also would appear to make TS 3.8.f inconsistent with the wording of remove its proposed existing TS 3.7.f. In addition, the NRC staff would like to verify that proposed TS 3.8.f addition of total site to would be consistent with a bounding calculation of dose from credible failure of a fueled current TS 3.8.f. NCSU experiment allowed by the proposed TSs. also stated it would provide revised dose calculations to allow the NRC staff to verify that current TS 3.8.f can continue to be met by the fueled experiments proposed in the LAR.
6.l The NRC staff notes that proposed TS 3.8.g appears to be redundant to TS 5.3. NCSU stated that it will remove its proposed addition of new TS 3.8.g.
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Proposed Technical Specifications - Technical Specification 4.4, Radiation Monitoring Equipment Question Question Resolution Number 7.a Should proposed TS 4.4.a additionally require channel calibration following replacement NCSU stated that it will of, or changes to, the stack monitoring systems? provide revised language for proposed TS 4.4.a, considering wording from ANSI/ANS-15.1 and NUREG-1537.
7.b Should proposed TS 4.4 require channel testing (e.g., daily) of the stack monitoring NCSU stated that as part systems? of its current startup checklist (performed prior to the first reactor startup of each day), it performs channel checks of these systems to verify operability. NCSU stated that it will provide written supplemental information justifying why this is sufficient and no additional TSs are needed.
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7.c Regarding proposed TS 4.4.c, it is not clear what is meant by the wording for as long as NCSU stated that it will the experiment is in operation. revise the proposed TS 4.4.c language for as long as the experiment is in operation to thereafter while the experiment is operational or similar.
NCSU clarified that its intent with this provision of proposed TS 4.4.c is that it would not be required to continue to perform the TS 4.4.c surveillance if vented fueled experiments are no longer being performed, for example, if the vented fueled experiment apparatus is removed.
7.d. Should proposed TS 4.4 require channel testing of the vented fueled experiment : NCSU stated that it radiation and flow monitors? would proposed a new TS (e.g., TS 4.4.d) requiring that prior to the first operation of a vented fueled experiment of the day (or similar wording),
it perform channel tests of the vented fueled experiment radiation and flow monitors.
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General Questions Question Question Resolution Number 8.a The NRC staff notes that, in issuing amendments to licenses, the amendment number NCSU understood/done.
and date is typically only updated on TS and license pages that include TS or license changes as part of the amendment.
8.b The NRC staff notes that the calculations provided by NCSU in its supplement dated NCSU clarified that the July 11, 2022, appear to be example calculations of proposed experiments, rather than calculations in its July 11, bounding calculations involving the maximum TS allowed time or fission rate. The NRC 2022, supplement are staff would like to confirm that NCSU calculations of experiments based on TS limits based on the proposed continue to result in acceptable doses. maximum TS allowed fission rate, but that this was not apparent because the supplement only specified thermal flux instead of total flux.
NCSU assumed an additional non-thermal flux equal to 30 percent of the thermal flux, to make the total thermal and non-thermal flux equal to the TS limit.
NCSU confirmed that the calculations provided in its July 11, 2022, supplement are based on similar assumptions to calculations in its original April 18, 2022, LAR (for example, same isotopes considered, and use of 0.1 correction factor for geometry inside of the reactor building).
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NCSU noted that the calculation results and assumption descriptions in its July 11, 2022, supplement contain several errors including:
- In Table 2, Column 2, 6x10 -9 mrem should read 6x10 -6 mrem
- In Table 2, Column 3, 1x10 -3 Ci should read 1.7x10 -3 Ci
- The July 11, 2022, supplement states that the encapsulated experiment accident release calculation (result Table 2, Column
- 4) assumed that the contents of the fueled experiment are evacuated from the reactor building over the course of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of fumigation conditions, but this should have stated 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
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NCSU stated it would provide revised dose calculation details on the portal, and provide updated/correct summary of assumptions and results in a written supplement.