The Calvert Cliffs Nuclear Power Plant, Inc. (the licensee) is the holder of Renewed Facility Operating License Nos. DPR-53 and DPR-69, which authorize operation of Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2 (CCNPP), respectively. The licenses provide, among other things, that the facility is subject to all rules, regulations, and orders of the Nuclear Regulatory Commission (NRC, the Commission) now or hereafter in effect.
The facility consists of two pressurized-water reactors located in Calvert County in Maryland.
Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.68, “Criticality accident requirements,” sets forth requirements for which a licensee shall comply in lieu of maintaining a monitoring system capable of detecting a criticality as described in 10 CFR 70.24. In particular, subsection (b)(1) of 10 CFR 50.68 requires that plant procedures shall prohibit the handling and storage at any one time of more fuel assemblies than have been determined to be safely subcritical under the most adverse moderation conditions feasible by unborated water.
By letter dated December 21, 2004, as supplemented on May 31, 2005, the licensee submitted a request for an exemption from the requirements of 10 CFR 50.68(b)(1) during the pent fuel pool (SFP) activities related to the underwater handling, loading, and unloading of the Transnuclear NUHOMS-32P® dry shielded canister (DSC), as described in its proposed Amendment to Materials License No. SNM-2505, dated December 12, 2003, for the plant-specific independent spent fuel storage installation (ISFSI) at CCNPP.
In summary, the licensee is unable to satisfy the above requirement for handling of the Transnuclear NUHOMS-32P® DSC authorized by 10 CFR Part 72 at CCNPP. Section 50.12(a) allows licensees to apply for an exemption from the requirements of 10 CFR Part 50 if the application of the regulation is not necessary to achieve the underlying purpose of the rule and special conditions are met. The licensee stated in its application that compliance with 10 CFR 50.68(b)(1) is not necessary for handling the Transnuclear NUHOMS-32P® DSC system to achieve the underlying purpose of the rule.
Pursuant to 10 CFR 50.12, the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of 10 CFR Part 50 when: (1) The exemptions are authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security; and (2) when special circumstances are present. Therefore, in determining the acceptability of the licensee's exemption request, the NRC staff has performed the following regulatory, technical, and legal evaluations to satisfy the requirements of 10 CFR 50.12 for granting the exemption.
3.1 Regulatory Evaluation
The CCNPP Technical Specifications (TSs) currently permit the licensee to store spent fuel assemblies in high-density storage racks in its SFP. In accordance with the provisions of 10 CFR 50.68(b)(4), the licensee takes credit for soluble boron for criticality control and ensures that the effective neutron multiplication factor (keff) of the SFP does not exceed 0.95, if flooded with borated water. Subsection 50.68(b)(4) also requires that if credit is taken for soluble boron, the keff must remain below 1.0 (subcritical) if flooded with unborated water. However, the licensee is unable to satisfy the requirement to maintain the keff below 1.0 (subcritical) with unborated water, which is also the requirement of 10 CFR 50.68(b)(1), during cask handling operations in the SFP. Therefore, the licensee proposed an exemption from 10 CFR 50.68(b)(1) to permit the performance of spent fuel loading, unloading, and handling operations related to dry cask storage without being analyzed to be subcritical under the most adverse moderation conditions feasible by unborated water.
Appendix A, “General Design Criteria (GDC) for Nuclear Power Plants,” to 10 CFR Part 50 provides a list of the minimum design requirements for nuclear power plants. According to GDC 62, “Prevention of criticality in fuel storage and handling,” the licensee must limit the potential for criticality in the fuel handling and storage system by physical systems or processes. Since CCNPP was licensed prior to the issuance of the Appendix A to 10 CFR Part 50, GDC 62 is not directly applicable. However, CCNPP was licensed to the 1967 draft GDC, as discussed in Appendix 1C of the CCNNP Updated Final Safety Analysis Report (UFSAR). The comparable draft GDC is Criterion 66, “Prevention of Fuel Storage Criticality,” that states: “Criticality in new and spent fuel storage shall be prevented by physical systems or processes. Such means as geometrically safe configurations shall be emphasized over procedural controls.” Start Printed Page 54413
Section 50.68 of 10 CFR Part 50 provides the NRC requirements for maintaining subcritical conditions in SFPs. Section 50.68 provides criticality control requirements that, if satisfied, ensure that an inadvertent criticality in the SFP is an extremely unlikely event. These requirements ensure that the licensee has appropriately conservative criticality margins during handling and storage of spent fuel. Section 50.68(b)(1) states, “Plant procedures shall prohibit the handling and storage at any one time of more fuel assemblies than have been determined to be safely subcritical under the most adverse moderation conditions feasible by unborated water.” Specifically, 10 CFR 50.68(b)(1) ensures that the licensee will maintain the pool in a subcritical condition during handling and storage operations without crediting the soluble boron in the SFP water.
The licensee is authorized under plant-specific Materials License No. SNM-2505 to construct and operate an ISFSI at CCNPP. The ISFSI permits the licensee to store spent fuel assemblies in large concrete dry storage casks. As part of its ISFSI loading campaigns, the licensee transfers spent fuel assemblies to a DSC in the cask pit area of the SFP. The licensee performed criticality analyses assuming the DSC fully loaded with fuel having the highest permissible reactivity and determined that a soluble boron credit was necessary to ensure that the DSC would remain subcritical in the SFP. Since the licensee is unable to satisfy the requirement of 10 CFR 50.68(b)(1) to ensure subcritical conditions during handling and storage of spent fuel assemblies in the pool with unborated water, the licensee identified the need for an exemption from the 10 CFR 50.68(b)(1) requirement to support DSC loading, unloading, and handling operations without being subcritical under the most adverse moderation conditions feasible by unborated water.
The NRC staff evaluated the possibility of an inadvertent criticality of the spent nuclear fuel at CCNPP during DSC loading, unloading, and handling. The NRC staff has established a set of acceptance criteria that, if met, satisfy the underlying intent of 10 CFR 50.68(b)(1). In lieu of complying with 10 CFR 50.68(b)(1), the NRC staff determined that an inadvertent criticality accident is unlikely to occur if the licensee meets the following five criteria: 
1. The cask criticality analyses are based on the following conservative assumptions:
a. All fuel assemblies in the cask are unirradiated and at the highest permissible enrichment,
b. Only 75 percent of the Boron-10 in the fixed poison panel inserts is credited,
c. No credit is taken for fuel-related burnable absorbers, and
d. The cask is assumed to be flooded with moderator at the temperature and density corresponding to optimum moderation.
2. The licensee's ISFSI TSs require the soluble boron concentration to be equal to or greater than the level assumed in the criticality analysis, and surveillance requirements necessitate the periodic verification of the concentration both prior to and during loading and unloading operations.
3. Radiation monitors, as required by GDC 63, “Monitoring fuel and waste storage,” are provided in fuel storage and handling areas to detect excessive radiation levels and to initiate appropriate safety actions.
4. The quantity of other forms of special nuclear material, such as sources, detectors, etc., to be stored in the cask will not increase the effective multiplication factor above the limit calculated in the criticality analysis.
5. Sufficient time exists for plant personnel to identify and terminate a boron dilution event prior to achieving a critical boron concentration in the DSC. To demonstrate that it can safely identify and terminate a boron dilution event, the licensee must provide the following:
a. A plant-specific criticality analysis to identify the critical boron concentration in the cask based on the highest reactivity loading pattern.
b. A plant-specific boron dilution analysis to identify all potential dilution pathways, their flowrates, and the time necessary to reach a critical boron concentration.
c. A description of all alarms and indications available to promptly alert operators of a boron dilution event.
d. A description of plant controls that will be implemented to minimize the potential for a boron dilution event.
e. A summary of operator training and procedures that will be used to ensure that operators can quickly identify and terminate a boron dilution event.
3.2 Technical Evaluation
In determining the acceptability of the licensee's exemption request, the NRC staff reviewed three aspects of the licensee's analyses: (1) Criticality analyses submitted to support the ISFSI license application and its exemption request, (2) boron dilution analysis, and (3) legal basis for approving the exemption. For each of the aspects, the staff evaluated whether the licensee's analyses and methodologies provide reasonable assurance that adequate safety margins are developed and can be maintained in the CCNPP SFP during loading of spent fuel into canisters for dry cask storage.
3.2.1 Criticality Analyses
For evaluation of the acceptability of the licensee's exemption request, the NRC staff reviewed the criticality analyses provided by the licensee in support of its ISFSI license application.
First, the NRC staff reviewed the methodology and assumptions used by the licensee in its criticality analysis to determine if Criterion 1 of Section 3.1 above was satisfied. The licensee stated that it took no credit in the criticality analyses for burnup or fuel-related burnable neutron absorbers. Specifically, the licensee stated that its criticality analyses did not take credit for integral burnable absorbers, integral fuel burnable absorbers, nor control element assemblies. The licensee also stated that all assemblies were analyzed at the highest permissible enrichment, 4.5 weight percent Uranium-235 at CCNPP. Additionally, the licensee stated that all criticality analyses for a flooded DSC were performed at temperatures and densities of water corresponding to optimum moderation conditions. Finally, the licensee stated that it credited 90 percent of the Boron-10 content for the fixed neutron absorber in the DSC. NUREG-1536, “Standard Review Plan for Dry Cask Storage System,” states that “[f] or a greater credit allowance [i.e., greater than 75 percent for fixed neutron absorbers] special, comprehensive fabrication tests capable of verifying the presence and uniformity of the neutron absorber are needed.” As part of an amendment to the Part 72 license for the Transnuclear NUHOMS-32P® design, the NRC staff reviewed and accepted the results of additional data supplied by the manufacturer that demonstrated that a 90-percent credit for the fixed neutron absorbers was acceptable. Therefore, for the purposes of this exemption, the staff finds a 90-percent credit acceptable on the basis that it has previously been reviewed and approved by the NRC. Subsequently, based on its review of the criticality analyses and the information submitted in its exemption request, the Start Printed Page 54414NRC staff finds that the licensee has satisfied Criterion 1.
Second, the NRC staff reviewed the proposed CCNPP ISFSI TSs and the licensee's criticality analyses credit soluble boron for reactivity control during DSC loading, unloading, and handling operations. Since the boron concentration is a key safety component necessary for ensuring subcritical conditions in the pool, the licensee must have a conservative ISFSI TS capable of ensuring that sufficient soluble boron is present to perform its safety function. The licensee stated that ISFSI TS Limiting Condition for Operation (LCO) 126.96.36.199 requires that the NUHOMS-32P® DSC cavity be moderated by water with a boron concentration greater than or equal to 2450 ppm to accommodate cask operations. In all cases, the boron concentration required by the ISFSI TS ensures that the keff will be below 0.95 for the analyzed loading configuration. Additionally, the licensee's ISFSI TS contain surveillance requirements (SRs) that assure it will verify the boron concentration is above the required level both prior to and during DSC loading, unloading, and handling operations. Specifically, SRs 188.8.131.52 and 184.108.40.206 require verification of the boron concentration in the SFP within 24 hours prior to either insertion of the first spent fuel assembly into a DSC for loading operations or flooding the DSC cavity for unloading operations. Additionally, both SRs require the licensee to reconfirm the boron concentration is above the TS LCO limit at intervals not to exceed 48 hours until such time as the DSC is removed from the SFP. Based on its review of the CCNPP ISFSI TS, the NRC staff finds that the licensee has satisfied Criterion 2.
Third, the NRC staff reviewed the CCNPP UFSAR and the information provided by the licensee in its exemption request to ensure that it complies with GDC 63. GDC 63 requires that licensees have radiation monitors in fuel storage and associated handling areas to detect conditions that may result in a loss of residual heat removal capability and excessive radiation levels and initiate appropriate safety actions. As previously described, since CCNPP was licensed prior to the issuance of the GDC listed in Appendix A to 10 CFR Part 50, GDC 63 is not directly applicable. However, CCNPP is licensed to the 1967 draft GDC as discussed in its UFSAR, Appendix 1C. The comparable draft GDC is Criterion 18, “Monitoring Fuel and Waste Storage,” that states the following: “Monitoring and alarm instrumentation shall be provided for fuel and waste storage and handling areas for conditions that might contribute to loss of continuity in decay heat removal and to radiation exposure.” The NRC staff reviewed the CCNPP UFSAR, 1967 draft GDC, and exemption request to determine whether the licensee had provided sufficient information to demonstrate compliance with the intent of GDC 63. In its exemption request, the licensee stated that three area radiation monitors are provided for detecting high radiation levels in the fuel storage areas. Specifically, the monitors are located in the SFP area, on the spent fuel handling machine, and in the new fuel storage area. At the montors' alarm setpoints, audible and visual alarms annunciate locally and in the Control Room. Based on its review of the exemption request, the CCNPP UFSAR, and the 1967 draft GDC, the NRC staff finds that the licensee has satisfied Criterion 3.
Finally, as part of the criticality analysis review, the NRC staff evaluated the storage of non-fuel-related material in a DSC. The NRC staff evaluated the potential to increase the reactivity of a DSC by loading it with materials other than spent nuclear fuel and fuel debris. The approved contents for storage in the NUHOMS-32P® cask design are listed in the CCNPP ISFSI TS LCO 3.1.1 (1), “Fuel to be Stored at ISFSI.” This ISFSI TS LCO restricts the contents of the DSC to only fuels (14 x 14 Combustion Engineering-type pressurized water reactor fuel) irradiated at CCNPP. As such, CCNPP is prohibited from loading other forms of special nuclear material, such as sources, detectors, etc., in the DSC. Therefore, the NRC staff determined that the loading limitations described in the CCNPP ISFSI TSs will ensure that any authorized components loaded in the DSCs will not result in a reactivity increase. Based on its review of the loading restrictions, the NRC staff finds that the licensee has satisfied Criterion 4.
3.2.2 Boron Dilution Analysis
Since the licensee's ISFSI application relies on soluble boron to maintain subcritical conditions within the DSCs during loading, unloading, and handling operations, the NRC staff reviewed the licensee's boron dilution analysis to determine whether appropriate controls, alarms, and procedures were available to identify and terminate a boron dilution accident prior to reaching a critical boron concentration.
By letter dated October 25, 1996, the NRC staff issued a safety evaluation (SE) on licensing topical report WCAP-14416, “Westinghouse Spent Fuel Rack Criticality Analysis Methodology.” This SE specified that the following issues be evaluated for applications involving soluble boron credit: the events that could cause boron dilution, the time available to detect and mitigate each dilution event, the potential for incomplete boron mixing, and the adequacy of the boron concentration surveillance interval.
In its exemption request, the licensee described the criticality analyses performed to determine the worst-case bounding keff. The CCNPP criticality calculations employed the KENO V.a code with the 44-group ENDF/B-V cross section library. The calculations determined the minimum soluble boron concentration required to maintain subcriticality (keff < 1.0) following a boron dilution event in a NUHOMS-32P® DSC loaded with fresh 4.5 weight percent enriched fuel assemblies that bound the CCNPP fuel designs (Combustion Engineering (CE) 14 x 14 fuel). The results of the calculations for the bounding case indicate that subcriticality is maintained with 1650 ppm of soluble boron in the SFP.
The TS requirements for the NUHOMS-32P® Cask System include a minimum boron concentration requirement of 2450 ppm boron when spent fuel assemblies with enrichments less than or equal to 4.5 weight-percent (wt-percent) U-235 are loaded into a DSC canister. The approval of this exemption is limited to the DSC loading, unloading, and handling of CE 14 x 14 fuel assemblies enriched to a maximum of 4.5 wt-percent U-235. The use of fuel-related burnable absorbers is credited in the analysis. The NUHOMS-32P® soluble boron TS requirements ensure that keff is maintained less than 0.95. TS SRs require the boron concentration in the DSC water to be verified within 24 hours prior to the insertion of the first spent fuel assembly into a DSC and reconfirmed at intervals not to exceed 48 hours until such time as the DSC is removed from the SFP.
The licensee contracted with Transnuclear to perform a criticality analysis to determine the soluble boron concentration that results in a keff equal to 1.0 for 4.5 wt-percent U-235 fuel enrichments using the same methodology as approved in the Standardized NUHOMS Cask System Final Safety Analysis. The analysis determined the critical boron concentration level for 4.5 wt-percent U-235 enriched fuel was 1650 ppm. The boron concentration within the canister would have to decrease from the TS limit to the critical boron concentration before criticality is possible. The licensee based its boron dilution analyses and its preventive and Start Printed Page 54415mitigative actions on dilution sources with the potential to reduce the boron concentration from the TS minimum values for the two fuel enrichment bands to the respective concentration for criticality.
During the current analysis the licensee identified all credible potential sources that could dilute the SFP to critical conditions. The licensee determined that the limiting boron dilution event occurs when water from the fire protection system (FPS), with a maximum flow rate of 1000 gpm from the most limiting hose (a 3-inch diameter with a 2-inch nozzle), is added to the SFP. The licensee's calculations show that at least 4 hours will be available to terminate the event before the DSC water boron concentration decreases from 2450 ppm to the critical concentration of 1650 ppm, assuming a straight dilution to the SFP overflow limit and a feed and bleed operation thereafter with instantaneous complete mixing.
To demonstrate that sufficient time exists for plant personnel to identify and terminate a boron dilution event, the licensee provided a description of all alarms available to alert operators, and plant controls that will be implemented. There is no automatic level control system for the SFP; therefore, the SFP will overflow on an uncontrolled water addition. However, a high level alarm in the control room would alert personnel of a potential boron dilution event within 15 minutes for a 1000 gpm dilution rate. In addition to the SFP high level alarm, annunciator alarms for the FPS exist in the Control Room, which would alert operators to identify and terminate the worst-case boron dilution source. This means that there would be more than 3 additional hours before the critical boron concentration of 1650 ppm within the DSC is reached. The NRC staff finds that this is acceptable.
The CCNPP's SFP is a large rectangular structure filled with borated water that completely covers the spent fuel assemblies. A 3.5-foot wall divides the pool, with the north half associated to Unit 1 and the south half associated to Unit 2. A slot in the dividing wall has removable gates, which allow movement of the fuel assemblies between the two halves of the pool. The slot is normally open and the removable gate stored in the Unit 1 SFP close to the west end of the south wall. However, to ensure the applicability of the assumptions in its dilution and criticality evaluations, the licensee has committed to revise the fuel-handling procedure to include an initial condition that requires the slot between the two pools to be open and the gate to be stored in its proper storage location when a DSC is present in the Unit 1 SFP.
To ensure that operators are capable of identifying and terminating a boron dilution event during DSC loading, unloading, and handling operations, operator training will be conducted. During training activities operators will receive revised alarm manual procedures which verify that the SFP boron concentration is in compliance with the new ISFSI TS limit prior to the loading of a NUHOMS-32P® DSC.
Based on the NRC staff's review of the licensee's exemption request dated December 21, 2004, as supplemented on May 31, 2005, and its boron dilution analysis, the NRC staff finds that the licensee has provided sufficient information to demonstrate that an undetected and uncorrected dilution from the TS required boron concentration to the calculated critical boron concentration is very unlikely. Based on its review of the boron analysis and enhancements to the operating procedures and operator training program, the NRC staff finds the licensee has satisfied Criterion 5.
Therefore, in conjunction with the conservative assumptions used to establish the TS required boron concentration and critical boron concentration, the boron dilution evaluation demonstrates that the underlying intent of 10 CFR 50.68(b)(1) is satisfied.
3.3 Legal Basis for the Exemption
3.3.1 Authorized by Law
This exemption results in changes to the operation of the plant by allowing the operation of the new dry fuel storage facility and loading of the NUHOMS-32P® DSC. As stated above, 10 CFR 50.12 allows the NRC to grant exemptions from the requirements of 10 CFR Part 50. In addition, the granting of the licensee's exemption request will not result in a violation of the Atomic Energy Act of 1954, as amended, or the intent of the Commission's regulations. Therefore, the exemption is authorized by law.
3.3.2 No Undue Risk to Public Health and Safety
The underlying purpose of 10 CFR 50.68(b)(1) is to ensure that adequate controls are in place to ensure that the handling and storage of fuel assemblies is conducted in a manner such that the fuel assemblies remain safely subcritical. Based on the NRC staff's review of the licensee's exemption request, the licensee has demonstrated that sufficient controls are in place to provide reasonable assurance that there is no undue risk to public health and safety given conservative assumptions in the criticality analysis (Criterion 1 above); surveillances periodically verify the boron concentration before and during loading and unloading (Criterion 2 above); radiation monitoring equipment is used to detect excessive radiation and initiate appropriate protective actions (Criterion 3 above); only fuel authorized by the ISFSI TS will be loaded and stored in the ISFSI (Criterion 4 above); and boron dilution events have been analyzed, and there are sufficient monitoring capabilities and time for the licensee to identify and terminate a dilution event prior to achieving a critical boron concentration in the cask (Criterion 5 above). Therefore, the NRC staff concluded that the underlying purpose of the rule has been satisfied and that there is no undue risk to public health and safety.
3.3.3 Consistent with Common Defense and Security
This exemption results in changes to the operation of the plant by allowing the operation of the new dry fuel storage facility and loading of the NUHOMS-32P® DSC. This change to the fuel assembly storage and handling in the plant does not affect the national defense strategy because the national defense is maintained by resources (hardware or software or other) that are outside the plant and that have no direct relation to plant operation. In addition, loading spent fuel into the NUHOMS-32P® DSC in the SFP does not affect the ability of the licensee to defend the plant against a terrorist attack. Therefore, the common defense and security is not impacted by this exemption request.
3.3.4 Special Circumstances
Pursuant to 10 CFR 50.12, “Specific exemptions,” the NRC staff reviewed the licensee's exemption request to determine if the legal basis for granting an exemption had been satisfied. With regards to the six special circumstances listed in 10 CFR 50.12(a)(2), the NRC staff finds that the licensee's exemption request satisfies 50.12(a)(2)(ii), “Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.” Specifically, the NRC staff concludes that since the licensee has satisfied the five criteria in Section 3.1 of this exemption, the application of the rule is not necessary to achieve its underlying purpose in this particular case. Start Printed Page 54416
Based upon the review of the licensee's exemption request to credit soluble boron during DSC loading, unloading, and handling in the CCNPP SFP, the NRC staff concludes that pursuant to 10 CFR 50.12(a)(2) the licensee's exemption request is acceptable. However, the NRC staff places the following limitations and/or conditions on the approval of this exemption:
1. This exemption is limited to the loading, unloading, and handling of the DSC for only the TN NUHOMS-32P® at CCNPP.
2. This exemption is limited to the loading, unloading, and handling in the DSC at CCNPP of Combustion Engineering 14x14 fuel assemblies that had maximum initial, unirradiated U-235 enrichments of 4.5 weight percent.
Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12(a), the exemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security. Also, special circumstances are present. Therefore, the Commission hereby grants the licensee an exemption from the requirements of 10 CFR 50.68(b)(1) for the loading, unloading, and handling of the components of the Transnuclear NUHOMS-32P® dry cask storage system at CCNPP. However, since the licensee does not have an NRC-approved methodology for evaluating changes to the analyses or systems supporting this exemption request, the NRC staff's approval of the exemption is restricted to those specific design and operating conditions described in the licensee's December 21, 2004, exemption request. The licensee may not apply the 10 CFR 50.59 process for evaluating changes to specific exemptions. Any changes to the design or operation of (1) the dry cask storage system, (2) the SFP, (3) the fuel assemblies to be stored, (4) the boron dilution analyses, or (5) supporting procedures and controls, regardless of whether they are approved under the general Part 72 license or perceived to be conservative, will invalidate this exemption. Upon invalidation of the exemption, the licensee will be required to comply with NRC regulations prior to future cask loadings.
This exemption is effective upon issuance.Start Signature
Dated at Rockville, Maryland, this 2nd day of September, 2005.
For the Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear Reactor Regulation.
1. The criteria have been used previously in the review of similar exemptions from the requirements of 10 CFR 50.68(b)(1) for Diablo Canyon Units No. 1 and 2 and Sequoyah Units No. 1 and 2. The evaluations for these exemptions are available in the Agencywide Documents Access and Management System under accession numbers ML040300693 and ML041540213, respectively.Back to Citation
[FR Doc. 05-18193 Filed 9-13-05; 8:45 am]
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