ML101180105

E-mail from Entergy Operations, Inc. Re ANO-2 License Amendment Request on Technical Specification Changes to Relocate Pressurizer Heater to Technical Requirements Manual

ML101180105
Person / Time
Site:	Arkansas Nuclear
Issue date:	07/30/2009
From:	David Bice Entergy Operations
To:	Kalyanam K Plant Licensing Branch IV
References
TAC ME1622
Download: ML101180105 (4)

Text

From: BICE, DAVID B [DBICE@entergy.com]

Sent: Thursday, July 30, 2009 2:51 PM To: Kalyanam, Kaly Cc: CLARK, ROBERT W

Subject:

RE: ANO-2 LAR on Technical Specification Changes To Relocate Pressurizer Heater to TRM

Kaly, I am checking with PRA folks to see when we could respond with more detail on PRA. Ill let you know as soon as they get back to me. It will probably be next week before I can get the info, but you can be assured we will commit to provide you whatever additional information we can on the subject.

I am very pleased that the reviewer has taken the time to allow us to provide further insights. Obviously, we will be more than happy to supplement our letter with any further information desired, within our capability. Please thank the reviewer for me. I realize this is a first-of-a-kind request and also realize this may require more sharing of extra information than what would occur with most requests. We are only asking the NRC to consider todays reality and not automatically dismiss our request just because of the thinking taking place back in 1978 (TMI).and it appears to me, the reviewer is taking all this under consideration and I am very thankful for that.

With regard to Question 2:

10 CFR 50.36(c)(2)(ii), Criterion 2 states: A process variable, design feature, or operating restriction that is an initial condition of a design basis accident or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.

On page 2 of Attachment 1 of our letter, we state: Accident analyses presented in the SAR do not take credit for Pressurizer heater operation; however, an implicit initial condition assumption of the safety analyses is that the RCS is operating at normal pressure.

While it is true that the heaters are a design feature of the pressurizer, the SAR assumption is that RCS pressure is within a certain band or range prior to the onset of an accident. In other words, the analyses restriction is a process variable or operating restriction, not a design feature. As you are aware, a plant cannot remain at power without the heaters. If heaters were lost for whatever reason (for example, both control channels of pressurizer level loss would result in a false low level signal to the heaters which would lock them out), pressure would immediately begin to trend downward due to ambient losses which occur continuously. The actual TS requirement that protects the analyses is TS 3.2.8, Pressurizer Pressure. In accordance with this TS, if pressure falls below normal operating band (2025 psia), it must be restored within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or plant power reduced to < 5%. However, in reality Operators would manually trip the reactor if the cause of heater loss could not be quickly resolved. This is because the Core Protection Calculators also have an acceptable pressure range (a relatively narrow range is required for these computers to be able to calculate or the DNBR/LPB calculations will fail) and, if that pressure range is exceeded, an automatic reactor trip on low DNBR / high LPD will be initiated. In addition, attempting a manual plant shutdown (which involves the RCS becoming cooler) with pressure already trending downward would be self-defeating. Therefore, the heaters themselves do not meet Criterion 2, but rather the process variable of Pressurizer Pressure (TS 3.2.8) is the controlling parameter. Of course, TSs are not intended to include components that are only required to maintain plant operation and are not relied upon for accident mitigation (if they did, wed have to add a lot of extra components to the TSs).

With regard to NUREG 0737, it was the general understanding at the time of the TMI accident that heaters were somehow vital to safe operation. While we know they are not vital, some plants may still require heaters in order to perform a Natural Circ cooldown. ANO-2 does not, as described in our letter.

No matter what the plant conditions, the credited end-all cooling source is feed and bleed. So regardless of preferences or margins, a Natural Circ cooldown is something desired, but not required.

Notwithstanding these facts, Section 4.0 of our letter discusses the historical TMI thinking and brings this thinking into perspective. To reiterate some of the discussion provided in the letter, a bubble is no longer a concern, at least not for ANO-2 design. While it is desired to maintain subcooled margin, drawing a bubble in the reactor vessel head does not challenge Natural Circ nor does it present any significant challenge to operators. While the ANO-2 simulator is not a cover-all justification, we did perform a Natural Circ cooldown for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and intentionally allowed a bubble to form and grow in the vessel head region to verify there would be no challenge to the core or to Operators. (Although in Licensing for last 9 years, I have nearly 20 years of Ops experience and was present during most of the 24-hour test st on the simulator, so I speaking from 1 hand information). In fact, the whole event was basically boring with nothing really for Operators to do, other than tweak the cooldown rate about once an hour as decay heat lessened. This was the most challenging condition we could think of. We could have maintained subcooling margin if we wanted to, but that would not have been challenging at all. ANO certainly welcomes an on-site visit by the NRC to our simulator facility if they would like to see some scenarios run. My point is that, while conservatively appropriate at the time, the TMI thinking for Natural Circ cooldown is not relevant to ANO-2 safety. Again, if a Natural Circ cooldown was being performed in conjunction with a small break LOCA, pressure reduction would be limited since the break remains within makeup capability of the normal charging system. Larger breaks would lead to feed and bleed operations, which is the standard for LOCAs. In summary, the concerns captured by NUREG 0737 relating the heaters are no longer of significant concern for plants like ANO-2.

With regard to whether the heaters are needed to maintain subcooling margin, this is not necessarily true. The rate of cooldown can be increased to increase margin and Pressurizer level raised to hold RCS pressure. This may not be sufficient if a small break LOCA is involved; however, heaters are not the credited device for small break LOCA mitigation. In addition, loss of subcooled margin does not equate to a loss of Natural Circ, nor does it present a significant challenge to Operators.

It is critically important to keep in mind that no one is eliminating any Pressurizer heaters. We have always had several banks of backup heaters which are not covered by TSsand the fact they are not in the TSs has in no way eliminated our desire to maintain them. The more heaters, the easier it is to accommodate the loss of a single (or more) individual heater elements. By relocating the two TS-required banks of heaters to the TRM, we can avoid an unnecessary TS-required shutdown (or NOED request) for cases where just a couple heaters in a bank are powered down or otherwise fail, provided plant operation is not affected. Entergy believes this is completely reasonable since a the heaters are not required for accident mitigation and a cooldown can be performed without the heaters.

Again, thanks for this opportunity to provide further thoughts on the subject. Please do not hesitate to call or respond if further information is desired.

David Bice ANO Licensing From: Kalyanam, Kaly [1]

Sent: Thursday, July 30, 2009 10:40 AM To: BICE, DAVID B Cc: CLARK, ROBERT W

Subject:

ANO-2 LAR on Technical Specification Changes To Relocate Pressurizer Heater to TRM

Dave, The two areas are:

1) Specifically, in the probabilistic risk assessment area, other than a single sentence that simply repeats the regulatory requirement, the current application does not explain the basis

(criterion used) for determining that the plant-specific PRA does not show the pressurizer heaters are risk significant. Thus, the LAR does not adequately address this area.

2) The staff position on compliance with 10 CFR 50.36(c)(2)(ii) considers that the heaters are (a) design feature of the pressurizer, (b) required to be operable to satisfy Criterion 2, and (c) though the heaters are not specifically used in accident analysis, yet as indicated in NUREG-0737, the heaters are powered from emergency power supply and are needed to maintain subcooling in the long term during loss of offsite power, therefore, it appeared that the LCO and Action b for the pressurizer heaters must remain with in the TS.

Please let me know by COB tomorrow, when you can respond to these questions.

If additional information is needed for the staff to complete its technical review, you will be advised by separate correspondence (by way our regular RAIs).

Thanks Kaly.

E-mail Properties Mail Envelope Properties (588D53831C701746A2DF46E365C018CE067B8EB0)

Subject:

RE: ANO-2 LAR on Technical Specification Changes To Relocate Pressurizer Heater to TRM Sent Date: 7/30/2009 2:51:59 PM Received Date: 7/30/2009 2:51:59 PM From: BICE, DAVID B Created By: DBICE@entergy.com Recipients:

Kaly.Kalyanam@nrc.gov (Kalyanam, Kaly)

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