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SECY NOTE: SECY-93-092 WAS RELEASED TO THE PUBLIC ON APRIL

14, 1993. THIS SRM AND THE VOTE SHEETS OF ALL

COMMISSIONERS WILL BE MADE PUBLICLY AVAILABLE 10

WORKING DAYS FROM THE DATE OF THIS SRM

July 30, 1993

MEMORANDUM FOR: James M. Taylor

Executive Director for Operations

FROM: Samuel J. Chilk, Secretary /s/

SUBJECT: SECY-93-092 - ISSUES PERTAINING TO THE

ADVANCED REACTOR (PRISM, MHTGR, AND PIUS) AND

CANDU 3 DESIGNS AND THEIR RELATIONSHIP TO

CURRENT REGULATORY REQUIREMENTS

This is to advise you that the Commission (with all Commissioners

agreeing) has approved the staff's recommendations in Enclosure 1

to SECY-93-092 as follows:

a. Accident Evaluation

The Commission approves the staff's recommendations as

well as its response to the ACRS comment.

b. Source Term

The Commission approves the staff's recommendations

including its agreement with the ACRS. Commissioner

Rogers questions whether there is sufficient

information on each specific reactor design and fuel

design extant to enable the staff's three conditions

for a mechanistic analysis to be met. He believes that

a mechanistic "scenario specific" source term for each

reactor concept warrants further consideration before

evaluating the acceptability of the design.

c. Containment

The Commission approves the staff's recommendations,

including the staff's agreement with the ACRS comment.
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The Commission believes that, for the MHTGR, the staff

should also address the following type of event. The

loss of primary coolant pressure boundary integrity

whereby air ingress could occur (from the "chimney

effect") resulting in a graphite fire and the

subsequent loss of integrity of the fuel particle

coatings.

d. Emergency Planning (EP)

The Commission, with all Commissioners agreeing,

believes that at this time it is premature to reach a

conclusion on emergency planning for advanced reactors.

For ongoing review purposes, the staff should use

existing regulatory requirements. However, the staff

should remain open to suggestions to simplify the

emergency planning requirements for reactors that are

designed with greater safety margins. To that end, the

staff should submit to the Commission recommendations

for proposed technical criteria and methods to use to

justify simplification of existing emergency planning

requirements.

The Commission agrees with the ACRS recommendation and

the staff's agreement that the work on EP should be

closely correlated with work on Accident Evaluation and

Source Term, in order to avoid unnecessary

conservatism. Also, the work on EP for advanced

reactors should be coordinated with the approach for

evolutionary and passive reactors.

(EDO) (SECY Suspense: 11/93 - priority)

e. Reactivity Control System

The Commission has approved the staff's position,

including its agreement with the ACRS comment.

f. Operator Staffing and Function

The Commission has approved the staff's position,

including its agreement with the ACRS comment.

g. Residual Heat Removal

The Commission has approved the staff's position,

including its agreement with the ACRS comment.

h. Positive Void Reactivity Coefficient

The Commission has approved the staff's position,

including its agreement with the ACRS comment.
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i. Control Room and Remote Shutdown Area Design

The Commission (with all Commissioners agreeing) agrees

"that, at this time, justification for recommending

departure from current requirements is not

established."

Additionally, the Commission agrees with both the staff

and the ACRS that the staff should be receptive to

considering justification for a departure, if it can be

provided by the applicants. The preapplication review

should be used to evaluate the preapplicant's design to

determine whether or not a different approach to

designing the main control room and remote shutdown

area would be acceptable.

The staff should be aware that pending decisions on the

control rooms of passive LWRs may not address

satisfactorily the issue of control of the multireactor modules presented by PRISM and MHTGR designs.

The staff should consider the fundamental design

differences between these plants and current LWRs when

determining the need for safety grade equipment,

seismic qualification, availability of a separate

shutdown location, etc., for these advanced reactor

designs.

j. Safety Classification of Structures, Systems, &

Components

The Commission (with all Commissioners agreeing) agreed

that resolution of this issue must await future design

developments because the MHTGR design is still at an

early stage. The staff should first classify the

passive LWR SSCs and then consider classification of

the MHTGR SSCs, taking into consideration whether

current LWR criteria for identification of safetyrelated SSCs can be applied to the MHTGR design.

The Commission agrees that a prototype for the CANDU-3 is not

required for design certification and that insufficient

information has been provided on the advanced reactor designs at

this time to pursue rulemaking on any of the 10 issues.

In approving the staff's recommendations on these issues, in a

number of cases the Commission is accepting general statements or

approaches by the staff on how it will proceed with its

preapplication review of the advanced reactor and CANDU-3

designs. If and when it becomes apparent that one or more of

these designs will be submitted for design certification, it will
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be necessary for the staff to identify the data, analyses,

acceptance criteria, confirmatory research, and program plans in

much greater detail in order that the Commission, the vendors,

and the public are more fully aware of the technical regulatory

requirements for prototype demonstration (N/A to CANDU-3) and

design certification.

On page 12 of Enclosure 1 to SECY-93-092, it is stated for the

MHTGR design that "... (2) there is a significantly long time

expected for the core to return to criticality after being shut

down by the Doppler coefficient without the reactor protection

system functioning (i.e., about 37 hours)." Commissioner Remick

would appreciate either receiving a copy of the analysis or an

informal briefing which explains the above statement. In

particular, a common plot of fuel temperature, core power level,

and reactivity versus time would be appreciated, if readily

available.

cc: The Chairman

Commissioner Rogers

Commissioner Remick

Commissioner de Planque

OGC

OCA

OIG

Office Directors, Regions, ACRS, ACNW, ASLBP (via E-Mail)