05000341/LER-2016-011, Regarding Standby Liquid Control Inoperable Due to Sodium Pentaborate Concentration Outside of Technical Specifications

Regarding Standby Liquid Control Inoperable Due to Sodium Pentaborate Concentration Outside of Technical Specifications

ML16356A280
Person / Time
Site:	Fermi
Issue date:	12/20/2016
From:	Polson K DTE Electric Company, DTE Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC-16-0072 LER 16-011-00
Download: ML16356A280 (7)

LER-2016-011, Regarding Standby Liquid Control Inoperable Due to Sodium Pentaborate Concentration Outside of Technical Specifications

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
LER closed by
IR 05000341/2017001 (1 May 2017)
3412016011R00 - NRC Website

text

Keith J. Poison Site Vice President 640 N.Dxi ighwy Newport, M'I 48166 Tel:~~~~~ 73.8644 Fa:34586,4172 SDTE Energy' 10 CFR 50.73 December 20, 2016 NRC-16-0072 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Reference:

Fermi 2 NRC Docket No. 50-341 NRC License No. NPF-43

Subject:

Licensee Event Report (LER) No. 2016-011 Pursuant to 10 CFR 50.73(a)(2)(i)(B) and 10 50.73(a)(2)(v)(A), (C), and (D), DTE Electric Company (DTE) is submitting LER No. 2016-011, Standby Liquid Control Inoperable due to Sodium Pentaborate Concentration Outside of Technical Specifications.

No new commitments are being made in this LER.

Should you have any questions or require additional information, please contact Mr. Scott A. Maglio, Manager -Nuclear Licensing, at (734) 586-5076.

Sincerely, Keith J. Polson Site Vice President

Enclosure:

Licensee Event Report No. 2016-011, Standby Liquid Control Inoperable due to Sodium Pentaborate Concentration Outside of Technical Specifications cc: NRC Project Manager NRC Resident Office Reactor Projects Chief, Branch 5, Region III Regional Administrator, Region III Michigan Public Service Commission Regulated Energy Division (kindschlamichigan.gov)

Enclosure to NRC-16-0072 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Licensee Event Report (LER) No. 2016-011, Standby Liquid Control Inoperable due to Sodium Pentaborate Concentration Outside of Technical Specifications

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY MB: NO. 3150-0104 EXPIRES: 103112018 (06-2016)

Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections LICENSEE EVENT REPORT (LER)

Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail (See Page 2 for required number of digits/characters for each block) to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a (See NUREG-1022, R.3 for instruction and guidance for completing this form means used to impose an information collection does not display a currently valid OMB control http://www.nrc.qov/readina-rm/doc-collections/nuregs/staff/sr1022/r3/)

number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collecton.

3. PAGE Fermi 2 05000 341 1 OF 5

4. TITLE Standby Liquid Control Inoperable due to Sodium Pentaborate Concentration Outside of Technical Specifications

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED FACIUITY NAME DOCKEr NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR N/A 05000 I INUMBER NO.

N/

05000_

FACILITY NAME DOCKET NUMBER 10 28 2016 2016 011 00 12 20 2016 N/A 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

Ei 20.2201(b) 0 20.2203(a)(3)(i)

[j 50.73(a)(2)(ii)(A)

[

50.73(a)(2)(viii)(A) 1 Ei 20.2201(d)

[] 20.2203(a)(3)(ii)

Ei 50.73(a)(2)(ii)(B)

E] 50.73(a)(2)(viii)(B) 20.2203(a)(1) 20.2203(a)(4) 0 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)

Ei 20.2203(a)(2)(i) 50.36(c)(1)(i)(A)

[] 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)

10. POWER LEVEL 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A)

/

50.73(a)(2)(v)(A) 73.71(a)(4)

Li20.2203(a)(2)(iii)

[]50.36(c)(2)

Li50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii)

/

50.73(a)(2)(v)(C) 73.77(a)(1) 100 20.2203(a)(2)(v) 50.73(a)(2)(i)(A)

[/] 50.73(a)(2)(v)(D)

E] 73.77(a)(2)(i) 20.2203(a)(2)(vi)

/

50.73(a)(2)(i)(B)

[I 50.73(a)(2)(vii) 73.77(a)(2)(ii) 50.73(a)(2)(i)(C)

Li OTHER Specify in Abstract below or in performances of this SR prior to this event were on September 15 and October 13 and both resulted in an acceptable sodium pentaborate concentration of 8.7%. It is not possible to establish exactly when the sodium pentaborate decreased below the TS SR 3.1.7.5 limit of 8.5%. However, it is reasonable to assume the concentration decrease was approximately linear which would indicate that the TS SR 3.1.7.5 limit was not met for several days prior to the event on October 28. As described previously, TS LCO 3.1.7 Condition B Required Action B.1 has a Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

If the Completion Time is not met, Condition C has a Required Action C.1 to be in MODE 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Since the sum of these two Completion Times is less than one day (i.e. 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />), it is reasonable to assume that the condition of the sodium pentaborate concentration not meeting SR 3.1.7.5 lasted longer than allowed by TS. This represents an operation or condition prohibited by the plant TS and is therefore reportable under Title 10 Code of Federal Regulations (10 CFR) 50.73(a)(2)(i)(B). There is no corresponding requirement for event notification to the NRC under 10 CFR 50.72.

The Fermi 2 Updated Final Safety Analysis Report (UFSAR) states that the SLC system provides a redundant, independent, and different way to bring the nuclear fission reactor to subcriticality and maintain subcriticality as the reactor cools. The SLC system permits an orderly and safe shutdown in the event that control rods cannot be inserted into the reactor core in sufficient number to accomplish shutdown in the normal manner. In addition, the SLC system is also credited for injecting sodium pentaborate into the reactor coolant system after a design basis loss of coolant accident (LOCA) in order to control the pH of Emergency Core Cooling System (ECCS) water to prevent iodine re-evolution. The SLC system consists of a SLC storage tank, two positive displacement pumps ((P)), two explosive valves, and associated piping and valves used to transfer the borated water from the storage tank to the reactor pressure vessel (RPV) ((RPV)).

Since there is only a single storage tank, conditions affecting the tank impact the operability of both SLC subsystems.

As described above, both SLC subsystems were declared inoperable due to the sodium pentaborate concentration being outside of the TS required range. This represents a condition that could have prevented the fulfillment of the safety functions of the SLC system described above. Since the conditions at the time of discovery on October 28 met the reporting criteria of 10 CFR 50.72(b)(3)(v)(A), (C), and (D) as an event or condition that could have prevented the fulfillment of a safety function needed to shut down the reactor and maintain it in a safe shutdown, control the release of radioactive material, or mitigate the consequences of an accident, an 8-hour non-emergency event notification (EN 52331) was made to the NRC. This LER 2016-011 is being reported under the corresponding requirements in 10 CFR 50.73(a)

(2)(v)(A), (C), and (D).

SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS

As described above, the SLC system performs two different functions: (1) enable safe shutdown in the event that control rods cannot be inserted into the reactor core and (2) lower the pH of ECCS water to prevent iodine re-evolution post-LOCA. The safety consequences and implications of each of these two functions are addressed below.

Regarding the first function, the SLC system is a redundant and independent means to control reactivity. A probabilistic risk assessment (PRA) was performed to determine the impact of the SLC unavailability. For a SLC unavailability lasting 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> (i.e. corresponding to the approximate time of the declared inoperability), the increase in conditional core damage probability (ICCDP) and large early release probability (ICLERP) are 9.4E-10 per year and 9.9E-10 per year, respectively.

Increases in ICCDP and ICLERP values of less than 1.0E-06 per year and 1.0E-07 per year, respectively, are considered to be of very low safety significance. As a sensitivity to the duration of the unavailability, a SLC unavailability of approximately 17 days would have had to occur to exceed the ICCDP or ICLERP values associated with very low safety significance. Since the worst-case unavailability is bounded by 15 days due to the known satisfactory concentration on October 13, the event is below the threshold of very low safety significance. In addition to the PRA results, a deterministic evaluation of this function was performed. The minimum boron concentration in TS SR 3.1.7.5 is based on a DTE

calculation which was performed to meet the Anticipated Transient Without Scram (ATWS) rule. The calculation contains an equivalency formula, consistent with an NRC-approved approach, for determining the sodium pentaborate concentration, B-10 enrichment, and SLC pump flow rate required to meet the rule. These three parameters are all related in that an increase in one parameter can offset a decrease in another parameter. Using this equivalency formula, ATWS rule compliance can be demonstrated for the sodium pentaborate concentration of 8.3% measured during the event even assuming the minimum B-10 enrichment of 65% in TS SR 3.1.7.10 and the minimum SLC pump flow rate of 41.2 gallons per minute (gpm) in TS SR 3.1.7.7. Therefore, although the SLC system was declared inoperable due to the low sodium pentaborate concentration, the actual SLC system parameters at the time of event would have ensured the capability to control reactivity in the unlikely event that the control rods could not be inserted. Note also that, during this event, the normal means of reactivity control (i.e. the control rods) was maintained.

The post-LOCA function of SLC to control pH is not modeled in the PRA. Therefore, only a deterministic approach was used to determine the safety consequences of the SLC system inoperability related to this function. The DTE calculation for pH assumes a certain minimum mass of sodium pentaborate available for injection. The minimum mass is based on the minimum tank volume and minimum sodium pentaborate concentration allowed by Figure 3.1.7-1 of TS 3.1.7.

Although the sodium pentaborate concentration of 8.3% during the event was below the minimum value assumed in the calculation, the volume of solution in the tank at the time was much greater than that assumed in the calculation (i.e. near the high level alarm setpoint). A sensitivity calculation using the approximate volume and concentration at the time of the event results in an available mass of boron that is greater than that assumed in the DTE calculation for post-LOCA pH.

The post-LOCA pH calculation assumes the manual injection of SLC is completed within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after the start of the LOCA. Using the approximate volume at the time of the event and the TS SR 3.1.7.7 minimum flow rate, the available mass of boron could be injected in approximately 75 minutes. Based on this sensitivity, although the SLC system was declared inoperable at the time of the event, the SLC system would have been capable of providing the sodium pentaborate mass required to ensure that post-LOCA pH control was successful.

Fermi 2 also has procedural guidance in place for an alternate means of injecting boron using the Standby Feedwater (SBFW) ((SJ)) system. The procedure requires that the SBFW system be capable of supplying water to the RPV and there be adequate water in the Condensate Storage Tank (CST) ((SD)) ((TK)). Both of these requirements were met during the event such that alternate means of boron injection would have been available.

Based on the discussion above, the safety significance of this event is very low and the event did not pose a threat to the health and safety of the public or plant personnel. There were no radiological releases associated with this event.

CAUSE OF THE EVENT

The cause of the SLC storage tank sodium pentaborate concentration being below TS SR 3.1.7.5 was leak-by of the SLC storage tank demineralized water isolation valves while in their closed position. The increase in SLC storage tank level due to the leak-by of demineralized water diluted the sodium pentaborate solution in the tank. The cause of the unexpected increase in tank level and corresponding decrease in sodium pentaborate concentration going undetected was an inadequate system monitoring plan that did not adequately trend these parameters.

Failed components: SLC suction line and SLC storage tank demineralized water supply valves Model number: 3624 (F316) CT, globe valve, 1-inch, stop valve assembly Manufacturer: Rockwell-Edwards Univalve

CORRECTIVE ACTIONS

Compliance with the TS requirement for sodium pentaborate concentration was restored by the addition of sodium pentaborate to the SLC storage tank once it was determined that the concentration did not meet the TS SR 3.1.7.5 limit.

The two demineralized water isolation valves were replaced on November 9, 2016 to prevent further leak-by. The chemistry specification for the SLC storage tank was revised on November 24, 2016 to clearly specify action levels for the tank level and sodium pentaborate concentration. The action level for sodium pentaborate concentration is now 9.0%,

which is the midpoint of the allowable concentration range in TS Figure 3.1.7-1 to provide additional margin to the TS SR.

The SLC system monitoring plan was revised on December 5, 2016 to incorporate trending tank level and sodium pentaborate concentration to prevent a future undetected increase in level and decrease in boron concentration.

Department human performance (HU) clock resets were conducted for Chemistry and Operations personnel to communicate lessons learned associated with this event.

Although not related to the increase in tank level and corresponding decrease in sodium pentaborate concentration, this event identified a small discrepancy between the MCR and local level indications that resulted in an alarm and the actual measured SLC storage tank level that was below the alarm setpoint as described in the narrative. The discrepancy was determined to be related to calibration. Re-calibration was performed on November 1, 2016 to resolve this issue.

PREVIOUS OCCURRENCES

A review of previous Fermi 2 LERs did not identify any reportable conditions affecting both SLC subsystems simultaneously. A review of the corrective action program did identify previous occurrences where an increase in SLC storage tank level was identified as resulting in a decrease in sodium pentaborate concentration. However, these occurrences were more than five years ago and none of these occurrences resulted in changes in level and concentration that were significant enough to exceed the TS SR. The corrective actions for one of these events did involve replacing a valve to eliminate potential leak-by of demineralized water into the SLC storage tank, similar to as discussed for this event.

However, since these previous occurrences did not indicate a significant decrease in boron concentration, these past occurrences did not indicate a need to immediately replace valves or perform additional trending and therefore would not have been able to prevent the occurrence of this event.Page 5

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