Kiyonobu Yamashita

Nuclear design of the high-temperature engineering test reactor (HTTR)

The high-temperature engineering test reactor has been designed whose outlet gas temperature is 950°C. That is the highest temperature in the world for a block-type high-temperature gas-cooled reac...

Annular core experiments in HTTR's start-up core physics tests

Abstract Annular cores were formed in start-up core physics tests of the High Temperature Engineering Test Reactor (HTTR) to obtain experimental data for verification of design codes. The first criticality, control rod (CR) positions at critical conditions, neutron flux distribution, excess reactivity, etc., were measured as representative data. These data were evaluated with the MVP Monte Carlo code, which can consider directly the heterogeneity of coated fuel particles (CFPs) distributed randomly in fuel compacts. It was made clear that the heterogeneity effect of CFPs on keff’s for annular cores is smaller than that for fully loaded cores. The measured and the calculated keff’s agreed with each other with differences <1%Δk. The calculated neutron flux distributions agreed with the measured results. A revised method was applied for evaluation of excess reactivity to exclude the negative shadowing effect of CRs. The revised and calculated excess reactivity agreed with differences <1%Δk/k.

Weapons-grade plutonium burning with high-temperature gas-cooled reactors using plutonium burner balls and thorium breeder balls

A concept for a new reactor system is developed where weapons-grade plutonium can be made worthless for weapons use. It is a pebble bed-type high-temperature gas-cooled reactor that uses plutonium burner ball and thorium breeder ball fuels. The residual amount of 239 Pu in spent plutonium balls becomes <1% of the initial loading. The power coefficient is made negative by reducing the parasitic neutron absorption reaction rate of 135 Xe.

Design of Advanced Reactors

Section 4.1 describes features of a fast reactor core and the procedure of the core design. The characteristics of reactivity and power distributions are explained in the nuclear design section and the reactivity control requirements are also explained in this section. The section of core thermal-hydraulic design explains the outline of the coolant flow allocation procedure and the evaluation methods of temperature distributions in a fuel subassembly. The author of Sect. 4.1 is Hiroo Osada.

Destruction of Weapons-Grade Plutonium with Pebble Bed Type HTGRs Using Burner Balls and Breeder Balls.

解体核兵器から出るプル トニウム(Pu)の 処理 方法として,ウ ラン(U)等の親物質と混合した燃 料を軽水炉等で燃焼する方法(1)やガラス固化 して 廃棄する方法(1)が提案されている。親物質と混合 した燃料を用いる前者の方法では,核 変換によっ て生成 した核分裂性物質を有効利用するため使用 済み燃料を再処理することが望まれる。また,ガ ラス固化による方法は,核 分裂性物質の有効利用 にならないだけでなく,核 分裂性物質が潜在的に 存在することから転用に対する監視が必要である と考えられる。 著者 らは,Puを 親物質と混合しない燃料球(燃 焼用燃料球)と,親 物質からなる燃料球(増殖用燃料 球)とに燃料を分離 し,こ れらをペブルベッド型 高温ガス炉の炉心内に混在 させて燃焼させ,そ れ ぞれを連続的に交換することにより,Puを 有効 的に消滅する方法を考案 した。そこで,こ の方法 を用いると再処理を行わず直接廃棄できるまで, 核分裂性物質(239Pu)を消滅できることを,核 特性 の面から明 らかにした。 本報では,本 原子炉の特徴を示すため,炉 内の 燃料の流れ,Pu消 滅率および燃焼用燃料球1個 の最大Pu装 荷量について述べる。