ML21351A317
| ML21351A317 | |
| Person / Time | |
|---|---|
| Site: | University of California-Davis |
| Issue date: | 12/17/2021 |
| From: | Frey W McClellan Nuclear Research Center |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML21351A317 (4) | |
Text
UNIVERSITY OF CALIFORNIA, DA VIS BERKELEY
- DA VIS * !RVlNE
- LOS ANGELES
- MERCED
- RIVERSIDE
- SAN DIEGO
- SAN FRANCISCO
{
\\
SANTA BARBARA
- SANTA CRUZ
___________________________ \\
McClellan Nuclear Research Center UNIVERSITY OF CALIFORNIA Davis (9]6)-614-6200 US Nuclear Regulatory Commission 11555 Rockville Pike MS 12-D3 Ro.ckville, MD 20852-2738 December 17th, 2021
SUBJECT:
UC Davis MNRC Response to NRC Staff Request for Additional Information Regarding Licensing Renewal Application Letter Issued November 301\\ 2021.
Enclosed are the UC Davis MNRC responses to the 3 requests for additional information issued by the NRC staff on November 30th 2021.
I have reviewed this submission and found it to be truthful and accurate. If there are any questions or concerns, please contact me directly.
I declare under penalty of perjury that the foregoing is true and correct executed on December 17th, 2021.
Sincerely,
[ti¥ 0-"v Wesley Ft'fy PhD Facility Director
NRC Request for Additional Information Item #1}
The regulation, 10 CFR 50.9 requires information to be complete and accurate in all material aspects. The guidance in NUREG-1537, Part 1, Section 1.4, "Shared Facilities and Equipment, 11 states, in part, that the application should describe systems and equipment that are shared with facilities not covered by the SAR.
Further, NUREG-1537 states that any safety implications that result from sharing facilities or systems should be evaluated in and referenced to the appropriate chapter of the SAR.
The NRC staff review of the licensee's SAR, Section 1.4.3, "Shared utilities, 11 could not ascertain if any of the utilities (electric, natural gas, water, phone, internet, etc.) used to support the operation of the reactor facility were shared with other facilities not described in the SAR, and/or if any safety implications could result from any shared utilities.
Describe whether any utilities are shared with other facilities not covered by the SAR, and if any safety implications could result from the loss of any shared utilities, or justify why no additional information is needed.
UCD/MNRC Response: All utilities provided to the MNRC are done by external providers. In contrast to many other research reactors the MNRC reactor is located in a standalone building. The only shared utility is electrical service that is shared with the building directly south of the MNRC which is owned by the McClellan Business Park. While offsite utilities are required to operate the facility, none are required to place the reactor in a safe and secure condition. The loss of offsite utilities cannot generate any accident scenario.
The two utilities of most interest to all reactors are electricity and water. In the event of loss of electrical power, the facility maintains a backup battery supply which provides power to the console, reactor magnets, and all reactor indication for 15 minutes. This gives the reactor operator ample time to shut the reactor down in a controlled manner and verity the reactor has been placed in a secure condition. No electrical service (onsite or offsite) is required to maintain this secure condition.
Offsite water service is not directly required to operate the reactor or during a LOCA. This is due to the very small loss of primary water from evaporation during 1 MW operations. Typically, it would take approximately 2 weeks to reduce the level of water in the reactor tank to below what is required by the technical specifications. In chapter 13 of the SAR the analysis shows that the reactor does not need additional water (presumably from an offsite source) to prevent unacceptable heating of the core during a complete LOCA event.
Loss of offsite water can occur and does indirectly effect reactor operations as offsite water provides the water for the evaporative cooling system (secondary system) that cools the primary cooling system of the reactor. In the event of the loss of offsite water to feed the secondary system, the reactor operator would have several hours to ascertaining the situation and place the reactor in a secure configuration. In this scenario, before the primary coolant exceeded the technical specification limit, the reactor operator would receive numerous warnings and alarms (e.g. cooling tower low float, secondary low flow alarm, and primary tank temperature warning) over the course of several hours, which would provide ample time to shut the reactor down.
NRC Request for Additional Information Item #2)
The regulation, 10 CFR 50.9 requires information to be complete and accurate in all material aspects. The guidance in NUREG-1537, Part 1, Section 1.8, "Facility Modifications and History," states, in part, that the SAR should indicate if the facility has not undergone significant or safety-related physical or operational modifications since it was initially licensed, or since the last renewal was issued and should reflect any significant modifications made to the non-power reactor.
The NRC staff review of the licensee's SAR, Section 3.1.3, "Protection by Multiple Fission-Product Barriers (Criteria 10-19 }," "Criterion 13: Instrumentation and Control," finds that the licensee states that "Note that square wave and pulse mode are no longer utilized at MNRC.
11 However, facility modifications needed to be implemented to prevent an inadvertent square wave or pulse operation were not able to be identified in the SAR by the NRC staff Provide the following information to support the NRC staff review:
- a. Provide a description of the facility modifications planned or implemented to prevent an inadvertent square or pulse operation of the MNCR.
- b. Provide an assessment of the potential for an inadvertent square wave or pulse event, including any changes or updates needed to the descriptions of any accident scenarios provided in the LRA SAR, Chapter 13, "Accident Analysis.
11
- c. Provide any changes to the proposed technical specifications, if applicable to the proposed facility modifications.
UCD/MNRC Response: The compressed gas (nitrogen) supply has been disconnected and locked out at the base of the transient rod drive. The compressed gas cylinder itself has been disconnected and removed from the facility. These modifications make rapid ejection of the transient rod physically impossible.
Therefore, pulses and square waves cannot be physically achieved by any means.
The square wave and pulse mode buttons on the console have been disable so.that they cannot be physically depressed. Prior to this when either of these buttons was depressed a circuit was completed so that if the reactor was below lkW, the NM-1000 would be disabled and the NPP-1000 would be readied for the reactor to perform a pulse or square wave. If the reactor was above 1 kW, the 1 kW interlock would prevent the bypass of the NM-1000 and would generate a warning to the reactor operator that the reactor cannot enter into pulse or square wave mode.
By physically preventing the pulse and square wave buttons from engaging the reactor cannot inadvertently be placed in a mode where the NM-1000 is bypassed. Therefore, the 1 kW interlock surveillance will no longer be required. Current and future operators will be trained on the specifics of these modification. All other references to pulse or square wave model will be removed from the technical specifications.
NRC Request for Additional Information Item #3)
The regulation, 10 CFR 50.9 requires information to be complete and accurate in all material aspects. The guidance in NUREG-1537, Part 1, Section 4.2.2, "Control Rods, 11 states, in part, that the applicant should discuss the design, composition, and reactivity effects of control rod followers. Section 4.1, "Introduction, 11 and Section 4.2.3.1, "Control Function, 11 of the SAR indicate that fuel-follower sections consist of 20 or 30
weight percent uranium. However, Section 7.3.1, "Control Rods, 11 of the SAR states that the weight percent of uranium in the fuel is 20.
Section 4.6.4.3, "Operating Core Configuration (OCC),
11 of the SAR indicates that the operating core configuration {OCC) only contains fuel-followers with 20 weight percent uranium. Changes made to the OCC to develop the limiting core configuration (LCC} are described in Section 4.6.4.4, "Future Cores and the Limiting Core Configuration (LCC},
11 of the SAR, but changes to the composition of control rod followers are not specified. Analysis of the OCC and LCC provides the basis for hot-channel power used in steady-state thermal hydraulic analysis of the MNRC core, as well as control rod worth values and power peaking factors used in the accident analyses. The 30/20 fuel-followers contain more uranium by weight than 20/20 fuel-followers and are expected to have a higher reactivity worth. If control rod followers are loaded in the core that differ from those modeled in the SAR, then control rod worth in the core may exceed that used in the accident analysis, and power density and peaking factors achieved in the LCC may not be limiting. The NRC staff requests the licensee to:
- a. Clarify what control rod followers are modeled in analysis of the OCC and LCC described in the SAR.
- b. Describe the allowable loading of control rod followers in the core.
- c. If the allowable loading differs from that modeled in analysis of the OCC and LCC, please provide additional basis to confirm that design and accident analysis remains applicable.
MNRC/UCD Response: In both the OCC and LCC only 20/20 fuel followed controls were analyzed for in terms of thermal output and peaking factors. A 30/20 fuel followed control rod would undoubtable have a notably higher reactivity worth, which would result in a larger thermal output and overall element peaking factor. Based on operational and modeling experience with standard 30/20 fuel elements along with the position of the fuel followed control rods, it is unlikely a 30/20 fuel followed control rod would produce a peaking factor beyond what is already analyzed for in chapter 4 of the SAR. However, this configuration has not been specifically analyzed for.
At this time the MNRC is willing to commit to a technical specification that restricts the use of fuel followed control rod to only the 20/20 type. If the M NRC wishes to utilize a different type of fuel followed control rod in the future, a license amendment will be submitted to the NRC for approval. MNRC has no intensions of reducing the total number of control rods in the core or their location.