ML20149L872
| ML20149L872 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/14/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20149L867 | List: |
| References | |
| NUDOCS 9611190204 | |
| Download: ML20149L872 (5) | |
Text
.
f"%
g*
UNITED STATES s
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066 0001 4
.... 4 4
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.131 j
TO FACllITY OPERATING LICENSE NO. NPF-49 NORTHEAST NUCLEAR ENERGY COMPANY. ET AL.
MILLSTONE NUCLEAR POWER STATION. UNIT NO. 3 DOCKET NO. 50-423
1.0 INTRODUCTION
By letter dated June 3,1996, as supplemented October 23, 1996, the Northeast i
Nuclear Energy Company, et al. (the licensee), submitted a request for changes i
to the Millstone Nuclear Power Station, Unit No. 3, Technical Specifications j
(TSs). The requested changes would amend the TSs for Millstone Unit 3 pertaining to Table 3.3-1.
The October 23, 1996, letter provided clarifying information that did not change the scope of the June 3,1996 request and the initial proposed no significant hazards consideration determination.
Millstone Unit 3 (MU3) was shut down mid-cycle due to a problem with the turbine-driven auxiliary feedwater pump discharge valves.
Subsequent to the shutdown, MU3 commenced a mid-cycle outage to resolve equipment problems and respond to NRC requests for information. While in the shutdown mode, the l
licensee noticed that the secondary sources in proximity to the Shutdown Margin Monitors (SMM) were decaying as MU3 remained in an extended mid-cycle outage. The licensee expected the count rate from these sources to fall below a minimum count rate in early July of 1996, at which point the SMM would not be able to detect the degraded count rate, and thus, the SHMs would be deemed inoperable. With the Sms deemed inoperable, MU3 cannot change modes during plant startup because the exclusion clause of Action Statement 5(b) of TS i
3.0.4 prevents them from doing so. Consequently, the licensee is requesting a TS change to remove this exclusion clause and allow the plant to change modes with the SMMs inoperable.
Past plant startup experience has shown that once the unit is in Mode 3, there will be sufficient neutron leakage to increase the count rate above the minimum count rate and the SMMs will again be deemed operable.
The licensee pointed out that this request is consistent with the approved Standard Technical Specifications, NUREG-1431, where entry into a higher Operational Mode is allowed with inoperable SMMs.
4 9611190204 961114 PDR ADOCK 05000423 P
t I
- I I.
As a result, the licensee proposes to revise MU3 Table 3.3-1 to allow changing i
to a higher mode with both SMs inoperable in accordance with Technical Specification (TS) 3.0.4.
Specifically, the change to Table 3.3-1 will be to delete the following statement from Action 5(b):
" Entry into an OPERATIONAL MODE pursuant to Specification 3.0.4 is not permitted," and adding the following clarification i
to Action 5(a) and 5(b): "via dilution and rod withdrawal." The i
references to 5(a) and 5(b) address positive moderator reactivity changes i
associated with mode changes.
Also, the licensee proposes to change two references in Action Statements 5(a) i and 5(b), from the now nonexistent Specification 4.4.1.4.2.3 to Specification 4.1.1.2.2.
Specification 4.4.1.4.2.3 was eliminated, and at the same time the substance contained therein was relocated to Specification 4.1.1.2.2, by License Amendment 99, issued December 29, 1994.
However, the corresponding j
editorial changes to reference the correct specification (Specification 4.1.1.2.2) in Action Statements 5(a) and 5(b) were inadvertently omitted from the request in connection with License Amendment 99.
This amendment would rectify this administrative error.
2.0 EVALUATION The safety function of the Shutdown Margin Monitors (SMM) is to mitigate the consequences of the inadvertent addition of unborated primary grade water into the reactor coolant system (RCS). Their function is to annunciate an increase in core subcritical multiplication allowing the ' operator at least 15 minutes i
response time to mitigate the consequences of the inadvertent addition of unborated water (boron dilution event (BDE)) into the RCS when the reactor is in a shutdown condition (Modes 3, 4, and 5). The SMM is not a credited for any function from other design basis events.
As the number of neutrons reaching the SMMs (the count rate) decrease, as is the case in MU3, the longer it takes the SMMs to respond. Consequently, the delay time in the SMs response increases. This delay time leads to the requirement of a minimum count rate for operability. As stated above, TS 3.0.4 does not permit modes changes with the SMMs inoperable (LC0 3.3.1, Action Statement 5B, TS Table 3.3-1).
MU3 is proposing to revise Table 3.3-1 to allow mode changes to higher modes, specifically Mode 3.
The licensee analyzed the proposed changes to the TS Table 3.3-1 and concluded that the change to the TS will not decrease the margin of safety provided by the SMs in operation. The same analysis dictates that with both the SMMs inoperable, and with the boron dilution flow paths locked closed, the SMMs are not required to provide an alarm to the operators to allow them to mitigate the BDE, and thus their continued operation provides no added safety benefit.
The Millstone Unit 3 Limiting Condition for Operation (LCO) for both the SMMs being inoperable does not require the plant to change modes, and therefore
~ --
i 4
l l- !
permits continued operation of the plant for an unlimited period of time. The proposed TS change will allow MU3 to increase modes while complying with the LCO Action Statements. These action statements must be performed to ensure safety and are stated below:
)
j a) All positive reactivity operations via dilution and rod withdrawal must be suspended.
a i
This action statement is intended to stop any planned dilution of the Reactor i
Coolant System (RCS). Typically, the SMs play no role in monitoring core reactivity during plant heatup (RCS temperature changes), and the alarm setpoint is routinely re-set during plant heatup due to the increasing count i
rate. _On the other hand, during plant cooldowns, as the count rate decreases, the baseline count rate are continually lowered automatically by the SMMs.
The licensee also pointed out that, if the situation arose where the SMMs are still inoperable in Mode 3, and entrance into Mode 5 (plant cooldown) is i
desired, entrance into Mode 5 under this hypothetical situation will put the plant in a safer configuration (removal of the stored energy in the RCS) as opposed to maintaining Mode 3 operation, b) All dilution flow paths must be isolated and placed under administrative control (locked closed). Also, the shutdown margin surveillance frequency must be increased from 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
This action is intended to provide redundant protection and defense in depth.
to the SM s.
In this configuration, a BDE is prevented and is the basis for not requiring a BDE analysis in Mode 6.
Since the occurrence of a BDE is prevented, the SMs are not required to be operable.
The proposed TS amendment will allow MU3 to enter into a higher operation mode with both SMMs inoperable.
Because the boron dilution flow paths are blocked, significantly reducing the probability of BDE, the safety of the plant has not been compromised. Based on past plant startups, the licensee anticipates that going to a higher mode (in this case RCS heatup), will cause the SMMs channels count rate to increase to above the minimum count rate for operability.
Furthermore, additional analysis by the licensee has shown that the Isothermal Temperature Coefficient (ITC) for Millstone 3 is NEGATIVE in the temperature range from cold shutdown conditions (68 degrees F) to no load hot (557 degrees F) temperature conditions. The ITC is the sum of both the moderator temperature coefficient and the fuel doppler coefficient.
For operating conditions where the core is uniformly heated or cooled, the associated reactivity change is due to the combined or isothermal effect of both the change in the fuel temperature and the moderator temperature.
Over reactor core life, the ITC becomes more negative with core age, primarily due to the reduction in RCS boron concentration. The net reactivity change due to burnup varies from an approximate low of -1300 pcm at beginning of core life-to an approximate high of -4100 pcm. Data provided by the licensee by letter dated October 23, 1996, shows that the change in reactivity as a function of plant heatup is negative. Also, the change in reactivity as a function of plant burnup is also negative.
In the case of Millstone Unit 3,
^
. changing temperature, i.e., heating up from Mode 5 (68 degrees F) to Mode 3 (557 degrees F) will introduce negative reactivity into the core, which is a move in the conservative direction.
Consequently, once the channels are above the minimum count rate for operability, the channels can be declared operable and the LC0 action statement can be exited. With the SMMs operable, the dilution flow paths can be returned to service in anticipation of the RCS boron concentration reduction during the approach to criticality.
The NRC staff has reviewed the reports submitted by the licensee for the continued operation of Millstone Unit 3.
The appropriate material was submitted in regard to Technical Specification changes pertaining to SMMs inoperability while changing modes. Based on this review, the staff has concluded that the requested TS change (s) are acceptable, and satisfy the staff's positions and requirements in these areas.
In regard to the proposed changes to Action Statements 5(a) and 5(b) to reference Specification 4.1.1.2.2 instead of Specification 4.4.1.4.2.3, which no longer exists, the staff finds that the changes are editorial in nature and are acceptable in light of the relocation of the substance of Specification 4.4.1.4.2.3 to Specification 4.1.1.2.2 by License Amendment No. 99, issued December 29, 1994.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (61 FR 31559 dated June 20,1996).
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
O
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: A. Attard Date: November 14, 1996 i
1