ML23039A207

University of California Davis Mcclellan Nuclear Research Center (Mnrc), Docket Number 50-607, License Number R-130, License Amendment Request 2023-01

ML23039A207
Person / Time
Site:	University of California-Davis
Issue date:	02/08/2023
From:	Frey W McClellan Nuclear Research Center
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
Download: ML23039A207 (1)

Text

Wednesday February 8th 2023

Attn: Document Control Desk US Nuclear Regulatory Commission Washington, D.C. 20555-01

Subject:

University of California Davis McClellan Nuclear Research Center (MNRC), Docket Number 50-607, License Number R-130, License Amendment Request 2023 -01 Summary of Request:

By way of this letter, it is requested that MNRCs technical specification section 3.3 item number 4 be changed to allow for reactor operation so long as tritium levels in the primary cooling water do not exceed 0.05 uCi/ml. The current technical specifications require tritium concentrations under 0.01 uCi/ml (based on 10 CFR 20 appendix B table 3) in order to operate the reactor, which MNRC is not able to meet. MNRC does not request that the limit for any non-tritium isotopes be changed. The analysis below provides reasonable assurance that this proposed change does not represent any undue risk to the public or environment.

Origin of Current Technical Specification Limits in Section 3.3 Item Number 4:

During early summer of 2022 MNRC was working with the NRC staff to finalize the technical specification as part of the facilitys relicensing effort. MNRC staff proposed the limits on technical specification section 3.3 item number 4 as the limits set forth in 10 CFR 20 appendix B table 3. This limit was consistent with other similar research reactors.

When proposing this new technical specification limit, MNRC Staff examined historical values for all non-tritium nuclides having half-lives greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. These nuclides are assayed at MNRC via high resolution gamma-ray spectroscopy. For these non-tritium nuclides, MNRC determined that the proposed limits could be satisfied. Separately, MNRC staff looked at the tritium concentration levels that are provided to MNRC via a private non-UC Davis laboratory. The latest result from this private laboratory was reviewed and confirmed MNRC would meet the new tritium limit of 0.01 uCi/ml by having a tritium concentration of approximately 1/40th of this value. Only this single tritium concentration report was checked as historical tritium levels were known to vary little from year to year.

On 1/31/2023 it was discovered that the private laboratory results were incorrect and were mistakenly underreported by a factor of 100. As a result, MNRCs primary cooling water tritium concentration was determined to be approximately 2.5 times the new technical specification limit. The exceeding of this limit was immediately reported to the NRC and reactor operations were suspended. A more extensive data review shows that MNRCs primary water tritium levels, during the past 10 years of 1 MW single-shift operation, were highly consistent ranging from a maximum of 0.026 uCi/ml to a minimum of 0.017 uCi/ml with an average concentration of 0.022 uCi/ml.

There has been no increase in the amount of tritium in MNRCs primary cooling water nor has any primary cooling water been released from the reactor tank since technical specification 3.3 item number 4 took effect on 11/21/22.

MNRC has secured an alternate laboratory at UC Davis to perform tritium analysis for future primary water and well samples. The currently utilized private laboratory, that misreported the primary coolant water tritium levels, will continue to be used for approximately 1 year. This will be done to ensure that the results of the two laboratories are in agreement before only having the UC Davis laboratory perform the tritium analysis.

Analysis For Changing of Technical Specification 3.3 Item 4:

There are two potential scenarios to consider when evaluating the limits of Technical Specification Section 3.3 item number 4, a slow leak of the primary water from the reactor tank and a catastrophic LOCA event.

These two scenarios will be discussed separately below.

Slow leak scenario: In the event of a slow primary water leak, primary coolant would leak into the space between the tank wall and the concrete monolith (SAR chapter 5) that forms the structural center and foundation of the facility. As a design feature of the facility, if a tank leak did form, primary water would most likely be discovered in the excavation under bay 4 (commonly referred to as bay 5) which is the lowest elevation point at MNRC. This slightly contaminated primary cooling water could largely be recovered in a 6,000-gallon retention tank to avoid allowing it from being released into the environment. In this scenario, it is possible for some small fraction of primary cooling water to slowly permeate through the concrete monolith and ultimately into the ground under the facility and eventually into the underground aquafer (described in SAR chapter 13.2.3). Unlike many other research reactor tanks, the MNRC reactor tank wall contains no penetrations. With no such penetrations it is unlikely the MNRC reactor will ever develop such a leak.

MNRC has a policy of not discharging liquid waste into the sanitary sewar and has never discharged primary coolant water into the sewer, nor does it have any plans to do so.

A part of routine operations, MNRC monitors the addition of water to the primary tank to track if tank losses increase over time beyond typical evaporation losses, which would be indicative of a reactor tank leak.

Ground water is monitored at a well approximately 3 miles west of the reactor facility. This location is selected as it is the most likely first point that any potential tritium released from MNRC would be introduced to the public. This well is monitored every three months and in the more than 20 years of MNRC operations has not contained any elevated tritium levels. The minimum detectable activity used in this analysis is approximately 1% of the EPA drinking water limit for tritium (20,000 pCi/l).

LOCA scenario: During a complete LOCA event the 7,000 gallons of primary water would flood bay 5 and the MNRC reactor would be uncovered. Per MNRCs existing technical specifications and emergency plan, MNRC is required to reflood the core along with bay 5 with approximately 60,000 gallons of water to recover the core with water to reduce skyshine to the public. This addition of 60,000 gallons of uncontaminated water would lower the proposed maximum tritium concentration in the primary water of 0.05 uCi/ml to 0.0052 uCi/ml or just over half the 10 CFR 20 appendix B Table 3 limit for tritium discharge to the sewer. There is no known mechanism for a complete LOCA event at MNRC and this scenario is only provided to demonstrate that even under a very unlikely and extreme event, the proposed change to technical specification 3.3 item 4 does not represent an undue risk to public safety or to the environment.

Attachments: Original Technical Specifications Page 11, Proposed Technical Specifications Page 11, historical primary water tritium concentrations, and historical monitored well water tritium concentration.

Affirmation: I declare under penalty of perjury that the foregoing is true and correct executed on February 8th 2023.

Wesley Frey PhD CHP MNRC Facility Director

Original Specification - The reactor shall not be operated unless the systems and instrumentation channels described below are operable, and the information is displayed locally or in the control room.

1. The bulk tank water temperature shall not exceed 45 °C;

2. The conductivity of the tank water shall be less than 5 mhos/cm when averaged over a one month period;

3. The reactor shall not be operated if water level drops below a depth of 19 feet from the top of the fueled region of the core; and

4. The reactor shall not be operated if the radioactivity of the pool water exceeds the limits of 10 CFR 20 Appendix B Table 3 for radioisotopes with halflives >24 hours.

5. The reactor core reflooding system is considered operable if the local pressure gauge on the system reads 20 psi or above.

Basis -

1. The primary coolant core inlet temperature alarm assures that large power fluctuations will not occur (SAR Chapter 4.6).

2. Maintaining the primary coolant water conductivity below 5 micromhos/cm averaged over a week will minimize the activation of water impurities and also the corrosion of the reactor structure.

3. The minimum height of 19 ft. of water above the fueled region of the core guarantees that there is sufficient water for effective cooling of the fuel and that the radiation levels at the top of the reactor tank are within acceptable limits. This height of water is also a bounding condition for the core thermal hydraulic analysis. (SAR Chapter 4).

4. This specification insures that in the event of a large scale release of primary coolant no effluence limits are exceeded.

5. This system will allow the facility to recover the core with water in the in the case of a complete LOCA in order to reduce potential exposure to the public to below 10 CFR 20 limits.

3.4 This section intentionally left blank

3.5 Ventilation and Confinement System

Applicability - This specification applies to the operation of the facility ventilation and the reactor room confinement system.

Objective - The objective is to ensure that the ventilation and confinement system shall be in operation to mitigate the consequences of possible releases of radioactive materials resulting from reactor operations.

Proposed Specification - The reactor shall not be operated unless the systems and instrumentation channels described below are operable, and the information is displayed locally or in the control room.

1. The bulk tank water temperature shall not exceed 45 °C;

2. The conductivity of the tank water shall be less than 5 mhos/cm when averaged over a one month period;

3. The reactor shall not be operated if water level drops below a depth of 19 feet from the top of the fueled region of the core; and

4. The reactor shall not be operated if the radioactivity of the pool water exceeds the limits of 10 CFR 20 Appendix B Table 3 for radioisotopes with halflives >24 hours except for tritium which shall have a limit of 0.05 uCi/ml.

5. The reactor core reflooding system is considered operable if the local pressure gauge on the system reads 20 psi or above.

Basis -

1. The primary coolant core inlet temperature alarm assures that large power fluctuations will not occur (SAR Chapter 4.6).

2. Maintaining the primary coolant water conductivity below 5 micromhos/cm averaged over a week will minimize the activation of water impurities and also the corrosion of the reactor structure.

3. The minimum height of 19 ft. of water above the fueled region of the core guarantees that there is sufficient water for effective cooling of the fuel and that the radiation levels at the top of the reactor tank are within acceptable limits. This height of water is also a bounding condition for the core thermal hydraulic analysis. (SAR Chapter 4).

4. This specification insures that in the event of a large scale release of primary coolant no effluence limits are exceeded.

5. This system will allow the facility to recover the core with water in the in the case of a complete LOCA in order to reduce potential exposure to the public to below 10 CFR 20 limits.

3.4 This section intentionally left blank

3.5 Ventilation and Confinement System

Applicability - This specification applies to the operation of the facility ventilation and the reactor room confinement system.

Objective - The objective is to ensure that the ventilation and confinement system shall be in operation to mitigate the consequences of possible releases of radioactive materials resulting from reactor operations.

Historical Primary Water Tritium Concentrations

MNRC Primary Water H-3 Assay Date Concentration (uCi/ml) 2.57E-02 04/01/13 2.41E-02 10/07/13 2.34E-02 04/14/14 2.24E-02 10/30/14 2.09E-02 04/06/15 2.25E-02 10/05/15 2.23E-02 04/04/16 2.02E-02 10/17/16 2.01E-02 04/10/17 2.06E-02 10/09/17 2.08E-02 04/26/18 2.08E-02 10/01/18 1.66E-02 04/01/19 2.07E-02 10/07/19 2.32E-02 04/20/20 2.43E-02 11/03/20 2.57E-02 04/05/21 2.25E-02 10/04/21 2.53E-04 4/4/2022*

2.37E-02 10/12/22

• Misreported results

Historical Monitored Well Water Tritium Concentration

Concentration of Sample Date Tritium (pCi/l)

<MDC of 300 12/22

<MDC of 254 10/22

<MDC of 258 4/22

<MDC of 296 12/21

<MDC of 392 10/21

<MDC of 335 7/21

<MDC of 346 3/21

<MDC of 344 12/20

<MDC of 251 10/20

<MDC of 257 7/20

<MDC of 294 3/20

<MDC of 281 12/19

<MDC of 272 9/19

<MDC of 275 3/19

<MDC of 252 1/19

<MDC of 256 10/18

<MDC of 266 7/18

<MDC of 243 3/18

<MDC of 232 1/18

<MDC of 222 10/17

Note: MDC is minimum detectable concentration